View Full Version here: : Ok, Stupid Question.
06-06-2012, 10:12 PM
Hi All, I got a few hundred shots of the transit today. Can anyone tell me why it described a U shape over the surface of the sun?. I just watched a video of the transit from Canberra which was only 30 miles from where I was and the planet transited straight across?..Im confused...(which isn't hard)
Were you using an Alt-Az mount?
My guess is field rotation.
06-06-2012, 10:48 PM
Info on this here (just before the table with transit times for major cities):
07-06-2012, 12:16 AM
As per Rob's comment/link... have a look at the orientation of the sunspots in your photos - you find that they rotate with the Sun's axis, as well as from our perspective.
07-06-2012, 03:15 PM
Cool, thanx for the link. I can understand the idea, but im still stuffed. I was using a Heq5, why would the slow (25 day) rotation of the sun effect the apparent postion of something passing in front of it over 6 hours?
08-06-2012, 03:10 PM
My best guess is that your mount wasn't correctly polar aligned. From Melbourne (so not too unlike many places in Australia), using an alt-az mount or without optical aid, Venus appeared near the bottom of the Sun on ingress, moved upwards and a little to the left as it crossed onto the face of the Sun, then slid off the Sun heading to the lower left - an apparent U-shape. But that's an illusion due to the changing orientation of the Sun during the day, combined with Venus' actual straight line across the Sun's face.
With a correctly-aligned equatorial mount, Venus' apparent path would have been straight across the Sun. With the mount incorrectly aligned, it is possible for you to create a variety of curved apparent paths for Venus across the Sun, depending on quite where the polar axis was pointed. A diagnostic test of poor mount alignment would be that you would have been having to adjust the declination axis all day as you tracked the Sun. If you didn't have to do that, I'm mystified!
Could there be any other source of image rotation, either of the camera (fixed on the eyepiece or separately mounted/held?), or in post-processing of images?
28-07-2012, 05:14 PM
Excuse me for my strange question. I am from Russia, so I canít see an answer by myself. Tell me please, what constellations you can see in 4 seasons. I talk about such constellations that can be such a symbol of a season (that are clear for observing).
30-07-2012, 09:50 AM
Hi Pupkin. Not such a strange question but here is a different answer. Have you got Stellarium or any other similar astro software ?
Just reset your location to another place in the world in the southern hemisphere eg Sydney, Aust or Auckland, NZ and check it out for your self. I have done it mysef to 'see' Northern Hemisphere skies when observers from up your way make mention of particular events or objects worth viewing.
Stellarium is particularly good with all the constellations marked and various diagrams to assist in finding it all.
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