An introduction to exoplanets
An introduction to exoplanets

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An introduction to exoplanets

Week 4: You’re in my light – transits


Last week you learned how astronomers detect exoplanets by measuring the wobble of their stars. This week you will learn about a different technique for spotting them – waiting for them to pass in front of, or transit, their parent stars. You’ll start off by looking at planets that transit in our own Solar System, and then move on to exoplanet detection.

Watch this video in which Carole Haswell talks about what you will be doing this week.

Download this video clip.Video player: boc_exo_1_video_week4_carole_upload.mp4
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Carole Haswell:
Now, you’re going to study one of the most beautifully simple techniques in 21st century astrophysics, the transit method for detecting and measuring the size of exoplanets. I love this so much that some of the early results prompted me to completely redirect my own research to study exoplanets instead. I wrote a book called Transiting Exoplanets, which was published in 2010. And I’ve used telescopes including the Hubble Space Telescope to study them.
This week, you’ll learn a lot more about transits and enough about stars to be able to appreciate how our knowledge of stars helps us to measure and work out the properties of their planets. Telescopes are obviously important tools for astronomy. What may be less obvious is the importance of calculus.
Calculus is a branch of maths, and it’s no coincidence that it was invented by the first person to work out the rules of gravity. This week, you’ll see a cartoon, which beautifully illustrates how calculus works. I hope you enjoy it.
Finally, we’ll bring it all together. You’ll see how we know the size of thousands of individual exoplanets even though we can’t see them.
End transcript
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By the end of this week, you will be able to:

  • state which planets in the Solar System are observed to transit the Sun, and explain why
  • outline how transits can be used to identify exoplanets and measure the size of stars and planets
  • state the relationship between radius and cross-sectional area for a sphere
  • show you understand the size ratio between the Sun, Jupiter and Earth
  • describe the relationship between transit depth and the ratio of radii of the planet and star (Rp /Rstar)2.

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