Unit 5 Astronomy Test part 1

How long a segment would represent the 3- million-year history of human life?

0.67 mm

If we represent the history of Earth by a line 1 m long, how long a segment would represent the 400 million years since life moved onto the land?

8.9 cm

We receive a radio message from civilization around a star about 40 lightyears from Earth. If we reply away, how long will it be between the time THEY sent the message and the time they receive our reply?

80 years

Which of the following can astronomers NOT learn from studying the spectrum of a star?

All of these can be learned from studying the spectrum.

The stars most likely to have inhabited plan- ets are

G to K main-sequence stars.

Which of the following spacecrafts is NOT leaving the solar system?

Galileo

If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?

In the hottest stars, hydrogen atoms are ionized, so there are no electrons to produce lines in the spectrum.

What is the Fermi Paradox?

It asks, if intelligent life is common out there, how come they have not contacted us?

Using a pair of binoculars, you observe a sec- tion of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it

It could be more than one of these; there is no way to tell which answer is right by just looking at the star.

After days and days of work, a group of graduate students has finally measured the wave- lengths of hundreds of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be of which spectral type?

M

Which of the following types of star is the coolest (has the lowest surface temperature)?

M

In a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advance civilization?

No, because such a star (and any planets around it) would not have the heavier ele- ments (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it.

Which of the following is a good summary of what most astronomers think about UFO reports?

So far there is no scientific evidence that UFOs have anything to do with life outside the Earth.

Why are astronomers much more interested in the luminosity of a star than its apparent brightness?

The luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth.

Why are massive main-sequence stars not likely to have planets that contain life?

These stars are on the main sequence for too short a time to allow life to evolve.

What evidence do scientists have about how life on Earth originated?

They have no direct evidence about the first life forms on our planet.

In which of the following places have as- tronomers NOT found evidence for the build- ing blocks of life (organic compounds)?

We have found evidence for such materials in all of the above sites.

From a scientific perspective, which of the following statements about life elsewhere in the universe is best supported by current evidence?

While we have evidence of the building blocks of life elsewhere in the universe, we have no definite evidence about life around other stars at this time.

Some objects in space just don't have what it takes to be a star. Which of the following is a "failed star," an object with too little mass to qualify as a star?

a brown dwarf

Which of the following is, to the best of our knowledge, in the habitable zone of its star?

a planet about 1.05 AU from a G-type main-sequence star

Astronomers have discovered stars even cooler than the traditional spectral-type M stars re- cently. Astronomers have given these cool stars a new spectral type L. If you wanted to go out and find more type L stars, what kind of instrument would it be smart to use?

a sensitive infrared telescope

A star moving toward the Sun will show

a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines).

Which of the following looks the brightest in the sky?

a star with magnitude −1

If alien beings found one of the Voyager space- craft in a million years, what would they find aboard?

an audio and video record

Which color star is likely to be the hottest?

blue-violet

At an astronomical conference, an astronomer gave a report on a star that has recently begun to interest astronomers because of hints that it may have a planet around it. In his report the astronomer gave the average speed with which this star is moving away from the Sun. How was this speed measured?

by observing the Doppler shift in the lines of the star's spectrum

Life on Earth is based on

carbon chemistry.

Scientists are impressed with extremophiles, life forms that can survive under what seems to humans to be extremely unpleasant condi- tions. In which of the following environments have we not found life?

conditions resembling the photosphere of the Sun

Astronomers arrange the stars into groups called spectral classes (or types) according to the kinds of lines they find in their spectra. These spectral classes are arranged in order of

decreasing surface temperature.

Which of the following is a biomarker that could be used from an observatory around a nearby star, with the right equipment, to identify the Earth as a planet with life?

free oxygen in the Earth's atmosphere

What limitation(s) make it impossible to travel between stars?

fuel requirements, the tremendous distances between stars, the finite speed at which objects can travel

A team of astronomers takes spectra of thou- sands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that their stars

have different temperatures.

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about

how much energy the star gives off each second.

If you wanted to find a type of atom in your little finger that has been in its present form (been the same element) since the beginning of the universe, which element should you look for?

hydrogen

Photosynthesis was a great step forward in the evolution of life on Earth, because with photosynthesis

life could extract chemical energy from sunlight.

One reason that some scientists think that there may be life under the ice-crust of Jupiter's moon Europa is that

life has been found on Earth, at the bot- tom of the ocean, deriving its energy not from sun-light but from hot mineral-laden vents coming from deeper inside our planets; some- thing similar could happen at the bottom of the ocean on Europa.

Current searches for extraterrestrial intelli- gence use radio telesopes to

listen to many frequencies at the same time.

An exhausted-looking astronomer comes off the mountain where her observatory is located and tells you she has been doing photometry. What has she been up to?

measuring the brightness of different stars

Astronomers believe that to have enough time to evolve intelligent life on a planet around them, stars must have main-sequence life- times of many billions of years. What fraction of stars in the Galaxy have main-sequence lifetimes this long?

much more than half of all the stars

Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look

nine times fainter.

The neutral hydrogen atom consists of

one proton and one electron.

Photosynthesis releases a particular gas as a byproduct. This gas is

oxygen.

Which band of the electromagnetic spectrum do astronomers suggest is likely to be the best for communication between civilizations around different stars?

radio waves

A graduate student spent a year doing a care- ful analysis of the spectrum of a star. While she found lines from many elements, there was not a trace of the element helium in the spectra she was analyzing. From this she can now conclude that

since helium shows lines only in hot stars, this star must be relatively cool.

The key piece of technology that makes the major new search for signals from civilizations around other stars possible is

software and hardware that can search billions of radio channels at once.

Think for a moment about an atom of the element lead (atomic number 82) inside the radio that you listen to in the morning. In which of the following places has this atom probably NOT been during the course of its existence?

the Sun

What recent series of discoveries has made astronomers more optimistic about our prospects of finding life out there?

the discovery of planets around more than a hundred nearby stars

The fastest speed at which we might commu- nicate with another technological civilization among the stars (according to our present un- derstanding of science) is

the speed of light.

The number of communicative civilizations in our galaxy is limited by

the survival of technological societies.

Absolute zero is

the temperature at which atoms have no remaining energy from which we can extract heat.