The time on the Greenwich meridian, used by astronomers worldwide to time events. UK winter time equals UT; summer time is UT + 1h (France: UT + 1h in winter, UT + 2h in summer). Always write UT in an observing log.
Related terms
- Sidereal time
Star time: local sidereal time is the right ascension currently on the meridian. A sidereal day lasts 23 h 56 min 4 s, about 4 minutes less than a solar day. That is why stars rise 4 minutes earlier each night, or 2 hours per month.
- Observing log
The notebook where you record each observation: date, time in UT, place, instrument, magnification, seeing, transparency and what you saw. It shows your progress and helps you find good settings again. Well recorded observations can also be useful to amateur societies.
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