Astronomy | Astrophysics Answers

If a planet moves around its orbit of the Sun, it’s maximum speed is twice its minimum speed.
What can we say about its orbit?
a. The orbit is nearly circular
b. The eccentricity is about 2
c. The planet is twice as far from the Sun at aphelion as at perihelion
d. The eccentricity is close to zero

Why is the highly reflective metal foil used to cover the hubble space telescope?

Using the drake equation. Estimate the number of human females in the US, who have a first name of Sarah, who ride a silver Prius, who were born April 6, and who have red hair and like raspberries?

Calculate the escape velocity from a red giant's atmosphere . Assume that the star's mass is 1 M sun and its radius is 100 R sun How does this compare with the speed at which a planetary nebula shell is ejected?

In planetary motion the line from the star to the planet sweeps put equal areas in equal times. This is a direct consequence of:
a) the conservation of energy
b) the conservation of momentum
c) the conservation of angular momentum
d) the conservation of mass
e) none of the above

At perihelion on Feb. 9, 1986, Halley’s comet was 8.79 × 10[sup]7[/sup] km from the Sun and was moving at a speed of 54.6 km s[sup]-1[/sup] relative to the Sun. Calculate its speed (a) when the comet was 1.16 × 10[sup]8[/sup] km from the Sun, and (b) at its next aphelion in the year 2024, when the comet will be 5.28 × 10[sup]9[/sup] km from the Sun.

Obtain an expression for the time period of a satellite orbiting the earth. At what altitude should a satellite be placed for its orbit to be geosynchronous?

Imagine that you are viewing a star, located about 100 parsecs away with an apparent magnitude of 0.2. The most likely absolute magnitue of the star is:
a. -4.8
b. 0.1
c. 0.2
d. 0.3

I know the answer is "a" which is -4.8, but I dont know how they got that answer?