ASTR 1102

Suppose we have an atom with two energy levels. It can absorb photons by transitioning from E1 to E2, or emit photons by transitioning from E2 to E1. Which of the following must be true?

Both photons have exactly the same energy

What are the different kinds of twilight we experience each day?

Civil twilight, nautical twilight, and astronomical twilight

Which of the following stars in the constellation Cygnus would be the brightest?

Delta (δ) Cygni

Light waves passing through any opening will diffract and form an interference pattern. So why don't we observe it when we see light passing through doors and windows?

For large openings, the pattern is nigh impossible to see

If fusing hydrogen releases energy, why don't hydrogen atom on Earth spontaneously fuse?

Getting the atoms close enough to fuse takes a lot of energy

Which of the following would increase the light gathering power of a telescope?

Increase the area of its primary mirror

Suppose we want to improve the resolution of a diffraction limited telescope. What should we do to the mirrors to make this happen? Remember that

Increase the diameter of the primary mirror

Suppose we wanted to search for protostars. What type of light should we sue to best observe them as the form?

Infrared

Which of the following would cause a scientific theory to be rejected?

It does not correctly predict experimental observations

As gas clouds collapse, they become denser. What happens to the temperature of the cloud as density and pressure increase?

It gets hotter

Suppose I hold a beach ball with a diameter of 1 meter. Initially it is 20 meters from you. What happens to its angular size as I move it further away from you?

It gets smaller

Suppose we have two telescopes. The first has a diameter of 1 meter. The second has a diameter of 5 meters. How does the light gathering power of the 5 meter telescope compare to the 1 meter telescope?

It is 25 times larger

Suppose we see the hydrogen alpha line in a distant star shifted from 656.3 nm to 700 nm. What can we conclude about that star's motion relative to us?

It is moving away from us

Newtonian mechanics, which describes the motion of an object when forces are exerted on them, was accepted as a scientific theory that describes nature approximately 400 years ago. It was accepted because:

It predicts how objects move under the action of a force

Suppose I hold a beach ball with a diameter of 1 meter. Initially it is 20 meters from you. What happens to its linear size as I move it further away from you?

It stays the same

Suppose Earth's distance from the Sun were to double. What would happen to the intensity of sunlight in our new orbit? Recall that intensity scales with distance squared.

It would be four times weaker

Suppose we throw a baseball in space, far away from any object. What would happen to it?

It would continue to travel in one direction forever

Suppose we put an object at the L5 Lagrange point. On long timescales, what would happen to that object? Recall that L5 is the trailing Lagrange point.

It would remain at L5 forever

What is the main source of energy at the Sun's core?

Nuclear fusion

What is the name of the North Star?

Polaris

Suppose we want to build a telescope to view ultraviolet light. Where should we put it?

Put it in space

All stars lose mass as part of their solar wind. How does the mass loss of a stellar mass AGB star compare to a stellar mass star on the main sequence?

The AGB star loses mass much faster

Suppose Earth's axial tilt were 5° instead of its current 23.5°. What would happen to the Arctic and Antarctic circles?

The Arctic circle would move north. The Antarctic circle would move south.

Why does the Earth experience seasons?

The Earth is tilted with respect to its orbit

The Sun exerts a gravitational pull on the Earth. What can we say about the gravitational pull of the Earth on the Sun?

The force on the Sun is equal and opposite to the force on Earth

Which is brighter: a supernova 1 AU from Earth, or detonating a hydrogen bomb pressed against your eyeball?

The supernova is brighter by a factor of 10^9

How do the surface temperatures of red giants compare to stars like the Sun?

They are much cooler

All of the supernova remnants pictured shine brightly with X-rays. What does that tell us about the temperature of the gasses?

They are orders of magnitude hotter than the surface of the Sun

A hydrogen atom is in the n=5 state. What transition would produce a photon with the largest wavelength?

To n=4

What is the current phase of the Moon?

Waxing crescent

Suppose we pass light through two narrow slits. What would we see on a distant screen after passing the light through both slits?

We would see a pattern of light and dark lines on the screen

Which of the following statements about light is false?

You see events as they happen

A telescope has a primary focal length of 3.2 m and an eyepiece focal length of 15 cm. What is the magnification of this telescope? Recall:

-21.33

A degree can be further divided into arcminutes and arcseconds. One degree contains 60 arcminutes, and one arcminute contains 60 arcseconds. Given this information, how many degrees is 15 arcseconds?

0.00417°

Suppose we were at the South Pole. How many sunrises would we expect to see each year?

1

A hydrogen atom transitions from the n=3 to the n=2 state. What is the energy of the emitted photon?

1.9 eV

Suppose we pass a ray of light through crown glass, n = 1.52. How fast does the ray of light travel while in glass? Remember, the speed of light in a vacuum is

1.97 x 10^8 m/s

The wave pictured is moving to the right at 200 m/s and its wavelength is 2 m. What is the frequency of this wave? Recall that v = λf

100 Hz

An hour contains 60 minutes. How many hours is 1000 minutes?

16.7 hours

Many green lasers emit light at exactly 532 nm. What is the energy of the individual photons from this laser? Recall that and hc = 1240 eV nm

2.3 eV

How many time zones are actually recognized on Earth?

24

How long will a 20 solar mass star live?

5.6 million years

A full circle has 360° or 2π radians. Given this, how many degrees are in 1 radian?

57.296°

Light travels at a speed of m/s. Green light has a wavelength of 500 nm . What is the frequency of this light wave? Recall that v = λf

6 x10^14 Hz

We live in Baton Rouge, at 30.4515° north latitude. Given this fact, what would be the angle between the North Star and the zenith? Recall that the zenith is the top of the sky.

60°

Suppose we have a corner mirror as shown in the figure. The two mirrors are at a right angle to each other. If a light ray is incident on the first mirror with , what is the angle of reflection off the second mirror?

70°

How many constellations are recognized in the night?

88

What is the angle between the zenith and the horizon?

90°

Consider the following white dwarfs. Which would have the smallest radius?

A 5 solar mass white dwarf

This image shows Sirius, the brightest star in the night sky. Suppose we see it rise at 9pm tonight. What time would it rise tomorrow night?

A few mins after 9pm

Suppose we have a system where a dwarf star is accreting mass from its binary companion. What type of binary system is possible here?

A semi-detached binary

What really happened at Roswell?

A top secret military cover up

Suppose we have two blackbodies, Alice and Bob, of the same size, shape, and material. Alice has a temperature of 2000 K. Bob has a temperature of 1000 K. How do their luminosities compare? Recall that

Alice is 16x as luminous as Bob

Which of the following stars in the constellation Lyra would be the brightest? α

Alpha (α) Lyrae

What of the following shapes best describes Earth's orbit?

An ellipse