Exam 1: A Modern View of the Universe

One of the main reasons the Hubble Space Telescope was built and launched was to measure how fast the universe is expanding. If the expansion turns out to be faster than we thought, our estimate for the age of the universe will be

The distribution of the mass of the Milky Way Galaxy is determined by

Imagine that you could drive your car in space. Assume that you can drive at a constant speed of 100 kilometers per hour. Suppose you started driving from the Sun. How long would it take, in years, to reach Earth?

Consider the following statement, and explain whether or not it is sensible: Someday we may build spaceships capable of traveling at a speed of 1 light- second per hour.

An astronomical unit (AU)is .

How many galaxies are there in the observable universe?

Briefly explain how the Sun generates energy.

How long does it take our solar system to complete one orbit around the Milky Way Galaxy?

Stellar and galactic crowding: The comparison of objects' sizes to the distance between them gives a sense of their relative density, i.e., how "crowded" they are. A typical human is about 1 meter across the shoulders. Compare the relative density of people in the case where they are standing on average 1 meter apart compared to a situation where they are on average 10 meters apart (hint: describe the separation in units of person- size). Now, compare the "crowding" of stars to that of galaxies. A typical star has a diameter of about 1 million km, while the average space between stars is about 5 light- years. A typical spiral galaxy in a cluster (such as the Milky Way)is 100,000 light- years across, and has another spiral galaxy within about 10 million light years.

How do scientists estimate how old the universe is?

How many seconds are in one year? (Calculate this, do not look it up.)

The Earth has a radius of about 6,000 km. How long would it take for an object traveling at the speed of light to circle the earth? (Recall that the speed of light is 300,000 km/s)

Place the following items in order of actual physical size, from smallest to largest.

Which of the following statements does not use the term light- year in an appropriate way?

If the entire galaxy (with a diameter of 100,000 light years)were represented by a circle with a diameter of 4,400 km (similar to the width of the continental United States), then how far apart would be the Sun and its nearest stellar neighbor, Proxima Centauri (which is 4.2 light years away)?

One light- minute is the distance light travels in one minute. The speed of light is about 300,000 km/s (3×105 km/s). How far is one light- minute?

Suppose we imagine the Sun to be about the size of a grapefruit. How big an area would the orbits of the eight planets of the Solar System cover?

Briefly explain why an expanding universe implies a beginning (called a Big Bang).

A television advertisement claiming that a product is light- years ahead of its time does not make sense because .

Most of the mass in the Milky Way Galaxy is located