Beginners’ guide to using the SSON robotic telescope (to obtain images for comet astrometry and photometry)
Updated 2017 January 14
The British Astronomical Association’s Robotic Telescope Project uses
the Sierra Stars Observatory
Network’s 0.61m f/10 Cassegrain telescope located
wishing to submit observations to the
UI Gemini 0.51m
This tutorial works through the planning for, telescope request for and downloading of images of comet 174P/Echelus input on 2014 August 20.
2.1. Where am I looking ?
task is to identify the area of sky visible for the date and time of the
planned observation. One of the simplest ways of doing this is to purchase a planisphere for the latitude of the robotic telescope. For
SSON I use a
Figure 1. Heavens Above chart for the SSON location at on 2014 August 20/21
2.2. Which comets are available for imaging?
Suitable comets can be determined using MPCSort or a planetarium program such as Megastar. More options are explained on the Known comets – observations planning tools and methods page
2.2.1. MPEC Sort
MPEC Sort can be downloaded from http://www.arksky.org/mpcsort To determine which comets are available to image;
- start the program
- click on Auto Import, or Comets Only
- under the View/Sort Data tab select for example;
- RA between 19 and 01 (two digits must be entered in each case, not 19 and 1)
- Dec between -20 and +90
- mag greater than 17
- Run Report
Comets (and asteroids) are listed as shown in Figure 2. This report will be for the date and time it is run – previous and future dates cannot be selected.
Figure 2. MPEC Sort report
Prior to plotting comet tracks it is advisable to download the latest orbital elements from http://www.minorplanetcenter.net/iau/Ephemerides/Comets/Soft12Cmt.txt
These should be saved in the Megastar folder as comet.txt. In addition to plotting the comet’s track it is advisable to plot that of the Moon to ensure it is not too close (>30º separation is advisable). Figure 3 shows the track of the comet for 10 days starting on 2014 August 21at 0 hrs local time. Comets for a specific location, date and time and faint magnitude limit can also be plotted.
Figure 3. Megastar track of comet C/2011 174P/Echeclus
2.2.3 ‘Light pollution’
Proximity to the Moon, a planet or a bright star can adversely affect the quality of the images. For the Moon it is advisable to ensure that the comet is at least 30 degrees away and probably the same distance for a bright star or planet. An example is shown In Figure 4 where the comet was separated from Jupiter (mag -1.9) by just less than 7 degrees. Comet 67P is approximately 1/3rd up from the bottom of the image and just to the left of Jupiter’s ‘tail’.
Figure 4. Comet 67P close to Jupiter
3.1 Determining exposure time
The exposure time must be set to avoid both trailing and over exposure of the comet. To determine the correct time both the comets nuclear magnitude (m2) and motion must be determined. The nuclear magnitude is obtained from the Cometas website at http://www.astrosurf.com/cometas-obs/ (Figure 5) and the motion from the Minor Planet Center Minor Planet and Comet Ephemeris Service (Figure 6).
Figure 5. Chart of nuclear magnitude of comet 174P/Echelus
For this example the following data was entered;
- comet ID, 174P
- start date and number of dates, 2014 08 20, 10
- ephemeris interval, 1 hour
- Observatory code, G68 for SSON
- Format for ephemeris output, MPC 8 line
- click Get ephemeris. The output is shown in Figure 6
Figure 6. MPC Minor Planet and comet Ephemeris Service output.
From Figure 5 the nuclear magnitude is estimated to be 17 and from Figure 6, the motion is 0.24 arcsecs/min Figure 7 was derived from experience of using SSON. When using the Warrumbungle telescope multiply the exposure time obtained from Figure 7 by a factor of 1.5 due to its smaller diameter mirror. Although the Gemini telescope has a smaller diameter mirror than SSON use the same exposure times as the higher Quantum Efficiency of its sensor makes up for this difference.
Figure 7. Exposure times for imaging with the SSON telescope.
The formula for determining the maximum exposure time (Tmax) to avoid trailing is;
Tmax = 60x(image scale in arcsecs/pixel)/(motion in arcsecs/min)
For SSON the image scale is 0.4 arcsecs/pixel, 0.8 arcsecs/pixel binned 2x2, Warrumbungle image scale is 0.54 arcsecs/pixel and therefore 1.1 binned 2x2 and Gemini image scale is 0.8 arcsecs/pixel binned 1x1.
From Figure 7 the exposure time for a mag 17 comet, to avoid over exposure, is 105.
Maximum exposure time to avoid trailing is 60x0.8/0.24 = 200
To avoid both over exposure and trailing the lesser of the two values is chosen i.e. 105 secs
3.2 SSON imaging request
Log in on the SSON home page, Figure 8, (having first registered and purchased credits more of which in section 4 below)
Figure 8. SSON Home page
There are five steps to scheduling a job starting with selecting ‘Create a Schedule’;
Step 1 Object
- on the Observation Request Form click on ‘Select an Object from the Object Catalog’, Figure 9
- select ‘Moving Objects’
- select ‘Moving Objects Catalogue’/Current Comets
- select comet 174P/Echeclus from the list (Figure 10). You will be taken back to the Observation Request Form and the selected comet will
appear in the Object Name box
Figure 9. Observation Request Form
Figure 10. Stationary and Moving Objects Catalogs (part)
Step 2 Title, Figure 11.
- Enter Title of your choosing and
Observer name. In this example,
Figure 11. Observation Request Form with Title and Observer boxes completed
Step 3 Date and Time (optional – I do not use this)
- if not used then job will run as soon as possible (it is advisable to check the position of the comet and moon if job is not run for several days)
- if used and job not run on input time and day then you need to cancel and reschedule the job
Step 4 Telescope/Filters, Figure 12
- select telescope (Sierra Stars Observatory)
- select filter (clear)
- enter exposure time (105 secs – from magnitude and motion))
- input number of times etc (5)
- input time delay (between images - 20 mins). A delay between images allows time for the comet to, hopefully, move away from any interfering star. If the
comet is near the horizon perhaps a smaller delay might be appropriate.
Figure 12. Telescope/Filters
Step 5 Submit,
- on the Observation Request Form the credits issued and used are listed, Figure 13
- select ‘Submit Schedule’
- then Run another job or View Job List
Figure 13. Submit form
3.3 Confirmation of job
Email(s) will be sent to you sent itemising each job and further emails will be sent after each job is run – examples below. It is worth checking the emails to make sure what you have asked for is correctly listed in both instances.
SSON Job scheduled on Telescope1; 174P/Echeclus
Job ID: 30361
Title: Outburst comets
Observers: Roger Dymock
Object Name: 174P/Echeclus
Catalog: Moving Objects Catalog
Time to repeat series: 5
Total Images: 5
UTC Date: N/A
You will receive another email when your job is completed.
Job 30363 is available in your SSON ftp account
Job Title: Outburst comets
Object Name: 174P/Echeclus
Duration String: 90
Filter String: C
Times To Repeat Series: 5
Please delete files after you download them. We delete images from our ftp server 3 weeks after the date they were created. Thanks for your business.
If any images are missing or of poor quality (cloud or trailed for example) immediately advise SSON and the credits used will be refunded (I have never known this not to be the case – feather in SSON’s cap)
4.0. Retrieving images
Calibrated images are available from Exavault (the account is set up when you register with SSON) as follows;
- log in to Exavault, Figure 14, which takes you to a list of your images available for download, Figure 15
Figure 14. Exavault login
- select images for download (zip) – the ‘Download All’ button will change to Download Selected if selection is used. With the Chrome browser you have the option of defining the Download location on your PC – presumably other browsers offer the same facility.
Figure 15. List of images with those due to be downloaded selected
- delete previously downloaded images by selecting and using the Delete button (I recommend downloading before deleting previously downloaded images as I have managed to delete the latest ones before downloading them on one occasion).
Example images are shown in Section 6 below.
4.0 Other SSON facilities
You only pay for imaging time. Rates are shown in Figure 16
- SSON is $100 per hour
- $1.67/60p for a 60 sec image
- approved BAA project 50% therefore 30p for a 60 sec image
Figure 16. SSON rates
4.2. Purchasing time tab
Login, select the Purchase Time tab and complete the form, Figure 17.
Figure 17. Purchasing Imaging Time on Sierra Stars Telescopes
4.3. Account tab
This feature shows your credit history and allows you to manage your own credits.
4.4. Telescope tab
Each telescope and current weather for its location is described under this tab.
4.5. About tab
How to use SSON, etc. is described here.
5.0. Example project
BAA Robotic Telescope Proposal
Name of Project: Comet outbursts
Observer Name: Roger Dymock
Observer Contact Email Address:
To monitor comets subject to outbursts in order to improve our understanding of such phenomena.
Comets were chosen based on those
In addition targets of opportunity as advised, for example, on the Comets mailing list.
17P 1 Jun – 1 Nov (23 wks)
29P 1 Feb – 1 Aug (27 wks)
52P 1 Feb – 1 Jul (23 wks)
174P 1 May – 1 Aug (14 wks)
C/2012 X1 1 Feb – 1 Mar (5 wks)
Comets to be imaged weekly (weather and Moon permitting).
0.6-m f/10 (Sierra Stars Observation Network)
Total Observing Time in minutes:
Plan is to obtain 5 unfiltered images during each week each
comet is observable. Exposure times will vary (from say 30 secs to 120 secs)
depending on brightness (to obtain reasonable
Assuming each comet can be imaged each week during the periods listed above;
5 x 60 sec images per week for 92 weeks = 460 mins
1 minute observing time on the SSON telescope costs $1.67.
460 mins exposure time costs $768.20 = £471.29 at £1 = $1.63 (Exchange rate 2014 January 15)
Cost to applicant = 50% of £471.19 = £235.64
Cost assumes comet can be observed on schedule which is not always possible due to poor weather, moon interference, etc. In such cases additional observations of the listed comets and targets of opportunity may be made on ‘good’ nights. Any unused credits can of course be reclaimed by the BAA.
Results (data and images) have been, and will continue to be, sent to;
· The British Astronomical Association’s Comet Section (comet observations are published in annual reports in the Journal of the BAA and the ‘Comet’s Tail’ newsletter)
The Comet Observation Database (COBS) at http://www.cobs.si This database logs both CCD and visual observations allowing immediate access to measurements and enabling comparisons between both types to be made.
BAA’s Robotic Telescope Project co-ordinator for
publication on the
· The Minor Planet Center (Published in Minor Planet Electronic Circulars ‘Observations of comets’ on a regular basis)
· Spanish Group (published more or less immediately on their website at http://astrosurf.com/cometas-obs/)
6.0 Example images
Some comets are quite faint, some are bright and sometimes you catch an unusual grouping.