I assume the question you're trying to ask is: How do you calculate the
exposure time to make a star trail of a given length in degrees?
Since the earth rotates 360 degrees in 24 hours a star will leave a
trail of 360/24 = 15 degrees per hour or 15/60 = 1/4 degree per minute.
To be perfectly precise the 24 hour day only pertains to the sun. When
talking about tracking the stars across the sky one uses what's called
the "sidereal" day which at 23 hours, 56 minutes and a few seconds is a
bit shorter than the solar day. But for your purposes the length of the
normal solar day will be fine. You're not talking about building a
stellar tracking device. :-)
Chuck Norcutt
On 5/8/2011 9:10 PM, Fernando Gonzalez Gentile wrote:
> Sorry, forgot the technical data: full moon as only light source,
> Zuiko 28mm ƒ/2,8 @ ƒ/5,6, tripod mounted plain Olympus OM 2, +2/3
> exposure compensation, KM.
>
> Another question comes again to my mind (asked this before, some 3
> years ago ... and forgot the answer): how does one calculate the
> exposure, from the angle of the arc of the star trails?
> I'm not _that_ smart in Maths ... ;-)
>
> Fernando.
>
> On Sun, May 8, 2011 at 9:42 PM, Fernando Gonzalez Gentile
> <fgonzalezgentile@xxxxxxxxx> wrote:
>
>> BTW - what do you List, think of this KM, exposed on April 1990?
--
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