What Is Sidereal Time?
Stellar time refers to a time measurement system based on the rotation period of the earth relative to the star. The time when the vernal equinox points to two consecutive days on the celestial sky is called the stellar day, which is equal to 23: 56: 4.09 seconds of flat solar time. , Measured by the vernal equinox hour. For the convenience of measurement, the stellar day is divided into 24 stellar hours, one stellar hour is divided into 60 stellar minutes, and one stellar minute is divided into 60 stellar seconds. All these units are collectively referred to as the Stellar Hour Unit for measuring time, referred to as the Stellar Hour Unit for short. Time is measured according to the above system, which is called stellar time in astronomy. [1]
Stellar time
- Stellar time is the celestial meridian circle indicated by astronomy and geodesy. It is a time system based on the true rotation of the earth:
- Stellar hour: the hour angle of the vernal equinox from the meridian circle. Corresponds to when there is a local star at each local meridian on Earth. Stellar time is Greenwich Mean Time (00:00 UTC).
- At this point, it can be seen that the astral constellation A (14:16 right ascension) is a little west of the meridian circle, and the astral Scorpio (16:29 right ascension) is east of the meridian circle. The local star time s required at any time in a certain place can be calculated by the following formula s = m + S o + M . Where m is the local peacetime, M is the Greenwich meantime corresponding to m , and S o is the world time 0h star of the day, = 1 / 365.2422.
- The start of stellar time
- From the known Beijing time to find the Nanjing local time m = 19h35m + (7h55m04s-8h) = 19h30m04s; check the astronomical popular calendar to know that the stellar hour S o = 12h33m52s of world time 0h on March 31; find the corresponding Greenwich mean time from local time m M = m = 11h35m, further obtain M = 1m54s.
- So the local star time s = m + S o + M = 8h05m50s. Hour t = local star time s-right ascension a
- If you do not know the 0h world time on a certain day, you can use s = right ascension a + hour angle. For example, the local stellar time at 19h35m Beijing time on March 31, 2019 in Nanjing. At that time, the angle of the Arcturian Nanjing was -6h12m12s (or 17h47m48s-24h), and the angular longitude of the Arcturian was 14h15m38.4s, so s = 14h15m38.4s-6h12m12s = 8h03m26.2s