Sidereal time is very ‘Significant’,
we must consider during calculation. This is like Ascension, being measured
along the celestial equator, but using hours, minutes and seconds instead of
degrees, minutes and seconds.
The two terms are in fact
convertible, either being employed according to convenience, right ascension
being open expressed in hours and minutes although strangely enough. Well, ‘Sidereal
time’ is never expressed in degrees. It is easy to convert one into the other
like this….
convertible, either being employed according to convenience, right ascension
being open expressed in hours and minutes although strangely enough. Well, ‘Sidereal
time’ is never expressed in degrees. It is easy to convert one into the other
like this….
1 Day = 360 degrees
1 House = 15 degrees
1 Minute = 15’
1 Second = 15”
1 House = 15 degrees
1 Minute = 15’
1 Second = 15”
In every observatory there is an ‘Astronomical
Clock’, an accurate adjusted chronometer, regulated in a way like 24 hours – no
more and no less, a one complete revolution of the earth.
Clock’, an accurate adjusted chronometer, regulated in a way like 24 hours – no
more and no less, a one complete revolution of the earth.
Suppose, the moment of the Vernal
Equinox, when the Sun has reached g0 °0’0” (an official commencement of the spring quarter) happen on March
21st each year. Let us suppose that at Greenwich Observatory, the Sun
is found to be culminating, exactly on the meridian (m.c.), perpendicular to
the east-west horizontal line. These are all different ways of saying the same
thing. In other words, it is exactly the noon.
Equinox, when the Sun has reached g0 °0’0” (an official commencement of the spring quarter) happen on March
21st each year. Let us suppose that at Greenwich Observatory, the Sun
is found to be culminating, exactly on the meridian (m.c.), perpendicular to
the east-west horizontal line. These are all different ways of saying the same
thing. In other words, it is exactly the noon.
The sidereal clock will show 0h.
0m. 0s. (Astronomical time, always counts from noon to noon or
civil time, from midnight to midnight) and this will then be the Sidereal Time
at Noon on that day.
0m. 0s. (Astronomical time, always counts from noon to noon or
civil time, from midnight to midnight) and this will then be the Sidereal Time
at Noon on that day.
Now let us suppose that a complete day elapses,
and the astronomer observes the Sun exactly culminating again, what will the
clock show?
and the astronomer observes the Sun exactly culminating again, what will the
clock show?
– 24h. 0m.
0s., or 0h. 0m. 0s.?
0s., or 0h. 0m. 0s.?
No, because in 24 hours, during which the earth
has made one complete rotation, the Sun has moved forward 1° or very nearly and consequently the earth must turn 361° or thereby, instead of only
360°, before the Sun can be
exactly on the meridian. Therefore, the clock will show about 0h. 4m. 0s. This will be the ‘Sidereal Time’ at noon on that day. Similarly,
next day at noon, the clock will show about 0h.
8m. 0s., so on every day, gaining about four minutes every 24 hours.
has made one complete rotation, the Sun has moved forward 1° or very nearly and consequently the earth must turn 361° or thereby, instead of only
360°, before the Sun can be
exactly on the meridian. Therefore, the clock will show about 0h. 4m. 0s. This will be the ‘Sidereal Time’ at noon on that day. Similarly,
next day at noon, the clock will show about 0h.
8m. 0s., so on every day, gaining about four minutes every 24 hours.
Hence on any particular day, according to the
time of the year the ‘Sidereal Time’ at Noon may be anything from 0h. 0m. 0s.
to 23 hours 56 minutes 0 seconds. It will be evident that the sidereal clock
must gain one whole day in the year.
time of the year the ‘Sidereal Time’ at Noon may be anything from 0h. 0m. 0s.
to 23 hours 56 minutes 0 seconds. It will be evident that the sidereal clock
must gain one whole day in the year.
Dr. A. Shanker
www.ShankerAdawal.com, www.ShankerStudy.com
Your Free Astro Queries, Visit below link…