Starship Asterisk*

Why are the stars radiating eight radial beams. I suppose this is an artifact of the camera iris whchc is a pity since it is not representative of some real aspect of the stars.

Its a style of image processing.. I'm not a fan of those spikes, but it comes down to personal preference.
I thought M4 deserved a mention and with its contrast in distance..

Mario

http://apod.nasa.gov/apod/ap080603.html

I believe the spiking is caused by the lens in the camera or telescope.

Orin

I had the same thought ... wow look at those stars with spikes, that's cool! no that's because of the camera, we wouldn't see it that way.

It is a very nice APOD anyway.

In today's APOD, I see stars against a black background on the right, stars against a white background to the left of center, and stars against a brownish cloudy background on the far left. Can someone explain these different areas for me?

keir wrote:Why are the stars radiating eight radial beams. I suppose this is an artifact of the camera iris whchc is a pity since it is not representative of some real aspect of the stars.

Those are diffraction spikes caused by the supports for the focal lens of the telescope. Most (reflective) telescopes have/show four spikes, a lot of the times they are digitally removed in the final picture. It’s not very common to see eight spikes.

jimmysnyder wrote:black background, white background, brownish cloudy background

The image is roughly towards the galactic center, so you're seeing a big portion of the Milky Way and its "fade out" away from that point.

Surprising to see that the summary didn't mention the bright Jupiter in the upper left... !

orin stepanek wrote:I believe the spiking is caused by the lens in the camera or telescope.

30 years ago, your explanation was the only one. Nowadays, when processing raw digital images with some form of the Bayer algoritm, recently i saw similar spikes without a telescope. When i used the same lens on another camera, these spikes were gone, so the lens can not be the culprit.

orin stepanek wrote:I believe the spiking is caused by the lens in the camera or telescope.

I asked a similar question for APOD 2007-10-11, where Venus has eight diffraction spikes. Noel convinced me they were there because passing light is being scattered by the straight edges of the 8-vaned aperture in/behind the lens.

henk21cm wrote:

orin stepanek wrote:I believe the spiking is caused by the lens in the camera or telescope.

30 years ago, your explanation was the only one. Nowadays, when processing raw digital images with some form of the Bayer algoritm, recently i saw similar spikes without a telescope. When i used the same lens on another camera, these spikes were gone, so the lens can not be the culprit.

It depends also on the aperture and the relative brightness of the light source. Narrower apertures produce a greater spike effect.

Bayer interpolation should at worst smear the light source around a little bit as a blur.

Camera star filter:

http://www.tiffen.com/star_filters.htm

Software star filter:

http://photoshoptutorials.ws/photoshop- ... ilter.html

Case wrote:The image is roughly towards the galactic center, so you're seeing a big portion of the Milky Way and its "fade out" away from that point.

Thanks, Case, for taking a look at this. I wouldn't call it 'fade out". There are relatively sharp demarcations between the white nebular material and the brown. Also, the brown material reminds me a little bit of vapor clouds you might see in the Earth's atmosphere. What is the white material and what is the brown material?

If it had not been for the Pipe Nebula link in the explanation I don't think I would have guessed that the Pipe Nebula is the brownish area with black strips that runs along and just in from the left edge.
Thanks Case for noting that the very bright object is Jupiter. I wondered what it was (I first thought is was Antares).

jimmysnyder wrote:

Case wrote:The image is roughly towards the galactic center, so you're seeing a big portion of the Milky Way and its "fade out" away from that point.

Thanks, Case, for taking a look at this. I wouldn't call it 'fade out". There are relatively sharp demarcations between the white nebular material and the brown. Also, the brown material reminds me a little bit of vapor clouds you might see in the Earth's atmosphere. What is the white material and what is the brown material?

The "Brown" material is interstellar gas and dust (which shines blue in reflection nebula)
The "White" material is light from hundreds of thousands of stars behind the dust

Thanks BMAONE23.

BMAONE23 wrote:The "Brown" material is interstellar gas and dust (which shines blue in reflection nebula)

Why does it shine brown in this image?

BMAONE23 wrote:The "White" material is light from hundreds of thousands of stars behind the dust

Why does it appear only in a relatively small portion of the image? There's none of it on the right hand side at all, you can see individual stars against a black background there.

jimmysnyder wrote:Thanks BMAONE23.

BMAONE23 wrote:The "Brown" material is interstellar gas and dust (which shines blue in reflection nebula)

Why does it shine brown in this image?

BMAONE23 wrote:The "White" material is light from hundreds of thousands of stars behind the dust

Why does it appear only in a relatively small portion of the image? There's none of it on the right hand side at all, you can see individual stars against a black background there.

The "DUST" has a naturally brown appearance due to the material that it is comprised of. The blue light from the star in the reflection nebula is reflected off the brown dust. When you energize the Hydrogen Gas in the area, the gas glows red.

The White light in the image lies very near the galactic center and the picture is oriented such that the left side is close to the middle of the central bulge and into the galactic plane where the stars are significantly closer together while the right hand side of the image actually lies north of the center, out of the mass of stars in the galactic plane, and covers an area of lesser stellar density.

BMAONE23 wrote: The "DUST" has a naturally brown appearance due to the material that it is comprised of. The blue light from the star in the reflection nebula is reflected off the brown dust. When you energize the Hydrogen Gas in the area, the gas glows red.

Thanks again BMAONE23. I finally get it on the bright white area. I still don't get the brown stuff though. Dust doesn't glow, it just reflects. What is lighting it up brown?

Ambient starlight is lighting everything up. It's pretty dim, but this is a long time exposure which shows everything a good bit brighter than it is normally.

To the original poster's comment about diffraction spikes not being natural...

I don't know about your eyes, but when I look at a bright light source at night I see flare/spikes/diffraction around it. My glasses make it even worse. To me images with diffraction spikes around very bright stars seem not only natural, but very beautiful.

It is also true that since the stars exceed the dynamic range of the camera by SO much, that comparison of the length and intensity of the diffraction spikes is an effective way to judge relative brightness of things far to bright too measure directly.

-Noel

jimmysnyder wrote:

BMAONE23 wrote: The "DUST" has a naturally brown appearance due to the material that it is comprised of. The blue light from the star in the reflection nebula is reflected off the brown dust. When you energize the Hydrogen Gas in the area, the gas glows red.

Thanks again BMAONE23. I finally get it on the bright white area. I still don't get the brown stuff though. Dust doesn't glow, it just reflects. What is lighting it up brown?

You're right...dust doesn't glow. The area has a vast ammount of diffuse hydrogen gas which does glow when energized, and as Noel said, Ambient starlight (photons) are lighting the area up. Antares is also flooding the area with light causing the yellowish brown glow in some of the dust. The rest is likely perception; The brain, in an effort to make sence out of chaos, will pick out the natural differentiation between the light and dark areas and interpret things in an effort to understand what it is seeing. Which is also why we see familier shapes in some of the nebulae.

BMAONE23 wrote:You're right...dust doesn't glow.

Minor nitpick. For the purposes of the OP's question, this is correct: we are seeing dust because it reflects (or in other pictures blocks) starlight.

However, technically anything warm glows as it radiates energy. Typically, this is far below the wavelength of visible light, so we can only see it with radio telescopes. For example, you can see body heat (around 310 Kelvin) with an infrared camera. As my physics professor pointed out, you'd need eyes the size of a house to see the glow of interstellar dust (around 3 Kelvin)!

iamlucky13 wrote:As my physics professor pointed out, ...

Yeah, like you had only one.

Thanks for your input iamlucky13. My nephew is an astrophysicist, so I called him and asked him what's up with the brown color. He said he'd get back to me. Then, his wife came to visit us. I asked her why her husband didn't come and she said that as long as he didn't have an answer for me, he wasn't coming. So I told her to tell her husband not to worry, I already know the answer. I wish I didn't say that cause it isn't true, but I can't stand losing a nephew either.

My latest and greatest guess is this. Since most reflection nebulae that I have seen are blue, there is a certain amount of uniformity in the chemical makeup of the dust in those nebulae. However, since these reflection nebulae are brown, they have a different chemical makeup. It may be that the 'cloudy' look of the nebula on the left hand side of the image is caused by wisps of nonglowing dust between us and the nebula.

Star spikes are sometimes added to images to "enhance" thier artistic value as well. I wouldn't do it, but I know its an option in some of the image processing software.

It could also be that the Blue reflection nebula are coming from the light from new hot Blue stars and the Yellow Brown color is coming from a larger, older yellow star