Astronomy Picture of the Day 5-10-03

NASA ^ | 5-10-03 | 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.

2003 May 10

NGC 7293: The Helix Nebula
Credit: NASA, NOAO, ESA, Hubble Helix Nebula Team, M. Meixner (STScI), & T. A. Rector (NRAO)

Explanation: Will our Sun look like this one day? The Helix Nebula is the closest example of a planetary nebula created at the end of the life of a Sun-like star. The outer gasses of the star expelled into space appear from our vantage point as if we are looking down a helix. The remnant central stellar core, destined to become a white dwarf star, glows in light so energetic it causes the previously expelled gas to fluoresce. The Helix Nebula, given a technical designation of NGC 7293, lies about 650 light-years away towards the constellation of Aquarius and spans about 2.5 light-years. The above picture is a composite of newly released images from the ACS instrument on the Hubble Space Telescope and wide-angle images from the Mosaic Camera on the 0.9-m Telescope at Kitt Peak National Observatory. A close-up of the inner edge of the Helix Nebula shows complex gas knots of unknown origin.

[petuniasevan]

Vacation Announcement

I will be on vacation from June 2nd through June 9th.
If anyone would like to volunteer to post APOD during that time, please FReepmail me.
Otherwise the APOD will not be posted as I will be visiting relatives in California.

On last night's thread, a FReeper posted a link to his brother's astrophotography website. It's good! Check out the site - these guys are serious photogs!

Big Cigar Astronomy

Close-up of a portion of the Helix Nebula (courtesy of Hubble)

The Helix Nebula, NGC 7293

Right Ascension	22 : 29.6 (h:m)
Declination	-20 : 48 (deg:m)
Distance	0.45 (kly)
Visual Brightness	7.3 (mag)
Apparent Dimension	16 / 28 (arc min)

This is one of those odd objects which is actually easier to find through a good pair of binoculars than through a telescope! Dark skies are required! An O-III filter is highly recommended! You may see something like this in an 8-inch 'scope:

[petuniasevan]

[petuniasevan]

It's ASTRONOMY DAY today, May 10th 2003.

Click on the link for information and activities in various locations.

http://www.astroleague.org/al/astroday/adactiv03.htm

[WSGilcrest]

Good evening, tunia. I think I asked this once before, do you know why those Hubble images always have the corner cropped? I would imagine the image is a mosaic, but why can't they complete the image.

[cardinal4]

Is that the real color of the nebula? Or is there a color filter?

[petuniasevan]

The Hubble Wide-Field Planetary Camera actually consists of 4 different instruments. Each gets an image; the images are then electronically "pasted" together to form the wider field image.

Here is the full explanation:

http://www.exploratorium.edu/origins/hubble/ideas/picture/picture6.html

[petuniasevan]

Are you referring to the main image? First of all, what your eye sees and what a camera sees are not necessarily the same. On Earth, you won't notice much difference because the light spectrum is so wide. On the other hand, the Helix is an emission nebula; it glows like a neon sign does (similar mechanism on a cosmic scale). It contains a few different gases; each has its own characteristic emission lines on a spectrum.

Most nebula images are taken through filters to bring out the colors and details desired. The Hubble contribution to the above image is like thus:

Helix was exposed in two filters, Ha+[N II] (F658N) and [O III] (F502N). The WFPC2 images, obtained in parallel, covered portions of the nebula in [O I] (F631N), He II (F469N), or Ha (F656N).

Those are different filters which allow light through at only a narrow band (such as the ionized oxygen line at 502 nanometers).

If you looked through a good-sized 'scope at low power, with perfect seeing, you might actually see the Helix as faintly blue-green! This doesn't mean the camera lies; it has different and greater sensitivity than does the human eye. Also remember that all such images are time exposures of several minutes to several hours.

Try looking at this web page to see what went into the composite image that graces today's APOD.

The Hubble Helix Observations

Amateur color images show the nebula as red:

As does a large observatory's instruments:

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By the way, thanks for asking, and thanks for visiting APOD!

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[WSGilcrest]

Thanks, tunia. I feel so smart now. Hope someone asks me that question. :)

[cardinal4]

Thanks for replying! And in such detail! I have seen some pretty spectacular pictures of Nebulas, in many different colors, but never really knew if the images were enhanced. What kind of scope would be needed to see the Helix as an amateur?

[WSGilcrest]

BTW, that Idea to Image video on that link you provided is fasinating. Almost a year from idea to image. 200 proposals from over 1000 to be chosen.

[petuniasevan]

Actually, you can see it with binocs if you have dark skies and know what to look for and where to look.

As for a 'scope, you'd want good quality. It doesn't have to be big. Low power and a nebula filter are the keys, along with good seeing (dark skies, minimal turbulence).

This page has lots of details:

http://members.aol.com/nlpjp/whatcan.htm

Talk to your local Astronomical Society; here's their web page. Star parties are a great place to "test drive" equipment and learn stuff!

http://www.slasonline.org/links.htm


By the way, watch out for bad weather in your area today. Be careful!

[cardinal4]

You are right about the weather! Thanks for the warning, and good night.

[firewalk]

Thanks for the ping