29769 (1999 CE28)

Early in the morning of Tuesday, May 29, 2018, I was fortunate enough to record a 3.2 second occultation of the 12.6 magnitude star UCAC4 359-140328 in Sagittarius by the unnamed asteroid 29769, originally given the provisional designation 1999 CE28.

Not only is this the first time this asteroid has been observed to pass in front of a star, it is the smallest asteroid I have ever observed passing in front of a star.  At an estimated diameter of 14.7 miles, had I been located just 7.4 miles either side of the centerline of the shadow path, I would have missed this event altogether!  This is also the first positive event I’ve recorded for an (as yet) unnamed asteroid, and the first positive event I’ve recorded for an asteroid having more than a four-digit number (29769).

As you can see in the map above, the predicted shadow path was quite a ways northwest of my location.  Even though I used the Gaia DR2 position for UCAC4 359-140328 for the path prediction, the existing orbital elements for asteroid 29769 did not yield a correspondingly accurate position for the asteroid.

Though a single chord across an asteroid does not give us any definitive information about its overall size and shape, it does give us a very accurate astrometric position that will be used to improve the orbital elements for this asteroid.

The central moment of this occultation event was 6:00:02.414 UT on May 29, 2018, which was about 20 seconds later than predicted.  The astrometric equatorial coordinates for the star UCAC4 359-140328 referenced to the J2000 equinox (using Gaia DR2 with proper motion applied) are

UCAC4 359-140328
α = 18h 21m 01.6467
δ = -18° 20′ 46.282″

Using JPL Horizons (with the extra precision option selected), the astrometric equatorial coordinates for the asteroid 29769 (1999 CE28), again referenced to the J2000 equinox, are

29769 (1999 CE28)
α = 18h 21m 01.6388
δ = -18° 20′ 46.320″

As we can see above, the actual position of the asteroid at the time of the event was 0.0079 seconds of time east and 0.038 seconds of arc north of its predicted position.  This observation will provide a high quality astrometric data point for the asteroid that will be used to improve its orbit.  Gratifying!

As of this writing, there are 523,584 minor planets that have sufficiently well enough determined orbits to have received a number.  Of these, only 21,348 have received names (4.1%).  So, I guess you could say there is quite a backlog of numbered asteroids awaiting to receive names.  The IAU should consider naming some minor planets after the most productive asteroid occultation observers around the world.  There aren’t very many of us, and this would certainly be an encouragement to new and existing observers.

Satellite (and Meteor ) Crossings 2017-2018

Edmund Weiss (1837-1917) and many astronomers since have called asteroids “vermin of the sky”, but since October 4, 1957 another “species” of sky vermin made their debut: artificial satellites.  In the process of video recording stars for possible asteroid occultations, I frequently see satellites passing through my ~¼° field of view.

I’ve put together a video montage of satellites I’ve recorded between June 21, 2017 and October 20, 2017.  The component events are presented chronologically as follows:

UT Date
6-21-2017
8-15-2017
9-4-2017
9-5-2017
9-12-2017
10-20-2017 (2 satellites)

Target Star
Tycho 5723-663-1
Tycho 1668-1258-1
Tycho 1281-225-1
UCAC4 553-20591
Tycho 5731-996-1
Tycho 6289-1504-1

Asteroid
798 Ruth
30981(1995 SJ4)
34532 (2000 SO213)
1294 Antwerpia
85985 (1999 JW)
25036 Elizabethof

You’ll notice that sometimes the satellite crosses the field as a moving “dash”.  That’s because sometimes I used longer exposure times to record a fainter target star.

 

In general, the slower the satellite is moving across the field, the higher is its orbit around the Earth.  One must also consider how much of the satellite’s orbital motion is along your line of sight to the satellite.  In the following video clip, you’ll see a slow-moving “tumbler” satellite moving from right to left across the top of the field.

UT Date
8-25-2017

Target Star
Tycho 676-828-1

Asteroid
179462 (2002 AJ202)

 

On January 10th of this year, I figured out how to identify satellites crossing the telescope field of view using the amazing program Guide 9.1, which I use for all my observatory research work.  On March 4th, I was hoping to be the first to record the asteroid 3706 Sinnott passing in front of a star.  This asteroid is named after Sky & Telescope Senior Editor Roger Sinnott, whom I had the good fortune to work with in writing the article “A Roll-Down-Roof Observatory” in the May 1993 issue of Sky & Telescope, p. 90.  Roger is amazing.  He took an article that I had written and edited it in a way that only lightly touched my original text yet ended up saying what I wanted to say even better than I was able to say it myself.  The mark of a great editor!  Anyway, I’m sure Roger remembers me and I was looking forward to giving him the news that I had observed the first stellar occultation by “his” asteroid.  Alas, it was not to be, because, as so often happens, the too-faint-to-be-seen asteroid passed either above or below the target star.  The consolation prize, however, was recording a third stage Long March Chinese rocket booster (CZ-3B R/B; NORAD 43004U; International # 17069D) passing through the field.  This rocket launched on November 5, 2017, and added two satellites to China’s Beidou positioning network.  As you can see in the light curve below, the rotation period of the rocket booster is a bit longer than the 19 seconds of usable video I had.

UT Date
3-4-2018

Target Star
UCAC4 556-42881

Asteroid
3706 Sinnott

 

Once in a great while, I record a telescopic meteor.  Here are two.

UT Date
7-15-2017
3-4-2018

Target Star
Tycho 6269-2747-1
UCAC4 561-14746

Asteroid
17136(1999 JE82)
6890 Savinykh

References
Hughes, D. W. & Marsden, B. G. 2007, J. Astron. Hist. Heritage, 10, 21

Obsolete But Still Relevant

Under the direction of Friedrich Argelander (1799-1875), astronomers at the Bonn Observatory spent seven years (1852 to 1859) measuring the positions and magnitudes of roughly 324,000 stars, one star at a time.  This phenomenal work resulted in the Bonner Durchmusterung (BD) catalog and atlas, which included stars down to approximately magnitude 9.5 and is a tribute to the foresight of Argelander and the diligence of his small staff.  The Bonner Durchmusterung was the last star catalog to be produced without the benefit of photography, and it is certainly the most comprehensive of the pre-photographic atlases.

Back in 2007, Alan MacRobert stated (Sky & Telescope, July 2007, p. 59), “Someday machines will measure the brightness of every star in the sky to some amazingly deep magnitude many times a night, and blind software will compile and analyze light curves automatically.”  No doubt, he is correct, but he does add that this has not happened yet, despite years of pregnant expectations.

But we are getting closer to that day, with the Large Synoptic Survey Telescope (LSST) scheduled to come online in 2022 and many other similar survey instruments in the pipeline or already operational.  That is one reason as an amateur astronomer with limited resources (including time) I focus on observing the occultation of stars by asteroids and trans-Neptunian objects.  It is one of the few areas where an amateur observational astronomer can provide location-dependent observations.  You are either in the shadow path or you are not.  Though truth be told I would rather be studying exoplanets, we can only do what we have the resources to do—regardless of talent or potential.

History is full of examples of skills and techniques made obsolete almost overnight by new technologies (or a different point of view), but what is seldom recorded is the sense of desolation and indeed mortality experienced by those unfortunate enough to live to see that their highly-developed skills are no longer wanted or needed.  As my meteor-watching friend Paul Martsching has said, “It is good we don’t live forever: we are a product of our times.”  He realizes full well that someday automated systems will count every meteor above the horizon far better and more completely than any visual meteor observer can, but for many years he has carefully recorded meteor activity many nights a year.  The data he collects will always be relevant as part of the historical record, at least, and the sheer joy of being out under the stars and away from light pollution can never be replaced by a computer.  To us, astronomy is something much deeper than what can be delivered through a computer screen.

We are a product of our times, and as we approach the twilight (or autumn) of our lives we don’t necessarily feel compelled to embrace every new thing that comes along.  Peace.

From the standpoint of daily life, however, there is one thing we do know: that we are here for the sake of each other—above all for those upon whose smile and well-being our own happiness depends, and also for the countless unknown souls with whose fate we are connected by a bond of sympathy.  Many times a day I realize how much my own outer and inner life is built upon the labors of my fellow men, both living and dead, and how earnestly I must exert myself in order to give in return as much as I have received. – Albert Einstein (1879-1955)

Satellite Crossings 2016-2017

Edmund Weiss (1837-1917) and many astronomers since have called asteroids “vermin of the sky”, but since October 4, 1957 another “species” of sky vermin made their debut: artificial satellites.  In the process of video recording stars for possible asteroid occultations, I frequently see satellites passing through my ~¼° field of view.

I’ve put together a video montage of satellites I’ve recorded between December 14, 2016 and August 5, 2017.  The component events are presented chronologically as follows:

UT Date
12-14-2016
1-15-2017
5-5-2017
6-7-2017
6-19-2017
7-25-2017 (2 satellites)
8-5-2017

Target Star
UCAC4 538-7253
Tycho 586-1051-1
Tycho 1422-911-1
Tycho 4997-136-1
Tycho 6799-309-1
Tycho 666-190-1
UCAC4 548-7392

Asteroid
2485 Scheffler
19807 (2000 SE16)
71612 (2000 EH12)
11133 Kumotori
68112 (2000 YC143)
491 Carina
151 Abundantia


In all cases, the asteroids were too faint to be recorded.  And, in all cases, the target star was not occulted by the asteroid (a miss).  In the final event, the satellite passed right over the target star (9:40:11.679 UT) during the period of time the event would be most likely to occur (9:40:10 ± 3 s)!  Fortunately, the seeing disc of the target star was never completely obliterated by the passing satellite, so I was able to determine unequivocally that the asteroid missed passing in front of the star from my location on Spaceship Earth.

Here’s a graph of the brightness of UCAC4 548-7392 during the last video clip.  You can definitely see the close appulse of the satellite with the star!

In general, the slower the satellite is moving across the field, the higher is its orbit around the Earth.  One must also consider how much of the satellite’s orbital motion is along your line of sight to the satellite.  In the following montage of two video clips, the first satellite is very slow moving and thus most likely in a very high orbit.  The second video clip shows a satellite that is quite faint.  Again, the asteroids are too faint to be recorded and no asteroid occultation event occurred.

UT Date
5-14-2017
6-8-2017

Target Star
Tycho 5011-133-1
Tycho 5719-308-1

Asteroid
190471 (2000 DG27)
321656 (2010 BM90)

References
Hughes, D. W. & Marsden, B. G. 2007, J. Astron. Hist. Heritage, 10, 21

Voyager 4.5 by Carina Software

My all-time favorite planetarium software program is Voyager 4.5 from Carina Software.  Hardly a day goes by when I am not using it, and my use of Voyager goes all the way back to 1993.  The current version for Mac OS X (and Windows) is 4.5.7.  Sadly, the last update was in 2010.  I wish there was something we could do to ensure that Voyager will be maintained and enhanced in the future.

Speaking of maintenance, in 2015 Voyager ceased being able to import comet and asteroid orbital elements through its automatic Updates process.  This happened because the URL changed for both.  Seems like a pretty easy fix to me.  If Carina won’t fix it, then maybe someone can edit the executable and change the two URLs?

Fortunately, you can still manually import these orbital elements by following these instructions.

Adding Comets
  1. Navigate your web browser to https://www.minorplanetcenter.net/iau/Ephemerides/Comets/Soft00Cmt.txt and save this page to a file, which will automatically be called Soft00cmt.txt.  You can save it anywhere, but I’d suggest you save it in the Import Files folder in the Voyager 4.5 main directory within your Applications folder.
  2. In Voyager, go to File : Import : Comet Orbit File…
  3. Navigate to Applications : Voyager 4.5 : Import Files : Soft00Cmt.txt and click Open.  You will get a message box asking “Before importing new data, do you want to delete all current asteroid/comet/satellite data?”  Click Yes.  Next you will see an Import results box showing you the number of comets added to Voyager’s database.  Click OK.
Adding Asteroids
  1. Navigate your web browser to https://www.minorplanetcenter.net/iau/MPCORB.html and under Available Files right click on MPCORB.DAT (uncompressed) and Save Link As… to your Voyager 4.5 Import Files folder.  Do not open this file in your web browser as it is over 147 Mb in size!  The file saved is called MPCORB.DAT.
  2. Navigate to Applications : Voyager 4.5 : Import Files : MPCORB.DAT and edit the MPCORB.DAT file with the editor of your choice.  Remove the header lines at the top of the file right down through the line of dashes, and save the file.
  3. In Voyager, go to File : Import : Asteroid Orbit File…
  4. Navigate to Applications : Voyager 4.5 : Import Files : MPCORB.DAT and click Open.  You will get a message box asking “Before importing new data, do you want to delete all current asteroid/comet/satellite data?”  Click Yes.  It will take a while to import all the asteroids, and then you will see an Import results box showing you the number of asteroids (and transNeptunian objects, by the way) added to Voyager’s database.  Click OK.

To Catch a Shadow

Many times each week, all manner of asteroids and trans-Neptunian objects pass in front of stars, casting shadows a few miles wide all over the Earth.  There are several potential events each week at any particular location.  I use the word “potential” because there is still significant uncertainty in the paths for many of these events.  The orbits of most small solar system objects are not yet precisely known, and, to a lesser extent, there is some uncertainty in the position of the occulted (obscured) star.

On Sunday evening, November 20, I got lucky.  Not only did I record a 1.02 second occultation event, but I was lucky to see it at all as I was significantly south of the predicted path.

The star affected was Tycho 5182-758-1 (also known as BD -3° 5037) in Aquarius and the object that moved in front of it was the asteroid 430 Hybris, a space rock about 20 miles across that orbits once around the Sun every 4.8 years.  Many asteroids have interesting names, and Hybris is no exception.  In Greek mythology, Hybris is a spirit of insolence, violence, and outrageous behavior.  It is also an alternative form of the word hubris.  All quite appropriate given the outcome of the U.S. presidential election less than two weeks earlier.

Here is the video I recorded of the event:

Occultation of the star Tycho 5182-758-1 in Aquarius by the asteroid 430 Hybris

And here is the light curve I derived from the video which clearly shows the event:

Steve Messner (near Northfield, Minnesota) and I were the only ones to observe this event.  It was a miss for Steve, and he was much closer to the predicted path!

Why do we do it? Even a single positive observation can greatly improve our knowledge of the orbit of the asteroid or trans-Neptunian object.  More than one positive observation gives us valuable information about its size and shape.  We can discover asteroid/TNO satellites and even rings!  But that’s not all.  These occultation events can also give us valuable information about the star.  Its size, position, and the separation and position angle of new or known companion stars.  Someday, we may even be able to use these events to discover exoplanets!

If you love observational astronomy and would like to contribute scientifically valuable observations by observing occultation events, contact me and I will help you get started.  The more observers we have, the more valuable our scientific contribution will be.