The Equinoctial System of Coordinates

Question 1

• an imaginary sphere surrounding the Earth

Answer 1

Celestial Sphere

Question 2

• centered around the Earth and depicts all celestial objects as if they were at the same distance away from the Earth

Answer 2

Celestial Sphere

Question 3

• a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant

Answer 3

Celestial Sphere

Question 4

TRUE OR FALSE

* Because astronomical objects are at such remote distances, casual observation of the sky offers no information on the actual distances

Answer 4

TRUE

Question 5

TRUE OR FALSE

* All objects seem equally far away, as if fixed to the inside of a sphere of large but unknown radius, which rotates from east to west overhead while underfoot, the Earth seems to stand still

Answer 5

TRUE

Question 6

TRUE OR FALSE

* For purposes of spherical astronomy, which is concerned only with the directions to objects, it makes no difference whether this is actually the case, or if it is the Earth which rotates while the celestial sphere stands still

Answer 6

TRUE

Question 7

• either of the two points at which a northward or southward projection of the Earth’s axis intersects the celestial sphere

Answer 7

Celestial Pole

Question 8

TRUE OR FALSE

* The North and South celestial poles are analogous to Earth's geographic poles and are used in determining right ascension in the equatorial coordinate system

Answer 8

TRUE

Question 9

• the point in the sky about which all the stars seen from the Northern Hemisphere rotate

Answer 9

North Celestial Pole

Question 10

• The North Star, also called ____________.

Answer 10

Polaris

Question 11

• the point in the sky about which all the stars seen from the Southern Hemisphere rotate

Answer 11

South Celestial Pole

Question 12

TRUE OR FALSE

    * The Sun is also a star, so the Sun also rotates around the North Celestial Pole

Answer 12

FALSE
~ SOUTH CELESTIAL POLE

Question 13

• the great circle of the imaginary celestial sphere on the same plane as the equator of Earth

Answer 13

Celestial Equator

Question 14

• by extension, it is also a plane of reference in the equatorial coordinate system

Answer 14

Celestial Equator

Question 15

• an abstract projection of the terrestrial equator into outer space

Answer 15

Celestial Equator

Question 16

• other term of ____________ is equinoctial

Answer 16

Celestial Equator

Question 17

• a great circle on the celestial sphere representing the sun’s apparent path during the year, so called because lunar and solar eclipses can occur only when the moon crosses it

Answer 17

Ecliptic

Question 18

• semi-great circles on the celestial sphere joining the celestial poles or projection of the earth’s meridians on the celestial sphere

Answer 18

Celestial Meridians

Question 19

• cut the equinoctial and the declination circles at 90°

Answer 19

Celestial Meridians

Question 20

• small circles on the celestial sphere parallel to the plane of equinoctial

Answer 20

Declination Circles/Parallels of Declination

Question 21

• may also be defined as projection of parallels of latitude on the celestial sphere

Answer 21

Declination Circles/Parallels of Declination

Question 22

The ecliptic intersects the equinoctial at two points called the __________________.

Answer 22

equinoctial points

Question 23

• the equinoctial point when the Sun appears to cross the equinoctial from South to North

Answer 23

First Point of Aries

Question 24

• denoted by symbol γ

Answer 24

First Point of Aries

Question 25

- this occurrence takes place on 21st March, at Vernal Equinox

Answer 25

* First Point of Aries

Question 26

- considered as fixed point on the celestial sphere

Answer 26

First Point of Aries

Question 27

- the equinoctial point when the Sun appears to cross the equinoctial from North to South

Answer 27

First Point of Libra

Question 28

- happens on September 22 or 23 each year

Answer 28

First Point of Libra

Question 29

- denoted by the symbol Ώ

Answer 29

First Point of Libra

Question 30

TRUE OR FALSE The First point of Aries and the First point of Libra were named after the constellations in which they once lay.

Answer 30

TRUE

Question 31

- the great circle on the celestial sphere which is equidistant from the celestial poles or whose plane is same as the plane of equator

Answer 31

Equinoctial

Question 32

- the reference plane from which declination of astronomical bodies is measured north or south

Answer 32

Equinoctial

Question 33

- the celestial meridian that passes through Greenwich

Answer 33

Celestial Meridian Passing of Greenwich

Question 34

_______________ of all celestial bodies is measured westward from this reference great circle

Answer 34

Greenwich Hour Angle (GHA)

Question 35

- the celestial meridian that passes through first point of Aries

Answer 35

Celestial Meridian of First Point of Aries

Question 36

______________ of all celestial bodies is measured with reference to this great circle

Answer 36

Sidereal Hour Angle

Question 37

- the arc of celestial meridian passing through the body contained between the Equinoctial and the body

Answer 37

Declination

Question 38

- may be also defined as arc of celestial meridian or the angle at the center of the earth contained between the Equinoctial and the declination circle passing through the body

Answer 38

Declination

Question 39

TRUE OR FALSE If the body is North of the equinoctial the declination is South

Answer 39

FALSE * If the body is North of the equinoctial the declination is NORTH

Question 40

TRUE OR FALSE If the body is South of the equinoctial declination is named South

Answer 40

TRUE

Question 41

TRUE OR FALSE * As it is angular measure it is expressed in degrees and minutes and its value is in between 0° to 90° N or S

Answer 41

TRUE

Question 42

- arc of the Equinoctial or the angle at the celestial poles contained between two celestial meridians

Answer 42

Hour Angle (HA)

Question 43

- the arc of the Equinoctial or the angle at the celestial poles contained between the celestial meridian of Greenwich and celestial meridian passing through the body, measured westward from celestial meridian of Greenwich

Answer 43

Greenwich Hour Angle (GHA)

Question 44

- expressed in degrees and minutes and its value is in between 0° to 360°

Answer 44

Greenwich Hour Angle (GHA)

Question 45

- an hour angle the arc of the Equinoctial or the angle at the celestial pole contained between the celestial meridian of the First point of Aries and that through the body, measured westward from Aries

Answer 45

Sidereal Hour Angle (SHA)

Question 46

- an hour angle contained between the celestial meridian of the First point of Aries and the celestial meridian passing through the body, measured eastward from Aries

Answer 46

Right Ascension (RA)

Question 47

- generally expressed in hours, minutes and seconds, instead of, in arc. Since SHA is measured westward and RA eastwards from the same point, the SHA and RA of any body will together always add up to 360°

Answer 47

Right Ascension (RA)

Question 48

TRUE OR FALSE * SHA* + RA* = 360°

Answer 48

TRUE

Question 49

- an hour angle contained between the observer’s celestial meridian and the celestial meridian through that body, measured westward from the observer

Answer 49

Local Hour Angle (LHA)

Question 50

If the angle or arc is measured eastward from the observer, it is known as the _______________ and not LHA.

Answer 50

Easterly Hour Angle (EHA)

Question 51

TRUE OR FALSE LHA* + EHA* = 360°

Answer 51

TRUE

Question 52

GIVE THE FORMULAS OF Longitude West GHA BEST

Answer 52

~ LHA* = GHA* − Long. (West) ~ GHA* = LHA* + Long. (West)

Question 53

GIVE THE FORMULAS OF Longitude East GHA LEAST

Answer 53

~ LHA* = GHA* + Long. (East) ~ GHA* = LHA* − Long. (East)

Question 54

Calculate the LHA of a star whose GHA is 70°, for an observer in longitude 147°E.

Answer 54

Solution: Longitude East GHA Least LHA* = GHA* + Long (E) = 70°+147° = 217° = 217°

Question 55

TRUE OR FALSE The solar system consists of the Sun, the planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto), the planetary satellites (moons), asteroids, comets and meteors.

Answer 55

TRUE

Question 56

The most important member of the Solar system is the ________.

Answer 56

Sun

Question 57

TRUE OR FALSE All the planets revolve eastward in elliptical orbits around the sun. The earth also rotates eastward on its axis.

Answer 57

TRUE

Question 58

TRUE OR FALSE * For the purposes of celestial navigation the earth is assumed to be stationary. Therefore due to eastward revolution of the Earth, the Sun appears to move eastwards on the celestial sphere, in the plane of the Earth’s orbit. the apparent motion of the Sun along the great circle on the celestial sphere, due to the eastward motion of the earth in its orbit.

Answer 58

TRUE

Question 59

The great circle on the celestial sphere in the plane of the earth’s orbit is called ___________.

Answer 59

Ecliptic

Question 60

TRUE OR FALSE The great circle on the celestial sphere in the plane of the earth’s orbit is called Ecliptic. It is so called because the Sun, Moon and Earth must be on this plane for a solar or lunar eclipse to occur.

Answer 60

TRUE

Question 61

TRUE OR FALSE The projection of the Moon on the ecliptic from successive positions of the earth in its orbit, appears to constantly move eastwards.

Answer 61

FALSE The projection of the SUN on the ecliptic from successive positions of the earth in its orbit, appears to constantly move eastwards.

Question 62

TRUE OR FALSE The earth’s axis is inclined to its orbiting plane by about 23° 26.7′. Therefore the equinoctial also makes the same angle with the plane of ecliptic.

Answer 62

TRUE

Question 63

The angle at which the plane of ecliptic cuts the equinoctial plane is called _________________.

Answer 63

Obliquity of Ecliptic.