Ephemeris Type Selection

The ephemeris type selection determines what kinds of data are calculated by Alcyone Ephemeris. The sources and accuracy of the ephemeris calculations are described in Sources and Accuracy. Select Ephemeris> Ephemeris data from the main menu or press Alt-T. The Ephemeris data dialog appears. Chose an ephemeris type from the Ephemeris type drop-down list.

The following ephemeris types are available:

       heliocentric ecliptical data

       heliocentric equatorial data

       geocentric ecliptical data

       geocentric equatorial data

       topocentric ecliptical data

       topocentric equatorial data

       topocentric horizontal data

       mean orbital elements

       osculating lunar orbital elements

       lunar libration

Then select the quantities to be shown in the ephemeris table from the checkbox list below the drop-down list. Depending on the selected Ephemeris type the following quantities are available:

1. heliocentric ecliptical data :

Longitude	Calculates geometric heliocentric longitude, referred to the mean equinox of the date, in degrees. Longitude is measured to the east from the vernal equinox.
Latitude	Calculates geometric heliocentric latitude, referred to the mean equinox of the date, in degrees. Latitude is measured positive north of the ecliptic.
Distance	Calculates heliocentric distance in astronomical units.
x, y, z	Calculates rectangular geometric heliocentric ecliptical coordinates referred to the mean equinox of the date in astronomical units. The x-axis is to the vernal equinox, the y-axis to a point 90º east of the vernal equinox, the z-axis is positive north of the ecliptic.
vx, vy, vz	Calculates heliocentric velocities (space motion vectors in x-, y-, z-axes) in kilometers per second or astronomical units per day, which are selected in Formatting dialog. The x-axis is to the vernal equinox, the y-axis to a point 90º east of the vernal equinox, the z-axis is positive north of the ecliptic.
orbital vel.	Calculates heliocentric velocity in the orbital plane in kilometers per second or astronomical units per day, which are selected in Formatting dialog.
ang. sep	Calculates heliocentric angular separation with respect to the Reference object in degrees.

2. heliocentric equatorial data :

right asc.	Calculates geometric heliocentric right ascension, referred to the mean equinox of the date, in degrees. Longitude is measured to the east from the vernal equinox.
declination	Calculates geometric heliocentric declination, referred to the mean equinox of the date, in degrees. Latitude is measured positive north of the equator.
distance	Calculates heliocentric distance in astronomical units.
x, y, z	Calculates rectangular geometric heliocentric equatorial coordinates, referred to the mean equinox of the date, in astronomical units. The x-axis is to the vernal equinox, the y-axis to a point 90º east of the vernal equinox along the equator, the z-axis is positive north of the equator.
vx, vy, vz	Calculates heliocentric velocities (space motion vectors in x-, y-, z-axes) in kilometers per second or astronomical units per day, which are selected in Formatting dialog . The x-axis is to the vernal equinox, the y-axis to a point 90º east of the vernal equinox along the equator, the z-axis is positive north of the equator.
orbital vel.	Calculates heliocentric velocity in the orbital plane in kilometers per second or astronomical units per day, which are selected in Formatting dialog .
ang. sep	Calculates heliocentric angular separation regarding to the Reference object in degrees.

Note: For the earth, the heliocentric quantities are computed for the center of the body, not the center of gravity of the earth-moon system.

3. geocentric ecliptical data :

longitude	Calculates apparent geocentric longitude (corrected for the effect of light-time and abberation), referred to the mean or true equinox of the date, in degrees. Longitude is measured to the east from the vernal equinox.
latitude	Calculates apparent geocentric latitude (corrected for the effect of light-time and abberation), referred to the mean or true equinox of the date, in degrees. Latitude is measured positive north of the ecliptic
distance	Calculates geocentric distance in astronomical units; for the moon, distance in kilometers, astronomical units or earth radii may be selected in Formatting dialog .
x, y, z	Calculates rectangular astrometric geocentric ecliptical coordinates, referred to the mean equinox of the date, in astronomical units. The x-axis is to the vernal equinox, the y-axis to a point 90º east of the vernal equinox, the z-axis is positive north of the ecliptic.
magnitude	Calculates apparent visual magnitude. There are three different magnitude calculations, selected in More settings dialog.
phase	Calculates phase (illuminated fraction of the disk). The phase may be in percent or decimal fraction, selected in Formatting dialog .
app. diameter	Calculates apparent diameter in seconds.
elongation	Calculates geocentric ecliptical elongation from the true sun. The elongation is the difference between the true geocentric ecliptical longitude of the body and the center of the solar disk. The elongations of inferior planets (planet minus sun) are positive to the east of the sun (evening phase) and negative to the west of the sun (morning phase). The elongations of superior planets (sun minus planet) and the moon (moon minus sun) are always positive and to the east of the sun.
mean elon.	Calculates geocentric ecliptical elongation from the 'mean sun'. The elongation is the difference between the true geocentric ecliptical longitude of the body and the longitude of the mean sun, the sun with only its mean motion in longitude, without its ecliptic inequality. The elongations of inferior planets (planet minus mean sun) are positive to the east of the mean sun (evening phase) and negative to the west of the mean sun (morning phase). The elongations of superior planets (mean sun minus planet) and the moon (moon minus mean sun) are always positive and to the east of the mean sun.
ang. sep	Calculates geocentric angular separation regarding  to the Reference object in degrees.

4. geocentric equatorial  data :

right asc.	Calculates apparent geocentric right ascension (corrected for the effect of light-time and abberation), referred to the mean or true equinox of the date, in degrees or hours, selected in Formatting  dialog. Right ascension is measured to the east from the vernal equinox.
declination	Calculates apparent geocentric declination (corrected for the effect of light-time and abberation), referred to the mean or true equinox of the date, in degrees. Declination is positive north of the equator.
distance	Calculates geocentric distance in astronomical units; for the moon, distance in kilometers, astronomical units or earth radii may be selected in Formatting dialog .
x, y, z	Calculates rectangular astrometric geocentric equatorial coordinates, referred to the mean equinox of the date, in astronomical units. The x-axis is to the vernal equinox, the y-axis to a point 90º east of the vernal equinox along the equator, the z-axis is positive north of the ecliptic.
magnitude	Calculates apparent visual magnitude. There are three different magnitude calculations, selected in More settings dialog .
phase	Calculates phase (illuminated fraction of the disk). The phase may be in percent or decimal fraction, selected in Formatting dialog .
app. diameter	Calculates apparent diameter in seconds.
con.	Calculates the constellation that the body is located in (see constellation abbreviations ).
ang. sep	Calculates geocentric angular separation regarding  to the Reference object in degrees.

5. topocentric ecliptical data :

longitude	Calculates apparent topocentric longitude for observer's location.
latitude	Calculates apparent topocentric latitude for observer's location.
distance	Calculates topocentric distance in astronomical units; for the moon, distance in kilometers, astronomical units or earth radii may be selected in Formatting dialog .
magnitude	Calculates apparent visual magnitude. There are three different magnitude calculations, selected in More settings dialog.
phase	Calculates phase (illuminated fraction of the disk). The phase may be in percent or decimal fraction, selected in Formatting dialog .
app. diameter	Calculates apparent diameter in seconds, due to topocentric distance.
con.	Calculates the constellation that the body is located in (see constellation abbreviations ).
ang. sep	Calculates geocentric angular separation regarding  to the Reference object in degrees.

6. topocentric equatorial data :

right asc.	Calculates apparent topocentric right ascension in degrees or hours, selected in Formatting dialog , for observer's location. Correction for refraction, with specification of atmospheric conditions, is selected inRefraction dialog .
latitude	Calculates apparent topocentric declination for observer's location.
distance	Calculates topocentric distance in astronomical units; for the moon, distance in kilometers, astronomical units or earth radii may be selected in Formatting dialog .
magnitude	Calculates apparent visual magnitude. There are three different magnitude calculations, selected in More settings dialog .
phase	Calculates phase (illuminated fraction of the disk). The phase may be in percent or decimal fraction, selected in Formatting dialog .
app. diameter	Calculates apparent diameter in seconds, due to topocentric distance.
con.	Calculates the constellation that the body is located in (see constellation abbreviations ).
ang. sep	Calculates geocentric angular separation regarding  to the Reference object in degrees.

7. topocentric horizontal data :

azimuth	Calculates apparent azimuth for observer's location. The origin of azimuth, from the south or north point of the horizon, may be selected in More settings dialog.
altitude	Calculates apparent altitude for observer's location.
distance	Calculates topocentric distance in astronomical units; for the moon, distance in kilometers, astronomical units or earth radii may be selected in Formatting dialog .
magnitude	Calculates apparent visual magnitude. There are three different magnitude calculations, selected in More settings dialog.
phase	Calculates phase (illuminated fraction of the disk). The phase may be in percent or decimal fraction, selected in Formatting dialog .
app. diameter	Calculates apparent diameter in seconds, due to topocentric distance.
con.	Calculates the constellation that the body is located in (see constellation abbreviations ).
ang. sep	Calculates geocentric angular separation regarding  to the Reference object in degrees.

Note: The observer's location may be selected in the Observer dialog. Parallax reduces altitude and can be large for the moon, about 54'-61' at the horizon, but is small for other bodies, reaching about 30" for Venus, 23" for Mars.

For all topocentric ephemeris data correction for refraction is available. Correction for refraction and specification of atmospheric conditions are selected in Refraction dialog. Refraction increases the altitude of all bodies equally and is large, about 34', at the horizon, but less than 1' above 45°.

The effects of parallax and refraction on ecliptical and equatorial coordinates depend upon the altitude of the body and the inclination of the ecliptic and equator to the horizon and to the vertical circle through the body at the observer's location. When correct for refraction is selected in Refraction dialog and a topocentric ephemeris type is selected, refraction appears in the status bar.

8. mean orbital elements :

Calculates mean elements of lunar and planetary orbits for the mean equinox of date:

semi maj. axis	the semimajor axis in astronomical units
eccentricity	the eccentricity
mean lon.	mean longitude in degrees
lon. of peri.	the longitude of perihelion (perigee) in degrees
lon. asc. node	the longitude of the ascending node in degrees
inclination	the inclination of the orbit to the ecliptic in degrees

9. osculating lunar orbital elements :

semi maj. axis	the semimajor axis in astronomical units
eccentricity	the eccentricity
lon. of peri.	the longitude of perigee in degrees
lon. asc. node	the longitude of the ascending node in degrees
inclination	the inclination of the orbit to the ecliptic in degrees

10. lunar libration:

l	Calculates the geocentric optical and physical lunar libration in longitude. Selenographic longitude is measured from the meridian passing through the mean center of the lunar disc, the center seen from the earth when the moon is at the mean ascending node and the node at mean apogee or perigee, and is positive to the west (toward Mare Crisium).. The libration, the displacement of the mean center from the sub-Earth point, the apparent center of the lunar disc seen from the Earth at any time, is resolved into the selenographic longitude l and latitude b of the sub-Earth point: When l is positive, that is, the sub-Earth point west of the mean center, the mean center is displaced to the east and a region on the western limb of the moon is visible; when l is negative, the sub-Earth point east of the mean center, the mean center is displaced to the west and a region on the eastern limb of the moon is visible.
b	Calculates the geocentric optical and physical lunar libration in latitude. Selenographic latitude is measured from the moon's equator and is positive to the north. When b is positive, that is, the sub-Earth point north of the mean center, the mean center is displaced to the south and a region on the northern limb is visible; when b is negative, the sub-Earth point south of the mean center, the mean center is displaced to the north and a region on the southern limb is visible.
PA axis	Calculates the position angle of the moon's axis of rotation, measured from north to east (counter-clockwise) from the celestial north point on the lunar disc to the north pole of the axis of rotation.
l (sun)	Calculates the selenographic longitude of the sun. The selenographic longitude and latitude of the sun, l (sun) and b (sun), are the selenographic longitude and latitude of the subsolar point, the center of the lunar disc seen from the sun, which is the center of the illuminated hemisphere of the moon. l (sun) is positive when the subsolar point is to the west of the meridian through the mean center of the lunar disc, negative when to the east, and is measured between ±180°.
b (sun)	Calculates the selenographic latitude of the sun. b (sun) is positive when the subsolar point is to the north of the moon's equator and negative when to the south.
col (sun)	Calculates the selenographic colongitude of the sun. Col (sun) = 90° - l (sun) mod 360°, is the selenographic longitude of the morning terminator, measured to the east, and corresponds approximately to the phase of the moon: new moon 270°, first quarter 0°, full moon 90°, last quarter 180°.
PA limb	Calculates the position angle of the midpoint of the bright limb. PA limb is measured from north to east (counterclockwise) from the celestial north point on the lunar disc to the midpoint of the illuminated limb, the subsolar point; it is equal to the angle at the celestial north point of the lunar disc subtended by the arc between the apparent center of the disc, the sub-Earth point, and the midpoint of the illuminated limb, the subsolar point, measured to the east.

The current selected ephemeris type is shown in the status bar.