Celestial 2
What is the astronomical triangle?
. The astronomical triangle is the triangle on the celestial sphere, whose vertexes are the elevated pole of the observer, the zenith of the observer and the position of the body. Its sides are the polar distance, zenith distance and co-lat. Its angles are the meridian angle at the elevated pole, the azimuth angle at the zenith of the observer, and the parallactic angle at the body
What is the Celestial Meridian of Greenwich (G)?
A great circle passing through Greenwich and the poles projected on the celestial sphere
What is the Local Celestial Meridian (M) ?
A great circle passing through the observer's meridian and the poles projected on the celestial sphere.
What is an Hour Circle of the body?
Great Circle passing through the Celestial Poles and the celestial body. Hour circle Moves with the body.
What are celestial Meridians?
Great Circles passing through the Celestial Poles. Celestial Meridians remain fixed over a terrestrial point on earth. Have an upper and lower branch
What are Hour Circles?
Great Circles similar to celestial meridians, except hour circles move with the body.
What are Vertical Circles?
Great circles, on the celestial sphere, that are perpendicular to the celestial horizon and passing through the zenith and nadir. Comparable to meridians in other coordinate systems
What is a vertical circle?
In the horizon coordinate system a vertical circle is a great circle that passes through the zenith and nadir and is perpendicular to the celestial horizon. It is similar to the hour circles and meridians of the other coordinate systems
What is an altitude?
In the horizon coordinate system an altitude is a vertical angle measured from the horizon to the body along the vertical circle of the body from 0° to 90°. It is similar to Declination in the Celestial Coordinate System and similar to Latitude in the terrestrial coordinate system.
What is declination?
Its the angular distance north or south the of the celestial equator.
What is polar distance?
Polar Distance/Co-Declination (Co-Dec) - angular distance a body is north or south of the elevated pole.
What are the three coordinate systems?
The Terrestrial Coordinate System establishes the observer's location on earth The Celestial Coordinate System establishes the location of the body on the celestial sphere. The Horizon Coordinate System locates the observed location of the body in relation to the terrestrial and celestial spheres.
What is the Zodiac?
The Zodiac is a circular band of the sky extending 8° on each side of the ecliptic.
What is the Meridian Angle (t)?
The angle measured east or west from the local celestial meridian to the hour circle of the body, 0°-180 °. Must have a suffix of East or West.
What is Right Ascension (RA)?
The angle measured eastward from the 1st Point of Aries to the hour circle of the body 0°-360 °.
What is Altitude (h) in the horizon coordinate system?
The angle measured from the celestial horizon to the body along the vertical circle of the body, 0°-90°. Similar to Latitude and Declination.
What is the Greenwich Hour Angle (GHA)?
The angle measured westward from Greenwich Celestial Meridian to the hour circle of the body 0°-360 °
What is the Sidereal Hour Angle (SHA)?
The angle measured westward from the 1st Point of Aries to the hour circle of the body 0°-360 °.
What is the Local Hour Angle (LHA)?
The angle measured westward from the local celestial meridian to the hour circle of the body, 0°-360 °.
What are Hour angles?
The angular measurement from a reference celestial meridian or hour circle of a reference body to the hour circle of the body up to 360°. ALWAYS MEASURED WESTWARD ! Similar to Longitude, except measured 0° - 360°
What is the azimuth angle, what is it converted to, and why does it need to be converted?
The azimuth angle is the interior angle located at the observer's zenith and measured from the local celestial meridian to the vertical circle of the body. It is converted from an azimuth angle to a true azimuth so the azimuth can be used on a plotting sheet to get the direction of the celestial body of the observer.
What is the base of Horizon Coordinate System?
The celestial horizon, a great circle that is the perpendicular bisector or a line connecting the zenith and the nadir.
What is Co-Altitude (Co-Alt) or Zenith Distance in the horizon coordinate system?
The complement of the altitude or 90° - Altitude (90° - h). Measured from the zenith of the observer to the body along the vertical circle of the body 0°-90°.
What is the Celestial Horizon?
The great circle that is every where perpendicular to a line drawn between the zenith and nadir. Comparable to the equator and equinoctial of other coordinate systems.
What is Azimuth (Zn)?
The horizontal angle measured clockwise from North, 0°-360°, to the vertical circle of the body. Always expressed with three whole digits and always referenced to True North.
What is the Azimuth Angle (Az or Z)?
The horizontal angle measured clockwise or counterclockwise from the north or south point of the horizon to the vertical circle of the body from 0°-180°. It is prefixed (N/S) with the name of the elevated pole and suffixed (E/W) with the direction of t.
What is the Ecliptic
The path the sun appears to follow - a great circle on the celestial sphere that is inclined at an angle of 23° 27' to the celestial equator.
What is the first point of Aries?
The position on the celestial sphere that corresponds to the position of the sun at the vernal equinox.
What is the Geographic Position of a Body (gp)?
The position on the earth's surface a celestial body appears to have when viewed from the center of the earth or when the perpendicular light beam from the body is projected onto the earth's surface.
What two angles of the astronomical triangle do we use?
The two angles are the meridian and azimuth angles.
What is a Vertical Circle of the Body?
The vertical circle that passes through the body. Similar to an hour circle.
What is the Principal Vertical Circle?
The vertical circle that passes through the north and south points of the horizon.
What is the Prime Vertical Circle?
The vertical circle through the east and west points of the horizon.
What is the Zenith Distance?
The zenith distance is the angular measure along the vertical circle of the body, measured from the zenith of the observer to the celestial body. It 90° - Altitude and is also known as the Co-Alt.
What leg of the Astronomical Triangle are we trying to compute?
The zenith distance or Co-Alt gives a distance from the GP of the body
What are circles of equal latitude?
The zenith distance or co-alt is the radius of a circle whose center is the geographic position of a body. Any observer measuring the same vertical angle (altitude) of that particular body at the same instant in time will find themselves on a circle of equal altitude the same distance from the GP
What are the celestial poles?
They are Pn Pole North and Ps Pole South extending out to the celestial sphere.
What is the Co-Dec or Polar Distance?
This is an angular distance measured along a celestial meridian from the elevated pole to the elevated pole. It is expressed as 90° ± Declination depending on whether the observer latitude and body's declination have the same or contrary names
What is the Co-Lat?
This is an angular distance measured along the meridian of the observer from the elevated pole to the observer's Zenith. It is expressed as 90° - Lat.
What is the Co-Alt or Zenith Distance?
This is an angular distance measured along the vertical circle of the body from the zenith of the observer to the body. It is expressed as 90° - Altitude of the body. It is similar to the distance in the great circle sailing. We use this leg to establish an LOP.
What is the Meridian Angle (t)?
This is the interior angle of the triangle whose vertex is the elevated pole and the angle is measured east or west from the local celestial meridian to the hour circle of the body, 0 ° - 180°. The angle is designated either east or west.
What is the Azimuth Angle (Az)?
This is the interior angle of the triangle whose vertex is the observer's zenith and the angle is measured from the meridian of the observer, 0°-180°, to the vertical circle of the of the body. It is designated with a prefix and suffix, the prefix is north or south depending upon the latitude of the observer and the suffix is east or west depending upon the direction of the meridian angle.
What is the apparent motion of all celestial bodies?
Westward
Two points one directly over head and the other directly below (other side of the planet)?
Zenith (Z) and Nadir (Na)
