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Beginner’s guide to observe transits of exoplanets

Plan your observation

All the information needed to plan your observation can be found on the Exoplanet Transit Dtatabase (ETD,

  1. Enter your Latitude and Longitude and see the planets that are transiting today.
  2. Be careful, the times shown are in UT! Add your local time zone and do not forget to add the one-hour summer time shift (when applicable).
  3. Choose the planet that you will observe, this should:
    a) be suitable for your equipment (be careful on magnitude ans transit depth, soon, we will provide list for specific targets per telescope size),
    b) have the whole transit occurring during night time (during astronomical night, preferably),
    c) have the whole transit occurring while the star has an altitude above 20o (above 30o, preferably).
  4. Start observing at least one hour before the start of the transit.
  5. Keep observing for one hour after the end of the transit.

Set your instrument

  1. Use a RED PHOTOMETRIC filter.
  2. Set your camera temperature to the lowest available (below -10o, preferably).
  3. Set your binning to 1.
  4. Test your exposure time. Keep the number of counts below the point where your camera becomes non-linear (below 2/3 of the full well-depth, preferably).
  5. Check for at least one good comparison star in the field (similar magnitude to the target). If there is no such star move your target away from the centre of the image and try to find one.
  6. You can use a subframe to reduce the size of the images but be careful to include at least one good comparison star (similar magnitude to the target).

Reduction frames

  1. Use the same camera temperature, binning and subframe as the science frames.
  2. For every transit (before or after) record:
    a) 5 bias frames (zero exposure, using a cover),
    b) 5 dark frames (same exposure time as the science frames, using a cover),
    c) 5 flat frames (pointing to a uniformly illuminated surface, with the counts at 2/3 of the full well-depth).


For the list of target suitable to your equipment, contact us at: