How to find asteroids and comets to observe

Asteroids are awkward; they don’t stay in one place!  Not only that, as the Earth rotates, different asteroids are visible from the Earth at different times.  You might therefore think that finding the position of an asteroid in the sky might be a difficult task.  Fortunately, much of the difficult work has already been done by various groups of people, and it is not as difficult as you might imagine finding the co-ordinates of an asteroid in the sky.  You will need to follow these instructions on the same day as your observing session.

Using the IASC Observation Planner

The IASC (International Astronomical Search Collaboration) provides an asteroid observation planner for recently discovered objects which urgently need follow observations to confirm whether or not they asteroids.

On the right you will see a list of observatories which each object is visible from e.g. FTN. You can click on the name of an object to get coordinates for the next couple of hours or if you are planning for a few days in the future, scroll down to the form at the bottom of the page and fill out the appropriate details:

  • Specify the date in the form YYYY MM DD,
  • Specify the number of value you would like (default is 8),
  • Enter the observatory code: for  Faulkes Telescope North it is F65 and for Faulkes Telescope South, E10 (the "F" and "E" must be capitalised).
  • Click "Get emphemeris/orbits" button

Choosing an Asteroid


Using this page, finding an asteroid is very easy.  Look at one of the coloured graphs next to an asteroid. First, we need to determine when an asteroid is visible. Assuming you have already booked an observing session, you already know what time you will be observing at.

The numbers across the top of this bar are hours in UT, so 10 is 10:00 UT (=2am Pacific = 5am Eastern). Below that time, the bar is green - so we know the asteroid is visible at that time. From the colour code above, we know that green shows us when the asteroid is 30 degrees above the horizon. We cannot observe an asteroid in the yellow or red times, as this is when the asteroid is too close to the horizon.

Run down the list of asteroids and pick out a few “green asteroids” that are visible during your session.


You also need to take into account the magnitude of the asteroid. Magnitude is how bright the asteroid is - we do not want to choose very bright or very dim asteroids. The magnitude of each asteroid is displayed along-side its name (e.g. V=20.7).

Out of the visible asteroids you have chosen, dismiss the ones that have a magnitude value outside the range of V=18 to V=21.

Please Note:  One aspect this planner fails to take into account is the Moon offset angle. Therefore we recommend choosing several asteroids that fit the above criteria in case one or some of them are too close to the Moon to observe.

Other Notes


Be careful of observing asteroids as they pass through the zenith of the observing site. The zenith is the point directly above an observer. Since the telescope can neither point or track objects close to the zenith, do not pick an asteroid that passes through this area in your session (the "alt" value is between 85˚-90˚).

Asteroid Ephemeris

When you have picked out a few asteroids, you need to find their co-ordinates in the sky during your observing session so that you know where to point the telescope to observe them. It is easy to do this - simply click on the name/number of the asteroid you are interested in. It’s a good idea to right click on each link and choose 'Open in new window' - this makes it easier to come back to the original page when choosing multiple asteroids.

When you click on a link, the website automatically sends a request to the Minor Planet Ephemeris Service, and you will get a page like the one below:

The important information here is the Right Ascension (R.A.) and Declination (Decl.) of the asteroid at the given times. Look for the time of your observing session and read across to get the correct RA and Dec.

These are the coordinates you will use when controlling the telescopes.

Observing Tips

Just like any other observing session, you need to plan your filters and exposure times carefully.

Exposure Time

You can use the lookup table below to help you decide what exposure times to use.

Object Magnitdue Exposure Time in seconds
 < 10  Avoid - too bright
 10-13  20
 14-16  30
 16-18  60
 18-20  90
 >20  Very faint - look in the FT forums


The best filter option to use when imaging asteroids is the 'solar' (under 'Advanced filters').  This allows more light to hit the CCD per unit time than using a color filter and allows you to have shorter exposure times. 

Please Note:  If you are unable to book an observing session there are example data sets available on the Faulkes Telescope Project website for you to use. However, you cannot submit results obtained from these files to the MPC but they are great fun to use!