APOD: NGC 2683: Edge On Spiral Galaxy (2012 Mar 17)

[APOD Robot]

NGC 2683: Edge On Spiral Galaxy

Explanation: This elegant island universe is cataloged as NGC 2683. It lies a mere 16 million light-years distant toward the northern constellation Lynx. A spiral galaxy comparable to our own Milky Way, NGC 2683 is seen nearly edge-on in the cosmic vista. Blended light from a large population of old, yellowish stars forms the remarkably bright galactic core. Their starlight silhouettes the dust lanes along winding spiral arms, dotted with NGC 2683's young blue star clusters. The sharp image was recorded through the lens of a refracting telescope that shows brighter foreground Milky Way stars as colorful and round, lacking diffraction spikes characteristic of images from reflecting telescopes with internal supports. The many more distant galaxies scattered through the background appear as fuzzy, extended sources.

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[orin stepanek]

WE are now discovering so many planets in nearby stars and there are so many stars in the galaxy. Yet there are so many galaxies in the universe that the amount of planets in the universe is unimaginable! The distance is so formidable that a very select few will ever be visited!

[mbridgford]

This is the best accompanying explanation for a photo that I have read because it not only exlains this particular photo but also teaches. Kudos to the writer.

[TJGeezer]

I agree with mbridgford - a very interesting entry. One sentence puzzles me:

The sharp image was recorded through the lens of a refracting telescope that shows brighter foreground Milky Way stars as colorful and round, lacking diffraction spikes characteristic of images from reflecting telescopes with internal supports."

This seems to mean internal supports cause the diffraction spikes but I don't understand how that would work. I'm so accustomed to seeing the spikes, it never occurred to me to ask what causes them - they're just all over the place in astronomy pics. When I saw this photo, I even thought those bits of no-spike lights looked peculiar but couldn't put my finger on why.

Actually, I still don't get it. What do internal supports have to do with spikes on nearby stars when you're focused on, say, a different galaxy? - or do I have it wrong? This would not surprise me; I probably know as much about optics as my dog, possibly less. Can you provide or link me to a simple explanation, maybe one targeted for junior high school students? (As I sink into senescence I mind less and less admitting ignorance. My grandkids kind of assume it anyway.)

I hope no one minds my asking. Thanks for maintaining such a consistently interesting site!

[neufer]

<<NGC 2683 is an unbarred spiral galaxy discovered by William Herschel on February 5, 1788. It was nicknamed the "UFO Galaxy" by the Astronaut Memorial Planetarium and Observatory. It is viewed nearly edge-on from Earth's location in space and is located between 16 to 25 million light-years away. It is receding from Earth at 410 km/s, and from the Galactic Center at 375 km/s.

The reddened light from the center of the galaxy appears yellowish due to the intervening gas and dust located within the outer arms of NGC 2683.>>

Shouldn't that be: The yellowish light from the center of the galaxy appears reddened due to the intervening gas and dust located within the outer arms of NGC 2683

[owlice]

What do internal supports have to do with spikes on nearby stars when you're focused on, say, a different galaxy?

Diffraction spikes are lines radiating from bright light sources in reflecting telescope images. They are artifacts caused by light diffracting around the support vanes of the secondary mirror. Refracting telescopes and their photographic images do not have the same problem.

More here: http://en.wikipedia.org/wiki/Diffraction_spike

[Sandstone]

Another reference on diffraction spikes (from APOD itself):

http://apod.nasa.gov/apod/ap010415.html

[Chris Peterson]

What do internal supports have to do with spikes on nearby stars when you're focused on, say, a different galaxy?

Diffraction spikes are lines radiating from bright light sources in reflecting telescope images. They are artifacts caused by light diffracting around the support vanes of the secondary mirror. Refracting telescopes and their photographic images do not have the same problem.

More here: http://en.wikipedia.org/wiki/Diffraction_spike

And it's not just spikes. Diffraction spikes are linear artifacts produced by diffraction from linear structures- usually supports holding a secondary mirror, but occasionally from a square aperture. Most telescopes have circular apertures, which produce diffraction artifacts as well. But the diffraction artifacts from circular apertures (and circular obstructions) are themselves circular. They are seen as a set of nested rings around point sources. On images made from the ground, they are not generally obvious, because atmospheric seeing blurs them out and all you get is a bloated star. But on HST images, where there is no distortion from seeing, these Airy rings are very often visible.

[Ann]

<<NGC 2683 is an unbarred spiral galaxy discovered by William Herschel on February 5, 1788. It was nicknamed the "UFO Galaxy" by the Astronaut Memorial Planetarium and Observatory. It is viewed nearly edge-on from Earth's location in space and is located between 16 to 25 million light-years away. It is receding from Earth at 410 km/s, and from the Galactic Center at 375 km/s.

The reddened light from the center of the galaxy appears yellowish due to the intervening gas and dust located within the outer arms of NGC 2683.>>

Shouldn't that be: The yellowish light from the center of the galaxy appears reddened due to the intervening gas and dust located within the outer arms of NGC 2683

I don't know. The overall color index of NGC 2683 is yellow, but not extraordinarily so. Its B-V index is 0.89, slightly paler than Pollux. Pollux, of course, is is sufficiently pale that most people would consider an artificial indoor light source with the color temperature of Pollux to be unpleasantly blue-white.

The reddening profile of NGC 2683 is interesting, however. The most reddened part appears to be where the dust lane is seen in front of the brightest part of the bulge. The light that reaches us from this part of the dust lane is strikingly orange. On the other hand, if our own galaxy had been seen from the same perspective, the dust lane almost certainly wouldn't have looked orange, but dark brown or black.

There is clearly a lot more dust in the Milky Way than in NGC 2683.

Ann

[rstevenson]

Here's a small version of a closer view, descendent of an earlier APOD, which seems to give a blander and perhaps more "realistic" version of the colour balance of the galaxy.

Rob

[ta152h0]

I thought recent discoveries that indicate the Milky Way is actually a barred spiral, true ?

[neufer]

I thought recent discoveries that indicate the Milky Way is actually a barred spiral, true ?

See: http://apod.nasa.gov/apod/ap101011.html