by Pete » Wed May 14, 2008 1:50 am
Hello and welcome, Lewis (Animation)!
Animation wrote:1) I've seen a few images where the galaxy spiral arms of our Milky Way show up in the image. A recent example was from May 3 (
http://antwrp.gsfc.nasa.gov/apod/ap080503.html ). In these images, for some reason the arch fills the sky as if it is a rainbow. i would think that instead I'd see an arch at a distance, but that it would approach the earth and then become indistinct as the section of the arch I'm in became the bulk of the stars in the sky. In other words, they always look like I'm on a Hardee's curly fry looking down or up to another level, and yet I always thought our galaxy was in the same plane largely. At least for the arches.
What is up with those types of image perspectives?
Our galaxy is basically an axisymmetric disk of stars and interstellar medium in which our solar system is embedded, so far in that there are stars all around us, as you wrote. The Milky Way is our view of this disk from the inside, and always looks like a straight band on the sky, brightest toward the galactic centre (although we can only see about 1/10 of the distance to the centre in visible wavelengths
).
The APOD to which you linked above is panoramic: it squeezes a wide field of view into one image. Looking at the left and right edges of that picture might be equivalent to turning your head 90 degrees to the left and right in real life. The apparent arch shape is due to panoramic distortion. Distortion-free panoramas are theoretically possible at times and places on Earth where the Milky Way is parallel to the horizon. However, since we're in the middle of our galaxy's disk, the Milky Way band neatly divides our sky into equal halves, so the ground and atmosphere will always block our view of a horizontal MW, and any given ground-based panorama will distort the band into an arch. Planetarium-style projection can fix that.
Non-panoramic, appropriately stitched, or satellite photos of the Milky Way clearly reveal it to be essentially an edge-on spiral galaxy. For example:
http://apod.nasa.gov/apod/ap960213.html - "7,000 Stars and the Milky Way"
http://apod.nasa.gov/apod/ap950908.html - "The Milky Way's Center"
Animation wrote:As an aside, I wonder if google sky or some other astronomy viewing program exists that lets you move our perspective from earth to any other vantage point (limited by what our known obstructions may be).
I'm not sure about Google Sky, but to fly pretty much anywhere, check out the free program Celestia. It's awesome.
http://www.shatters.net/celestia/
BMAONE23 wrote:Imagine being on a planet orbiting a star at the very edge of a galaxy, During one season of your orbit you would see nothing but the stars of your own galaxy but during the opposite season, you would see only other galaxies (and any other inferior/superior planetary bodies)
True, provided that the planet's orbital plane coincided with the plane of the galaxy (not so in our case). Such a configuration would inspire some wacky mythology!
Hello and welcome, Lewis (Animation)!
[quote="Animation"]1) I've seen a few images where the galaxy spiral arms of our Milky Way show up in the image. A recent example was from May 3 ( http://antwrp.gsfc.nasa.gov/apod/ap080503.html ). In these images, for some reason the arch fills the sky as if it is a rainbow. i would think that instead I'd see an arch at a distance, but that it would approach the earth and then become indistinct as the section of the arch I'm in became the bulk of the stars in the sky. In other words, they always look like I'm on a Hardee's curly fry looking down or up to another level, and yet I always thought our galaxy was in the same plane largely. At least for the arches.
What is up with those types of image perspectives?
[/quote]
Our galaxy is basically an axisymmetric disk of stars and interstellar medium in which our solar system is embedded, so far in that there are stars all around us, as you wrote. The Milky Way is our view of this disk from the inside, and always looks like a straight band on the sky, brightest toward the galactic centre (although we can only see about 1/10 of the distance to the centre in visible wavelengths :( ).
The APOD to which you linked above is panoramic: it squeezes a wide field of view into one image. Looking at the left and right edges of that picture might be equivalent to turning your head 90 degrees to the left and right in real life. The apparent arch shape is due to panoramic distortion. Distortion-free panoramas are theoretically possible at times and places on Earth where the Milky Way is parallel to the horizon. However, since we're in the middle of our galaxy's disk, the Milky Way band neatly divides our sky into equal halves, so the ground and atmosphere will always block our view of a horizontal MW, and any given ground-based panorama will distort the band into an arch. Planetarium-style projection can fix that.
Non-panoramic, appropriately stitched, or satellite photos of the Milky Way clearly reveal it to be essentially an edge-on spiral galaxy. For example:
http://apod.nasa.gov/apod/ap960213.html - "7,000 Stars and the Milky Way"
http://apod.nasa.gov/apod/ap950908.html - "The Milky Way's Center"
[quote="Animation"]As an aside, I wonder if google sky or some other astronomy viewing program exists that lets you move our perspective from earth to any other vantage point (limited by what our known obstructions may be).
[/quote]
I'm not sure about Google Sky, but to fly pretty much anywhere, check out the free program Celestia. It's awesome. http://www.shatters.net/celestia/
[quote="BMAONE23"]Imagine being on a planet orbiting a star at the very edge of a galaxy, During one season of your orbit you would see nothing but the stars of your own galaxy but during the opposite season, you would see only other galaxies (and any other inferior/superior planetary bodies)[/quote]
True, provided that the planet's orbital plane coincided with the plane of the galaxy (not so in our case). Such a configuration would inspire some wacky mythology!