Astronomy Formulas -- Page One

PERIODICITY FORMULAS -- DEFINITIONS -- NOTATION -- TIME FORMULAS

Page Two -- ILLUMINATION GEOMETRY -- MISC. FORMULAS -- PLANETARY DATA
PERIODICITY FORMULAS:
Sidereal Orbit (365.25636042 + 1.1 x 10-7 TE) days
Tropical Year (365.24219878 - 6.14 x 10-6 TE) days
Eclipse Year (346.620031 + 3.2 x 10-5 TE) days
Anomalistic Year
(365.25964134 + 3.04 x 10-6 TE) days
Sidereal Lunar Orbit (27.3216610 - 2.0 x 10-7 T) days
Lunar Mean Daily Sidereal Motion (13.1763582975 - 1.0224 x 10-8 T)°
Lunar Synodical Period (29.5305992 - 2.0 x 10-7 T) days
Centenial General Precession Longitude (1.396291666... + 0.0006180555...T)°
Given TE = Julian centuries from day 0.5, 1900 ET
Given T = Tropical centuries from 1900.0 N
Download the Epoch Calc v2012 Excel spreadsheet
to calculate and view updated formulas.  You just enter the date.
Since 1997, when this page was published, many astronomy formulas have been refined.

PERIODICITY FORMULAS -- NOTATION -- TIME FORMULAS -- PAGE TWO

DEFINITIONS:
Sidereal Orbit is a revolution relative to a fixed celestial position.
Sidereal Noon is the instant of transit of mean equinox relative to a fixed meridian position.
Fundamental Epoch
of Sidereal Time
(FE) is the instant 12 hours, 0 days, 1900 years A.D. with hours in mean sidereal time.
Ephemeris Time is the actual count of solar days from a fixed meridian.
Tropical Year (YT) is the period from equinox to equinox.
Eclipse Year (YE) is the period between the earth and lunar orbit planes node crossings.
Temporal Unit (TU) is 36,525 mean solar days since Jan. 0.5, 1900, UT.
Greenwich Mean
Sidereal Time (GT)
= 0.0 hours UT = 12 hours + aFMS
Universal Time (UT) has replaced Mean Solar Time due to a recognition of the non-uniform rotation rate of the earth.
Lunar Synodic Period (S9) is the period of time from one full or new moon to another, that is the time between consecutive alignments of the sun, earth and moon on a plane perpendicular to the plane of solar revolution.
Julian Date (JD) The Julian Date is the Julian day number for the preceding noon plus the fraction of the day since that instant. A Julian Date begins at 12h 0m 0s and is composed of 86400 seconds. It is recommended that JD be specified as SI seconds in Terrestrial Time (TT) where the length of day is 86,400 SI seconds.
Julian Day Number (JDN)

The Julian day number is the solar day number assigned in a continuous count of days beginning with zero assigned to Greenwich mean noon on 1 January 4713 BC, Julian proleptic calendar -4712.

Precession (PR) is the retrograde rotation of the earth's axis relative to fixed celestial reference.
Annual Parallax is the viewpoint difference due to the change in the earth's position relative to the sun.  For the nearest star the angle is about 0.000222.°
Annual Aberration is the angular shift in apparent position resulting from motion velocity of viewing from orbiting (moving) earth.
Diurnal Parallax is the viewpoint difference due to the rotation of the earth. The amount varies with the latitude of the observer.
Diurnal Aberration is the result of observing from a spining observing position on the surface of the earth.  Velocity of the observer causes apparent shift to a maximum correction of about 0.0008333° at the equator.
Atmospheric Refraction is the bending of light rays by the earth's atmosphere.

PERIODICITY FORMULAS -- DEFINITIONS -- TIME FORMULAS -- PAGE TWO

NOTATION:

aFMS
Ficticious Mean Solar position
DMS Day, Mean Sidereal
d, h, m, s, day, hour, minute, second
ES Ephemeris Second
ET
Ephemeris Time
FE
Fundamental Epoch
GT
Greenwich Mean Sidereal Time
JC
Julian Century
JD
Julian Day
Longitude of the Mean Sun
Period of Sidereal Rotation
T
Tropical Centuries from 1900.0 N
TE Temporal Epoch
TU
Temporal Solar Based Unit
UT Universal Time

PERIODICITY FORMULAS -- DEFINITIONS -- NOTATION -- PAGE TWO

TIME FORMULAS:
aFMS
0.776919398148d + 8640184.s628 TU + 0.0929 TU2
DMS
86,400.s
DMS / P°
0.999999902907 - 5.9 x 10-11 TE
DMS / P°
(1.000000097093 + 5.9 x 10-11 TE) -1
ES
Tropical Year 1900 / 31,556,925.9747
FE
12h 0d 1900 A.D. (hours in mean sidereal time)
FE
geometric mean solar longitude : mean equinox @ 279.6966777...°
GT
12h + aFMS
GT
0.279057325232d + 8640184.s8138 T'U + 0.s0929 T'U 2
JC
36,525 days ephemeris time
297.69667777...° + 36,001.2914583° TE + .0003025° TE2
Mean Solar Day
: Mean Sidereal Time
1.002737909265 + 5.89 x 10-11 TU
Mean Solar Day
: Mean Sidereal Time
(0.997269566414 - 5.86 x 10-11 TU) -1
TE
One JC from 0.d5, 1900 (JD 2,415,020.)
TU
36,525 mean solar days from 12h, Jan. 0, 1900 UT.
T'U
36,525 mean solar days from 12h, Jan. 0, 2000 UT1.

ASTRONOMY FORMULAS, PAGE TWO

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©1997 by James Q. Jacobs.  All rights reserved.
What's missing here? Your comments, etc. are appreciated: Contact.
Published Oct. 31, 1997.  Cite as: http://www.jqjacobs.net/astro/astrofor.html


Pleasant Creek Petroglyph Panel.
Viewing the moon in a deep, rocky desert canyon.

Download the Epoch Calc v2012 Excel spreadsheet
to calculate and view updated formulas and values.  You just enter the date.