Alborz Mountain Milky Way: Galaxy Perspectives (03 May 2008)

[henk21cm]

The scale of the picture was initially a bit puzzling. Here some hints. The leftmost part is roughly NorthWest. The bar of Ursa Major is nearly vertical. The "Snow-capped stratovolcano" is North, Polaris, α Ursa Minoris, is slight left from the peak of the volcano, at NNE Cassiopeia is rising, just over the right flank of the volcano. Deneb, α Cygni, is in the NorthEast, Altair, α Aquilae, is in the East. Jupiter is in the SouthEast, whereas Antares, α Scorpii, is in the South.

So the length of the image is about 225°, its height is about 60°

[orin stepanek]

Here's link http://apod.nasa.gov/apod/ap080503.html
I thought the panorama was neat. I love views with the Milky-way.
Orin

[Animation]

All,

My favorite images on APOD are the ones of galaxies. This post isnt related to any specific galaxy image from the APOD, but it is inspired by all the ones I have seen. I have 2 questions, one real and one more of a hypothetical question/statement/rambling thing.

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?

2) The second item, I'm not even sure if it is a question. I know that our Galaxy is orbited by a couple of minor or dwarf (dont remember the correct term, sorry) galaxies. I always wonder ... if there were a life-bearing world on the fringe of one of the minor galaxies or nodes that orbits ours, could there be a star or a planet that has a huge galaxy filling most of its night sky? With our sun buried deep in a spiral arm (deep enough that we seem to have stars all around us), I always wonder what the night sky would be like if we were on the peripheral of a spiral arm's thickness, or even better if we were in a close adjacent galaxy, not buried too deep.

Would our understanding of Galaxies have been clearer, would we have discovered their concepts sooner, if we had a huge dramatic galaxy that spanned across our whole night sky?

Thanks,

Lewis

[Case]

1) What is up with those types of image perspectives?

As I understand it, we are located in a small segment called the Orion Arm (or Local Spur), which seems to be a local concentration that doesn't extend like the major arms. Looking towards the galactic center, we see the Sagittarius arm. Looking in the other direction, we see the Perseus Arm. So it seems that the Milky Way arc that we see is a combination of those two major arms, as they visually fade into each other from our perspective.

2) What if we had a huge dramatic galaxy that spanned across our whole night sky?

I think the spiral arms would be about as faint in the sky as the Milky Way we know, but the galactic core would be quite bright. (I'm sure someone could calculate how bright...) How such a view would impact a civilization, that would be food for thought for imaginative writers, I guess.

[Animation]

Case,

Thanks for the reply. For question (1) I could see what you mean from the linked image. I would still think that the shape would make the "blended arch" (made from the perspective on the other two arms) seem to be a line, or come towards us, instead of making a rainbow pattern. Hmm.

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).

For question 2, I'm surprised that you think the spiral arms would be as faint as in the original image I linked. I would think that having no other stars in the sky would make it stand out more (in my scenario, I was proposing a vantage point on a star on the edge of a dwarf galaxy, such that there are NO intervening stars between the observer's world and the very "nearby" galaxy.

Ah well, I guess I'm more dreamer than anything else, but I do appreciate the response! Now I'm all charged up to think about it even more.

Lewis

[astrolabe]

Hello Animation,

Welcome! Great place to get a thought out for comment.

I know what you mean; seeing some of the galaxy clusters has always caused me to wonder about being on the edge of one and imagining looking up (out) at night (not "raining"?) and maybe seeing FOUR or FIVE just floating around at odd angles and distances!

[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)

[Pete]

Hello and welcome, Lewis (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?

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"

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/

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!

[Animation]

Pete,

Thanks for the explanation about the panoramic images.

Also, thanks to everyone for the replies!

Lewis

[NoelC]

I know what you mean; seeing some of the galaxy clusters has always caused me to wonder about being on the edge of one and imagining looking up (out) at night (not "raining"?) and maybe seeing FOUR or FIVE just floating around at odd angles and distances!

And this is not far from what you'd see (e.g., of M31, M33, etc.) if you had REEEEEALLY dark skies (or were space walking) and REEEEALLY sensitive eyes.

Consider that the span of the Andromeda galaxy (M31) is something like 7 times the width of a full moon.

-Noel