Astronomy Ch.1

The laws of physics developed in laboratories on Earth are generally assumed to be valid

everywhere in the universe

The scientific method is a major force in science and has been developed to ensure that

theories about physical phenomena agree with what we find in experiments and observations.

Heavy elements, such as those throughout Earth and within our bodies, appear to have been formed

deep inside some now-vanished star.

Larger stars have more thermonuclear “fuel”

but they also consume their fuel at a larger rate and thus live the a shorter time than smaller stars which have less fuel but consume it more slowly.

A globular cluster of stars is measured to have an angular diameter of 20.6 arcseconds, and its distance from Earth is measured to be 200,000 light-years. What is its approximate physical diameter in light-years?

20 ly

An astronomer finds an object at a distance of 6.8 AU from Earth. Based on the distance, which of the following is this object most likely to be?

a comet in our solar system

Astronauts on the Moon look back at Earth, a distance of about 400,000 km away. If the cities of Washington, D.C., and New York are separated by about 300 km, what will be the angle between them when viewed from the Moon?

2.5 arcminutes

Astronauts on the Moon look back at Earth, whose diameter is about 12,800 km. Since Earth-Moon distance is about 400,000 km, how much bigger will Earth appear in their sky than the Moon does in our sky?

3.7 times

At what distance would a friend have to hold a dime (about 1 cm diameter) for it to subtend an angle of 2 arcseconds?

1 km

By what approximate factor in powers-of-ten notation is a human being (height about 2 m) larger than the nucleus of a hydrogen atom, or proton (diameter about 10^–15 m)?

2 × 10¹⁵

How great a distance is one light second, the distance light travels in one second?

300 million meters

How many arcseconds are there in a full circle?

360 × 3600

If we could view each of the following objects from the same distance, which would be the brightest?

a quasar

If you were able to travel out into space until the angular distance between Earth and the Sun was 1 second of arc, how far would you be from the Sun? (Assume that Earth-Sun line is at right angles to your line of sight.)

1 pc

In 2004, an inhabitant of a planet orbiting a distant star observes the flash of the first nuclear explosion on Earth, which occurred in July 1945. Approximately how far away is his solar system from Earth?

17.1 pc

New stars appear to be formed in

nebulae.

On January 1, 2004, the planet Saturn had an angular diameter of 20.6 arcseconds as viewed from Earth. Which of the following is a correct statement about this angular diameter?

This value changes. The angular diameter gets larger as the distance to Saturn becomes smaller, and smaller as the distance to Saturn becomes larger.

On a particular night, Jupiter subtends an angle of 42 arcseconds as seen from Earth. This angle is

roughly three-quarters of an arcminute.

One billionth divided by one millionth is equal to

10^–3.

One light-year is the

distance that light travels in one year.

So far, our study of the other bodies in our solar system is based on

telescopic observations from Earth and spacecraft plus information from manned landing on about half the planets.

Suppose a star rises due east, passes directly overhead, and then sets twelve hours after it rose. What is its average angular speed (in arcseconds per second)?

15

Suppose that at the same time on the same night we see one supernova (a star exploding) in the Andromeda Galaxy, 2 million light-years away from us, and another in the galaxy M82, 6 million light-years away from us. Which of the following statements is correct?

The supernova in the Andromeda Galaxy actually occurred after the one in M82.

The angle subtended at an observer by a city transit bus (length 9 m) at a distance of 1000 m is close to

1/2°.

The distance from Earth to the star Betelgeuse (in the constellation Orion) has been measured as 520 light-years. Expressed in parsecs, this is approximately

160 pc.

The following distance units, arranged in size from smallest to largest, are

km, AU, ly, pc

The hydrogen atom has a radius of about 5×10^-9

cm. The radius of the observable universe is about 14 billion ly. How many times larger than a hydrogen atom is the observable universe radius?

2.65 x 10³⁶

The idea of thermonuclear fusion, the release of energy following the conversion of hydrogen nuclei into a helium nucleus, was first suggested as the source of energy in

The lifetime of a typical star (like our Sun) appears to be

The mean distance of Jupiter from the Sun, 778,300,000 km, can be written in shorthand notation as

The mean distance of Jupiter from the Sun, 778,300,000 km, can be written in shorthand notation as

 

7.783 × 10⁸ km.

The oldest objects in the solar system whose age has been measured are

meteroites

The speed of light is approximately 3 × 10⁸ meters/sec. This is the same as

6.71 × 10⁸ mi/hr

The study of galaxies gives astronomers important clues about the

creation of the universe.

The time taken for light to travel from Jupiter to Earth when they are closest to each other is (you need to think carefully about this, and draw a diagram)

34 minutes.

The time taken for light to travel to Earth from a galaxy that is 10 Mpc away is

3.26 × 10⁷ years.

Two very bright fireworks are exploded at the same time during the July 4 celebrations, one in New York, the other in Los Angeles (4000 km apart). How far apart in angle will these flashes appear to astronauts on the Moon, who are 400,000 km from Earth?

34.4 arcminutes

What is the distance between Earth and the nearest star?

1 AU

Which of the following is not considered to be part of our solar system?

the Orion Nebula

If a stick of length 5.18 meters is placed so that the ends just touch a circle of radius 10 meters, the stick will subtend a 30° angle when viewed from the center of the circle. What does the small angle formula give you as the length of this stick?

5.24 meters

A circle of radius 10 meters has a circumference C = 2πR = 62.83 meters. A 30° angle would intercept an arc that is 30/360 or 1/12 of this, namely 5.24 meters. What does this result (along with the result in the previous problem) suggest about the validity of the small angle formula?

The formula actually calculates the length subtended by a given angle at a given distance. Thus the formula computes a length that is longer than length D in the small angle formula.