The Equinoctial System of Coordinates Flashcards
- an imaginary sphere surrounding the Earth
Celestial Sphere
- centered around the Earth and depicts all celestial objects as if they were at the same distance away from the Earth
Celestial Sphere
- a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant
Celestial Sphere
TRUE OR FALSE
* Because astronomical objects are at such remote distances, casual observation of the sky offers no information on the actual distances
TRUE
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
TRUE
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
TRUE
- either of the two points at which a northward or southward projection of the Earth’s axis intersects the celestial sphere
Celestial Pole
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
TRUE
- the point in the sky about which all the stars seen from the Northern Hemisphere rotate
North Celestial Pole
- The North Star, also called ____________.
Polaris
- the point in the sky about which all the stars seen from the Southern Hemisphere rotate
South Celestial Pole
TRUE OR FALSE
* The Sun is also a star, so the Sun also rotates around the North Celestial Pole
FALSE
~ SOUTH CELESTIAL POLE
- the great circle of the imaginary celestial sphere on the same plane as the equator of Earth
Celestial Equator
- by extension, it is also a plane of reference in the equatorial coordinate system
Celestial Equator
- an abstract projection of the terrestrial equator into outer space
Celestial Equator
- other term of ____________ is equinoctial
Celestial Equator
- 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
Ecliptic
- semi-great circles on the celestial sphere joining the celestial poles or projection of the earth’s meridians on the celestial sphere
Celestial Meridians
- cut the equinoctial and the declination circles at 90°
Celestial Meridians
- small circles on the celestial sphere parallel to the plane of equinoctial
Declination Circles/Parallels of Declination
- may also be defined as projection of parallels of latitude on the celestial sphere
Declination Circles/Parallels of Declination
The ecliptic intersects the equinoctial at two points called the __________________.
equinoctial points
- the equinoctial point when the Sun appears to cross the equinoctial from South to North
First Point of Aries
- denoted by symbol γ
First Point of Aries
- this occurrence takes place on 21st March, at Vernal Equinox
- First Point of Aries
- considered as fixed point on the celestial sphere
First Point of Aries
- the equinoctial point when the Sun appears to cross the equinoctial from North to South
First Point of Libra
- happens on September 22 or 23 each year
First Point of Libra
- denoted by the symbol Ώ
First Point of Libra
TRUE OR FALSE
The First point of Aries and the First point of Libra were named after the constellations in which they once lay.
TRUE
- the great circle on the celestial sphere which is equidistant from the celestial poles or whose plane is same as the plane of equator
Equinoctial
- the reference plane from which declination of astronomical bodies is measured north or south
Equinoctial
- the celestial meridian that passes through Greenwich
Celestial Meridian Passing of Greenwich
_______________ of all celestial bodies is measured westward from this reference great circle
Greenwich Hour Angle (GHA)
- the celestial meridian that passes through first point of Aries
Celestial Meridian of First Point of Aries
______________ of all celestial bodies is measured with reference to this great circle
Sidereal Hour Angle
- the arc of celestial meridian passing through the body contained between the Equinoctial and the body
Declination
- 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
Declination
TRUE OR FALSE
If the body is North of the equinoctial the declination is South
FALSE
* If the body is North of the equinoctial the declination is NORTH
TRUE OR FALSE
If the body is South of the equinoctial declination is named South
TRUE
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
TRUE
- arc of the Equinoctial or the angle at the celestial poles contained between two celestial meridians
Hour Angle (HA)
- 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
Greenwich Hour Angle (GHA)
- expressed in degrees and minutes and its value is in between 0° to 360°
Greenwich Hour Angle (GHA)
- 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
Sidereal Hour Angle (SHA)
- 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
Right Ascension (RA)
- 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°
Right Ascension (RA)
TRUE OR FALSE
* SHA* + RA* = 360°
TRUE
- an hour angle contained between the observer’s celestial meridian and the celestial meridian through that body, measured westward from the observer
Local Hour Angle (LHA)
If the angle or arc is measured eastward from the observer, it is known as the
_______________ and not LHA.
Easterly Hour Angle (EHA)
TRUE OR FALSE
LHA* + EHA* = 360°
TRUE
GIVE THE FORMULAS OF Longitude West GHA BEST
~ LHA* = GHA* − Long. (West)
~ GHA* = LHA* + Long. (West)
GIVE THE FORMULAS OF Longitude East GHA LEAST
~ LHA* = GHA* + Long. (East)
~ GHA* = LHA* − Long. (East)
Calculate the LHA of a star whose GHA is 70°, for an observer in longitude 147°E.
Solution:
Longitude East GHA Least
LHA*
= GHA* + Long (E)
= 70°+147°
= 217°
= 217°
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.
TRUE
The most important member of the Solar system is the ________.
Sun
TRUE OR FALSE
All the planets revolve eastward in elliptical orbits around the sun. The earth also rotates eastward on its axis.
TRUE
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.
TRUE
The great circle on the celestial sphere in the plane of the earth’s orbit is called ___________.
Ecliptic
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.
TRUE
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.
FALSE
The projection of the SUN on the ecliptic from successive positions of the earth in its orbit, appears to constantly move eastwards.
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.
TRUE
The angle at which the plane of ecliptic cuts the equinoctial plane is called _________________.
Obliquity of Ecliptic.
