Question 1

Astronomers were at first surprised to find complicated molecules in the interstellar medium. They thought ultra-violet light from stars would break apart such molecules. What protects the molecules we observe from being broken apart?

Accepted Answer

Complicated molecules in the interstellar medium are protected by the presence of dust in the clouds where they form, which shields them from being broken apart by ultra-violet light.

Question 2

If an astronomer wanted to find some relatively complex molecules in space, what technique should she use?

Accepted Answer

Complex molecules in space are typically found in regions where there is a lot of interstellar dust, such as molecular clouds. These molecules have characteristic rotational and vibrational transitions in the radio wavelength range, which can be detected by radio telescopes. Therefore, pointing a radio telescope into regions with a lot of dust is the best technique for finding complex molecules in space.

Question 3

An astronomer wants to observe a cloud of dust in a relatively close part of the Galaxy. Unfortunately, this dust cloud is not located in the direction of a crowded region of stars. What instrument would be the most help in finding this cloud.

Accepted Answer

A sensitive infra-red telescope in orbit around the Earth would be the most helpful in finding the dust cloud. This is because dust clouds in space emit more strongly at longer wavelengths, such as infrared, and are not easily visible in visible light. A telescope designed specifically to detect infrared sources would be most effective. X-ray telescopes would not be helpful in this search as they are used for detecting high-energy sources, such as black holes and neutron stars, and would not be sensitive to the low-energy emissions from dust clouds. The other options, a vat of cleaning fluid and a spectroscope, are not relevant to this type of observation.

Question 4

You are observing a binary star system and obtain a series of spectra of the light from the two stars. In this spectrum, most of the absorption lines shift back and forth as expected from the Doppler Effect. A few lines, however, do not shift at all, but remain at the same wavelength. How can we explain the behavior of the non-shifting lines?

Accepted Answer

The fact that only a few lines are not shifting suggests that they are not coming from the stars themselves, but from interstellar matter between us and the stars. This matter is not affected by the motion of the stars and therefore its absorption lines will not shift.

Question 5

A friend of yours who has not taken an astronomy class looks at your textbook and really likes the picture of the Pleiades, a cluster of stars surrounded by a bluish reflection nebula. She wants to know what causes that beautiful blue glow. To explain it to her, you want to compare the process that causes the blue glow to something that is in your friend's everyday experience. Which of the following terrestrial phenomena is the result of the same type of process that makes a reflection nebula in space?

Accepted Answer

The blue color of the Earth's sky is caused by the scattering of sunlight off of the atmosphere's molecules, specifically oxygen and nitrogen. This process is similar to the scattering of light off of small dust particles in a reflection nebula, which creates the bluish glow. Therefore, the blue color of the Earth's sky is the terrestrial phenomenon that is most similar to the process that causes the blue glow in a reflection nebula.

Question 6

An HII region is

Accepted Answer

HII stands for "ionized hydrogen" and refers to a region around a hot star where the intense radiation causes the hydrogen atoms to lose their electrons and become ionized (HII). This ionized gas emits light at specific wavelengths, which can be observed with telescopes.

Question 7

Which of the following is NOT a way astronomers discover clouds of interstellar matter that have a large amount of dust in them?

Accepted Answer

Astronomers do not typically discover clouds of interstellar matter with a large amount of dust by detecting x-rays from hot gas surrounding the dust cloud. Instead, they typically rely on methods such as blocking the light of stars behind the cloud, observing the reflection of nearby starlight, or detecting infrared radiation emitted by the dust. The reddening of starlight caused by dust is also a well-known method for identifying dust clouds.

Question 8

When astronomers discuss a nebula, what are they talking about?

Accepted Answer

Astronomers are talking about a cloud of gas and dust between or among the stars when they discuss a nebula.

Question 9

Astronomers have found large quantities of cold, neutral hydrogen gas in our galaxy. How is this gas distributed?

Accepted Answer

Cold, neutral hydrogen gas is mainly found in a flat layer extending throughout the disk of our galaxy. This is because the gas tends to follow the same general distribution as the stars and other matter in the disk of the galaxy.

Question 10

How do fragile structures like acetaldehyde (CH₃CHO) molecules survive in the harsh environment of interstellar space? Why are they not destroyed by high-energy radiation from stars?

Accepted Answer

Fragile structures like acetaldehyde molecules are found only in dense clouds that have a lot of dust. The dust acts as a shield and keeps the radiation from hot stars from reaching the molecules, thus protecting them from destruction.

Question 11

You are an astronomer whose supervisor has just forbidden drinking alcoholic beverages near the observatory. In frustration, you under?take a search for alcohol molecules in space. Where would your search be most likely to succeed?

Accepted Answer

Interstellar clouds of gas and dust, also called molecular clouds, are known to contain various molecules, including organic molecules such as methanol, ethanol, and even more complex molecules like amino acids. These molecules are formed through chemical processes in these clouds and can be detected using radio telescopes. Therefore, the search for alcohol molecules in space would be most likely to succeed in an interstellar cloud of gas and dust.

Question 12

Which of the following statements about interstellar matter is FALSE?

Accepted Answer

If the interstellar matter were spread out evenly, it would actually be much less dense than the Earth's atmosphere. The correct statement would be that interstellar matter is very diffuse, with an average density of about 1 atom per cubic centimeter.

Question 13

An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task?

Accepted Answer

A radio telescope tuned to a wavelength of about 21 centimeters would be most useful for observing a cloud of cold neutral hydrogen, as this is the wavelength at which the hydrogen emits radiation. This type of observation is commonly used in astronomy and is known as 21-centimeter line spectroscopy. Option A is not appropriate, as x-rays are not emitted by cold neutral hydrogen. Option C would not be as effective as a radio telescope for this specific task, as visible light does not provide direct information about the existence of cold neutral hydrogen clouds. Option D is not appropriate because neutrinos are not emitted by cold neutral hydrogen. Option E is incorrect, as it is possible to observe clouds of hydrogen that are not near a star.

Question 14

The red color we see on a lot of photographs of nebulae comes from which element?

Accepted Answer

The red color in photographs of nebulae typically comes from the emission of hydrogen gas. This emission occurs when electrons in the gas become excited and then transition back down to their original energy state, releasing energy in the form of light. This particular transition corresponds to a wavelength of light that appears red to our eyes.

Question 15

Astronomers now understand that the dark regions or rifts visible in parts of our Galaxy that are otherwise crowded with stars are caused by:

Accepted Answer

Dark regions or rifts in our Galaxy are caused by clouds with a significant amount of dust that obstruct the light of stars behind them.

Question 16

What happens in the process of fluorescence?

Accepted Answer

In the process of fluorescence, atoms absorb ultraviolet rays and convert them to visible light as their electrons cascade to lower energy levels. This is what causes the glowing effect often seen in fluorescent materials.

Question 17

Supposing we launched a very fast dart from the Space Shuttle, pointed in some direction away from any planet, so that it could travel beyond the solar system. What would it be most likely to hit first after traveling outward for a while?

Accepted Answer

Interstellar gas is much more common than stars or planets, so the fast dart is most likely to hit an atom of interstellar gas first. The chances of it intersecting a star or planet, or even another galaxy, are much lower.

Question 18

Astronomers use the term interstellar matter to refer to:

Accepted Answer

Interstellar matter refers to the gas and dust that exists in the space between stars. This material can have a significant impact on the formation and evolution of galaxies and stars. Options A, B, and D are incorrect as they are not included in the definition of interstellar matter. Option E is not a scientifically valid concept.

Question 19

In order for a cold atom of hydrogen to emit a 21-cm wave, it must first be in a slightly higher energy state. What event usually "kicks" the hydrogen atom up to this higher state?

Accepted Answer

The 21-cm line emission in hydrogen atoms occurs when the electron and proton within the atom flip their spins from being parallel to anti-parallel. This transition to a slightly higher energy state before emitting the 21-cm wave is typically caused by collisions between gas atoms within the cloud.

Question 20

Some of the interstellar gas in our Galaxy has been heated to millions of degrees, a temperature that surprised astronomers when it was first discovered. How do we now think that gas between stars gets that hot?

Accepted Answer

Very powerful shockwaves from exploding stars are believed to be the cause of interstellar gas being heated to millions of degrees. This was initially surprising to astronomers but has since become the accepted explanation.

Quiz 20: Between the Stars