What was the exposure time of this photo?
about 10 seconds
about 10 minutes
about 1 hour
about 8 hours
The length of stars trails is pretty much the same as the distance travelled by an hour hand of clock during 30 minutes. But the Earth rotates twice as slow compared to the hour hand of a clock (one rotation per day, while clock's hour hand makes two).
reach: rather globalastronomyphotographytechnologytime
+3 Very interesting! globalquiz.org