Starship Asterisk*

[quote=AVAO post_id=335193 time=1700545529 user_id=144694]
[quote=johnnydeep post_id=335190 time=1700516376 user_id=132061]
Despite the title of this APOD, I think NGC 2023 is the real star of this show. Also, I think it is noteworthy how similar to this image from Mark Hanson is the image from Ken Crawford seen here http://www.imagingdeepsky.com/Nebulae/Horsehead/Horsehead.htm, though this APOD is nicer and has a slightly larger FOV. But I guess that's just because the Horsehead / NGC 2023 pair are so photogenic!
[/quote]


I think that this cosmic region is also very photogenic in IR.
Maybe JWST should also take a look here in the future :roll:


[imghover="https://live.staticflickr.com/65535/53346012581_f6bcf0a2a1_b.jpg"]https://live.staticflickr.com/65535/53345132237_3c61aacf83_b.jpg[/imghover]
[size=75]Image Source: Herschel / Original data: NASA/ESA[/size]

...
[/quote]

Wow - that makes it look like the Flame Nebula extends all the way to the Horsehead!

[quote=johnnydeep post_id=335190 time=1700516376 user_id=132061]
Despite the title of this APOD, I think NGC 2023 is the real star of this show. Also, I think it is noteworthy how similar to this image from Mark Hanson is the image from Ken Crawford seen here http://www.imagingdeepsky.com/Nebulae/Horsehead/Horsehead.htm, though this APOD is nicer and has a slightly larger FOV. But I guess that's just because the Horsehead / NGC 2023 pair are so photogenic!
[/quote]


I think that this cosmic region is also very photogenic in IR.
Maybe JWST should also take a look here in the future :roll:


[imghover="https://live.staticflickr.com/65535/53346012581_f6bcf0a2a1_b.jpg"]https://live.staticflickr.com/65535/53345132237_3c61aacf83_b.jpg[/imghover]
[size=75]Image Source: Herschel / Original data: NASA/ESA[/size]


[img2]https://live.staticflickr.com/65535/53346275368_6966635aed_b.jpg[/img2]
[size=75]False colors composit Euclid/ods / Original data: NASA/ESA[/size]


[img2]https://live.staticflickr.com/65535/53346334999_03a73515c8_b.jpg[/img2]
[size=75]NGC 2023 False colors composit Euclid /ods / Original data: NASA/ESA[/size]

Despite the title of this APOD, I think NGC 2023 is the real star of this show. Also, I think it is noteworthy how similar to this image from Mark Hanson is the image from Ken Crawford seen here http://www.imagingdeepsky.com/Nebulae/Horsehead/Horsehead.htm, though this APOD is nicer and has a slightly larger FOV. But I guess that's just because the Horsehead / NGC 2023 pair are so photogenic!

[quote=George post_id=335185 time=1700502292]
Re Ann's comment: "The Horsehead Nebula has formed because there is a brilliant O-type star, Sigma Orionis, located close to a molecular ridge, and the brunt of the ultraviolet light from Sigma Orionis is bearing down on the ridge, ionizing it but also evaporating it."

I don't see how interstellar "gas" can "evaporate."

Liquids can evaporate to form a gas, and solids can sublimate to forma a gas, but once a gas is a gas, it can't evaporate further/again.
[/quote]

"Evaporate" is synonymous with "disperse" in this context.

Re Ann's comment: "The Horsehead Nebula has formed because there is a brilliant O-type star, Sigma Orionis, located close to a molecular ridge, and the brunt of the ultraviolet light from Sigma Orionis is bearing down on the ridge, ionizing it but also evaporating it."

I don't see how interstellar "gas" can "evaporate."

Liquids can evaporate to form a gas, and solids can sublimate to forma a gas, but once a gas is a gas, it can't evaporate further/again.

[attachment=1]Horsehead_Hanson_960.jpg[/attachment]
IC 434(HORSEHEAD NEBULA) AND NGC 2023
[attachment=0]pets-vs-furniture-cat-squeezed-in-couch.jpg[/attachment]
Aw! poor kitty

[quote="APOD Robot" post_id=335172 time=1700456728 user_id=128559]
[url=https://apod.nasa.gov/apod/ap231120.html] [img]https://apod.nasa.gov/apod/calendar/S_231120.jpg[/img] [size=150]The Horsehead Nebula[/size][/url]

[b] Explanation: [/b] [url=https://apod.nasa.gov/apod/ap080313.html]Sculpted by[/url] stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed this [url=https://en.wikipedia.org/wiki/Seahorse]recognizable shape[/url]. Fittingly named the [url=https://en.wikipedia.org/wiki/Horsehead_Nebula]Horsehead Nebula[/url], it is some 1,500 light-years [url=https://youtu.be/hgTrLozRj40]distant[/url], embedded in the vast [url=https://apod.nasa.gov/apod/ap070125.html]Orion cloud[/url] complex. About five light-years "tall," the dark cloud is cataloged as [url=http://messier.seds.org/xtra/ngc/b33.html]Barnard 33[/url] and is visible only because its [url=https://apod.nasa.gov/apod/ap230129.html]obscuring dust is silhouetted[/url] against the glowing red emission nebula IC 434. [url=https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/]Stars are forming[/url] within the dark cloud. [url=https://apod.nasa.gov/apod/ap160608.html]Contrasting[/url] blue reflection nebula NGC 2023, surrounding a hot, young [url=https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve]star[/url], is at the lower left of [url=https://apod.nasa.gov/apod/image/1912/Horsehead_Hanson_2604.jpg]the full image[/url]. The featured gorgeous [url=https://www.hansonastronomy.com/ic-434ngc2023]color image[/url] combines both [url=https://www.thepoke.co.uk/wp-content/uploads/2016/09/pets-vs-furniture-cat-squeezed-in-couch.jpg]narrowband[/url] and [url=https://s-media-cache-ak0.pinimg.com/736x/e1/6c/e4/e16ce47242406ac2d278f10619282d13.jpg]broadband[/url] images recorded using several different telescopes.


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[/quote]
As always, I need to point out that the head is not the featured part of the horse's anatomy in this nebula.
_
[attachment=0]hh-ass.jpg[/attachment]

We've heard the Moonlight Sonata or seen the Girl with a Pearl Earring a zillion times but that doesn't take away their beauty! A dark horse head against a deep red background is an utmost stunning sight… One has to imagine seeing this for the very first time to be stunned over and over again (plus the thing is five light-years tall!)

The Horsehead Nebula is one of the most well-known and most frequently photographed deep-sky objects out there, so for me it is getting a bit old. But there is a lot to see in today's APOD:


[float=left][img3="The Horsehead Nebula.
Image Credit & Copyright: Mark Hanson & Martin Pugh, SSRO, PROMPT, CTIO, NSF"]https://apod.nasa.gov/apod/image/2311/Horsehead_Hanson_960.jpg[/img3][/float][float=right][attachment=0]APOD 20 November 2023 annotated.png[/attachment][/float]
[clear][/clear]


The Horsehead Nebula has formed because there is a brilliant O-type star, Sigma Orionis, located close to a molecular ridge, and the brunt of the ultraviolet light from Sigma Orionis is bearing down on the ridge, ionizing it but also evaporating it.


[img3="Sigma Orionis is the bright star at lower center right. The molecular ridge being ionized and evaporated by Sigma's harsh ultraviolet light is at left. Image credit: Lithopsian at Wikipedia."]https://upload.wikimedia.org/wikipedia/commons/thumb/4/48/Sigma_orionis_cluster.jpg/1280px-Sigma_orionis_cluster.jpg[/img3]


The Horsehead Nebula is a pillar, the same type of object as the famous Pillars of Creation. Both the Horsehead Nebula and the Pillars of Creation have been formed in the same way, when ultraviolet light from very hot stars ionizes but also evaporates gas structures. The densest gas structures remain standing the longest.


[img3="The Pillars of Creation in the Eagle Nebula. Note that the 'bent head' of the tallest pillar resembles the head of the Horsehead Nebula. Credit: SCIENCE: NASA, ESA, CSA, STScI. IMAGE PROCESSING: Joseph DePasquale (STScI), Anton M. Koekemoer (STScI), Alyssa Pagan (STScI)"]https://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Pillars_of_Creation_%28NIRCam_Image%29.jpg/519px-Pillars_of_Creation_%28NIRCam_Image%29.jpg?20221019202730[/img3]


Herbig-Haro objects are created by stars in the process of forming. As they accrete matter, they eject jets.


[img3="This Hubble image shows a Herbig-Haro object labeled HH 111. Image credit: NASA / ESA / Hubble / B. Nisini."]https://cdn.sci.news/images/2021/08/image_10009-HH-111.jpg[/img3]


As for NGC 2023, it is a beautiful reflection/emission nebula (mostly a reflection nebula really) surrounding a newborn star of spectral class B3:


[img3="NGC 2023 in the Horsehead's Shadow.
Image Credit & Copyright: Steve Mazlin, Mark Hanson, Warren Keller, Rex Parker, Tommy Tse,
and Peter Proulx (SSRO / PROMPT / CTIO)"]https://apod.nasa.gov/apod/image/1803/NGC2023master2_1024.jpg[/img3]


Note that the red background of the Horsehead Nebula is very red. The nearby Flame Nebula, which is a combined emission nebula ionized by brilliant O-type star Alnitak and a molecular cloud, the birth site of an unborn cluster of baby stars, is very yellow by comparison.



[float=left][img3="The Horsehead Nebula seen against a red background and the yellow Flame Nebula. Image credit: Christian Gloor."]https://www.constellation-guide.com/wp-content/uploads/2021/06/Alnitak-Flame-Nebula-and-Horsehead-Nebula.webp[/img3][/float][float=right][img3="A combined X-ray/infrared picture of the Flame Nebula, revealing the young cluster inside. Credit: X-ray: NASA/CXC/PSU/K.Getman, E.Feigelson, M.Kuhn & the MYStIX team; Infrared: NASA/JPL-Caltech"]https://upload.wikimedia.org/wikipedia/commons/thumb/3/36/NASA-FlameNebula-NGC2024-20140507.jpg/1024px-NASA-FlameNebula-NGC2024-20140507.jpg[/img3][/float]
[clear][/clear]


Ann

[url=https://apod.nasa.gov/apod/ap231120.html] [img]https://apod.nasa.gov/apod/calendar/S_231120.jpg[/img] [size=150]The Horsehead Nebula[/size][/url]

[b] Explanation: [/b] [url=https://apod.nasa.gov/apod/ap080313.html]Sculpted by[/url] stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed this [url=https://en.wikipedia.org/wiki/Seahorse]recognizable shape[/url]. Fittingly named the [url=https://en.wikipedia.org/wiki/Horsehead_Nebula]Horsehead Nebula[/url], it is some 1,500 light-years [url=https://youtu.be/hgTrLozRj40]distant[/url], embedded in the vast [url=https://apod.nasa.gov/apod/ap070125.html]Orion cloud[/url] complex. About five light-years "tall," the dark cloud is cataloged as [url=http://messier.seds.org/xtra/ngc/b33.html]Barnard 33[/url] and is visible only because its [url=https://apod.nasa.gov/apod/ap230129.html]obscuring dust is silhouetted[/url] against the glowing red emission nebula IC 434. [url=https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/]Stars are forming[/url] within the dark cloud. [url=https://apod.nasa.gov/apod/ap160608.html]Contrasting[/url] blue reflection nebula NGC 2023, surrounding a hot, young [url=https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve]star[/url], is at the lower left of [url=https://apod.nasa.gov/apod/image/1912/Horsehead_Hanson_2604.jpg]the full image[/url]. The featured gorgeous [url=https://www.hansonastronomy.com/ic-434ngc2023]color image[/url] combines both [url=https://www.thepoke.co.uk/wp-content/uploads/2016/09/pets-vs-furniture-cat-squeezed-in-couch.jpg]narrowband[/url] and [url=https://s-media-cache-ak0.pinimg.com/736x/e1/6c/e4/e16ce47242406ac2d278f10619282d13.jpg]broadband[/url] images recorded using several different telescopes.


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