by Chris Peterson » Wed Jan 26, 2011 10:28 pm
Indigo_Sunrise wrote:
Today's image, of course, looks
like this.
But in a link from the description,
here, it looks to be rotating the other way.
I was just curious whether there is a reason why it has been flipped, or if it's more of an 'imager's choice' type of thing.
It is always the imager's choice. The type of telescope matters, as well, in determining the orientation of the raw image. The most common convention is north up, east left, which (with respect to using the eye) provides an unmirrored image with a standard rotation. Today's image is close to that- unmirrored but south up. But there's no rule, just convention, and that convention is often broken- especially with images taken with an aesthetic intent.
All the same, the mirrored orientation of the second image you reference is unusual- a point that was
discussed on this forum when that APOD was published. The vast majority of M51 images you see will be like today's APOD, although with different rotations.
[quote="Indigo_Sunrise"]
Today's image, of course, looks [url=http://apod.nasa.gov//apod/image/1101/m51ir_hubble_big.jpg]like this.[/url]
But in a link from the description, [url=http://apod.nasa.gov//apod/image/1006/M51_peris.jpg]here,[/url] it looks to be rotating the other way.
I was just curious whether there is a reason why it has been flipped, or if it's more of an 'imager's choice' type of thing.[/quote]
It is always the imager's choice. The type of telescope matters, as well, in determining the orientation of the raw image. The most common convention is north up, east left, which (with respect to using the eye) provides an unmirrored image with a standard rotation. Today's image is close to that- unmirrored but south up. But there's no rule, just convention, and that convention is often broken- especially with images taken with an aesthetic intent.
All the same, the mirrored orientation of the second image you reference is unusual- a point that was [url=http://asterisk.apod.com/viewtopic.php?f=9&t=19757]discussed[/url] on this forum when that APOD was published. The vast majority of M51 images you see will be like today's APOD, although with different rotations.