Shadows of distant worlds sighted from York

Since 1995, more than 200 extrasolar planets have been detected orbiting around distant stars like our Sun but outside our solar system. About 16 of those planets are known to eclipse the stars they orbit – if you’re watching from Earth.

Right: Simulated NASA image of an extrasolar planet transiting its host star

Watching from Earth is just what Patrick Hall’s astronomy students were doing this past academic year in the hopes of observing the shadow cast by one of these planets as it transited in front of its parent star. They were not disappointed.

"I had the students use our 60-cm campus telescope to detect the shadow of a planet orbiting a distant star, as the planet passed between us and the star," said Hall of the assignment he gave those enrolled in his Astronomical Techniques class. "These extrasolar planets were known to exist and to transit the face of their parent star, so we knew when and where to look, but nonetheless these weren’t easy measurements to make."

The shadows these planets cast on their stars can be detected even with relatively small telescopes, says Hall. Because the parent stars are so bright – in some cases visible to the naked eye – York’s location in a light-polluted city was not a handicap.

Some of Hall’s students focused on Aitken Double Star #16402B. They learned that its planet – called a ‘hot Jupiter’ because it’s as big as Jupiter but closer to its sun than Mercury is to ours – circled the star every four and a half days. Using a camera attached to the telescope, they began photographing during one of the planet’s transits across the face of the star. It took a few hours for the planet to transit the star, but it took months of painstaking analysis for students to be sure they had detected the transit. They confirmed that the star’s brightness increased by about one and a half percent as the planet moved out from between the star and Earth.

"These are the first observations of such extrasolar planet transits obtained at a Canadian university by undergraduates as part of their coursework," says Hall.

Below: Undergraduate students plotted this transit of Aitken Double Star #16402B based on their observations from York’s observatory. It shows that the apparent brightness of the star increases by 1.5 per cent when the planet moves out from in front of the star. Sarah Sadavoy plotted the transit using data obtained with Sandy Hsu and David Milks.