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).
 globalquiz.org
                
reach: rather globalastronomyphotographytechnologytime
Answers by country
about 10 seconds
about 10 minutes
about 1 hour
about 8 hours
answers
 South Africa
South Africa11
 Australia
Australia42
 France
France18
 Switzerland
Switzerland18
 Unknown
Unknown25
 Germany
Germany209
 the United States
the United States316
 the United Kingdom
the United Kingdom115
 Poland
Poland8160
 India
India336
 the Netherlands
the Netherlands11
 Pakistan
Pakistan31
 Greece
Greece16
 the United Arab Emirates
the United Arab Emirates12
 Austria
Austria40
 the Philippines
the Philippines32
 Canada
Canada20
 Republic of Ireland
Republic of Ireland10
 Nigeria
Nigeria12