What is Sidereal Time ?

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Dear Astrology lovers,

 

Sir Shuhil ji has taught- how to calculate ascendant by sidereal time . Here

I am posting the definition of Sidereal time. Please read this information that

is very important to know to learners.

 

Thanks

 

Gunjan thakur

 

 

Sidereal time is time measured by the apparent diurnal motion of the vernal

equinox, which is very close to, but not identical with, the motion of stars.

They differ by the precession of the vernal equinox relative to the stars.

 

Solar time is measured by the apparent diurnal motion of the sun, and local

noon in solar time is defined as the moment when the sun is at its highest point

in the sky (exactly due south in the northern hemisphere and due north in the

southern hemisphere. The average time taken for the sun to return to its highest

point is 24 hours.

However, the stars appear to move in a slightly different way. During the

course of one day, the earth has moved a short distance along its orbit around

the sun, and so must rotate a small extra angular distance before the sun

reaches its highest point. The stars, however, are so far away that the earth's

movement along its orbit makes a generally negligible difference to their

apparent direction (see, however parallax), and so they return to their highest

point in slightly less than 24 hours. A mean sidereal day is about 23h 56m 4.1s

in length.

 

Sidereal time is defined as the hour angle of the vernal equinox. When the

meridian of the vernal equinox is directly overhead, local sidereal time is

00:00. Greenwich Sidereal time is the hour angle of the vernal equinox at the

prime meridian at Greenwich, England; local values differ according to

longitude. When one moves eastward 15° in longitude, sidereal time is larger by

one hour (note that it wraps around at 24 hours). Unlike computing local solar

time, differences are counted to the accuracy of measurement, not just in whole

hours. Greenwich sidereal time and UT1 differ from each other by a constant rate

(1.00273790935). Sidereal time is used at astronomical observatories because

sidereal time makes it very easy to work out which astronomical objects will be

observable at a given time. Objects are located in the night sky using right

ascension and declination relative to the celestial equator (analogous to

longitude and latitude on Earth), and when sidereal time

is equal to an object's right ascension, the object will be at its highest

point in the sky, or culmination, at which time it is best placed for

observation, as atmospheric extinction is minimized.

 

 

 

 

 

 

 

 

 

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