163693 Atira

As mentioned in a recent post on observing Atira-class minor planets, I had tried to observe Atira herself last fall but was not able to pick it up. So I was interested to spot it on the MPC Bright Recovery List a few weeks ago, where it looked like it would be observable from the Slooh Canary Island Observatory.

I scheduled a couple of sessions before dawn on the night of 7 Feb and was glad to see nice images come back. But they were quite crowded with stars! Turns out the object was near the edge of the Milky Way between Cygnus and Lyra. Still, the object was clearly visible and did not overlap any stars in a few of the images, so I was able to measure and submit a few observations from that session. I was successful again a couple of nights later, so there are visible observations on Atira from a couple of nights this year. The previous reports are from May 2015.


Atira is numbered and has an uncertainty factor of 2, so the orbit was not updated by the MPC. Still, it’s probably useful to confirm she is on track!

A few days later, I happened across the Arecibo Planetary Radar Science page and saw that they had observed Atira by radar a couple of weeks earlier on 20 Jan. At the time, she was passing 0.20 AU from Earth and reaching zenith around 1 PM, so I’m guessing they acquired the radar data during the day.

In the radar return image, a small satellite to Atira can be seen nearby, so the group discovered that 163693 is a binary system. From a Twitter posting on the finding:

It looks like Atira is continuing to move away from the Sun and should be well situated to try again on or after the next New Moon, so I’ll try to follow up.

I’ve made observations of a few other close approachers in 2017. In January I tried to pickup the NEO Confirmation object LM06iuE and was able to find it. I submitted the observations the following morning and just made the discovery publication for 2017 BQ6. The new Apollo-class PHA was first observed by the Space Surveillance Telescope, Atom Site on 2017-01-26. The NEO is estimated to be around 180m in size and passed by Earth at around 6 LD (Lunar Distances) on 7 Feb.

2017 BQ6 was imaged by the Goldstone radar site at that approach, showing a rough, jagged body compared to Dungeon and Dragon dice! It’s been a few years, but I seem to recall the game having a number of different kinds of dice. I suppose they meant the 20-sided die, but they did not mentioned whether or not we’d get a save through if 2017 BQ6 is ever on a collision course, as they measured it to be around 200m across.

More recently, I reported observations on 2017 BW which was pinged by Arecibo on 14 Feb. It was also imaged at Goldstone over several days and estimated to be around 40 m across on it’s longest axis. I also happened to catch 2015 BN509 which was imaged from Arecibo as well.

Though it was pure coincidence, it’s nice to see that a few of my recent observations may have contributed to refining the orbits of these radar candidates. Will have to keep an eye out on the radar groups’ sites to check for more!





In my last post, I described a utility called OrbBroswer I’ve developed to help identify minor planets that might be useful or interesting to observe. From time to time, I download the Near Earth Asteroid orbit elements file (NEA.dat) from the Minor Planet Center data page and run it through the utility to look for objects that may be in need of follow up observations.

One approach I’ve tried is to select from all NEAs those having an Uncertainty value of 2 through 5. This helps find NEOs that may need additional observations to improve their orbit, while being good enough not to require an extensive search. This filter brings the number of candidates from around 15,000 to 5,000. Next these are loaded into the planetarium program C2A and filtered to identify observable objects at an apparent magnitude of 20, reducing the count further down to about 150.

These can be viewed in C2A at their estimated positions from a given observing location and time. Checking the sky at the onset of (full) darkness and again before the sky starts to lighten should show all objects that will be observable during the night. Leaving out objects right on the horizon or in the Milky Way, and having a sufficient magnitude to detect, should indicate all of the reachable targets from this set.

Since I only have the name of the objects displayed, I then look up each one in the MPC Observation Database to see the type of object, it’s uncertainty value and the time of last orbit update and observation. Then I can select minor planets that might be useful to observe that have not been seen for a while or have a small number of recent observations.

When I tried this a while back in September, I noticed a numbered minor planet, 418265, belonging to the Atira or Inner Earth Object (IEO) class of minor planet.  It had an uncertainty value of 4 and was last observed on 10 December, 2014.

The Atira-class family of minor planets has their orbits entirely within that of Earth’s and is relatively recently known. The first known object in this class, 163693 Atira, was discovered in 2003 at the Lincoln Laboratory Experimental Test Site observatory in New Mexico. As of today, there are only 26 of these known out of nearly half a million asteroids. Six of these have been observed enough to receive a number designation, but at least two have sparse observations and are effectively lost. So these are pretty rare!

Most of the planets and minor planets have orbits outside of the earth’s, in the “Outer” solar system. When these are on the same side of the sun as the Earth, they are visible in the night sky. And when they are located directly behind us (relative to the Sun), they will rise in the evening, transit around mid night and set at dawn – just like the Full Moon. In this orientation they are said to be in “opposition”. They are also nearly fully illuminated and at their brightest at this time.

In contrast, the inner planets are only observed around the time of sunset or dawn. Mercury is quite close and never gets too far from the Sun in the sky, so it stays quite close to the horizon. But since it is a good-sized planet, it is possible to see it before the sky is fully dark, especially with a pair of binoculars – provided the Sun is safely below the horizon of course! Venus is the Morning or Evening “Star” and can range fairly high in the sky because it is further away from the Sun and can get closer to us. Currently it is near its greatest elongation and is high and bright at around 30 degrees from the horizon in the evening sky.

Ephemerides of Atira-class 418265 indicated that it would be low in the sky at 10-20 degrees above the horizon before dawn from the Slooh observatories in the Canary Islands. I was able to get a time slot around dawn on one night and give it a try. A moving object was visible around the expected position of the IEO but it was quite faint. Checking the predicted position on future nights, it looked like it would be a bit higher up in the sky later in September, so I tried again. This time I was able to get good positions on two nights and submitted them to the Minor Planet Center.

The observations were accepted and published and these stand as the only positions on the body since 2014. The orbital uncertainly remains at 4, but the positions I obtained agreed very closely to the expected positions determined by the find_orb package, so 418265 was right where it was expected. And since it has an estimated size of 2200 meters across, that’s a good thing to know!

Atira-class 418265 has an orbit that ranges from 0.4 AU to 0.8 AU. Its closest approach to Earth is a very safe 0.18 AU. But since it is fairly far from the Sun and gets somewhat close to us, it will can range fairly high up in the sky when it is in our neighborhood. That and it’s large size make it fairly easy to catch when it is nearby. It will have a fairly close approach in 2026 but hopefully it will be visible before then for more orbit updates.

A little later in the Fall, I noticed that Atira itself might be observable from the Southern Hemisphere, so I tried it from the Slooh observatory in Chile. I was able to get images at around 30 minutes before the end of complete darkness but was not able to see any moving objects. The estimated magnitude was 17.5 but this was probably not bright enough to pick it up with this telescope so close to the horizon.  I also tried from the iTelescope observatory in Australia but Atira was below the horizon limits of the scope I used. So these can be hard to get!

Looking over candidates again in November, I noticed another Atira-class object, 2008 UL90, deep in the southern sky at a declination of -60 and moving further south. I was able to capture some images at the expected location and then realized the object was in the southern end of the Milky Way and was not discernible in images containing many hundreds of stars. The object continued to move south as it passed close to the Earth and then started to move back quickly north in December after it’s closest approach on the 12th. I was not able to get observations for a few nights but then was able to catch it on the nights of the 20th and 21st from the iTelescope.net site in New Mexico.

A number of observatories from the Northern Hemisphere have also observed 2008 UL90, so it has had quite a few positions reported recently. This object will be visible well into January and is getting lots of additional observations on this pass. I think will be a candidate to receive a numeric designation since it has been seen on 5 “oppositions”.

Atira 2008 UL90 is considered an Potentially Hazardous Asteroid (PHA) because it has a considerable size of 800 meters, and also because it’s aphelion is in our neighborhood at 0.96 AU, with an estimated closest approach of 0.026 AU based upon it’s current known orbital elements. So this one is certainly worth keeping an eye on! As can be seen from the diagram below, the object ranges close to our distance from the Sun but is significantly inclined:


So I was able to get a look at and report on two Atira’s this past year. Since there are only 26 I think that’s pretty fortunate. Looking over all of the 26 known, it looks like (163693) Atira should be visible in March around a close approach. Another numbered Atira, 413563, may be visible around then too at mag 18.5. All of the others look to be hard to see or extremely faint over the coming year. But since two new Atira’s were discovered in 2016, so there’s always the chance of catching a new one!




Since February, I’ve been continuing to capture images of Near Earth Objects using the “internet” telescopes of Slooh.com with a few attempts from iTelescope.net. I’ve made over 20 submissions to the Minor Planet Center on some 18 different minor planets and comets. The observations have been fairly routine updates, so I’ve not felt compelled to blog about each submission, but will report from time to time on anything interesting observed.

As mentioned, the first submission I made was for minor planet (163243) 2002 FB3 in February, which I found out after taking the images is an Aten-class NEA that was on the MPC Critical List for observation. The minor planet Aten-class asteroids are defined as having a semi-major axis of less than 1.0 AU with an aphelion of greater than 0.983 AU. So these have an orbit entirely or largely inside of the Earth’s orbit but have the potential to cross the Earth’s path or come to a close proximity. For example, here is the orbit of Aten 162117 described in more detail below. It’s orbit extends somewhat beyond Earth’s but has a high inclination:


Out of 14,576 minor planet orbits listed in the MPC’s NEA data file as of today, 1056 are given the Aten orbit classification. The semi-major axis ranges from 0.63 AU for 325102 2008 EY5 to 0.9996724 AU for 2010 TK7. There are 49 Atens classified as being over 1 KM in size and 106 on the MPC critical list. These stats are as of 3 Sept 2016 and obtained using a utility I developed called OrbBrowser for filtering and browsing the MPC minor planet orbit files, that I’ll describe in more detail in a later post.

Back in April, I noticed Aten (308242) = 2005 GO21 on the MPC Bright Recovery Page.  Since it was visible in the southern sky, I tried to schedule “missions” from the Slooh observatory near Santiago, Chile designated W88. The site was experiencing clouds and rain for a spell so I got no results after trying for a few nights. I tried once more even though the forecast did not look so good. Luckily, there was a clearing later that night and I was able to get 2 sets of images before dawn when the object was up in the sky. Two observations from that night were submitted and accepted and published in MPEC 2016 H38 as the first new observations on the object since July 2014. The orbit was not updated at that time, but I suppose my data were used in the next orbit update later in the year.

I noticed another Aten on the Bright Recovery List, (136818) Selqet, that had not been observed since 2008! It was brightening in the southern sky, so I tried again from Slooh W88 but got shut out again by the weather. I had previously signed up and had tried a few missions from the iTelescope site in Siding Spring, Australia, so I gave that a try. I was able to get observations in on 2 successive nights, even with a fairly full moon in the sky and submitted them:


The submissions were accepted, but I was not sure if they would be published without assignment of a Program Code, so I asked to MPC staff to check the observations for publication. After that they were published in MPEC K25 along with data from observatory Y00 SONEAR Brazil, and these were used in an orbit update. So I was excited to get observations on a NEO that had not been reported in nearly 8 years!

The Aten was brightening and visible in the southern sky for quite some time, so I submitted follow up observations from W88 in June as well.

Another Aten bright recovery I saw on the list was (2100) Ra-Shalom, last observed in 2013. This is a large body, estimated to be some 2.7 km in diameter and has been observed and studied in a number of light-curve and radar campaigns. Observations were published in MPEC 2016-L118.

Aten (5381) Sekhmet was also on the Bright Recovery page, last observed earlier in 2016. It’s a 1+ KM designated NEO also on the Critical List. Since the Orbit Uncertainty had a value of 3, I took and submitted observations from 1 night from W88, published in MPEC 2016-M17.

Recently, Aten (162117) 1998 SD15 was listed with a previous observation date in 2008. It was estimated at a visible magnitude of around 19 but it looked like it would be brightening over the next month or so. I scheduled missions from the Slooh Teide T1 telescope, and after trying for a few nights obtained 3 sets of images. The object was moving at around 4 arcsec per minute but was distinctly visible in each image. So I selected an observation from each set and submitted them and they were reported in MPEC 2016-R33.

After Googling this object, I noticed it is scheduled for radar observation from Arecibo on 21 September, so I decided it would be worth trying for more data on it. The object is currently right around 1.0 AU from the Sun, but 0.18 AU from the Earth. The orbit has a fairly high inclination of 26 degrees, so it is safely 25 million km “above” us as shown in the orbit diagram above. The object is moving south in the sky and will cross behind the Earth a little later this month and reach a closest approach of 0.12 AU around 19 September. The magnitude will increase to 16 at that time and the apparent motion will get somewhat faster at over 10 arcsec / minute.

Data were obtained from both the Slooh Teide observatory and the iTelescope Mayhill NM observatory the night of 3 Sept and submitted. I plan to follow up as the object brightens and picks up speed and try using stacking of short exposures to get locations as the relative motion brightens.

So far this year, I’ve reported on 8 different Aten class NEAs that had not been observed in 3 months to nearly 8 years! Will definitely keep an eye out for more including the archetype Aten itself. I’ve also caught a few Apollo-class minor planets and those are certainly of interest as well.


2016 EL56 – a newly discovered PHA

After having my first NEO observations accepted and published, I’ve been looking to observe some other interesting objects and thought I would try some brighter entries on the MPC NEO Confirmation Page. This page lists newly discovered minor planets or comets thought to be in or potentially reaching our neighborhood in the Solar System. Most of these are very faint bodies picked up by large telescopes used in the various sky surveys and are typically confirmed by high powered professional or amateur observatories dedicated to follow up confirmation and recovery work.

Still, a few brighter objects can be found on the list, and it looks like these are a little more common in the Southern hemisphere. So I thought it would be worth trying some of these from the Slooh observatory in Chile.

The first one I tried was a NEO candidate designated M50sG6S on the list on March 8th. It had an estimated magnitude of 18.2 and a projected declination of 35S so it looked like it should be detectable from Chile. I scheduled missions from W88 that night but did not see any moving object in the images obtained. No confirmations were made for this object over the coming week so it was removed from the list and not confirmed.

The next day, I saw an entry A100jOx in the southern sky with an estimated brightness of 18.9 at declination 25S. This magnitude is a bit of a stretch but it looked to be fairly high up in the sky on a moonless night so I gave it a go. Image files came in the next day, and I also noticed that the object had already been confirmed and given the designation 2016 EL56 by checking on the previous designation page. So other observatories had already confirmed the object!

The images looked quite good, so I took a look in Astrometrica to see if I could pick up the new object. First, I updated the MPC orbit database since the object was just designated and should now have an orbit available. A faint moving object was seen in most of the images, near but not at the exact location predicted by Astrometrica. Since this was a newly discovered object with 2 days of observations, the orbit would have a significant degree of uncertainly and this discrepancy was to be expected.

Since the object was faint, I tried the “Stack and Track” feature in Astrometrica. Using the Slooh protocol “Faint Mono” normally produces 4 monochromatic or luminence files, though sometimes these are not all produced. I had 4 images from the first timepoint and 3 from the second, so I made 2 stacks from each set.

“Track and Stack” will read in a series of images and shift them according to the expected motion of the desired target. The motion can be entered, but if the object is known it can be looked up from the orbit database. So I selected the newly minted designation 2016 EL56 and the program shifted and stacked the images from the estimated motion rate and position angle or direction. Here is one of the stacked and shifted images:


In the picture above, the images are shifted so the stars in the picture show up as a series of dots or a solid line. An object moving at the expected rate and direction will fall around the same position and show up as a single spot. So the weaker peaks in the individual images can add up to give a stronger signal over the background. The position will be a little less uncertain but the curve fit will work better so it can enhance the measurement overall. I’ve noticed that noise on a single image will also show up as a single spot so it’s important to look over the individual frames!

Running the observations in find_orb showed consistency with the other observations made to date and a positive influence on the overall fit. So I prepared a report and submitted it to the Minor Planet Center that day. Since I had a program code already assigned, this time the observations were published the very next day in the Daily Orbit Update MPEC 2016-E112 and later in the Minor Planet Supplement MPS 690473.

Minor planet 2016 EL56 is a Potentially Hazardous Asteroid (PHA) with an estimated size of 150 meters. The ESA site classifies it as an Apollo class asteroid ranging from around 4 AU down to about 0.3, with the next expected close approach in 2045 at 0.15 AU from Earth. It looks like the object was picked up after it passed by us in February, so it is now heading away and fading in brightness. It is not expected to have in impact in the future but any observations made while it is still accessible will help greatly in predicting it’s position and recovery when it returns!


3453 Dostoevsky

After taking a few comet images from Slooh.com recently, I came across a group there called the A-Team that observes and reports on minor planets – particularly Near Earth Objects or NEOs. Through this group, users can gather observations and report them to the Minor Planet Center after completing a tutorial syllabus and qualifying for submissions. I was very excited to find out about this resource, as I have been wanting to contribute to this field but really do not have the conditions and equipment to do this from my own back yard!

I don’t want to cite or reproduce the A-Team pages from the Slooh site but can mention some of the public resources the group suggests and results of some early observations.

To start, they recommend taking observations on a few brighter objects, and this is what the Minor Planet Center also requires before qualifying for a new observatory code. To help identify some candidates, I went to the JPL SB Whats Observable site. You can enter a time and location and other parameters such as a magnitude cut-off and get a list of minor planets and comets observable at a given location.

I put in the parameters of interest and generated a list of over 2000 objects! Did not see a download option but was able to take the list, save it to a file and coax it into Excel. From this list I identified some targets around mag 15 and selected a subset of the sky that would be at a good elevation – and also away from bright Jupiter and crowded star fields in the Milky way.

Many choices were available, but my eye caught 3453 Dostoevsky, whom I always enjoyed reading in college – plus evoking Mel Brooks’ The Twelve Chairs. At an expected magnitude 15.8 this looked like a reasonable choice to try.

I booked sessions at the Slooh Canary Island site but was thwarted by clouds for a few days, but then managed to get some images from their site near Santiago, Chile. I scheduled 3 sessions 30 minutes apart. The first time point looked fine but the second showed pretty severe streaking. The third set looked OK so I went with the first and third exposure times.

After entering the telescope, camera and analysis parameters recommended for the site, Astrometrica solved the images nicely and identified a clearly moving bright object as 3453 Dostoevsky with these values:


03453         C2016 01 15.29433 08 37 33.89 +18 20 19.2          16.0 V      W88

03453         C2016 01 15.33310 08 37 31.45 +18 20 23.6          15.9 V      W88

To check observations, the group recommends using an online tool for calculation residual values at fitsblink.net. After loading the above this site returned:

(3453) = (03453)
1. 03453 C2016 01 15.29433 08 37 33.89 +18 20 19.2 16.0 V W88 -0.16 -0.03
(3453) = (03453)
2. 03453 C2016 01 15.33310 08 37 31.45 +18 20 23.6 15.9 V W88 -0.09 +0.12

This shows differences in the measured and expected coordinates of less than 0.2 arc seconds, so it looks like I have the right object!

Next I tried choosing a fainter target and found a pair of minor planets well below mag 16 and quite close to each other: 3900 Knezevic and 2287 Kalmykia. The Chile observatory was booked up, so I set up 3 times at CI spaced about 40 minutes apart. The weather cleared up that night and I got 3 sets of very nice image files.

If you have 3 or more files from a given location, Astrometrica can reduce the images and look for objects that have a consistent displacement across the set. This identified 4 moving targets in the frames! These looked good from visual inspection, and no other moving objects could be clearly seen. (There were a number of single hot spots and streaks that were likely artifacts).

The expected targets were seen, as well as 2360 Volgo-Don at mag 16.6 and 32729 “5179 T-3” at mag 17. Volgo-Don was at the edge of the frames but clearly seen in all 3 images so this looked to be real.

So here we have 4 objects and 3 times or 12 observations from Astrometrica

02287 C2016 01 17.20921 09 39 10.29 +19 25 12.5 16.8 V G40
02287 C2016 01 17.24113 09 39 08.71 +19 25 24.9 16.8 V G40
02287 C2016 01 17.27185 09 39 07.19 +19 25 36.6 16.8 V G40
02360 C2016 01 17.20921 09 41 16.58 +19 26 19.0 16.7 V G40
02360 C2016 01 17.24113 09 41 15.08 +19 26 27.7 16.6 V G40
02360 C2016 01 17.27185 09 41 13.64 +19 26 36.3 16.7 V G40
03900 C2016 01 17.20921 09 39 45.51 +19 23 09.8 16.9 V G40
03900 C2016 01 17.24113 09 39 43.75 +19 23 14.2 16.7 V G40
03900 C2016 01 17.27185 09 39 42.07 +19 23 18.8 16.9 V G40
32729 C2016 01 17.20921 09 40 01.34 +19 17 13.1 16.9 V G40
32729 C2016 01 17.24113 09 40 00.46 +19 17 31.8 16.9 V G40
32729 C2016 01 17.27185 09 39 59.61 +19 17 49.7 17.0 V G40

Running these through Fitsblink gave:

(2360) = (02360)
   1.  02360         C2016 01 17.20921 09 41 16.58 +19 26 19.0          16.7 V      G40    -0.14    +0.07
(2360) = (02360)
   2.  02360         C2016 01 17.24113 09 41 15.08 +19 26 27.7          16.6 V      G40    -0.04    +0.06
(2360) = (02360)
   3.  02360         C2016 01 17.27185 09 41 13.64 +19 26 36.3          16.7 V      G40    +0.00    +0.31
(2287) = (02287)
   4.  02287         C2016 01 17.20921 09 39 10.29 +19 25 12.5          16.8 V      G40    -0.13    +0.02
(2287) = (02287)
   5.  02287         C2016 01 17.24113 09 39 08.71 +19 25 24.9          16.8 V      G40    -0.03    +0.12
(2287) = (02287)
   6.  02287         C2016 01 17.27185 09 39 07.19 +19 25 36.6          16.8 V      G40    -0.01    +0.01
   7.  32729         C2016 01 17.20921 09 40 01.34 +19 17 13.1          16.9 V      G40    -0.17    +0.08
   8.  32729         C2016 01 17.24113 09 40 00.46 +19 17 31.8          16.9 V      G40    -0.06    +0.12
   9.  32729         C2016 01 17.27185 09 39 59.61 +19 17 49.7          17.0 V      G40    -0.14    +0.12
(3900) = (03900)
  10.  03900         C2016 01 17.20921 09 39 45.51 +19 23 09.8          16.9 V      G40    -0.10    +0.16
(3900) = (03900)
  11.  03900         C2016 01 17.24113 09 39 43.75 +19 23 14.2          16.7 V      G40    -0.13    -0.03
(3900) = (03900)
  12.  03900         C2016 01 17.27185 09 39 42.07 +19 23 18.8          16.9 V      G40    -0.07    +0.20

Some variability, but all except one are under 0.25″. It looks like this telescope and camera yields accurate positions across the whole image frame!

The following animated GIF shows 3 of the objects closest to the center:


Good fun! Next step will be to taking and stacking longer exposures to try to detect some of the many fainter objects out there.


C/2013 US10 Catalina

Comet Catalina C/2013 US10 is currently visible in the Northern Hemisphere using binoculars or a small telescope. After rounding the Sun late in November, it has been up in the pre-dawn sky, creeping up higher each night.

It was observable in early December in New England, but very low in the sky before sunrise. I tried to get a look at it a few times using binoculars but was not able to see it well between the trees at home! Had hoped to see it later in December, but skies have been very cloudy and foggy for the past few weeks as part of a very unusually mild and damp weather pattern.

Having some time off recently, I thought I would try to see the comet using one of the internet telescope services available, and was able to get some images of it after signing up for a trial on slooh.com

After logging in and watching some of the getting started videos, I was able to book a timeslot (or “mission” as they call it) to see the Catalina comet on one of their telescopes in the Canary Islands . The site has a page titled “What’s Up” that gives a lot of great suggestions for currently observable objects to look at including planets, deep sky objects and visible comets. You simply select an available time, select the desired object you’d like to see and you are all set!

But for comets and other moving objects you need to determine the coordinates the target will be at and create a “Coordinate Mission” for that location of the sky. I used Stellarium to determine where Comet Catalina would be from the observatory location at the time of the reservation. Since the reservation times are in UTC, it is also handy to set the TimeZone plugin in Stellarium to work in that time zone. That way, you can check the position at a given time in UTC and not have to convert to your local time. (Or I guess you can change your workstation to UTC time and keep it there)! The coordinates calculated in Stellarium can be a bit off, so to get accurate positions expected from the coordinates of the actual observatory it’s good to use the MPC Minor Plan and Comet Ephemeris Service or the JPL Horizons site.

After you enter the coordinates, you select the type of object you are observing, so I selected the “bright comet” option. Apparently this setting determines the exposure time and image processing used for the session. The site appears to confirm that the coordinates are observable at the time selected and will even warn you if a fainter object is too close to the moon to be seen.

Once you set this all up, that’s it! You can stay on and watch the images from the telescope as they are taken. Since my reservation was around 1 AM local time, I just went to sleep while my images were being acquired!

The next day, I signed back into the site, selected the My Images page and found 4 images taken of the comet. The session used both a high magnification telescope (17″ CDK af f7) and a wide field APO refractor telescope. Images were taken at the same time, processed and made available as color and mono PNG files in the size of the original CCD images. These can be viewed on the site, downloaded, or annotated and emailed or shared to your favorite social media site.

Here is the high magnification image of C/2013 US 10 Catalina from this session on 30 Dec 2015:


It’s hard to see in the above version, but there is a faint tail extending up and right – I believe this is the dust tail. The ion tail extends a short ways down from the comet center. (North is up in this image).

I noticed several fuzzy objects around the comet. Not more comets, but apparently Catalina US10 was passing through an area with a few galaxies.

Slooh also provides FITS files from the CCD cameras. These are downloaded from the observatory at the end of each night and made available through the Slooh website and as well as an email notification.

So I was able to take the FITS file of the unfiltered or luminance image and reduce in Astrometrica. Then I could take estimated coordinates of each of the galaxies visible in the picture and check them against positions in TheSky. In the image above there are 5 clearly visible. I marked these in Astrometrica and they are shown in the image below, along with the fit and estimated location of the comets:


The dual tails are more clearly visible in the inverted image. I could also try stacking the color and luminance FITS files to see if I could bring these out better in the positive image. But I kind of prefer the above as it reminds me of working with AgBr imaging!

I took an image of the comet on the next night, and recently tried combining the FITS files to make my own LRGB composite using MaximDL. I need to better understand how to bring out the tails in that package but got a fairly good result:


The dust trail to the upper right appears to have a fork in it at this time – taken on 31 December.

The Catalina comet will continue to be visible through January and then fade as it moves away from the sun. Turns out this comet will not be back to greet us but will continue on outside of the solar system for parts unknown. Apparently is was a deep solar object that had its orbit perturbed enough to be knocked into an ejection trajectory that will take it outside of the Solar System.

Next, I will try capturing some of the other comets in the sky using Slooh and perhaps another similar service.




2015 TB145 Confirmation

After capturing a few shots of the recent flyby of asteroid 2015 TB145, I thought I would look into software tools for astrometry to determine the location of the object and confirm it was in fact TB145 in my images. This analysis is used to discover, confirm and observe new asteroids and comets and to produce observation reports.

The image processing and planetarium packages I own do support astrometry, but only at higher license levels than I purchased. So I looked up a program I had used quite some years ago called Astrometrica, and was very happy to see it was still available – and very much supported!

Astrometrica is a shareware package created specifically for analysis and reporting of solar system objects, written and maintained by Herbert Raab from Austria. You can download and try out the package for free for a generous 100 days, and it is well worth the purchase price of 25 Euro.

The images from the session taken early in the morning on Halloween were acquired using Maxim DL and saved as FITS files which can be read right into Astrometrica. First, though, it is vital to enter the image parameters as Program Settings in order to correctly interpret and fit the images. The first settings are for Location which are key for reporting observations (my actual values changed somewhat):


The next set on the CCD tab is critical as it defines the scale and orientation of the image. These are used to convert the location of detected stars and objects to the coordinates of the star catalog used:


The focal length is that of the lens or telescope used in the imaging. I have entered the nominal value of 750mm +/- 5% for my 6″ Netwonian. After calibrating an image this could be set to a more accurate value and a lower variation for a faster fit, but this should work for a first pass. I’ve also set the Pointing error quite high, as I know the object is somewhere in the frame but don’t know the image center location very accurately. So we’re asking it to do a pretty wide search.

The CCD chip is 5.2 x 5.2 microns for the Canon DSLR, with no binning. Another key factor is the Position Angle that specifies the orientation of the camera on the telescope. Note that this can depend on whether the mount has flipped or not. Also, the image may need Horizonal or Vertical flipping depending on the type of  scope used and attachments. I spent quite a long time trying to work these out but could not get a fit at all with the settings I was expecting.

Then I remembered I had taken some shots of the Moon earlier in the session. Looking back at those, Tycho is on the left hand side of the images, and rotating 90 degrees counter-clockwise puts that and the other features in the “right” place with North at the top. As is, the image has East at the top, so the Position Angle is set to 90. All of the images could be rotated to have North at the top, but it’s probably best to leave them as is and have the program work out the orientation of reference stars. I was expecting that the image should also be flipped but it looks like that is not needed, so the Flip check marks are off.  Perhaps the camera takes care of mirror flipping the image, since it would need to do so for the camera lens as well.

There are other settings to get the correct time from the file, and the remaining tabs have other parameters to adjust for fitting, but these seem to be OK as is. So next I loaded in the set of 3 images from the second location used in the session.

The program has a great blinking tool, and that can be run without all of the setup details above. Simply select the Blinking Tool icon or menu item and this will extract objects and then align and display an animation of all of the select images in a new window. You can set the blinking rate, and stop and step through to take a closer look at anything moving. The images in this first set show a clear streak moving across a fair portion of the display towards the right hand side of the section below:


But to determine the actual coordinates of the streaker, we need to run the Data Reduction tool to fit the star field. From the Astrometry menu, we select Data Reduction and are prompted for a location. We can enter the known or estimated center of the image, or have the tool look up a given object and estimate the position for us. So we enter 2015 TB145 (after loading the MPCOrb database) like so:


The location could be off a ways for our quickly moving neighbor, and it is not at the center of the screen, but we’ve asked for a pretty wide search in the settings. Now we select OK and Astrometrica will run the fit. To do so, it needs a detailed star catalog. These can be downloaded and installed locally, but the tool can now fetch stars for a given region using an Internet service from a configured source – provided we are on line!

After that works its magic for a while we see:


This result indicates a poor fit, but we do have over 50 reference stars aligned. If we are way off in the settings, we would only see one match or a handful which would indicate we are probably lost! In this data set, the images have a lot of distortion and are not calibrated for brightness, so the fitting is pretty rough. If we accept the automatic fit we get a summary table:


Not sure how to interpret all of this, but it looks like we can determine locations in the images to about 1/3 of a minute in RA and Dec which seems pretty good to me! So now we can select any point and see its estimated position. If we select a star for example:


This object was identified as a potential star found in 2 or more images but was not included in the fit, presumably because it did not meet the entered fit parameters. But this is not the asteroid – we want to find the streak on each image and mark it’s position at the center of the streak like so:


Next we look up known objects in the area by selecting the button next to Object Designation and see:


We select the one known object in the vicinity, enter an optional note and then Accept to generate the observation for the selected object. (Some of the sets also indicated a nearby bright asteroid but that appeared to be just off of the frame). After selecting the Known Object K15TE5B which seems to be the official designation of TB145, it is labelled on the screen:


After doing this for the 3 images in the set, we can view the results, formatted for submission to the Minor Planet Center. To ACTUALLY submit the observations, I would have to be vetted and assigned an Observatory Code, but we can see just what the submission would look like:

COM Long. 72 07 24.2 W, Lat. 41 07 24.2 N, Alt. 30m
ACK MPCReport file updated 2015.11.16 21:41:42
K15TE5B C2015 10 31.39037 05 19 38.34 +18 56 12.5 12.1 V XXX
K15TE5B C2015 10 31.39209 05 19 57.11 +19 02 17.4 11.8 V XXX
K15TE5B C2015 10 31.39337 05 20 10.47 +19 06 39.7 12.1 V XXX
—– end —–

This shows 3 observations for K15TE5B or 2015 TB145 on Oct 31 with the time expressed as a fraction of a Julian Day, followed by the RA and Dec values and the estimated brightness or magnitude around 12. The default Observatory Code XXX is used for this example.

The other sets were fitted in a similar way, resulting in 16 observations of the asteroid over the session.

The positions determined from the fit were a ways off from the estimates provided by the program, so how do we confirm this was in fact TB145? The Minor Planet Center site has a number of tools to check results.

The MP Checker takes a time and location and reports any known objects in the area. We can enter the details on the form including a limiting magnitude and get


This shows our expected friend TB145. Note that if we increase the limiting mag to 20 the service returns a couple of dozen minor planets in this limited area – so there’s always a lot of them up there in the sky!

So it looks like we did find it! But how close are the positions we determined from the fit? One way to check is to compare the observed position with the result from the MPC Ephemeris  service page. We can enter a list of objects and desired time and get calculated positions based on the current orbital parameters. The MPC presumably received lots of accurate observations from the flyby, so we can assume the position should be pretty well known. After getting a list of positions at each minute over the session, here is a comparison of the estimated positions vs my observed position in the first set of 3 images:


The Observed positions (Obs above) are compared to calculated positions on the surrounding minutes. The coordinates are all between the bracketing positions, so this looks fairly good! At a glance, there is considerable variation between the observed results and the interpolated positions, so there is definitely a fair amount of error in my results. But this looks quite good for something moving so fast and close by!

So next I think I will try this out on some of the brighter and slower Main Belt minor planets, and further explore use of Astrometrica.



2015 TB145

Earlier this week, I started seeing a lot of a buzz about the “Spooky” asteroid, 2015 TB145 set to pass close by to Earth on Halloween day. It was only discovered quite recently as it has an unusual orbit for an asteroid, well outsize of the ecliptic plane.

In a previous post, I discussed the likelihood of a cometary collision. Comets are relatively few and far between, so impact probability with these is very low – though they are large and fast moving when they come in and contact would be catastrophic. There are many, many thousands of known asteroids or minor planets much closer to home and these are somewhat more likely to strike.

Of course, the bulk of the asteroids are in the Main Belt and circling in a safe Indy 500 pattern out between Mars and Jupiter – there are likely millions out there large and small. The Trojan asteroids are in stable orbits of various kinds and are generally OK. Then there are the rogue NEO asteroids. While many of these are safely out of range, there are a number that we do have the potential to cross paths with.

The NEO asteroids are generally smaller in size and don’t have cometary tails and so are quite hard to spot. A number of very powerful telescopes around the world are watching as constantly as they can to find and catalog minor planets of every type. (And they find most of the comets these days as well). But a new one could pop up at any time that could pose a threat. 2015 TB145 was found just a few weeks ago by the Pan-STARRS survey and this is an excellent example of why these surveys are very important.

Still, there is a lot of room out there and luckily this pass of TB145 will be at a safe 1.25 times the lunar distance. The object is estimated to be 600m across. That’s not enough to be very bright normally, but at the closest approach the apparent magnitude was projected to increase to about 10 or so. This is not bright enough to see with the naked eye but pretty easy to spot in a modest telescope.

At least, when the Moon is not out! The asteroid was projected to reach closest approach on Halloween day around 17:00 UT or 2 PM my time in the US Eastern timezone. But estimates of the brightness showed it to be visible on the approach around 4-6 AM local time, with a track along the top of Orion – but passing fairly close to a nearly full moon.

I wasn’t sure if catching the flyby would be doable, but I set up my scope the night before and aligned it as described in the previous post.

There were a number of articles on line with finder charts and tables giving locations for the passage. But with an asteroid passing this close, the apparent position against the star background varies significantly in different places due to parallax. So it looked like using a start charting program that can track and display solar system small bodies would be the best way to go. I recently upgraded my ancient copy of The Sky and used that, but a number of other packages have this capability including Stellarium.

So I started up The Sky and worked out how to lookup and import the orbital elements for TB145 from the database at the venerable Minor Planet Center. Here is what I imported the day before:

TheSky-TB145-importThis very handily brings in all the values for you as-is without typing which is a huge help! But I wasn’t sure whether the program would give you the position of the body relative to the center of the Earth or calculated for my actual location. So I went to the JPL site to calculate the local ephemeris and had an hourly chart for that as well.

So after taking a few shots of the Moon as described previously, I pointed to the rough location of the TB145 and scanned a bit by eye just to see what would be visible. I could see a number of stars but not very many, so it was unclear whether I’d be able to see the asteroid or not. (At 600 meters across, I’m calling it an asteroid!).

I had also recently bought cables allowing my CGEM mount to be accessed by a computer. Celestron includes a program to do this, but a telescope interface is also supported by my version of The Sky, and this can be done by other packages as well. The hand controller has a telephone-style plug providing an RS-232 serial interface. I haven’t had a computer having one of these in quite some time, so I also had to get an adapter to convert to USB. I set this up the night before, and after installing the driver and rebooting, was able to find the telescope at a virtual COM4 and connected.

With The Sky, when you connect the telescope, it’s position is displayed on the chart as a yellow circle so you can see where the telescope is pointing. Or at least where it THINKS it is pointing!You can also enter an object or coordinate and slew to that position from the program. I had never used a computerized mount before, so this was awesome!

Of course, this is only as good as the alignment of the mount, but this seemed work quite well in the neighborhood where I had aligned to. The CGEM has functions to calibrate further but I thought I would give it a shot with the initial polar alignment and 2 star alignment. The smaller sized scope and DSLR give about a 1 x 1.5 degree viewing area, so getting in the ballpark would be good enough.

Now things were set to point the scope to the expected location of TB145 and take some pictures. To start, I slewed to the expected position and took two 10 second exposures there at 5 minutes apart. Then I had the computer slew again to the current expected position. Since that was actually a fair ways away from the first location, I decided to take a series of three exposures 2 minutes apart to better find a moving object. (Also after learning early on in science experimentation that if you can take 2 measurements of something you may as well take 3!)

So I ended up taking 5 series of shots from about 05:15 local to 6 AM. I decided to use the position provided by The Sky since that was easiest, and that turned out very well! Here’s what it looked like at the time (rolling the clock back):

TheSky-TB145-pointThe display shows RA/Dec in Topocentric and epoch 2000.0 coordinates. I wasnt sure whether this compensates for the parallax or not, but it did seem to. At least, I did find the body in all of the shots given the position it provided!

So I took and saved the shots, naming they by the group and approximate time of capture. I glanced at the images and could see a number of stars. There were a fair number of them and they looked in good focus so I just saved them without looking further. I guess I was expecting the asteroid to have a pinpoint star-like appearance with only a 10 second exposure. At least that was the case when I imaged a few main belt asteroids a while back – but those are much farther away!

So I came in from the cold to have a look and tried looking at some images side-by-side. I could see bright pixel sized spots that appeared to move, but then noticed there were a lot of them and they would move or disappear at random! So these are hot spots and I guess you get more of these in an uncooled stock DSLR. Maxim DL comes with the blinking utility SN Search designed to look for supernova. That looks at pairs of images placed in 2 separate folders. So I took a few files and made copies to try it. After fiddling for a bit I worked out how to do the blink comparison and saw a faint streak that appeared to move in the first pair I took. I was able to find similar streaks in all 5 pairs, so it looked like I had it!

Here are sections of the third group I took around 05:30 local having the streak:

group3-snipThe stars around the streaks can be easily aligned across the 3 images, but the streaks clearly travel in a line across the stellar background, so this appears to be TB145 passing by at a good clip.

So this looks to be it, or at least some kind of fast moving object! I’ve yet to calculate the positions and confirm this is TB145, but I was able to see it in each group around where it was expected. Next, I’ll look into how to calculate the position based on nearby stars and compare against the expected locations.

This was very exciting to see and well worth getting up very early for. I was also watching reports on Twitter and saw a number of other people chasing TB145 early  that morning and saw some great results. And I could not resist posting the above picture myself!

While this did turn out well, there were a couple of lessons learned for me. For one, if I had looked more at the info provided by The Sky or other sources, I could have seen that the rate of movement of TB145 at the time was an expected 2.1 arcsec/sec in RA and 2.6 arcsec/sec in DEC. That gives a total movement of over 3 arc-seconds per second! So a 10 second exposure would show a movement of 30 arc seconds or 20 pixels or so at the resolution used. So I should have expected that the body would streak at this exposure time. Taking images 2 min apart would show a travel of 200 pixels which was a pretty good guess, though using a 1 minute interval and taking 4 or more would have given a more interesting collage. And with this rate, it would have been worth taking some time to look over the first set while I was at the telescope, as the streaks would have been pretty noticeable.

But this turned out great all in all, and I’m very happy to be getting a handle on using the CGEM mount – with a small scope at least!

Luna 2

After getting a few fair shots of the recent Lunar Eclipse, I thought I would try taking some more pix of the Moon. One thing I noticed from the previous session was variation in the focus of the stars around the moon. I had refocused with each shot by looking through the viewfinder, but was obviously not getting that very consistent!

Friends in my local astro club recommended using a Bahtinov mask to help with this problem. It’s a very clever focusing aid having a series of grid patterns at different orientations. These create diffraction lines that converge to a common center when your telescope or camera is in focus, and diverge when off focus. This provides a very sensitive indicator of when you are at the very right spot.

My clubbies offered to make a mask for me, but I found some reasonable ones on line and went the lazy way. The mask I got is plastic with some movable plastic screws you can adjust to fit around the end of a telescope or dew shield. It stays on pretty loosely but that seems to work out OK.

I tried playing with this a couple of times and it seemed to work nicely, but I did not set up to take pictures. Then I went out very early in the morning yesterday to catch the Halloween asteroid 2015 TB145. Since a very big, bright moon was in  the way, I took a few shots of that while waiting for the main subject to come up above the horizon.

I had setup the scope the evening before and did a rough polar alignment and a single-star alignment. Since there were a number of bright stars visible in the early morning Fall sky, I was able to try and complete a two star alignment of the mount. That was the first time I was able to do so at home as I have so many trees around the house. This turned out to be very helpful in catching the asteroid later on!

Then, I pointed to a bright star and placed the mask over the 6″ Newtonian used previously and the Canon DSLR attached. Looking through the viewfinder, it was pretty easy to focus the scope and get the diffraction lines to cross near the same point. I plugged the camera into my laptop and started Maxim DL to acquire an image. Limiting the image to an area around the star, I was able to tweak the focus a few times and get the pattern pretty close. Here’s what it looked like:

focus1This looked reasonable to go with, so I slewed over to the Moon and tried taking some shots. The Moon was about 4 days past full but still very bright and up near the zenith at 4 AM. I tried taking a number of exposures down to 1/200th. Looking at the brightness histogram in Maxim DL, 1/100 seemed a reasonable exposure so I took a few shots at that time.

Here is one, cropped, saved out to JPEG and reduced to 40%m00n-01-crop-redThis looks pretty good and you can certainly make out craters and other large features. Looking at a section of this at 100% resolution

m00n-01-detailYou can see some smaller features but they are not very clear!

Looking at this at first, I thought there was a problem with the capture – perhaps it was still out of focus some or getting blurred through vibration. But maybe the detail is about as good as it can be with this setup. The 6″ Newtonian used has a focal length of 750 mm, which is only several times higher that a decent zoom lens. At this resolution, the Moon spans about 1350 pixels. With a diameter of 3500 km, the resolution is about 2.5 km / pixel at the center. So any feature spanning 5-10 pixels the eye can make something out of would be very big indeed!

One way to increase the resolution is to get a longer focal length, so re-trying this with my C-8 would be worth doing for sure. Another approach is to take a picture of the magnified image through an eye piece – which is what you do when you look through a telescope. I could give that a try as well with the SLR but would also like to try getting a bracket for a phone camera and playing with that.

After getting a few Moon shots I then tried taking some pictures to try to capture the “Halloween asteroid” 2015 TB145. That came out way better than expected, as described in the next post!



After getting a fair picture of the Sun with my 6″ reflector and DSLR, the next logical target is the Moon! Had a great opportunity to try this out with last week’s Lunar Eclipse.

And this was not just any eclipse, but the widely touted #SuperBloodMoon eclipse of the century. There are some interesting facts behind this sensational term and the hype around the event, so let’s break this down a bit.

A lunar eclipse occurs when the Moon passes behind the Earth at night and falls into the Earth’s shadow. Of course, the “moonlight” we see at night (or during the day) is actually sunlight striking the “daytime” portion of the Moon. When the Moon is directly behind the Earth, we see the whole daytime face and it appears as a Full Moon. When the Moon is to either side of the Earth we see half of it’s lighted surface at the First and Last Quarter. When the Moon is in front of the Earth, it is light on “far side” of the moon, so we normally cant see the “New Moon” when is is up during the day – unless it happens to cross in front of the Sun in a Solar Eclipse. Note that a “day” on the Moon lasts about 28 days as it rotates once around the Earth.

So you may ask, why doesn’t a Lunar Eclipse happen every month, when the Moon goes behind the Earth? One factor is the relative scale of the bodies. As illustrated in the great video To Scale: The Solar System mentioned previously, the Moon is quite a ways off from the Earth relative to its size. The Moon is about 3500 km across and orbits around the Earth at 380,000 km on the average. So if you have a model of the Moon and hold it at an arm’s length away (about 1m) it would be a bit less than 1 cm across at that scale – pretty small! The Earth is about 12,750 km across or 3.5 times larger – so it would be around 3 cm across at this scale. So the Moon really has to be directly behind the Earth to fall into its shadow.

Put another way, the Moon takes up about 1/2 a degree of arc when viewed from Earth, which turns out to be about the same arc angle as the Sun. (An important fact for Solar Eclipses). The Earth viewed from the Moon would be about 1.8 degrees across, so it casts a larger shadow then the Moon does on Earth.

The other factor behind the frequency of the Lunar Eclipse is the inclination of the Moon’s orbit around the Earth – which is a good 5 degrees. So while the Moon is traveling around us, it is also moving up and down relative to the Earth’s track around the Sun, so it will be in sunlight nearly all of the time, even when it’s behind the Earth at the Full Moon. The apparent path the Moon takes across our sky follows the path the Sun takes (the Ecliptic) which rises higher in the Summer and sinks lower in the Winter. But the Moon will wander 5 degrees up and down from that path, so it can get quite low and high in the sky when viewed month to month.

The Moon will cross the Ecliptic twice a month and if it does so right when it is directly behind the Earth it will fall into the Earth’s shadow – and this is the Lunar Eclipse. If the Moon is directly behind the Earth this will result in a Total Lunar Eclipse but this occurs in stages. First, the Moon starts to enter the Earth’s shadow and the Sun is partially blocked. This will result in a dimming of the Moon’s brightness in this phase, called the Penumbra. A while later, an observer on the Moon at the leading edge of the Eclipse will see the Sun totally covered and that area of the Moon will go dark. The shadow continues across the Moon until it is completely covered at totality, and this can last some time as the Earth is larger than the Moon. Eventually the Sun re-appears on the leading edge and the Moon moves out of shadow and back into full sunlight.

If the Moon’s path is a off-center when it passes behind the Earth it can result in a Partial eclipse where the Moon is partially in darkness. Even farther off center you can have a Penumbral eclipse where the Moon is just dimmed, though this is pretty unusual. A picture is worth a thousand words here, so this excellent page on Lunar Eclipses illustrates the different cases nicely.

During a total lunar eclipse, the Moon is not totally dark but often visible with a faint reddish glow. This is because the Earth has an atmosphere which refracts some light around and behind the Earth. The light is reddish due to Rayleigh scattering, which makes the sky blue and the sunrise and sunset red. So some of that red light is passing through the sky, hitting the Moon and bouncing back to us!

The color and brightness of the Moon at totality can vary with the amount of dust or ash in the Earth’s atmosphere, and also the distance of the Moon. The Moon’s orbit is fairly eccentric and its distance can range from about 360,000 to 400,000 km.

During last week’s eclipse, the Moon was also at Perigee – at the closest value above. At perigee, the Moon is about 5% closer and would have about 10% more area and brightness. This is the Super Moon, as it’s become to be known of late.

Last Sunday, the weather was quite nice all day but forecasters were calling for clouds to set in for my area. So I wasn’t sure whether or not to setup my telescope to try getting some pictures. It still looked very nice in the evening, so I quickly setup on my deck where I had taken a picture of the Sun – not thinking that the Sun is not visible there until late in the morning! So when the Eclipse did arrive it was quite spectacular but hidden well behind the trees.

The Moon did poke out at the back end of the eclipse when it started to get bright again. So I took a number of shots, focusing through the viewfinder. A shot at 1/4 second just showed the bright edge, so I increased exposure to 8 seconds and decreased down as the Moon continued to brighten.

This is first shot I got when the Moon was fully out from the trees at 8 seconds, using the same setup as for the Sun previously, an Orion 6″ Newtonian f5 with a Canon DSLR:

Luna1rFeatures are somewhere clear, but the telescope was slightly out of focus. This later shot at 5 sec is well focused but the subject is getting washed out:

Luna2rOk, not too bad for a first try!

So we saw that the Moon was a “Super Moon” on that night,  but what’s up with Blood Moon? Turns out this past Lunar Eclipse was the 4th total eclipse in a row, completing a Lunar Tetrad. This is fairly rare but happens from time to time. And it turned out that this Tetrad happened to start and end around religious holidays, so some have taken this event as a portent of End Times.

Personally, I don’t care too much about what folks believe along these lines, so long as they leave others alone who choose not to! In any case I’m glad we survived this event and the killer comet advertised last month as well. But the next time we have this sequence of lunar events in 2032-33, can’t we just call it a #RecurringTotalLunarEclipseAtPerigee?