Star Trails

by ILoveTTATT 36 Replies latest social entertainment

• 

  AnnOMaly

  ILoveTTATT: I evidently took pictures of the celestial equator. That is why the stars on the top part of the pic seem to curve differently than the ones in the bottom part of the pic.

  Yep, he's right, prologos. He was facing south or south-east. You can see the stars are rising and culminating (thus south of the celestial equator). It looks like his first 2 pics are in reverse time order.

  To get a similar trail effect in the southern hemisphere, he'd have to be facing north to north-west where they'd have passed culmination (north of the celestial equator here) and would be on their way to setting.
• 

  Twitch

  so if that is the case you live in the southern hemisphere, and are wellcome to visit and see Polaris

  It would stand to reason you cannot see Polaris, the North Star from the southern hemisphere more a few latitudes south of the earth's equator.

  your pictures did not capture the rotation of the earth at all, but the rotation of your camera?

  Since stars do not move (with respect to our timeframe) the photo is proof of the earth's rotation. The camera is static and moves with the earth, the exposures taken over a number of hours.

  A very basic astronomical concept actually

  http://en.wikipedia.org/wiki/Celestial_pole
• 

  AnnOMaly

  Since stars do not move (with respect to our timeframe) the photo is proof of the earth's rotation. The camera is static and moves with the earth, the exposures taken over a number of hours.

  And 2 hours of exposure have produced star trails measuring 30° of arc.
• 

  Twitch

  And 2 hours of exposure have produced star trails measuring 30° of arc.

  24 hrs exposure time would thus produce 360 degrees of arc

  Talk to me about declination and hour angle.
• 

  AnnOMaly

  Talk to me about declination and hour angle.

  Which star trail?
• 

  prologos
• 

  prologos

  I couls not figure out how the apparent center of these circles around polaris could point to what appears to be BELOW the horizon, that of course can exist, at our vacation home its only 15% above up here in the 40s.

  I see now that the upper circles actually appear to be convex. still I would like to see a presentation that explains it in lay-[wo]mans terms.
• 

  Twitch

  I couls not figure out how the apparent center of these circles around polaris could point to what appears to be BELOW the horizon, that of course can exist, at our vacation home its only 15% above up here in the 40s.

  The concentric centre of star trails would be around Polaris if this photo was taken in the southern hemisphere. Polaris would be obscured by the earth, as it shows.

  The photo was taken in the northern hemisphere as per the shooter.

  So it's looking towards the south celestial pole, not Polaris. The celestial equator is the middle "band"of trails. Polaris would be "above to the left". A very wide angle shot here would show the trails bending the other way at top left around the North Star.

  I see now that the upper circles actually appear to be convex. still I would like to see a presentation that explains it in lay-[wo]mans terms.

  Does this help?

  PS. I misread earlier regarding who lived where, my apologies.
• 

  prologos

  Twitch thanks, -now it is explained, the star trails form circles, as they must, around either polaris or the southern celestial pole, and this camera

  pointed south, toward the southern pole. but

  could you answer this clarifying question:

  All I can see is objects revolving around polaris lining up above my rear yard fence. where in the Seattle area could I point my camera and get circles like that, rotating about the other celestial pole?
• 

  AnnOMaly

  All I can see is objects revolving around polaris lining up above my rear yard fence. where in the Seattle area could I point my camera and get circles like that, rotating about the other celestial pole?

  Nowhere in the Seattle area. The south celestial pole with its circumpolar stars can only be seen south of Earth's equator. You'd have to travel to S. America, I'm afraid.