One of the great things about Slooh.com is that you can point the telescope anywhere in the sky, giving you complete flexibility to observe a visible target.

One interesting aspect of observing is getting images of comets. This article explains how you can find comets that are visible in the sky and how to plan and book missions to view the comet using the Slooh.com telescopes.

You’ll use a couple of different websites in this tutorial to view candidate comets and plan your missions – this article provides you with the links to the sites and explains how to use them,

Selecting a Comet

There are all sorts of comets in the sky and not necessarily all of them are visible. For example, a comet might be potentially visible but its apparent magnitude might be too low to view using a telescope. To narrow down the listing of possible comets, I use this website which lists all currently visible comets:

http://aerith.net/comet/weekly/current.html

There’s quite a bit of information on the page, however, we’re only concerned with the name of the comet – for this example, I’ll use the first comet in the list which is C/2002 T2 (Palomar).

Now that we have selected a comet, we need to get its coordinates so we can use them to book  Slooh.com missions to observe the comet.

Generating Ephemeris

The listing of coordinates of the comet at a particular date, time, and location are called the ephemeris and we use the JPL Horizons web interface to get the listing of coordinates. Here’s the link to the JPL Horizons web interface:

https://ssd.jpl.nasa.gov/horizons.cgi

If you don’t see anywhere to make selections, click the App tab, then follow the directions below.

You need to enter some information to generate the coordinates:

  • For Target Body, click the Edit button, enter C/2020 T2 in the search box and click the Search button
  • For Observer Location click the Edit button, enter G40 in the box, and click Search
  • For Time Span, click the Edit button and enter a start and end date in yyy-MM-dd format, use a step size of 1 hour, and click Use Specified Times
  • For Table Settings, click the Edit button, click the option next to #4 Apparent AZ & EL, find the elevation cutoff and enter 30 next to it, and then click Use Specified Settings
  • Click the Generate Ephemeris button to generate the coordinates

The website produces a lot of output – here’s what some of it means. Here’s an example of one line of the output:

2021-Jun-25 23:00  m  13 46 41.03 +12 20 46.1 251.7453  52.9322  13.593  15.789 1.55774762131550  10.9690594 104.5425 /T  28.4847
  • The first column lists the date, followed by the time – in this case it is 2021-June-25 at 23:00 UT
  • The column labeled Elev shows the object’s elevation above the horizon, in this case it is 52.9322 degrees above the horizon
  •  The coordinates for this comet at this particular time are in the RA and Dec columns. In this example, the RA is 13 46 41.03 and the Dec is +12 20 46.1 degrees
  • You’ll also see a line in the output that says ‘Elevation Cut-off Requested. This is here because we requested that the object be above 30 degrees to show us the ephemeris and anything below 30 degrees is not of interest to us because the Slooh.com telescopes’ minimum elevation is 30 degrees

I selected this particular line because there was a mission slot available on the Canary One or Two telescope at the time. You can look through the results to check other time slots.

Note that you entered G40 for the location – this is the code for the Slooh.com Canary Island location. If you want to use the Slooh.com Chile telescope, use code W88.

Booking a Coordinate Mission

When you’re ready, book a mission as follows

1. Select the telescope icon at the upper-left of any Slooh.com screen

2. Click Mission Setup

3. Select By Telescope

4. Select the telescope you wish to use

5. Select an available timeslot, guided by the ephemeris that you generated earlier

6. Select By Coordinates

7. Select Comet as the object type

8. Copy the three digits that make up the RA into the RA field

9. Copy the three digits that make up the Dec into the Dec field

10. Enter the name of the target

11. Click Check Visibility

12. Select a processing option – Generic is likely the best option for processing FITS files

13. Click Preview Mission

14. Click Schedule Mission

You might want to schedule several missions – you can use the same coordinates for each mission if they occur within a couple of hours of one another.

If the mission succeeds, you’ll get your image the next day and can then process the FITS images using something like JS9, MaxIM DL, PixInsight, or whatever software you prefer to use. The PNG images you get from Slooh.com might be good as well.

Conclusion

In this article, you learned how to select candidate comets for observing, you generated ephemeris for the comet, and you learned how to book a coordinate mission for the comet.