An introduction to exoplanets
An introduction to exoplanets

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An introduction to exoplanets

Week 5: How to measure your exoplanet


Over the last two weeks you’ve learned two methods for detecting exoplanets: radial velocity and transits. This week, you’re going to look in more detail at the first transiting exoplanet to be discovered, HD 209458 b, and learn how astronomers have measured its properties.

Watch the following video with Carole Haswell.

Download this video clip.Video player: boc_exo_1_video_week5_carole_upload.mp4
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Carole Haswell
A famous astronomer called Otto Struve wrote about the possibility of exoplanet transits back in the 1950s. The transit of a planet like Jupiter across a star like the Sun could be detected by the technology available to astronomers then, including the telescope named after him, the 82 inch or 2.1 metre Otto Struve telescope at McDonald Observatory.
I used this telescope a lot when I was training to become an astronomer. It makes me smile to know that I’ve used the same equipment as somebody as far sighted as Struve. Struve was Russian and I’m English. Our connection is through a telescope in remote West Texas.
Astronomy is truly a global science. We all share the same sky, and a feeling of connection to it seems to me to be hardwired into the human psyche. There are a few thousand professional astronomers in the world, and we interact via the internet every day.
Astronomy is a bit like a small town. If two astronomers don’t know each other, the chances are they will at least have a mutual acquaintance. It’s now completely normal for astronomers to work intensively with colleagues they’ve never physically met. And in this way, we have solved and continue to solve some of the most amazing space conundrums, one of which is how to measure a planet you can’t actually see.
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By the end of the week, you will be able to:

  • know HD 209458 b was the first transiting exoplanet
  • explain how astronomers measure an exoplanet’s size and mass
  • appreciate the importance of transiting exoplanets
  • describe the numbers of exoplanets discovered by the transit and radial velocity methods
  • know that close-in exoplanets are more likely to transit.

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