Minor Planet Search command (Research | Analyze Folder of Images)

Please note: As with all items on the Research menu, you must perform a pre-analysis on your data prior to searching.

The minor planet search routine takes as input three or more images of the same area of the sky. You can have more than one set of images in the image list; they will be scanned one group of images at a time. Each group can cover a different area of the sky. In the example that follows, there are three sets of three images. The search routine is extremely sensitive, and can locate minor planets that might not be readily visible to the eye.

The time interval between the acquisition of the images within a set should be long enough to show the motion of any minor planet that might be present. Most minor planets move approximately 0.25 to 1.0 arcseconds each minute. A good separation between subsequent images would be about 5-10 pixels as a practical minimum.

For example, if your image scale is 2 arcseconds per pixel, then a minor planet must move through 10 arcseconds to show a 5-pixel movement, or 20 arcseconds to show a 10-pixel movement. The length of the exposure required to do this depends on the rate of movement of the minor planet across the sky. A slow, distant minor planet might move at about 0.25 arcseconds per minute. That would require a 40-minute delay between exposures to yield a 5-pixel change in position. A faster, nearby minor planet might move at 1.25 arcseconds per minute. That would require only a 7-minute delay. In other words, the longer the time interval between exposures, the greater the likelihood of finding slow-moving, distant minor planets.

If your aperture is small, or your light pollution is at suburban or worse levels, you won’t be able to image dim minor planets, so you could choose to focus your efforts on nearby minor planets using shorter intervals. If you are using a large aperture instrument, you can make good use of longer intervals.

You can use the following formula to come up with a reasonable range of times between exposures of the same area of the sky: The estimated shortest useful delay in minutes (based on movement of 1.0 arcseconds per minute):

image_scale * number_pixels

Estimated longest useful delay in minutes (based on movement of 0.25 arcseconds per minute):

(image_scale * number_pixels)/ 0.25

For example, if you are imaging with an ST-7E on a 10-inch SCT at f/10, your image scale is 0.74 arcseconds per pixel (see the formula near the start of this chapter). If you want to see a 5-pixel movement, and you have dark skies that justify using a long delay that will show dim/distant minor planets, then:

(0.74 * 5)/ 0.25  = 14.8 minutes

A delay of at least 15 minutes between exposures of the same area of the sky would give you a good shot at being able to find any minor planet that might be lurking in that area.

Tips on Searching for Minor Planets

CCDSoft provides two ways to search for minor planets. The first method, a Quick Search, simply allows you to quickly scan each set of images using the Blink Comparator (click Research | Comparison | Blink Comparitor). CCDSoft automates the process, presenting each set of images in turn for you to view.

The second method, the Detailed Search, presents a magnified view of every minor planet candidate. You can examine just the portion of the image that contains a candidate, and then either generate a report for the Minor Planet Center, or move on to the next set of images.

Exposure Intervals

The most efficient way to take images for a minor planet search is to take a sequence of images at different locations in the sky, and to then repeat that sequence at least two more times so that you have at least three images of each location in the sequence. Things you can do to make your hunt more successful:

• Determine the minimum delay between images that you find suitable for your location and equipment.

• Determine the amount of time for a complete exposure, including exposure time (see tips below), download time, time to move to next position, etc.

• Calculate the number of exposures at other locations that you need to provide the minimum delay. For example, if your minimum delay is 15 minutes, and it takes 2 minutes 45 seconds from the start of one exposure to the next, then you can take six images giving an actual delay of 16.5 minutes. Of course, you could also elect to take 24 images in each sequence, giving you a delay of 66 minutes between images at the same location. The suggested delay is a minimum, not an absolute recommendation. As long as the minor planet doesn’t move outside of the field of view, longer intervals are fine, and may provide greater precision.

It is not important to have the same interval between images or sequences of images. As long as the minor planet stays within the field of view in each exposure, you will get useful results.

Since things can and do go wrong, you might consider making at least four imaging sequences. Three images is the minimum number needed to perform a search, and if one of your images is bad then that area of the sky cannot be searched reliably.

If you have very bright or dark skies, or an extremely small or large image scale, you can modify the calculation for recommended minimal interval between exposures of the same area to suit your circumstances.

Exposure Duration

Various exposures can be workable, but the following guidelines will help you choose an appropriate exposure:

Undiscovered minor planets within reach of typical amateur instruments tend to have magnitudes in the range of 16-20. Your exposure time should be long enough to show point sources of this magnitude. You can insert AutoAstrometry into a test image to determine how deep your system can image successfully in a given amount of time, and adjust your exposure duration accordingly.

Avoid blooming of stars. Blooming can interfere with astrometry by creating false objects, or causing the astrometry routines to miss stars, or even cover up a potential find. Blooming will not necessarily be fatal, since you can still blink-compare the images manually should AutoAstrometry fail.

Make sure your exposure is long enough to overcome any skyglow or light pollution at your location. Test exposures of objects with a known magnitude in the range of 16-20 will show you what your system is capable of with various exposure times.

The ability of your mount to track accurately may limit your exposure times. If you are performing an automated search without autoguiding, then your polar alignment and your mount’s periodic and random errors will set an upper limit on exposure duration.

The focal ratio of your telescope determines exposure duration. Slower focal ratios (e.g., f/8, f/10) require longer exposures; faster focal ratios (e.g., f/2, f/5) require shorter exposures.

In typical situations, exposures of one to five minutes are often used for minor planet searches. You can adjust your exposures to suit local conditions and equipment.

Performing a Quick Search

Once you have images and have performed the pre-analysis, you are ready to start hunting. The Quick Search steps you through each set of images using the Blink Comparator. The following example shows you how to search for moving objects (e.g., minor planets, but the search will work with comets as well). The steps for a supernova search are very similar; the only difference is that CCDSoft is not following a moving target.

If you’d like to follow along with the example, copy all 51 images from the Images\QSearch folder on the CD-ROM to a folder on your hard disk. Then add the folder to the Pre-Analyze tab of the Data Analysis dialog using the Folders button. If necessary, remove any folders that are already in the Folders dialog before you work through the tutorial. Mark all of the options in the Pre-Analyze tab and enter the image scale. (It is especially important to get the Image Scale correct: 1.47 arcseconds per pixel), and then click Start. This begins a computationally intensive operation that may require several minutes on slower computers.

Now click on the Comparative Search tab. This tab supports searches for both minor planets and supernovas. It can also be used to search for faint comets, though of course bright, known comets will be detected as well. The main difference between the Minor planets and Supernovas radio buttons is that the Minor Planets button will search for moving objects.

Click the Minor planets radio button in the Search for section of the tab. Leave Create Minor Planet Center (MPC) observations unchecked for now. Choose Entire image in the Blink section, and All images in the Examine section.

If you cannot see any objects in the images, right-click on the active image and then click Histogram to display the Histogram tool. Use this tool to lower the white point. You may need to do this more than one time to see extremely dim objects. The right-side triangle under the histogram graph indicates the current white point. You can also drag that triangle toward the left to lower the white point.  

The goal is to lower the white point enough to show any objects that may be present. The minor planet can be seen to move in the three images thanks to the Blink Comparator..

You can change the rate of the Blink Comparator by moving its scroll bar left (slower) or right (faster).

If you find a minor planet candidate while doing a Quick Search, make a note of the filename (you can usually find this in the title bar of the image window). You can use this information to perform a Detailed Search when the Quick Search is complete. A Detailed Search allows you to create a Minor Planet Center observation report. The Quick Search allows you to quickly scan through your images, but it doesn’t include the features available in a Detailed Search.

Performing a Detailed Search

The Detailed Search displays a magnified view of the area around suspected minor planets or supernovas. In addition, if you check the Create Minor Planet (MPC) observations option, the MPC observation report is written to disk each time you positively identify a minor planet candidate.

Note: MPC observation reports are written to the CCDSoft version 5 “MPC Obervations” folder on your hard disk. The default folder is:

C:\Program Files\Software Bisque\CCDSoft Version 5\MPC Observations

The default filename is:

AutoMPCObservationXXX.txt

where “XXX” is a sequence number, starting at 1.

To perform a Detailed Search, use the following settings on the Comparative Search tab. This works for both minor planets and supernovas.

Click the Individual Objects radio button in the Blink section. Instead of seeing the entire image in the Blink Comparator, you will be presented with a magnified portion of the image surrounding search candidates.

If you have previously found image sets that contain minor planet or supernova candidates, click the Selection of Images radio button in the Examine section. This will cause only the currently highlighted image set in the Image List to appear in the Blink Comparator. If you have more than one image set on which you want to perform a Detailed Search, you can either select All images or perform multiple searches using Selection of images.

If you are searching for minor planets, and wish to submit your observation, check Create Minor Planet Center (MPC) observations. If your Examine setting is All images, an MPC observation will be written for each candidate you identify during the Detailed Search.

The Blink Comparator makes it very easy to identify candidate objects. When you are performing a Detailed Search, the appearance of the Blink Comparator dialog changes. The Blink Comparator asks you a question: Is this a minor planet? If you click Yes, a Minor Planet Center observation report is created in the MPC Observations folder of the CCDSoft installation folder, and the next object appears for your examination. If you click No, the Blink Comparator will present the next object without writing the report. If there is no next object, the Blink Comparator returns you to the Comparative Search tab.

The minor planet is the only object that moves from one image to the next. Using the Blink Comparator with the magnified view, the movement of the minor planet is immediately obvious. If you don’t see a minor planet, use the Histogram tool to lower the white point.

When the Create Minor Planet Center (MPC) observations checkbox is checked, CCDSoft writes out a text file with the observation information in it. The filename is

AutoMPCObservationXXX.txt

where “XXX” is the next sequential number. This number is incremented each time CCDSoft creates a new observation text file. The file is located in the CCDSoft program folder (default location: C:\Program Files\Software Bisque\CCDSoft Version 5) and it contains the report to send to the Minor Planet Center. A typical report is shown below.

DELETE all lines below here (including this line)

The name of the file that includes your observatory details is

"MPC Observatory Details.txt".

Edit this file to include information about your observatory.

Please see http://cfa-www.harvard.edu/iau/info/ObsDetails.html for a

complete specification of the format of this file.

DELETE all lines above here (including this line)

COD XXX

CON S. Holmes, 221B Baker Street, London NW1 4JW, England

CON [sholmes@mycroft.holmes.gov.uk]

OBS H. Poirot, P. Mason, L. Columbo, C. Chan

MEA J. Watson

TEL 0.50-m f/3.0 reflector + CCD

NET GSC

ACK Batch 001

AC2 dwatson@mycroft.holmes.gov.uk

     BSQ006   C1999 05 10.22103 13 57 22.91 -09 49 28.9          19.3        XXX

     BSQ006   C1999 05 10.24512 13 57 21.68 -09 49 19.1          19.4        XXX

     BSQ006   C1999 05 10.26865 13 57 20.44 -09 49 09.3          19.3        XXX