The Celestial Sphere

Question 1

What is the equator and what is it’s latitude?

Answer 1

The equator is the line around the Earth which is equidistant from the poles, and has a latitude of 0°.

Question 2

What are the tropics and what are their latitudes?

Answer 2

The tropics are the lines above and below the equator which have latitudes of 23° 26’ N or 23° 26’ S. The line above the Equator is the Tropic of Cancer and the line below is the Tropic of Capricorn.

Question 3

What is longitude and latitude?

Answer 3

Lines of longitude are vertical lines which connect the poles of the Earth and go from 180°W to 180°E, with 0° being the Greenwich Meridian.
Line of latitude are horizontal lines parallel to the Equator and range from 0° to 90°N or 90°S (0° is the Equator).

Question 4

What is the definition of Horizon?

Answer 4

The line at which the Earth’s surface and the sky appear to meet.

Question 5

What is the definition of Meridian?

Answer 5

North-South line which passes through the Zenith.

Question 6

What is the definition of Zenith?

Answer 6

The point in the sky directly above the observer.

Question 7

What is the Celestial Sphere?

Answer 7

An imaginary sphere with Earth as the centre and on which all celestial objects are considered to lie.

Question 8

What is the Ecliptic and what always lies on it?

Answer 8

The Earth-Sun orbit projected onto the Celestial Sphere. The sun always lies on the Ecliptic and planets are found close to the Ecliptic - 12 constellations of the ZODIAC lie on the Ecliptic (Zodiacal Band).

Question 9

What is Declination and what are its units?

Answer 9

Lines similar to latitude but measured from 90° at the North Pole to -90° at the South Pole (0° at the equator).
Its units are degrees, minutes and seconds (°, ‘ and ‘’).

Question 10

What does 1 minute equal and what does 1 second equal in degrees (in terms of Declination)?

Answer 10

1' = 1/60 °
1'' = 1/3600 °

Question 11

What is Right Ascension?

Answer 11

There are 24 lines of right ascension which go from 0 hours to 24 hours.

Question 12

What does 1hour of RA equal?

Answer 12

1h of RA = 360°/24 = 15°

Question 13

What is Elevation?

Answer 13

The angle between the horizon and the zenith.

Question 14

What is the declination of Polaris and why does it appear stationary in the night sky?

Answer 14

90° when at the North Pole and it appears stationary because it is very close to the North Celestial Pole meaning it lies near the Earth’s rotational axis.

Question 15

What can you deduce from the elevation of Polaris depending on where you are?

Answer 15

The elevation of Polaris can give you an indication of your latitude.

Question 16

What is Culmination?

Answer 16

Culmination occurs when a star is crossing the observers meridian and is therefore due South at it’s greatest elevation.

Question 17

What is meant by the term ‘Circumpolar’ and what is needed for a star to be circumpolar?

Answer 17

A circumpolar star is one which never sets below the observers horizon. For a star to be circumpolar its declination must be greater than or equal to 90° - their latitude.

Question 18

When is the Spring Equinox and at what RA and Declination does it occur?

Answer 18

21st of March with a declination of 0° and a RA of 0h.

Question 19

When is the Summer Solstice and at what RA and Declination does it occur?

Answer 19

21st of June and a declination of 23° and a RA of 6h.

Question 20

When is the Autumn Equinox and at what RA and Declination does it occur?

Answer 20

21st of September and a declination of 0° and a RA of 12h.

Question 21

When is the Winter Solstice and at what RA and Declination does it occur?

Answer 21

21st of December and a declination of -23° and a RA of 18h.