I
Roger Dymock
The quest for ‘ET’ (Exoplanet Transits, not
aliens!)
f you thought that detecting exoplanets is the purview of professional astronomers only, then
think again. e dips in brightness caused by some exoplanets as they transit their star can be
detected by amateurs using medium- or large-aperture telescopes, astronomical CCD cameras and
some suitable processing software.
With this in mind, the Exoplanets Division of the British Astronomical Association (BAA) is
collaborating with both amateur and professional astronomers to provide ground-based observations
of exoplanet transits in support of the ARIEL (Atmospheric Remote-sensing Infrared Exoplanet
Large survey) mission, which was formally given the green light by the European Space Agency in
November and will launch in 2029. So why not try your hand at observing an exoplanet transit, and
participate in a new pro-am project to support ARIEL, called ‘ExoClock’.
Measuring exoplanetary transits isn’t as difficult as it sounds. An exoplanet transit is similar to a
transit of Mercury or Venus in that the exoplanet passes between its host star and Earth. As it does
so there is a very small drop in the brightness of the host star as the planet blocks some of the star’s
light – we’re talking thousandths of a magnitude, or millimagnitudes (mmag). is ratio of the size
of the transiting planet to that of its star is indicated by the depth of the transit on a light-curve
(which measures how the brightness of an object changes with time). Observers who are familiar
with measuring the magnitudes of variable stars, asteroids and comets should nd measuring these
small magnitude changes quite a similar process, but if you are new to this aspect of astronomy, then
don’t be put off – with a little practice you too can get involved and thus make a signi cant
contribution to the project.
ExoClock