SDSU ASTR 101 EXAM #2

Seasons are the result of

A) the changing distance between the Earth and the Sun as the Earth travels on its elliptical orbit

B) the 23.5 degrees tilt of the Earth's equator relative to its rotation axis

C) the tilt of the equinox axis relative to the perihelion

D) a planet's spin axis not being parallel to its orbital axis

a planet's spin axis not being parallel to its orbital axis

Kepler's 3rd law is an powerful tool that enables us to measure the size of an orbit ("a") based on the time it takes to complete one orbit ("P"). What exactly is the semimajor axis "a" of an ellipse?

A) the distance from one focus to any point on the ellipse

B) the distance from one focus to the center of the ellipse

C) half of the largest diameter of the ellipse

D) half of the distance between the foci of the ellipse

half of the largest diameter of the ellipse

On 2023 October 14th, an annular solar eclipse occurred that was visible from several western states in the US. Which of the following is TRUE about an annular eclipse?

A) the phase of the Moon must be full

B) the Moon's orbit is not circular, and the Moon is further from the Earth during an annular eclipse than during a total eclipse

C) the Moon's orbit is not circular, and the Moon is closer to the Earth during an annular eclipse than during a total eclipse

D) annular eclipse can only occur when the Moon is not on the ecliptic

the Moon's orbit is not circular, and the Moon is further from the Earth during an annular eclipse than during a total eclipse

Nearly all of what we know is astronomy comes from the analysis of light. But recently there is another way to learn about the universe: We can now use __________

A) gravitational waves

B) obliquity radiation

C) the Boltzmann effect

D) Kelvan-Kirchhoff radiation

gravitational waves

Knowing the peak emission wavelength of a blackbody (in other words, where the intensity is maximum for thermal radiation) allows you to determine its ________.

A) temperature

B) distance

C) luminosity

D) mass

temperature

What is meant in astronomy by the phase "active" of "adaptive" optics?

A) Vibration-free mounts activity compensate for wind and ground shake

B) The optical elements are actively heated to maintain the proper temperature

C) the telescope is continuously adjusted to keep it pointed toward the target object

D) Rapid modifications of the mirror correct for effects of atmospheric distortion

Rapid modifications of the mirror correct for effects of atmospheric distortion

Which of the following is NOT a true statement (FALSE) about atomic structure?

A) The number of photons (atomic number) defines an element

B) An ion is an atom that has either gained or lost electrons

C) Transitions to levels higher OR lower in energy can occur from the ground state

D) Transitions between two energy levels can occur only at one specific photon energy

Transitions to levels higher OR lower in energy can occur from the ground state

The Doppler Effect allows us to measure an object's ___________.

A) temperature

B) chemical composition

C) radius

D) line-of-sight speed (radial velocity)

line-of-sight speed (radial velocity)

This design combines light from different telescopes to greatly enhance resolution:

A) Prime focus reflector

B) Reflector

C) Interferometer

D) Cassegrain reflector

Interferometer

What is the reason planet Earth has seasons?

A) its changing distance from the Sun causes the seasons

B) the tilt of its semi-major axis with respect to its orbital axis

C) its spin axis is tilted and this creates an elliptical orbit

D) its equatorial plane (defined by the spin) is not aligned with its orbital plane (ecliptic plane)

its spin axis is tilted and this creates an elliptical orbit

Which of the following forms of light has the shortest wavelength?

A) radio waves

B) visible light

C) infrared

D) gamma rays

gamma rays

Mars has a semimajor axis of 1.52 AU. Thus,

A) Mars must take 1.52 years to orbit the Sun

B) Mars must take 2.31 (=1.52 squared) years to orbit the Sun

C) Mars must take 1.32 (=cube root of 1.52 squared) years to orbit the Sun

D) Mars must take 1.88 (=square root of 1.52 cubed) years to orbit the Sun

Mars must take 1.88 (=square root of 1.52 cubed) years to orbit the Sun

What is the relationship between color and wavelength for optical (visible) light?

A) Wavelength is content for optical light

B) Wavelength decreases from blue (violet) to red

C) Wavelength increases from blue (violet) to red

D) Wavelength increases from blue (violet) to yellow-green, then decreases to red

Wavelength increases from blue (violet) to red

When an electron jumps from a lower level to an upper level due to light,

A) a photon is emitted

B) a photon is absorbed

C) the atomic number increases

D) the atomic charge increases

a photon is absorbed

Which of the following laws helps us compute the total amount of electromagnetic energy emitted by a star per second? (Hint: Stars radiate like blackbodies)

A) Stefan-Boltzmann law

B) Coude's law

C) Kepler's law

D) Kirchhoff's law

Stefan-Boltzmann law

Who invented the reflector type telescope?

A) Galileo

B) Kepler

C) Planck

D) Newton

Newton

If the Sun's temperature quadrupled, but its size remained the same, how much brighter (more luminous) would it be?

A) it would be 4.0 times brighter

B) it would be 8.0 times brighter (=square root of 64)

C) it would be 16.0 times brighter (4 squared)

D) it would be 256.0 times brighter (4 to the 4th power)

it would be 256.0 times brighter (4 to the 4th power)

The hydrogen H alpha absorption line created when an electron jumps from level 2 to level 3 has a wavelength of 656.285 nm in the star you are researching. Which of the following is true:

A) the star is moving away from us

B) the star has a radius velocity v = c x (-0.285 nm/656.285 nm)

C) the star has a radius velocity v = c x (+0.285 nm/656.285 nm)

D) the star is redshifted

the star has a radius velocity v = c x (-0.285 nm/656.285 nm)

Antares in the constellation Scorpius is the 15th brightest star in the sky and has a surface temperature of roughly 3600 K. It is much, much more luminous than the Sun. But how can this be, if its temperature is so much lower than the Sun's? Why is it so bright?

A) it has a much larger radius than the Sun

B) it has a much larger redshift than the Sun

C) it has much more of the strong (nuclear) force than the Sun

D) it has a much faster rotation than the Sun

it has a much larger radius than the Sun

In the spectrum of the red giant star Antares, the hydrogen alpha line has a wavelength of 656.278 nm. From this information, we can tell that

(Hint: the true (at rest in the lab) wavelength of the H alpha line is 656.278 nm.)

A) Antares is approaching the Earth

B) Antares is moving away from the Earth

C) Antares is neither moving towards or away from the Earth

D) Antares is redshifted

Antares is moving away from the Earth

Which of the following is most energetic?

A) X-ray photon

B) UV photon

C) white photon

D) infrared photon

X-ray photon

Which of the following forms of light can most easily penetrate interstellar dust? (Hint: Think of the video "More Than Your Eyes Can See" that you were asked to watch for homework: what kind of light did the fireman use to see through smoke?)

A) ultraviolet

B) red

C) infrared

D) x-ray

infrared

Why does the science of astronomy require space-based observations when much larger ground-based telescopes are far less expensive?

A) Being in space, the telescope I closer to the objects astronomers wish to study.

B) Space telescopes provide the ability to observe at wavelengths that do not reach the surface of the Earth. There is no other way to detect the light at these wavelengths.

C) In space there is no light pollution or clouds or bad weather.

D) Being in space allows the telescope to avoid the blurring effects of the Earth's atmosphere

Space telescopes provide the ability to observe at wavelengths that do not reach the surface of the Earth. There is no other way to detect the light at these wavelengths.

Kirchhoff's 2nd law states that

A) electrons in upper levels have more energy than electrons in low levels

B) weight depends on both mass and the force of gravity

C) planets have a higher velocity at periastron than at the apastron of their orbit

D) a hot, low-density gas will produce an emission line spectrum

a hot, low-density gas will produce an emission line spectrum

Hubble Space Telescope (HST) has a 2.4-meter diameter primary mirror. Telescopes on the ground can have many mirrors many times larger. So what makes the HST so very useful?

A) It has mirrors with far superior optical qualities

B) Being in space, it is much closer to stars, planets, etc

C) It was the largest telescope at the time it was built and has the best lenses

D) It is above the Earth's atmosphere so it has diffraction-limited angular resolution

It is above the Earth's atmosphere so it has diffraction-limited angular resolution

The most common design for modern research telescopes today uses a

A) Cassegrain focus

B) Keplerian focus

C) adaptive focus

D) Newtonian focus

Cassegrain focus

Which star has a surface, the red star Antares or the blue-white star Rigel?

A) Antares

B) Rigel

C) We can not tell without knowing the distances to these stars

D) We can not tell without the chemical composition of these stars

Rigel

Which of the following is TRUE?

A) stars do not twinkle; the Earth's atmosphere causes twinkling

B) there is no gravity in space

C) the Earth's shadow creates the phases of the Moon

D) something that is opaque in visible light must be opaque in infrared light

stars do not twinkle; the Earth's atmosphere causes twinkling

Suppose two stars have the same radius, but one star has a temperature of 3000 K and the other 9000 K. How much brighter (more luminous) is the hotter star?

A) 3 times

B) 16 times

C) 27 times

D) 81 times

81 times

The term "refraction" means

A) the change of the direction of a wave as it passes from one substance to another

B) the change in wavelength of light as it passes from one substance to another

C) the change in the frequency of light when it reflects off a mirror

D) the spreading out of a wave or the beading of a wave around corners

the change of the direction of a wave as it passes from one substance to another

Why is NASA's Chandra X-ray Observatory telescope located in space?

A) By being above the Earth's atmosphere, astronomers don't have to worry about clouds or bad weather

B) By being above the Earth's atmosphere, astronomers don't have to worry about the atmosphere blurring the images

C) X-rays cannot penetrate the Earth's atmosphere

D) The X-rays that Chandra emits are harmful to humans

X-rays cannot penetrate the Earth's atmosphere

What problem does active and/or adaptive optics correct?

A) Defects in the optics of the telescope, such as with the original Hubble mirror

B) Diffraction of gravitational waves at the Coude focus

C) Turbulence in the Earth's atmosphere which creates poor seeing

D) The opacity of the Earth's atmosphere to some wavelengths of light

Turbulence in the Earth's atmosphere which creates poor seeing

The main reason why astronomers require large telescopes is to be able

A) to provide higher magnification and make distant objects appear closer

B) to collect a wider range of wavelengths (beyond what we can see visually)

C) to measure the quantum flux of light very precisely

D) collect more light from stars and distant dim objects

collect more light from stars and distant dim objects

What are the main components of an optical refracting telescope?

A) two curved mirrors

B) a spectrograph and a mirror

C) a prism and a diffraction grating

D) an objective lens and an eyepiece lens

an objective lens and an eyepiece lens

Which of the following is FALSE (not true)

A) gamma rays have the highest energy photons

B) Cassegrain's law says that hotter objects are bluer

C) radio waves have the lowest energy photons

D) the force of gravity depend on the inverse of the distance squared

Cassegrain's law says that hotter objects are bluer

Kepler's first law states that a planet moves around the Sun

A) in a circle, with the Sun at the center

B) in an elliptical orbit, with the Sun at the center of the ellipse

C) in an elliptical orbit, with the Sun at one focus

D) in a circle, with the Sun on the ecliptic

in an elliptical orbit, with the Sun at one focus

Which of the following is TRUE?

A) Twinkling is caused by the Earth's atmosphere

B) Deuterium is an isotope of H and therefore an atom of deuterium must have two electrons

C) The primary purpose of an astronomical telescope is to make images of distant objects appear closer

D) The main reason why astronomers require large telescopes is to be able to provide higher magnification

Twinkling is caused by the Earth's atmosphere

Astronomers use the term "seeing" to describe which of the following?

A) the ability to see wavelengths of light other than optical wavelengths

B) the distortion of light due to turbulence in the Earth's atmosphere

C) the amount of light-gathering power of a telescope

D) the amount of magnifying power of a telescope

the distortion of light due to turbulence in the Earth's atmosphere

Which of the following is FALSE (NOT TRUE)?

A) the number of waves passing an observer per second is the frequency in Hertz (Hz)

B) bigger telescopes always produce images with higher resolution

C) if you double the wavelength of light, you reduce its frequency by a half

D) when an electron transitions between two atomic energy levels only one very specific photon energy can be emitted or absorbed

bigger telescopes always produce images with higher resolution

Suppose a star's has an emission line at 297nm. At rest in the lab, this line is normally at 300 nm. What can we tell about the star?

A) it is moving towards us at 1% the speed of light

B) it is moving towards us at 3% the speed of light

C) it is moving away from us at 1% speed of light

D) it is moving away from us at 3% speed of light

it is moving towards us at 1% the speed of light

Suppose you launch a space probe into a circular orbit around the Sun and it takes 10 years to orbit the Sun. How far from the Sun is the space probe?

A) square root of 10 (=3.16) AU

B) 10 AU

C) cube root of 10 squared (=4.64) AU

D) square root of 10 cubed (=31.6) AU

cube root of 10 squared (=4.64) AU

Suppose an electron jumps from every level n=4 to level n=1 and releases a photon Compared to photon produced when an electron jumps from level n=3 to n=1, the 4 --> 1 transition photon has

A) less energy

B) more energy

C) lower frequency

D) longer wavelength

more energy

Suppose you wanted to know how fast a rocket on its way to Mars is moving away from the Earth. To find out, you could use which of the following?

A) the Stefan-Boltzmann law

B) Doppler's law

C) Kirchhoff's law

D) Kepler's 3rd law

Doppler's law

Which of the following is FALSE (NOT true)?

A) Radio waves are a form of sound waves

B) Humans are capable of seeing light between roughly 400 and 750 nm

C) Modern research telescopes are of the reflector type, not refractor type

D) The competition between gravity and pressure is an important theme in astronomy

Radio waves are a form of sound waves

The thermal blackbody curve has another name, in honor of the scientist who explained the shape of the curve. It is called:

A) the Cassegrain function

B) the Boltzmann function

C) the Planck function

D) the Kelvin function

the Planck function

Suppose a strange rogue planet is discovered far from any star and it has a very, very cold surface temperature of only 2.9 K. At what wavelength does the planet emit the most light (what is the wavelength of the maximum intensity)?

A) -2.9 nm

B) 2.9 nm

C) 0.001 m

D) 7.1 nm (=2.9 to the 4th power)

0.001 m

Suppose an absorption line in a galaxy is redshifted by +1 nm from its normal (rest) wavelength of 1000 nm. What is the velocity of the galaxy with respect to us?

A) 1 km/s

B) -100 km/s

C) 300 km/s

D) 1000 km/s

300 km/s