Mastering Astronomy: Homework One
Why does the local sky look like a dome?
Because we see half of celestial sphere at any time.
When we see Saturn going through a period of apparent retrograde motion, it means:
Earth is passing Saturn in its orbit, with both planets on the same side of the Sun
Which of the following correctly lists our "cosmic address" from small to large?
Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe
Estimate the number of stars in the Milky Way, using the provided data. Assume that the stars are distributed uniformly
NestMilkyWay = 3.7×1010 stars
In winter, Earth's axis points toward the star Polaris. Earth is passing Saturn in its orbit, with both planets on the same side of the Sun
Polaris
Choose the correct definition of precession, and the correct explanation how does it affect what we see in our sky.
Precession is the change of direction in which Earth's axis points. The celestial poles slowly move relative to the stars. In about 13000 years the star Vega will be the North star instead of Polaris.
What is the most possible reason why estimation differs from the actual number?
Stars are distributed non-uniformly in the galaxy.
Define astronomical unit
The average distance between Earth and the Sun, which is about 150 million kilometers.
When we say the universe is expanding, we mean that
The average distance between galaxies is growing with time
Define light-year
The distance that light travels in 1 year, which is about 9.46 trillion kilometers
What can be said about the tonight's night sky in these two places?
The sky will look about the same.
Choose the correct explanation why does the statement make sense (or is clearly true) or does not make sense (or is clearly false): NASA will soon launch a spaceship that will photograph our Milky Way Galaxy from beyond its halo
The statement doesn't make sense. Even if NASA could build a spaceship that traveled close to the speed of light, it would take tens of thousands of years to get into the halo and then the same time for image to get back to Earth
Last night I saw Jupiter right in the middle of the Big Dipper. Choose the correct explanation why does the statement above make sense (or is clearly true) or does not make sense (or is clearly false). (Hint: Is the Big Dipper part of the zodiac?)
This statement does not make sense. Jupiter, like all the planets, is always close to the ecliptic in the sky. The ecliptic passes through the constellations of the zodiac, and the Big Dipper of the Ursa Major is far from the zodiac
Usually we assume that the number of stars in the Milky Way Galaxy is 100 billions. How your value from the previous part compares to that value?
We underestimated number of stars in part A
Because we see half of celestial sphere at any time.
Zenith is the highest point in the sky, directly overhead. Meridian is the semicircle extending from the horizon at north through the zenith to the horizon at south. Horizon is the boundary line dividing the ground and the sky.
If the Sun rises precisely due east.....
it must be the day of either the March or the September equinox
How can we describe the location of an object in the local sky?
specifying its altitude and azimuth
How long does it take a message to travel from Earth to a spacecraft at Mars at its farthest from Earth (about 400 million km)?
t = 22.2 min
How long does it take a message to travel from Earth to a spacecraft at Mars at its closest to Earth (about 56 million km)?
t = 3.11 min
How long does it take a message to travel from Earth at Pluto at its average distance from Earth (about 5.9 billion km)?
t = 5.46 h
A week after full moon, the Moon's phase is:
third quarter.
We are located about 27,000 light-years from the galactic center and we orbit the center about once every 230 million years. How fast are we traveling around the galaxy, in km/hr?
v = 7.98×105 km/h
The star Betelgeuse is about 600 light-years away. If it explodes tonight,
we won't know about it until about 600 years from now
