Astronomy Picture of the Day 8-21-02

NASA ^ | 8-21-02 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 August 21

Spiral Galaxy NGC 300
Credit: M. Schirmer (IAEF, Bonn), W. Gieren (Univ. de Concepción, Chile), et al., ESO

Explanation: NGC 300 is so interesting because it is so normal. An Sc-type spiral galaxy in the nearby Sculptor group of galaxies, NGC 300 shows typical flowing blue spiral arms, an expected compact nucleus, and the requisite amount of stars, star clusters, and nebulae. Therefore, studying NGC 300 should indicate how, exactly, a normal spiral galaxy works. Toward this goal, NGC 300 and the surrounding area were studied in exquisite detail, creating and combining a series of high-resolution images to create the above conglomerate picture. NGC 300 lies only 7 million light years away, spans nearly the same amount of sky as the full moon, and is visible with a small telescope toward the constellation of Sculptor.

[petuniasevan]

Astronomy Fun Fact:

Estimated distances to nearby galaxies such as NGC 300 seem to be fairly accurate. This is because astronomers measure using "standard candles" called Cepheid Variable Stars. This is a class of giant stars which are periodic variables, with very regular fluctuations. The periodicity depends on the brightness (which depends on mass). Brighter equals slower. Thus if we know how BRIGHT the star is at, say, a standard distance (absolute magnitude), we can determine a distant Cepheid's brightness (apparent magnitude) and so figure the galaxy's distance. We know how bright the Cepheid SHOULD be by its period of variability.
The fly in the ointment, so to speak, is the presence of intergalactic dust which will absorb some light. Measurements at various wavelengths on the electromagnetic spectrum may help to determine the amount of absorption.

Typical light curve for a Cepheid variable star

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[petuniasevan]

Does the above graphic work as a PING or should I also type "PING"? Any confusion?

[RightWhale]

Don't know if it's normal, but it sure is a textbook classical spiral galaxy like we think ours is. Think that might be the best, most evolutionary, productive form of galaxy?

[sleavelessinseattle]

Re: Cookie graphic... Its fine! I wish there were more cookies, but I'm on a diet...Saving the big jpeg for my slideshow screensaver! WOW!

[petuniasevan]

I'll bet it is! Just look at all those nice chunky star clusters, supernova remnants, and dust lanes.

All that's missing is the sign "Building Materials In Use"!

[Bikers4Bush]

Works for me as a ping. Cool pic today.

[BossyRoofer]

Looks like a comic ROSE! AWSOME!

[sleavelessinseattle]

I was watching Jack Horkheimer the star hustler last night and he actually pointed to galactic center of our Milky way...Antares the "heart" star of the constellation Scorpio.
I've been frustrated for years trying to find someone who could tell me which direction in the heavens our "core" is!
Also Sagitarius the Archer's arrow points right at Antares as a second reference and the spout of the Teapot Asterism is the arrow point. What he did NOT specify was whether the Star Anares is IN the milky way or more remote and just really bright...I believe he quoted 300 times the size of Sol.

[formerDem]

Thanks! I saved the photo under the name "wow galaxy'.

I have the milky way as my wallpaper. Now I'll have to alternate.

[RightWhale]

Yep, Teapot it is. We can't see that from Fairbanks. Even Sirius is a little south of the horizon at its highest point, but Procyon is barely above. Antares is fairly bright and not so far from here. It's one of our neighbors inside the Milky Way.

[sleavelessinseattle]

Thanks for confirming That RW...I feel more "centered" now!