Suppose you monitor a large number (many thousands) of stars over a period of 3 years, searching for planets through the transit method. Which of the following are necessary for this program to detect an extrasolar planet around one of these stars?State all that apply:
1. You must be able to precisely measure variations in the planet's brightness with time.
2. You must be able to precisely measure variations in the star's brightness with time.
3. As seen from Earth, the planet's orbit must be nearly face-on (perpendicular to our line-of-sight).
4. The planet must have an orbital period of more than about 3 years.
5. As seen from Earth, the planet's orbit must be seen nearly edge–on (in the plane of our line-of-sight).
6. You must repeatedly obtain spectra of the star that the planet orbits.
7. The planet must have an orbital period of less than about 1 year.
8. You must repeatedly obtain spectra of the planet itself.

2. You must be able to precisely measure variations in the star's brightness with time.

5. As seen from Earth, the planet's orbit must be seen nearly edge–on (in the plane of our line-of-sight).

6. You must repeatedly obtain spectra of the star that the planet orbits.

Explanation:

The transit method is a very important and effective tool for discovering new exoplanets (the planets orbiting other stars out of the solar system). In this method the stars are observed for a long duration. When the exoplanet will cross in front of theses stars as seen from Earth, the brightness of the star will dip. To observe this dip following conditions must be met:

1. The orbit of the planet should be co-planar with the plane of our line of sight. Then only its transition can be observed.

2. The brightness of the star must be observed precisely as the period of transit can be less than a second as seen from Earth. Also the dip in brightness depends on the size of the planet. If the planet is not that big the intensity dip will be very less.

3. The spectrum of the star needs to be studied and observe during the transit and normally to find out the details about the planets.

4. Also, the orbital period should be less than the period of observation for the transit to occur at least once.

i guess it’s a and b