Question 1

The number of arcseconds in 1° is

Accepted Answer

There are 3600 arcseconds in 1 degree, as 1 degree equals 60 arcminutes and 1 arcminute equals 60 arcseconds, thus 60 x 60 = 3600.

Question 2

If Venus has an angular diameter of 30 arcseconds when viewed from Earth at a particular time, how does this angular diameter compare with the typical angular diameter of the Moon?

Accepted Answer

The typical angular diameter of the Moon when viewed from Earth is about 1800 arcseconds (or 0.5 degrees). Since Venus has an angular diameter of 30 arcseconds, it is 60 times smaller than the Moon's angular diameter (1800 arcseconds / 30 arcseconds = 60).

Question 3

The so-called "pointer stars" in Ursa Major, the Big Dipper, are separated by about 5 degrees on the sky. How many Moon diameters would fit between them? See Figure 1-5 for a diagram of these stars in context.

Accepted Answer

The answer of The so-called "pointer stars" in Ursa Major,...

Question 4

For an observer at a fixed location on Earth, the angle between the north celestial pole and an observer's horizon depends on the

Accepted Answer

The angle between the north celestial pole and an observer's horizon directly corresponds to the observer's latitude. For example, at the equator (0° latitude), the north celestial pole is on the horizon, and at the North Pole (90° North latitude), the north celestial pole is directly overhead. Longitude, time of day, and time of year do not affect this angle.

Question 5

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

Accepted Answer

The angle can be approximated using the small angle formula, which in radians is angle = length / distance. Converting 9/1000 radians to degrees (since 1 radian = 57.2958 degrees), we get approximately 0.515 degrees, which is close to ½ of a degree.

Question 6

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

Accepted Answer

The angle can be estimated using the small angle formula, which is angle = (size/distance) * (180/pi), where size is the distance between the two cities (300 km), and distance is the distance from the Moon to Earth (400,000 km). Converting the angle to degrees and then to arcminutes (since 1 degree = 60 arcminutes), the result is approximately 2.5 arcminutes.

Question 7

The angle between an observer's horizon and the north celestial pole is governed by

Accepted Answer

The angle between an observer's horizon and the north celestial pole directly corresponds to the observer's latitude. This is because the Earth's surface is curved, and the celestial pole's elevation angle matches the observer's latitude.

Question 8

The number of degrees in a semicircle is

Accepted Answer

A semicircle is half of a circle, and since a full circle is 360 degrees, a semicircle contains 180 degrees.

Question 9

An arcsecond is a measure of

Accepted Answer

An arcsecond is a unit of angular measurement equal to 1/3600th of a degree. It is commonly used in astronomy to measure the apparent sizes of objects in the sky and the separation between celestial objects.

Question 10

1 arcminute is equal to

Accepted Answer

1 arcminute is equal to 1/60 of a degree, not a full circle or an arcsecond, and it is not equal to 1/3600°, which defines an arcsecond.

Question 11

From a location in the northern hemisphere, the pole star always appears at an angle above the northern horizon equal to

Accepted Answer

The pole star, or Polaris, appears at an angle above the northern horizon that is equal to the latitude of the observer's location in the northern hemisphere. This is because the Earth's axis points towards Polaris, making it a fixed point in the sky that directly corresponds to the observer's latitude.

Question 12

The system of declination and right ascension is similar to the system of latitude and longitude used on the surface of Earth. In the Earth system, the zero of longitude is called the

Accepted Answer

The prime meridian is the reference line from which longitude is measured on Earth, similar to how the zero point of right ascension is defined in celestial coordinate systems.

Question 13

The Moon's angular diameter in the sky is measured to be 0.5°. From this measurement, one can find the

Accepted Answer

The angular diameter and the actual distance to the Moon can be used together to calculate the Moon's physical diameter in kilometers using simple trigonometry. Without knowing the distance, the bulk density cannot be directly determined, nor can the Moon's diameter or distance be accurately calculated without additional information.

Question 14

The Crab has a diameter of about 10 light-years and is at a distance of 6300 light-years. What angle will this supernova remnant subtend in the sky?

Accepted Answer

The angular size can be calculated using the formula: θ = (d / D) × (206265), where d is the diameter and D is the distance. Substituting the given values, θ = (10 / 6300) × 206265 ≈ 5.5 arcminutes.

Question 15

What fraction of a full circle is the angle of 60° between the line from the Sun to Jupiter and the line from the Sun to a Trojan group of asteroids?

Accepted Answer

A full circle is 360°, and 60° is 1/6 of 360°.

Question 16

Which of these statements about angle is correct?

Accepted Answer

15 arcminutes is equivalent to 1° because 1° is equal to 60 arcminutes, making C the correct statement.

Question 17

Astronauts on the Moon look back at Earth, whose diameter is about 12,800 km. Because the Earth-Moon distance is about 400,000 km and the Moon's diameter is about 3500 km, how much bigger or smaller will Earth appear in their sky than the Moon does in the sky?

Accepted Answer

The apparent size of an object in the sky is determined by its angular diameter, which depends on the object's actual size and its distance from the observer. Since the Earth's diameter is about 12,800 km and the Moon's diameter is about 3,500 km, the Earth is approximately 3.7 times larger in diameter than the Moon. Given the distances involved, this ratio roughly translates to how much larger the Earth would appear to an observer on the Moon compared to how the Moon appears from Earth, despite the difference in distances.

Question 18

The elevation angle between the northern horizon of a fixed observer and the north celestial pole is

Accepted Answer

The elevation angle between the northern horizon of a fixed observer and the north celestial pole is equal to the observer's latitude. This is because the north celestial pole appears directly above the Earth's North Pole, and its angle above the horizon corresponds to the observer's latitude.

Question 19

1 arcsecond is equal to

Accepted Answer

1 arcsecond is equal to 1/3600 of a degree, as there are 60 arcminutes in a degree and 60 arcseconds in an arcminute, making 3600 arcseconds in a degree.

Question 20

When viewed from Earth on a particular night, Jupiter subtends an angle of 42 arcseconds. This angle is

Accepted Answer

Jupiter subtends an angle of 42 arcseconds, which is about 1 arcminute.

Quiz 1: Discovering the Night Sky