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[quote="geckzilla"][quote="Ann"]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[/quote]
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-bib_query?2008JAVSO..36...90M&db_key=AST&nosetcookie=1[/quote]

Thanks, Geck!

Ann

[quote="Ann"]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[/quote]
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-bib_query?2008JAVSO..36...90M&db_key=AST&nosetcookie=1

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

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.

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.

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.

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.

[quote="Jim Armstrong"]...
Wouldn't the field span that that no matter what the distance? The distance is specified earlier. [/quote]
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.

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.
Jim Armstrong
Potter Valley, CA

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

Nice looking wide shot... :D

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[url=http://apod.nasa.gov/apod/ap150523.html][img]http://apod.nasa.gov/apod/calendar/S_150523.jpg[/img] [size=150]NGC 7822 in Cepheus[/size][/url]

[b] Explanation: [/b] Hot, young stars and [url=http://www.eso.org/public/news/eso1518/]cosmic pillars[/url] of gas and dust seem to crowd into NGC 7822. At the edge of a giant [url=http://archive.ncsa.illinois.edu/Cyberia/Bima/GMC.html]molecular cloud[/url] 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 [url=http://www.cieloprofundo.com/cesar/pagina_gral_banda%20estrecha/paginas_banda%20estrecha/NGC7822.html]colorful skyscape[/url]. The image includes data from [url=http://apod.nasa.gov/apod/ap060324.html]narrowband[/url] filters, mapping emission from atomic oxygen, hydrogen, and sulfur into blue, green, and red hues. The atomic emission is [url=http://apod.nasa.gov/apod/ap051223.html]powered by[/url] 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 [url=http://hyperphysics.phy-astr.gsu.edu/hbase/astro/gravc.html#c1]gravitational collapse[/url], but as the pillars are eroded away, any forming stars will ultimately be cutoff from their reservoir of [url=http://heritage.stsci.edu/2015/01/index.html]star stuff[/url]. This field spans around 40 light-years at the estimated distance of NGC 7822.

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