# Transits of the Sun by planets in our Solar System

Astronomers on Earth are trying to find planets around other stars by searching for transits: brief dips in brightness which last as long as a planet covers a portion of the stellar disk.

Imagine that alien creatures, on their alien planet, are trying to detect planets in the Solar System in this same way.

The method works only if planets pass in front of the star; in other words, if the observer sees the system edge-on. Actually, the system doesn't have to be EXACTLY edge-on, as long as the planets still pass over a portion of the stellar disk. Consider Jupiter moving across the face of the Sun.

1. Draw a diagram showing the Sun and Jupiter, drawn to show the size of the Sun and the distance between it and Jupiter properly to scale.

2. Use your diagram to estimate the maximum angle from edge-on at which alien astronomers could still see Jupiter cover some portion of the solar disk.

3. Find a star, any star, which is located in the right direction to see a transit of Jupiter. In other words, name a star which lies within this maximum angle of the plane of the solar system. (Hint: the plane of the solar system is also called "the ecliptic". It's shown on many star charts....)

4. What is the maximum time a transit of Jupiter could last?

5. What is the maximum fraction of the Sun's light Jupiter could block?

6. Draw a "light curve", like that shown in the lecture on planets around other stars, for a transit of Jupiter, as seen by alien astronomers.