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?
a. You must be able to precisely measure variations in the planet's brightness with time.
b. You must be able to precisely measure variations in the star's brightness with time.
c. As seen from Earth, the planet's orbit must be nearly face-on (perpendicular to our line-of-sight).
d. The planet must have an orbital period of more than about 3 years.
e. As seen from Earth, the planet's orbit must be seen nearly edge-on (in the plane of our line-of-sight).
f. You must repeatedly obtain spectra of the star that the planet orbits.
g. The planet must have an orbital period of less than about 1 year.
h. You must repeatedly obtain the spectra of the planet itself.

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

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

g) The planet must have an orbital period of less than about 1 year.

Explanation:

The following are necessary for this program to detect an extrasolar planet around one of these stars:

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

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

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

g. The planet must have an orbital period of less than about 1 year.

Explanation:

Although it might be difficult to observe the brightness of a planet, their star's dip in brightness will be used to detect the star. The star brightness reduce by small percentage to signal passing each of extrasolar planet. Spectral of star can be obtained from the planets

Also, using direct imaging from the interferometer, extrasolar planets can be observed nearly edge-on in the plane of our sight.

Each planet must be able to complete some revolutions around to star within the observation time(3 years for this question).

the answer is the last option or letter d)

heat from the core of the earth causes convection currents to occur in the mantle. these currents slowly move the crust around.