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Astro*Dictionary by Michael Erlewine

 

 

 

 

25 articles for "Sidereal"

Sidereal Age [Astro*Index]

For the Sidereal Zodiac (SVP), the following dates obtain for the beginning of the great ages:

Age   SVP
  GEM    BC 6230  
  TAU    BC 4080  
  ARI    BC 1930  
  PIS    AD 221  
  AQU    AD 2371  

 

See also:
♦ Exaltation ♦ Hindu Age ♦ Sidereal Zodiac
Sidereal Astrology [Astro*Index]

Applies to various branchs of astrology which uses a non-rotating, Ecliptic coordinate system (with respect to the stars), and is, therefore, called sidereal. Western Sidereal Astrology has its fiducial, or zero-point, of longitude not marked by any star. Instead, the mean longitude of the Vernal Point of the epoch BY1950.0 is specified to be exactly 335°57'28.64", which is equivalent to stating that its Ayanamsha is 24°02'31.36". Longitudes of the Vernal Point for other dates are designated by the term SVP (Synetic Vernal Point) and are determined by applying Precession and Nutation to the epoch value. Eastern Sidereal Astrology, also called Hindu Astrology, uses a set of different values for the Ayanamsha. Sidereal Astrology has its own variations of the usual astrological techniques, plus some techniques peculiar to it.

See also:
♦ Sidereal Techniques ♦ Ecliptic Coordinate System ♦ Vernal Point ♦ Epoch ♦ Ayanamsha ♦ Synetic Vernal Point ♦ Precession ♦ Nutation ♦ Hindu Astrology
Sidereal Astrology [Munkasey M.]

That branch of astrological study which uses afixed point of Aries for measurements along the Ecliptic and Celestial Equator. Because a fixed reference point is used the zodiacal signs precess backwards is space through the years. See also: "Ayanamsa", and, "Tropical Astrology".

See also:
♦ Sidereal Techniques ♦ Ecliptic Coordinate System ♦ Vernal Point ♦ Epoch ♦ Ayanamsha ♦ Synetic Vernal Point ♦ Precession ♦ Nutation ♦ Hindu Astrology
Sidereal Clock [DeVore]

A clock found in every astronomical observatory, which is set to register oh om os when 0° Aries is on the Zenith. Formerly a noon point, but since 1925 a midnight point, it moves forward in the zodiac by 1°, or 4 minutes, each day, hence the Sidereal Time at noon (or midnight if since 1925) on any day shows what sign and degree is on the M.C. at that particular moment. For example, ST at 0h, or midnight, on May 1, 1945 is 14h 34m 14s: approx. 874m ö 4 = 218 degrees = approx. 8° Scorpio on M.C. The Sidereal Clock indicates 24h, while the solar chronometer registers 23h 56m 4.0906s of Mean Solar Time. It does not register A.M. or P.M., but divides the dial into 24 hourly periods. The so-called Army and Navy time of World War 11 indicates the eventual universal use of the same system applied to solar time, whereby for example, 2 P.M. will be known as 1400.

After the Sidereal clock has been set at oh to coincide with the moment of the Earth's crossing the intersecting point of the Ecliptic and Equator, the next noon it will read something like 12:04 — the distance the Earth has travelled in orbit in one solar day, shown in units of time. Thus each successive day at noon it shows the cumulative amount of the Earth's orbital travel since noon on the day of the equinox. Thereby sidereal time becomes the hour angle of the Vernal Equinox, and the Earth's position at Greenwich Noon on any day can be expressed in terms of hours, minutes and seconds. Its position along the ecliptic is expressed in degrees and minutes of longitude, and along the equator in degrees and minutes of Right Ascension.

 

See also:
♦ Time ♦ RAMC ♦ Right Ascension of the Midheaven (RAMC)
Sidereal Day [Astro*Index]

The observed interval of time between two successive transits of the Vernal Point over the Upper Meridian of the observer. The mean length of one sidereal day is 23h56m04.09054s (86164.09054s) of Civil Time. Note that this interval slightly shorter (0.0084s) than the mean time required for a fixed star to twice transit the Upper Meridian, due to the Precession which occurs in a single day.

See also:
♦ Transit ♦ Vernal Point ♦ Meridian ♦ Civil Time ♦ Fixed Stars ♦ Precession
Sidereal Day [Munkasey M.]

A specific length of time measured when a body which isat a distant point in space returns to the same meridian after one rotation of the Earth. Measured in Solar day terms a Sidereal Day is: 23 Hours, 56 Minutes, and 3.44464 Seconds in length.

See also:
♦ Transit ♦ Vernal Point ♦ Meridian ♦ Civil Time ♦ Fixed Stars ♦ Precession
Sidereal Day [DeVore]

The interval between two successive transits of the first point of Aries over the upper meridian of any place. The Sidereal Day is equal to 23h 56m 4.09s of mean solar time, and it has sidereal hours, each of 60 sidereal minutes, each minute of 60 sidereal seconds.

See also:
♦ Transit ♦ Vernal Point ♦ Meridian ♦ Civil Time ♦ Fixed Stars ♦ Precession
Sidereal Hour Angle [Astro*Index]

An angle measured westward from the Vernal Point to the foot of the Hour Circle through a body. It is, normally, expressed in arc-units ( ° ' " ), and is numerically equal to (360°-RA) of a given body.

See also:
♦ Vernal Point ♦ Hour Circle
Sidereal Hour Angle [Munkasey M.]

An angle measured in degrees which is numerically equivalent to 360 degrees minus the value for the Right Ascension of a given body.

See also:
♦ Vernal Point ♦ Hour Circle
Sidereal Month [Astro*Index]

The Moon's period of revolution relative to the stars. The duration of the mean sidereal month is 27.32166 days, or 27d07h43m05s. Because of the many disturbances in the Moon's motion, this interval can vary as much as 7 hours.

See also:
♦ Time ♦ Month
Sidereal Noon [Munkasey M.]

The time determined when the upper transit of the equinox (or-point of Aries) occurs over a designated place.

See also:
♦ Time
Sidereal Period [Astro*Index]

Literally, a star-to-star interval. The period it takes a body to return to the same point in relation to the fixed stars. This is also called its sidereal year.--or, The interval of time required for a planet to make one revolution around its central body in reference to the fixed stars.

Sidereal Periods in Civil Days

PlanetPeriod
  Moon    27.321661   + 16.e-8*T
  Mercury    87.96925577   + 1.e-8*T
  Venus    224.70079804   - 1.e-8*T
  Earth    365.25636042   + 11.e-8*T
  Mars    686.9797021
  Jupiter    4332.587611
  Saturn    10759.20468
  Uranus    30685.45046
  Neptune    60189.48544
  Pluto    90241.47708

 

See also:
♦ Fixed Stars ♦ Sidereal Year
Sidereal Period [Munkasey M.]

Sidereal period literally refers to a "slar to astar" period. It implies the measurement of a rotational or orbital period based upon the return of the same meridian to alignment with a star or other very distant body in space.

See also:
♦ Fixed Stars ♦ Sidereal Year
Sidereal Techniques [Astro*Index]

Techniques used in conjunction with sidereal charts. These include: Sidereal Natal charts, Sidereal Solar Returns and Sidereal Lunar Returns, Natal Quotidians, Solar Quotidians, Lunar Quotidians, Progressed Sidereal Solar Returns, Sidereal Anlunar Returns, Kinetic Solar Returns, Kinetic Lunar Returns, Kinetic Anlunar Returns, Navamsa Solar Returns (Enneads).---The primary tools of Western Sidereal Astrology are: Sidereal Natal chart, Sidereal Solar Return (SSR), Sidereal Lunar Return (SLR), and the Progressed Sidereal Solar Return (PSSR). Additional tools include set of Quotidians, which are a kind of Secondary Progression of various charts: The Q1-quotidian is based on the rule "one Sidereal Day equates to one Tropical Year"; the Q2-quotidian is based on the rule "one Civil Day equates to one Tropical Year." For hand computational procedures, a small "correction" called the Bija is sometimes employed when computing the Q2 charts. When the Natal chart is progressed by the Q2 method, the result is called the NQ2; when regressed by the same method, the result is called the RNQ2. Progression or regression of the Natal chart by the Q1 method yields the NQ1 and RNQ1 charts, respectively. Similarly, the SSR may be treated in like manner, yielding the Solar Quotidian Charts: SQ1, RSQ1, SQ2, and RSQ2. The SSR is also progressed at still another rate: Taking the difference in Sidereal Times for two Sidereal Solar Returns (computed the same location) and adding 24h gives a value (with a mean value of 30:09:13), which is divided by the diffence in the times (in UT) of the two charts. The result gives the rate at which the SSR is to be progressed, yielding the PSSR (Progressed Sidereal Solar Return) chart. Note that the Sidereal Time of the PSSR advances at about 5m/day, and that the PSSR rotates about 1.25 revolutions between the two Solar Returns. Still other tools include: Sidereal Anlunar Return (SAR), which is a Lunar Return based on the Moon of the SSR; Kinetic Solar Return (KSR), which is a Solar Return to the position of the Progressed Sun (NQ2 method). The KSR requires an iterative computational procedure, as the Progressed Sun moves at a rate of 59'08"/year, or 9.7"/day.

 

See also: ♦ Sidereal Natal Chart ♦ Sidereal Solar Return ♦ Sidereal Lunar Return ♦ Natal Quotidian ♦ Solar Quotidian ♦ Lunar Quotidian ♦ Progressed Sidereal Solar Return ♦ Sidereal Anlunar Return ♦ Kinetic Solar Return ♦ Kinetic Lunar Return ♦ Kinetic Anlunar Return
Sidereal Time Calculation [Astro*Index]

The computation of Sidereal Time begins with the definition of the RAUMS (Right Ascension of the Universal Mean Sun). Then, the GST is computed by adding the HAUMS (Hour Angle of the Mean Sun):

GST = RAUMS + HAUMS

In hand computation, the GST is interpolated from the printed ephemeris, applying the "10-second correction" (actually, 9.856s/hour) to the UT interval since the previous tabular value.

 

The computation of Sidereal Time begins with the definition of the RAUMS (Right Ascension of the Universal Mean Sun).

RAUMS (Right Ascension of the Universal Mean Sun) is defined by Newcomb:
RAUMS = 18h38m45.836s + 8640184.542sT + 0.0929sT2 + NUTRA

where: T is measured in units of 36525 days of Universal Time from the epoch:
      1900 JAN 00.5 UT = JD 2415020.0
and NUTRA = NUTLON cos(obliquity)
      NUTLON = Nutation in Longitude

 

E x a m p l e:

Find the GST and LST for 1960 JUL 07,04:44:30 EST for an observer at longitude W85°15' (=05:41:00):

                      1970 JUL 07,04:44:30 EST
                      EST to UT = +05:00
          _____________________________________
                       1970 JUL 07,09:44:30 UT
       
         GST (1970 JUL 07,0h UT) = 18:58:11.392
                     UT interval = 09:44:30
                    10-sec corr. =     1:36.015
         ______________________________________
                             GST = 28:44:17.410
                       longitude =-05:41
         ______________________________________
                             LST = 23:03:17.411

 

See also:
♦ Raums ♦ Greenwich Sidereal Time ♦ Universal Time ♦ Haums
Sidereal Time [Astro*Index]

The Hour Angle of the Vernal Point. Mean Sidereal Time is measured by the diurnal motion of the mean Vernal Point ("mean equinox of date"), which is affected the secular quantities of Precession; Apparent Sidereal Time is measured by the position of the true Vernal Point ("true equinox of date"), which is affected by Nutation. The difference (Apparent minus Mean) is called the Equation of the Equinoxes (called Nutation in Right Ascension, before 1960). Apparent Sidereal Time on the observer's meridian is called LST (Local Sidereal Time); on the Greenwich meridian, it is called GST (Greenwich Sidereal Time). The difference (LST-GST) is equal to the geographic longitude of the observer. The value of GST is tabulated in an ephemeris under the heading "ST" or "Sidereal Time." The argument used to compute the GST is the UT (Universal Time), which differs from the ET (Ephemeris Time) used to compute the planets. Sidereal Time is a direct measure of the diurnal rotation of the Earth, and is, therefore, independent of the value of Delta-T.

See also:
♦ Sidereal Time Calculation ♦ Raums ♦ Meridian ♦ Hour Angle ♦ Celestial Sphere ♦ Vernal Point ♦ Ecliptic ♦ Mean Sidereal Time ♦ Zenith ♦ Diurnal Motion ♦ Precession ♦ Apparent Sidereal Time ♦ Nutation ♦ Equation of the Equinoxes ♦ Local Sidereal Time ♦ Greenwich Sidereal Time ♦ Geographic Longitude ♦ Ephemeris ♦ Universal Time ♦ Ephemeris Time ♦ Delta-T
Sidereal Time [Prima]

There are various ways of telling time. Sidereal time, used by astrologers and astronomers, is based on a cyclic recurrent conjunction between a point on the Earth — projected onto the celestial sphere via a meridian of longitude — and a second point on the celestial sphere.

A sidereal year is defined as the time between successive transits of the center of the Sun (geocentric perspective) from the ecliptic meridian of a chosen star back to that same star. The ecliptic meridian of a star is the intersection on the celestial sphere of the ecliptic with a circle passing through the star and the observer's zenith.

A sidereal year is 365d 6h 9m 9.5s. (some 20 minutes longer than a tropical year, which is the time between successive transits of the Sun to 0° Aries on the ecliptic). By convention, there are 24 hours in a sidereal year, each day being approximately four sidereal minutes long.

The sidereal year begins when the Sun is simultan- eously at 0° Aries on the ecliptic (vernal equinox) and on the observer's meridian. Each 15° of the Sun's motion along the ecliptic equates to 1h of sidereal time or 1/24th of a sidereal year.

A sidereal day is defined as the time between successive transits of 0° Aries (ecliptic) over the meridian of a place. This occurs due to the Earth's diurnal motion and is equal to 23h 56m 4.09s.

Mean Sidereal Time is measured by the diurnal motion of the mean vernal point (affected by precession). Apparent Sidereal Time is measured by the position of the true vernal point (affected by nutation). The difference (Apparent ST minus Mean ST) is called the "equation of the equinoxes" (also called "nutation in Right Ascension" before 1960).

Apparent Sidereal Time on the observer's meridian is called LST (Local Sidereal Time); on the Greenwich meridian, it is called GST (Greenwich Sidereal Time). The difference (LST minus GST) is equal to the geographic longitude of the observer. The value of GST is tabulated in an ephemeris under the heading ST or Sidereal Time.

See also:
♦ Sidereal Time Calculation ♦ Raums ♦ Meridian ♦ Hour Angle ♦ Celestial Sphere ♦ Vernal Point ♦ Ecliptic ♦ Mean Sidereal Time ♦ Zenith ♦ Diurnal Motion ♦ Precession ♦ Apparent Sidereal Time ♦ Nutation ♦ Equation of the Equinoxes ♦ Local Sidereal Time ♦ Greenwich Sidereal Time ♦ Geographic Longitude ♦ Ephemeris ♦ Universal Time ♦ Ephemeris Time ♦ Delta-T
Sidereal Time [Munkasey M.]

The time that is determined from the observations of the passages of bodies over meridians. The sidereal time is numerically a measure of the hour angle of the equinox or point of Aries. See also: "Greenwich Sidereal Time".

See also:
♦ Sidereal Time Calculation ♦ Raums ♦ Meridian ♦ Hour Angle ♦ Celestial Sphere ♦ Vernal Point ♦ Ecliptic ♦ Mean Sidereal Time ♦ Zenith ♦ Diurnal Motion ♦ Precession ♦ Apparent Sidereal Time ♦ Nutation ♦ Equation of the Equinoxes ♦ Local Sidereal Time ♦ Greenwich Sidereal Time ♦ Geographic Longitude ♦ Ephemeris ♦ Universal Time ♦ Ephemeris Time ♦ Delta-T
Sidereal Time [DeVore]

A method of time-reckoning based upon the period elapsing between two successive passages of some particular star, taken as a fixed celestial point, over a given point on the circumference of the Earth. During one such rotation the Sun's apparent orbital travel has amounted to approximately 1°, hence the return of a given point on the Earth to the same relationship with the Sun requires added travel to the extent of 1° of arc or 4 minutes of time. Thus each calendar anniversary shows an annual net gain of 1°, which is the basis of all systems of progressed influences. The S.T. at any moment is the angular distance along the Ecliptic from 0° Aries, the point of the Spring Equinox, to the meridian of a given place at noon on a given day, expressed in h. m. s. The Right Ascension of the Meridian (RAMC) is a similar angular distance along the Equator expressed in degrees and minutes of arc.

When the Spring equinoctial point is on the observer's meridian it is S.T. 0h. When that degree has moved 15° it is 1h S.T. Thus the time required for the equinoctial degree to move to a certain advanced position becomes the unit through which that position is expressed. To determine the sidereal time for a given moment at a certain place, take from the ephemeris the ST for that date and apply certain corrections, viz.: If the ephemeris is for any other meridian than Greenwich make sure to take that into account, adding or subtracting your distance from this meridian, not from Greenwich; also add or subtract 12 hours if you are calculating your time-interval from midnight.

Additions to this S.T. for stations west of the zone meridian are made in degrees expressed in solar mean time, four minutes for each degree, which must be further converted by adding 0s.657 for each degree to reduce the additions to sidereal time. The hours added for the elapsed time since oh must also be adjusted in the same proportion. v. Time.

See also:
♦ Sidereal Time Calculation ♦ Raums ♦ Meridian ♦ Hour Angle ♦ Celestial Sphere ♦ Vernal Point ♦ Ecliptic ♦ Mean Sidereal Time ♦ Zenith ♦ Diurnal Motion ♦ Precession ♦ Apparent Sidereal Time ♦ Nutation ♦ Equation of the Equinoxes ♦ Local Sidereal Time ♦ Greenwich Sidereal Time ♦ Geographic Longitude ♦ Ephemeris ♦ Universal Time ♦ Ephemeris Time ♦ Delta-T
Sidereal Vernal Point [Munkasey M.]

That point on the Ecliptic in zodiacal longitude where measurements for the Sidereal Zodiac begin. The equivalent of the zero Aries point for the Sidereal Zodiac.

See also:
♦ Precession ♦ Vernal Point ♦ Vernal Equinox ♦ Synetic Vernal Point
Sidereal Year [Astro*Index]

Time required for the Earth to return exactly to the same position with reference to the same fixed star. This requires 365.25636 days, or 365d06h09m10s.

See also:
♦ Fixed Stars
Sidereal Year [Munkasey M.]

The time that it takes the Sun, as seen from the sameplace on Earth, to return to a designated body.

See also:
♦ Fixed Stars
Sidereal Year [DeVore]

v. Year.

See also:
♦ Year
Sidereal Zodiac [Astro*Index]

One of several zodiacs used by various astrologers, both ancient and modern, which is fixed with reference to the stars. Conversion from the Tropical Zodiac to a Sidereal Zodiac is normally specified by giving the longitude of the Vernal Point in terms of the Sidereal Zodiac, or (equivalently) the value of the Ayanamasha for a specific date. Western sidereal astrologers use the value of the SVP (Synetic Vernal Point) specified by Fagan and Allen, which defines the mean longitude of the Vernal Point of the epoch BY1950.0 to be exactly 335°57'28.64", which is equivalent to stating that its Ayanamsha is 24°02'31.36". The Fagan-Allen determination leads to a Zodiac which is identical to that used by ancient astrologers (Egyptian, Babylonian, Persian, Arabian, Magi). Its use has been established to within 0.1° for the period BC786-AD500, and to within less than 5° as early as BC2767. All ancient astrologers used the same Sidereal Zodiac, but its universality diminished from the time of Claudius Ptolemy (about 75AD) until its re-discovery by Cyril Fagan in our century. Modern Hindu Astrology, which is clearly derived from Greek sources after the Alexandrian conquests which followed his rise to power in BC336, and reflect much of the work of Ptolemy, uses one of a set of Ayanamshas, which yield coordinate systems some of which are only approximately fixed with reference to the stars.

See also:
♦ Exaltation ♦ Eternity, Horoscope of ♦ Zodiac ♦ Sidereal Astrology ♦ Tropical Zodiac ♦ Svp ♦ Ayanamsa / Ayanamasha ♦ Fagan, Cyril ♦ Vernal Point ♦ Synetic Vernal Point ♦ Hindu Astrology
Sidereal Zodiac [Prima]

One of the two major zodiac systems, it is the zodiac traditionally used by Eastern (i.e. Indian, Tibetan) astrologers.

In the sidereal (Latin = stellar) zodiac, the 12 signs are based upon the constellations of the fixed stars. The signs of the sidereal zodiac coincided with the signs of the tropical zodiac approximately 2000 years ago. This is no longer so, due to the movement of the fixed stars — approximately 50 seconds per year (or 1 degree in 72 years; 1.396325 degrees in century). This motion is known as precession.

A Sanskrit term, ayanamsa (meaning "yearly degree") is used to indicate the difference in arc between the starting points of the tropical and sidereal zodiacs.

See also:
♦ Exaltation ♦ Eternity, Horoscope of ♦ Zodiac ♦ Sidereal Astrology ♦ Tropical Zodiac ♦ Svp ♦ Ayanamsa / Ayanamasha ♦ Fagan, Cyril ♦ Vernal Point ♦ Synetic Vernal Point ♦ Hindu Astrology

 

Astro*Index Copyright © 1997 Michael Erlewine

 

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