This list of suggestions is a slightly modified version
of
message 15480 on the Yahoogroups MPML group,
written by Tim Spahr on August 9, 2005.
and also includes material described by Richard Kowalski
in
message 15482 on the MPML.
-- Michael Richmond
Table of Contents
I see lots of posts on the Minor Planet Mailing List (MPML), as well as direct messages to the Minor Planet Center (MPC), concerning target selection. The first and most important question is thus: What do you, the amateur, wish to contribute? If you wish to improve the orbital element catalog of NEOs, read on. If you're just out to observe stuff, this message is probably not for you, and might even be offensive! But please, nobody should be offended. This is a guide to helping the small-scale observer contribute astrometricallyin an ever more difficult-to-contribute area.
NOTE: This is directed at the astrometric observer only! There is a *great* need for precise photometry etc of many objects, including scores of MBAs.
If your aim is to improve the orbit of an object, the first question you should ask is "what is the Current Ephemeris Uncertainty?". We'll call this the CEU. If the CEU is larger than the RMS of your standard measurements, you can generally improve the orbit. The larger the CEU, the better the improvement when you recover the object. Keep in mind, though, with a CEU too large you'll have to hunt for the object, and that can be time-consuming and frustrating. In addition, if your RMS is larger than the CEU, you are definitely not helping the orbit.
As a rule, objects with CEU < 1 arcseconds (hereafter written as 1") or so really don't need observations. The mean RMS of all orbits is about 0.4" or so. So while these objects might need the occasional observation, they sure do not need routine monitoring. Of course, if they are RADAR or Spacecraft targets,or potential impactors, then yes, continue to observe them, but only until the RADAR or Spacecraft missions are completed. The main point here is that bright, low-uncertainty objects probably DO NOT need the observations in nearly all cases. And besides, these objects are going to very likely be observed by observatory codes 699, 703, 291, 691, 704, G96, E12 or 413 during the course of any given month. The sad truth is that somewhere around 90% of all NEO observations submitted by amateurs are simply not needed. What to do then?
First, let's target things that NEED observing. How do we do this? Check here:
http://scully.cfa.harvard.edu/~cgi/NEAObs.COM
Try putting in your faint limit, say, 19.5, and ephemeris uncertainties (1 sigma) from 0.5 to 1". Notice how small this list is! Objects with uncertainties < 0.5" hardly ever need additional observations. In fact, I generally select > 0.6", as this is the pixel size on the 48-inch reflector at the Fred Lawrence Whipple Observatory on Mt. Hopkins that I generally use. Anyway, this gives a small manageable list for starters. Notice how few multi-opposition objects are listed here. Those rocks just generally don't need the observations.
Below is sample output from the NEAObs.COM form, with uncertainties between 0.5 and 1.0 arcseconds.
(39572) Pos = (13 18, -17.9), V = 18.8, El. = 68.6, 1-sig unc. = 0.7", b = +44.5, Mot. = 0.819 deg/day, PHA, Amor, brightening
1998 ST49 Pos = (01 47, -27.1), V = 19.2, El. = 116.6, 1-sig unc. = 0.5", b = -77.7, Mot. = 0.405 deg/day, Apollo, brightening
1999 NC5 Pos = (23 18, -39.2), V = 18.3, El. = 144.6, 1-sig unc. = 0.6", b = -67.1, Mot. = 0.882 deg/day, Amor, brightening
2002 UM11 Pos = (04 26, +36.5), V = 19.5, El. = 66.5, 1-sig unc. = 0.7", b = -08.7, Mot. = 0.686 deg/day, Amor, brightening
2002 WP11 Pos = (01 25, +24.9), V = 18.4, El. = 106.8, 1-sig unc. = 0.8", b = -37.3, Mot. = 0.709 deg/day, Amor
2005 HA8 Pos = (17 26, -39.3), V = 19.3, El. = 125.1, 1-sig unc. = 0.8", b = -02.2, Mot. = 0.668 deg/day, 1-opp Amor, fading
2005 MG5 Pos = (18 21, +06.1), V = 19.1, El. = 131.5, 1-sig unc. = 0.6", b = +09.6, Mot. = 0.897 deg/day, 1-opp Amor, fading
2005 NJ1 Pos = (04 20, +27.5), V = 19.5, El. = 68.6, 1-sig unc. = 0.5", b = -15.9, Mot. = 2.456 deg/day, 1-opp PHA, Apollo, fading
2005 OV1 Pos = (22 59, -27.0), V = 19.4, El. = 153.5, 1-sig unc. = 0.6", b = -65.1, Mot. = 1.846 deg/day, 1-opp Amor, fading
2005 OE3 Pos = (22 02, -50.6), V = 16.1, El. = 144.1, 1-sig unc. = 0.6", b = -50.3, Mot. = 2.687 deg/day, 1-opp PHA, Apollo, brightening
2005 OH3 Pos = (00 29, -35.2), V = 19.5, El. = 132.9, 1-sig unc. = 0.5", b = -80.6, Mot. = 3.423 deg/day, 1-opp Amor, fading
2005 PJ2 Pos = (22 36, -19.0), V = 18.9, El. = 160.5, 1-sig unc. = 0.7", b = -58.0, Mot. = 0.850 deg/day, 1-opp PHA, Apollo, brightening
Next, run the uncertainty out to 20 arcminutes or so. This will give you some recovery targets. Always a good choice.
Below, output from NEAObs.COM form, with uncertainties between 10 and 1200 arcseconds.
2002 DP3 Pos = (03 47, +09.4), V = 19.1, El. = 80.1, 1-sig unc. = 92.5", b = -34.0, Mot. = 0.801 deg/day, 1-opp Amor, brightening
2005 FC3 Pos = (20 53, +31.1), V = 15.5, El. = 132.7, 1-sig unc. = 255.5", b = -08.6, Mot. = 4.706 deg/day, 1-opp Apollo, fading
Then there's the Near Earth Object Confirmation Page (NEOCP). Anything here that needs observing? I realize that without the CEU it is hard to guess. But it is in my mind much more likely that something on the NEOCP needs observing than something with several oppositions. Keep in mind, though, that often these objects too are overobserved.
Below, a sample of the default output from Near Earth Object Confirmation Page (NEOCP).
UHAS96 No comments so far! Date UT R.A. (J2000) Decl. Elong. V Motion Uncertainty h "/min P.A. 2005 08 09 16 04 42 40.1 +19 53 01 65.3 20.7 2.90 093.9 Map/Offsets 2005 08 09 17 04 42 52.4 +19 52 49 65.3 20.7 2.90 094.0 Map/Offsets 2005 08 09 18 04 43 04.7 +19 52 37 65.2 20.7 2.90 094.0 Map/Offsets 2005 08 09 19 04 43 17.0 +19 52 24 65.2 20.7 2.90 094.0 Map/Offsets 2005 08 09 20 04 43 29.3 +19 52 12 65.2 20.7 2.90 094.0 Map/Offsets 2005 08 09 21 04 43 41.7 +19 52 00 65.2 20.7 2.90 094.0 Map/Offsets 2005 08 09 22 04 43 54.0 +19 51 48 65.2 20.7 2.90 094.1 Map/Offsets 2005 08 09 23 04 44 06.3 +19 51 35 65.2 20.7 2.90 094.1 Map/Offsets 2005 08 10 00 04 44 18.6 +19 51 23 65.2 20.7 2.90 094.1 Map/Offsets
Now, what if we had a list of one or two-night potential Near Earth Objects (NEOs)? Anyone interested in that? The idea would be to pick objects from this set with > 10% chance of being an NEO based on motion and brightness. If this strikes your fancy, there will be a page full of these starting in the fall! This will be separate from the NEOCP, as the NEOCP page contains only those objects with very high probabilities of being NEOs or comets.
Consider this the first in a set of tools to help observers with target selection.
The Lowell Observatory devotes much of its efforts to the study of members of our Solar System. Lowell astronomers have created a number of tools to help others work efficiently.
I'll mention just a couple of these in this guide.
The Hierarchial Observing Protocol for Asteroids (HOP) service helps observers to pick potential targets for their particular site, instrument and interests. For a detailed description of the HOP forms, you can read a guide to the parameters of HOP. I'll show just a quick example here.
After supplying a bit of identification, the user will face a set of boxes which describe the limitations of his particular setup:
| Limiting Magnitude (Mag) | Maximum Zenith Angle (Deg) | Minimum Solar Elongation (Deg) | Minimum Lunar Elongation (Deg) |
|---|---|---|---|
| Galactic Latitude (Deg) | Probability of Imaging (%) | Field of View (arcsec) | |
|---|---|---|---|
| RA | Decl. | ||
Fill these in based on what you know about your equipment: for example, if you know that scattered light from the Moon will ruin any images closer than 30 degrees from the Moon, then change the Minimum Lunar Elongation value to 30. The Galactic Latitude box places a limit on how close you wish to go to the plane of the Milky Way; the fainter your limiting magnitude, the more crowded the field will be at low latitudes.
Next, you'll be asked to pick one or more variety of target for the night:
| Asteroid Types | |||
|---|---|---|---|
| Transjovians (Excluding Trojans) |
MBOs (Including Trojans and unusual MBOs) |
Mars Crossers | Inner-Planet Crossers |
By default, all four types of asteroids are given a priority of zero; that means "of no importance at all." Therefore, you must modify at least one box to change its priority to some non-zero value. The higher the value, the more important a given type is considered.
The final (major) bit of input you must provide is the reason that one asteroid might be more important than another.
Again, you must set at least one box to a non-zero priority.
When you have finished modifying the form, click the Find Asteroid button to start the procedure. After a brief wait, you should receive a list of targets for the coming night, something like this:
| Asteroid Name |
Schedule for Observation (or Scheduling Observatory) |
Arc (days) |
RA | Decl |
RA Motion s/day |
Decl Motion "/day |
Vmag |
Uncertainty (1-sig) arcsec |
Selection scores T L U N C I M S |
Relative Score |
| 2000 UA29 | 2279 | 23 48 59.97 | -01 44 23.9 | -27.03 | -3.94 | 19.6 | 585.55 | 3 1 2 0 0 0 0 0 | 100 | |
| 2001 UL96 | 54 | 23 24 08.76 | -03 47 49.3 | -29.19 | -4.59 | 19.5 | 582.88 | 3 1 2 0 0 0 0 0 | 100 | |
| 2002 AP197 | 20 | 23 23 25.70 | -01 16 36.3 | -38.42 | -0.45 | 19.7 | 589.42 | 3 1 2 0 0 0 0 0 | 100 |
If you are interested in a long-term strategy for improving the orbital elements of a particular asteroid -- perhaps because it appears in a list like the one above -- then you can use another Lowell tool: Asteroid Observation Strategy Chart Builder. This program will look at one particular asteroid and figure out when observations might best be scheduled, over a span of several years. For example, it will calculate the change in apparent magnitude, motion across the sky, altitude above the local horizon, etc. The program will produce a graph showing the overall uncertainty of the asteroid's apparent position as a function of time, like this:
The grey regions in the graph indicate the periods of time when observations would be most effective.
This is a copy of material at http://cfa-www.harvard.edu/~tspahr/astrom.howto , which should be checked for updates.
Dear Observers,
We all too frequently receive error-filled submissions of astrometry here at the MPC, and I've decided to write a little "how-to" describing what common pitfalls can be avoided, and how to improve, in general, what folks submit to the MPC.
First, read this:
http://cfa-www.harvard.edu/iau/info/Astrometry.html
These two documents overlap significantly. Please read both carefully.
This/these are the most common mistakes when submitting to the MPC. Professional observers still make this mistake. The key is to avoid lining up these objects and "creating" a real object. By far the easiest thing to do is simply DITHER THE TELESCOPE BETWEEN SUCCESSIVE IMAGES. This will eliminate 99% of all false detections immediately. At CSS, we had this problem, and we eventually settled on simply moving the telescope after each image. So... image 1 was at the expected coordinates. Image two was 30 arcsec NORTH of this location. Image 3 was 30 arcsec SOUTH of the expected coordinates, while image 4 was 30 arcsec SOUTH AND WEST of the expected coordinates. This simple procedure makes is nearly impossible for anything fake to line up with linear motion within a few arcsec tolerance!
The second problem with false detections is using a bare minimum of images. I would never use 2 images for discovery purposes unless I had very small pixels (0.5" /pixel or so) and I had a good point-spread function for both detections. Three images is in my opinion the bare minimum for consideration, but I do not like this. USE MORE THAN 3 IMAGES, AND DITHER THE TELESCOPE.
Another very common mistake is absolute bare-minimum time intervals between images. It is best to have at least 30 minutes worth of coverage on each and every object. Note that CSS, LINEAR, and Spacewatch all have t > 30 min. LINEAR averages around 70 minutes interval on each object. This gives a more robust Vaisala orbit, better linking probabilities on the subsequent nights, and lastly, prevents bad links by the observer and the MPC. These short-interval links are often misidentified, or worse, spurious objects! The MPC now requires t > 20 minutes for designations except in extreme circumstances. Keep in mind this is t > 20 min on EACH night. In addition, almost all false detections won't show linear motion over a 20 or 30 minute interval... most of them come from very short intervals.
It is surprising that this is the second most common problem, and perhaps the most annoying. We often get observations of objects that are so clearly wrong, a simple cursory examination would show this. For example, we DAILY receive reports of objects that are reversing direction of motion between 3 measurements, or worse, two good positions and one that is off by 5 arcmin or something. In this category is also bad links by the observer. This also happens on an almost daily basis. For example, an observer will go to the expected coordinates for an NEOCP object, find a bright object, measure it, and send it in as the NEOCP, only to find later this was a routine numbered asteroid. This is precisely why the NEOCP, and the MPC Ephemeris service gives you the SPEED AND DIRECTION of the object in question. I'm sure you'd be surprised how many routine MBAs moving 30" / hour are turned in where the observer thought this was an NEOCP object that was supposed to be moving 300" / hour. We also receive bad links where observers simply went to the MPChecker, found the object closest to their object, and pasted this designation in the observation string. This causes me no end of grief, because in most cases, it is simply easier to paste a new observer-assigned TEMPORARY designation on each object submitted. In this fashion all "new" objects are identified by our automatic software, and designations are e-mailed automatically. If the observer doesn't receive a designation, it usually means that the object is a new one. This also reduces e-mail traffic back-and-forth between parties, one thing that definitely helps me, since I get a few hundred e-mails per day :)
Of all things, this should *NEVER* be a problem, but is routinely, and perhaps a day-to-day error in observations sent to the MPC. IT IS AN IMPERATIVE TO CHECK YOUR CLOCK EACH AND EVERY TIME YOU OBSERVE. Badly timed images are not only an amateur problem. EVERY SINGLE professional survey has had some sort of timing problem, from bad local - UT time corrections, bad computer clock time, mistiming the exposure start and end, and messing up the midpoint of the exposure. Yes, these were all done in one form or another by professional surveys. Amateur observers, however, really excel in messing this up. We're constantly fixing or deleting poorly timed images. Please be careful here. There's no excuse for this one. And trust me, I'm talking from experience. CSS had a -12 second error on all images due to improper coding of the start time in the FITS header. And this is more or less my fault for not checking it...
Another frequent problem is astrometry that is clearly the right object that also clearly does not fit. This arises in some cases for horrible or non-converged fits on astrometric solutions. If your RMS on your solution is extremely small and uses only 3 or 4 stars, it is probably wrong. Likewise, if it is over about 0.7", you've also probably got a problem. Keep a close eye on those solutions!
A good chunk of objects need no astrometry whatsoever, and yet we still will receive literally THOUSANDS of observations each month of these objects. Bright numbered asteroids, unless they are occultation targets, radar targets, or mission targets, really don't need astrometry. So don't go out of your way to target them. You may, and should, measure them if they just happen to appear in your frames. But targeted astrometric observations of routine numbered MBAs by amateur facilities is almost certainly a waste of time. Likewise, many non-numbered NEOs are absolutely hammered by amateurs for no apparent reason. A good rule of thumb is to only observe objects that you and your system can actually help. So if the current ephemeris uncertainty is only 0.3", there is no possible way you can dramatically improve the orbit if your astrometry is only good to 0.5". Also, given the sky coverage and sheer number of professional surveys in action, it is very likely that your hard work will simply be obviated the next night by a survey.
Now, some notes regarding professional programs: At this point, it is probably important also for amateurs to know a thing or two about the professional programs. LINEAR takes FIVE (5) images of each field, total spacing about 1 hour. CSS, E12, and LONEOS all take FOUR (4) images of each field, with intervals varying from 20 - 60 minutes from first to last image. SPACEWATCH and NEAT take only 3 images, spaced by 20-60 minutes, but they both have SMALL ( ~ 1 arsec) PIXELS. Each and every of the aforementioned programs submits *all* objects as new objects. Meaning, each object observed on a given night has its own, observer-assigned unique temporary designation. These observations pass flawlessly through our automatic processing code, and the remaining one-night objects that might be NEOs are left for further examination. Given that a good deal of MPC effort has been put forth to process the bulk of the data this way, other observers should consider operating in a like manner.
Tim Spahr
Near Earth Object Technical Specialist at the MPC
Former observer with the Catalina Sky Survey
Addendum 1 (Dec 20, 2004):
Please cease and desist from sending single positions of any object
on a given night, unless this object is **CRITICALLY** important, and
then only do so with gratuitous comments regarding the accuracy of
the measure, and why no other measures were obtained. For example,
this might be OK for NEOs and comets from skilled observers. But
single, isolated positions for MBAs are very likely to be deleted.