Searching for a picture

orpheus · #1 by **orpheus** » Nov 10, 2011 9:21 pm

Some time ago I saw a composite picture of the night sky, showing the actual angular size of the Andromeda galaxy. It was stunning and rather terrifying to look at - to realize that if the naked eye could see it in its entirety (not just the bright center), then we would see that it takes up a sizable chunk of sky.

I think this might have been on the APOD site, but I've searched there to no avail. I did find - on APOD and elsewhere - a pic that compares Andromeda with the Moon. But that's not the one I mean. The one I'm looking for shows it in the night sky from Earth.

Help?

LIFE · #2 by **LIFE** » Nov 10, 2011 9:57 pm

Was it from the perspective of a person looking out of a window?

orpheus · #3 by **orpheus** » Nov 10, 2011 10:38 pm

May have been. But I seem to remember that it was from the perspective of someone outside in a field; there was a house to the right. I could be totally wrong about this, though. It might have been what you describe. Sorry I can't recall exactly!

LIFE · #4 by **LIFE** » Nov 10, 2011 10:40 pm

Though I'm guessing it's neither of those...

orpheus · #5 by **orpheus** » Nov 10, 2011 10:44 pm

No, but those are wonderful - thanks!

Actually, I seem to recall that it was not colorful at all; may have been black and white. It wasn't an artist's rendering, either; it used actual telescope photos, placed into a composite. I think the Andromeda was tilted almost vertical.

orpheus · #6 by **orpheus** » Nov 10, 2011 11:10 pm

Found it on my hard drive:

Weird how I misremembered it. I don't see Amdromeda here (though I'm not an astronomer). But I remember the caption saying the idea was the same - that these are the true angular sizes of the objects. This is what we'd see if they weren't so dim. I'd like to find this on APOD, to see specifically what it said.

Anyway, someone should do this with Andromeda.

Berceuse · #7 by **Berceuse** » Nov 10, 2011 11:38 pm

http://apod.nasa.gov/apod/ap090411.html

EDIT: And for future reference, you can reverse image search on Google either by uploading the image directly or pasting the URL of the image. Pretty neat and convenient. :grin:

orpheus · #8 by **orpheus** » Nov 10, 2011 11:47 pm

Berceuse wrote:http://apod.nasa.gov/apod/ap090411.html

EDIT: And for future reference, you can reverse image search on Google either by uploading the image directly or pasting the URL of the image. Pretty neat and convenient.

Hey, that's great! Thanks.

Thanks, too, Life, for those other pics. Pretty cool.

Onyx8 · #9 by **Onyx8** » Nov 11, 2011 1:14 am

orpheus wrote:Found it on my hard drive:

Weird how I misremembered it. I don't see Amdromeda here (though I'm not an astronomer). But I remember the caption saying the idea was the same - that these are the true angular sizes of the objects. This is what we'd see if they weren't so dim. I'd like to find this on APOD, to see specifically what it said.

Anyway, someone should do this with Andromeda.

So what are those objects? Random nebulae? I don't recognise the starscape.

orpheus · **#10** by **orpheus** » Nov 11, 2011 2:00 am

From the link Berceuse kindly provided above:

Astronomy Picture of the Day wrote:
Explanation: Intricate, glowing nebulae that shine in planet Earth's night sky are beautiful to look at in deep images made with telescopes and sensitive cameras. But they are faint and otherwise invisible to the naked-eye. That makes their relative location and extent on the sky difficult to appreciate. So, consider this impressive composite image of a wide region of the northern winter sky. With a total exposure time of 40 hours, the painstaking mosaic presents a nebula-rich expanse known as the Orion-Eridanus Superbubble above a house in suburban Boston, USA. Within the wide and deep view are nebulae more often seen in narrower views, including the Great Orion Nebula, the Rosette Nebula, the Seagull Nebula, the California Nebula, and Barnard's Loop. The familiar constellation of Orion itself is just above the foreground house. Brightest star Sirius is left of the roof, and the recognizable Pleiades star cluster is above the tree at the right. A version of the big picture that includes simple constellation guidelines is available here.

Onyx8 · **#11** by **Onyx8** » Nov 11, 2011 2:12 am

Oops, thanks.

klazmon · **#12** by **klazmon** » Nov 11, 2011 11:52 am

The angular extent of M31 is about four degrees. The Moon and Sun are close to half a degree. The field is too wide for most scope camera combinations to capture M31 in a single frame. Many pictures you see of M31 are actually mosaics that are stitched together.

Here is quite a good three frame mosaic taken with a 105mm F5 refractor (ie focal length = 525mm) :

http://www.noao.edu/outreach/aop/observers/m31.html

I notice that the image shows diffraction spikes which are not native to the optical system used. I guess they must have deliberately put cross hairs over the lens to create the effect on the brighter stars you get from the spider of a reflector. I guess it is done for artistic reasons but I'm not sure I approve.