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Right ascension is the celestial equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a primary direction (a zero point) on an equator. Right ascension is measured from the Sun at the March equinox i.e. the First Point of Aries, which is the place on the celestial sphere where the Sun crosses the ...
In this case, the longitude is also called the right ascension of the ascending node (RAAN). The angle is measured eastwards (or, as seen from the north, counterclockwise) from the FPA to the node. [2] [3] An alternative is the local time of the ascending node (LTAN), based on the local mean time at which the spacecraft crosses the equator.
Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the vernal equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Declination is measured northward or southward from the celestial equator, along the hour circle passing through the point in question.
This is both because of the fluctuation in inclination mentioned above, and because the moon has to arrive at right ascension 6 hours or 18 hours (90° or 270°). The lining up occurs once every 6798.38 days on average (18.613 Julian years of 365.25 days, or 18 years and 223 or 224 days), although the node undergoes a fluctuation of amplitude 1 ...
Conjunction (astronomy) Visual conjunction between the Moon and the planet Venus, the two brightest objects in the night sky. In astronomy, a conjunction occurs when two astronomical objects or spacecraft appear to be close to each other in the sky. This means they have either the same right ascension or the same ecliptic longitude, usually as ...
Meridian (astronomy) The meridian on the celestial sphere. An observer's upper meridian, a semicircle contains their zenith and both celestial poles; the observer's local meridian is the semicircle that passes through their zenith and the north and south points of their horizon. In astronomy, the meridian is the great circle passing through the ...
Hour angle. The hour angle is indicated by an orange arrow on the celestial equator plane. The arrow ends at the hour circle of an orange dot indicating the apparent place of an astronomical object on the celestial sphere. In astronomy and celestial navigation, the hour angle is the dihedral angle between the meridian plane (containing Earth's ...
Lunar node. The lunar nodes are the two points where the Moon's orbital path crosses the ecliptic, the Sun's apparent yearly path on the celestial sphere. A lunar node is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic. The ascending (or north) node is where the Moon ...