# Astronomy Physics Midterm And Final

Midterm

Name________________________Questions that you don’t want graded___________________

Open book. Open notes. No consultations with other students. Show all work for full credit. Do 20 of the 25 questions. Each question is worth 5 points. Points will be deducted if you answer more than 20 questions. No direct copying off the internet.

1) You discover an Earth-like planet around another star (50 light years away from Earth) with the same mass and diameter as the Earth. You determine that it takes 400 days for the planet to make one orbit around the star. One scientist says that the planet has to have semi-major axis that is greater than 1 AU. Another scientist corrects him and says that it is possible for the planet to have a semi-major axis of less than 1 AU. How could the second scientist be correct?

2) Your friend says there is a star with an azimuth of 8 degrees, altitude of 74 degrees, and an apparent magnitude of 2.0 in the sky at 10:00 pm on July 28, 2014 in South Hadley. It is a perfectly clear night. Should you be able to see this star in South Hadley on July 28, 2014 at 10:00 pm using just your eyes? Why or why not?

3) In movies, planets appear to have the same acceleration of gravity as the Earth. Would you typically expect this be true for planets in our galaxy? Give a reason to support your answer.

4) If you are floating in space, is the force of attraction between you and the Earth exactly zero? Why or why not?

5) You travel to another star system and meet some aliens. They say there are 50 constellations in the sky and not 88? Why would they say this?

6) Somebody says the reason the Earth has seasons is because the Earth is closer to the Sun during the summer and farther away during the winter. Is this person correct? If the person is incorrect, give a reason why that person is incorrect.

7) A photon has a wavelength of 3 meters. What is this photon’s frequency and energy? What part of the electromagnetic spectrum does this photon fall in? Where are the telescopes that observe this part of the electromagnetic spectrum usually located? Why?

8) A 20-km asteroid is discovered by a spacecraft to currently be on the exact opposite side of the Sun from the Earth so it is currently not observable with telescopes on Earth. It is in a counter-clockwise orbit around the Sun. It has a semi-major axis of 1.0 AU and its orbit is almost completely circular with an eccentricity of 0.0167. Would you expect this asteroid to be ever visible in the sky with a telescope from Earth? Why or why not?

9) Do you think Eris should be considered a planet? Why or why not? Give two reasons for your opinion.

10) The bottom spectrum contains spectral lines measured in a laboratory while the top spectrum contains spectral lines measured for a supernova (exploding star). Are the star’s spectral lines redshifted or blueshifted? How do you know for sure? Estimate the velocity the supernova appears to be moving away or towards you.

11) What are two reasons why one star may appear brighter than another star in the sky on a perfectly clear night?

12) A newly discovered element has an atomic number of 114 and an atomic mass of 289. How many protons, neutrons, and electrons does a neutral atom of this element have?

13) An asteroid takes 12 years to orbit the Sun. What is its semi-major axis?

14) Why can radio telescopes be located on the surface of the Earth while gamma-ray telescopes are not?

15) Why do people say when you are looking at galaxies, you are looking backwards in time?

16) An object is 200 oC. What is this temperature in Kelvin? What would happen to water at this temperature on the surface of the Earth?

17) What are two problems with building a refracting telescope with a 2-meter diameter lens?

18) Over the summer, you see an object travelling through the constellation Orion. Could it be one the eight planets?

19) In a perfect vacuum, would you expect visible wavelength photon or a gamma-ray photon to travel faster? Why or why not?

20) What would have a larger force on you when you were born: a doctor in the delivery room or the star Sirius. Show all calculations for full credit.

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21) Why was Pluto considered a planet when it was discovered in 1930 but is now considered a dwarf planet? Be detailed in your answer.

22) Would you expect a star that appears red in the sky to have a hotter surface temperature than the Sun or a cooler one? Why?

23) If you can travel at the speed of light, approximately how long will it take you to travel to the star Sirius (8.611 light years away)?

24) Why has the number of known planets in our solar system changed over the last ~200 years?

25) Name one thing that you have learned so far in the class that you didn’t know before.

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