Assignment 2

The stars appear to move through the sky as a result of the Earth's rotation. Polaris, the North Star, appears to never move. It is fixed at almost exactly the same point in the sky at all times, early or late, winter or summer. The other stars appear to move in counter-clockwise circles around Polaris, one circle every 24 hours. As a result stars never move closer to Polaris or farther from Polaris.

Suppose this evening here in Montana, you look up at the sky, and you see a bright star low on the horizon, exactly due East. Where will that star appear to be six hours later? (Hint: It will NOT be directly overhead.)

High in the South

Suppose this evening here in Montana, you look up at the sky, and you see a bright star low on the horizon, exactly due East. Where will that star appear to be 12 hours later?

Low in the West

Suppose this evening here in Montana, you look up at the sky, and you see a bright star low on the horizon, exactly due North. Where will that star appear to be 12 hours later?

At the zenith/directly overhead

In June, where does the Sun rise? (South? Southwest? West? Somewhere else?)

In the Northeast

Here in Montana, when is the Sun directly overhead, at the zenith?

Never, due to the Earth’s tilt on its axis

Suppose you look up some evening and see a first quarter moon: The right half of the moon is lit up and the left half is dark. You observe that as the moon moves across the sky, this shading does not change. Six hours later it is still lit up on the right half and dark on the left half. Explain: Why is the left half dark? What object blocks the Sun's light to make the left half of the Moon dark?

Only the right side is receiving light from the Sun, causing the Moon to “cast a shadow on itself” and the same side continues to face the Sun as it goes around the Earth

What time of day does the full moon rise? (Estimate the hour: 1 pm? 2pm? etc. and explain your answer.)

Roughly 6 pm (sunset)

At what time of day does a First Quarter Moon rise?

Around noon

If the Moon is rising at 3am, what is the Moon’s phase?

Waning crescent

Suppose we discover an asteroid that is a distance of 9.2 AU away. Convert this number to kilometers. Hint: Your answer should be something × 10^9 km

1\.38 x 10^9 km

A comet is 8.71 × 10^10 km from the Sun. Using the speed of light calculate how long it takes for light from the Sun to reach this comet. Convert your answer to hours. Hint: Your answer should be between 40 and 90 hours.

80\.6 hours

Suppose a planet is so far away that its light takes 30 minutes to reach us. Calculate the distance to this planet. Give your answer in kilometers. Hint: Your answer should be something × 10^8 km

5\.4 x 10^8 km

What are the most important ways in which the development of modern science affected the lives of ordinary people?

Advancements in medicine (increased life expectancy, getting rid of disease); enabling transportation and vocational choices

Suppose you hear that tonight the planet Mars is in retrograde motion, but the planet Jupiter is not in retrograde motion, but instead is moving normally. Will Jupiter rise in the East and set in the West, or will it rise in the West and set in the East?

Rise in the East and set in the West

Suppose you hear that tonight the planet Mars is in retrograde motion, but the planet Jupiter is not in retrograde motion, but instead is moving normally. Will Mars rise in the East and set in the West, or will it rise in the West and set in the East?

Rise in the East and set in the West

How would you observe the planet Mars in order to confirm that it is undergoing retrograde motion? In other words, what observations would you have to make? Write up a detailed set of instructions, telling someone how they could make a set of observations to determine whether or not Mars is in retrograde motion.

Map its location in relation to a fixed point over time

How did Ptolemy’s geocentric model explain why the planets sometimes move backwards?

Each planet moves on a small circle whose center moves around Earth on a larger circle. A planet following this circle-upon-circle motion traces a loop as seen from Earth, with the backward portion of the loop causing apparent retrograde motion.

How did Copernicus’ heliocentric model explain why the planets sometimes move backwards?

Believed that planets were in a certain order away from the Sun; the closer to the Sun, the faster the planet’s orbital speed, which means that some planets will appear to be moving backwards, even though they are only moving slower

Kepler’s 3rd law, p^2 = a^3, applies to all objects orbiting our Sun.In this law p is the period of time it takes an object to orbit the Sun, as measured in years, and a is the semi-major axis of this planet’s orbit (its average distance to the Sun), as measured in AU.Using algebra we can solve for either p = a^(3/2) or a = p^(2/3). \n \n 18) Suppose we discover an asteroid that is 4.0 AU from the Sun. How much time would it takes this asteroid to complete an orbit?

8 years

Suppose we discover a comet that orbits the Sun every 100 years. What would be this planet’s average distance (semi-major axis) from the Sun?

21\.5 AU