star rotation questions..?

[Shutter]

not sure if this should be in a less specific forum area but...

can someone explain to me, why when shooting stars the more north you face the more curved the star trails are? also why do you get full circles of stars near polaris after just a short while of shooting - why doesnt it take a whole day (rotation of the earth... =/ )


thanks for my complete lack of ability to draw sense on this! cheers

 

[arad85]

not sure if this should be in a less specific forum area but...

can someone explain to me, why when shooting stars the more north you face the more curved the star trails are?

If a star passes directly above you (and you could take a picture of it with a very wide angle lens) it would appear to have a line as a star trail as it would rise in the East and set in the West. The closer you get to Polaris, the more curved the lines become. It's much easier if you think of the stars as fixed (which they are) and the Earth rotating in space.

also why do you get full circles of stars near polaris after just a short while of shooting - why doesnt it take a whole day (rotation of the earth... =/ )

You don't get full circles after a short period. You may be seeing a number of star trails combine to give what looks like a circle. It takes (or would do if you had 24 hr darkness) 24 hours (give or take a smidge) for the earth to rotate and for each star to rotate around Polaris (which isn't actually AT North, although it is close).

 

[Shutter]

If a star passes directly above you (and you could take a picture of it with a very wide angle lens) it would appear to have a line as a star trail as it would rise in the East and set in the West. The closer you get to Polaris, the more curved the lines become. It's much easier if you think of the stars as fixed (which they are) and the Earth rotating in space.

ok cheers. so if we lived in the southern hemisphere would it be the opposite way around?

You don't get full circles after a short period. You may be seeing a number of star trails combine to give what looks like a circle. It takes (or would do if you had 24 hr darkness) 24 hours (give or take a smidge) for the earth to rotate and for each star to rotate around Polaris (which isn't actually AT North, although it is close).

ah ok. thought so. cheers

 

[arad85]

ok cheers. so if we lived in the southern hemisphere would it be the opposite way around?

Yup, the circles would appear to go around the southern pole (which doesn't have a visible star as close to it as the northern hemisphere does).