APOD: NGC 7822 in Cepheus (2015 May 23)

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APOD: NGC 7822 in Cepheus (2015 May 23)

Post by APOD Robot » Sat May 23, 2015 4:09 am

Image NGC 7822 in Cepheus

Explanation: Hot, young stars and cosmic pillars of gas and dust seem to crowd into NGC 7822. At the edge of a giant molecular cloud toward the northern constellation Cepheus, the glowing star forming region lies about 3,000 light-years away. Within the nebula, bright edges and dark shapes are highlighted in this colorful skyscape. The image includes data from narrowband filters, mapping emission from atomic oxygen, hydrogen, and sulfur into blue, green, and red hues. The atomic emission is powered by energetic radiation from the hot stars, whose powerful winds and radiation also sculpt and erode the denser pillar shapes. Stars could still be forming inside the pillars by gravitational collapse, but as the pillars are eroded away, any forming stars will ultimately be cutoff from their reservoir of star stuff. This field spans around 40 light-years at the estimated distance of NGC 7822.

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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Boomer12k » Sat May 23, 2015 7:29 am

Nice looking wide shot... :D

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Craine
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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Craine » Sat May 23, 2015 1:12 pm

FYI: Part of the center of this image, shot in infrared, was an earlier (and rather spectacular) APOD:
http://apod.nasa.gov/apod/ap141201.html

Jim Armstrong

Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Jim Armstrong » Sat May 23, 2015 3:49 pm

I visit this webpage every day as I assume most here do.
I am not an astronomer, but I try to read the entire explanation and try to understand most of it.
The last sentence today: "This field spans around 40 light-years at the estimated distance of NGC 7822" left me wondering what I was missing.
Wouldn't the field span that that no matter what the distance? The distance is specified earlier.
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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by bystander » Sat May 23, 2015 4:34 pm

Jim Armstrong wrote:...
Wouldn't the field span that that no matter what the distance? The distance is specified earlier.

Fields of view are typically described in fractions of degrees of arc (arc seconds). The further from the observer, the larger the distance spanned by the same field of view.
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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Jim Armstrong » Sat May 23, 2015 5:05 pm

Thanks for the reply, bystander.
Sorry for the repeated "that" in my first post.
I do expect such descriptions in degrees of arc, so my question seems unanswered.

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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Craine » Sat May 23, 2015 5:12 pm

I am guessing the authors included the '40 light year' measurement to give an indication of the size of the cloud complex. A measurements in degrees of arc would give an indication of apparent size in the skies. Sorry...but I am too tired to do the math right now.

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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by geckzilla » Sat May 23, 2015 5:25 pm

If you think of the edges of the bright part of the nebula as forming a kind of equilateral triangle, the edges are all around 50' in length. The image is about 1.75° wide.

Above information courtesy of the measurement tool in Aladin.
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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Guest » Sat May 23, 2015 6:13 pm

If the image is ~1.75deg wide, then the image would be ~90 ly wide for a distance of ~3000 ly. The 40 ly quoted appears to originate from an earlier APOD on NGC 7822 with a smaller field of view.

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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Ann » Sat May 23, 2015 7:44 pm

I'm trying to figure out which star is ionizing this nebula. The only O-type star I can find in NGC 7822 is SAO 21019, an O7V-type star. It is a member of the small cluster seen slightly left of and above center in today's APOD. Does anyone here know of any other O-type star in this nebula?

Ann
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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by geckzilla » Sat May 23, 2015 8:06 pm

Ann wrote:I'm trying to figure out which star is ionizing this nebula. The only O-type star I can find in NGC 7822 is SAO 21019, an O7V-type star. It is a member of the small cluster seen slightly left of and above center in today's APOD. Does anyone here know of any other O-type star in this nebula?

Ann
Here's a paper which shares some details learned about the star just north of the one you've mentioned.
http://cdsads.u-strasbg.fr/cgi-bin/nph- ... etcookie=1
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Re: APOD: NGC 7822 in Cepheus (2015 May 23)

Post by Ann » Sat May 23, 2015 8:15 pm

geckzilla wrote:
Ann wrote:I'm trying to figure out which star is ionizing this nebula. The only O-type star I can find in NGC 7822 is SAO 21019, an O7V-type star. It is a member of the small cluster seen slightly left of and above center in today's APOD. Does anyone here know of any other O-type star in this nebula?

Ann
Here's a paper which shares some details learned about the star just north of the one you've mentioned.
http://cdsads.u-strasbg.fr/cgi-bin/nph- ... etcookie=1
Thanks, Geck!

Ann
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