APOD: The Horsehead Nebula (2019 Oct 06)

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APOD: The Horsehead Nebula (2019 Oct 06)

Post by APOD Robot » Sun Oct 06, 2019 4:06 am

Image The Horsehead Nebula

Explanation: The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red emission nebula in the center of the above photograph. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will surely alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. On the image left is the Flame Nebula, an orange-tinged nebula that also contains filaments of dark dust. Just to the lower left of the Horsehead nebula featured picture is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars.

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by Ann » Sun Oct 06, 2019 5:34 am

The Horsehead region. Photo: José Jiménez Priego
The subject matter of today's APOD is something all astronomy nerds have seen before. But why not show it again on a Sunday, which is the repeat day anyway?

Today's APOD is not the best picture I've seen of this part of the sky, but I'm going to guess that José Jiménez Priego is an amateur with limited equipment, in which case his picture is very nice indeed. As a color commentator, I applaud his colors. The reds are red, the blues are blue, the yellows are yellow and the pinks are pink. What more can you ask for?



The Horsehead Nebula. Canada-France- Hawaii Telescope.









Let's look at some of the constituent parts of this iconic skyscape, and let's start with the Horsehead Nebula itself! As you can see from the picture at right, the Horsehead is a fluffy, tenuous, evaporating dust pillar. In the picture at right, you can just make out a star being born at the top of "the head of the horse", and you can see a faint bright outline along the "head". So the Horsehead Nebula is giving birth to a starat the same time as it is evaporating.





The Horsehead being carved out by Sigma Orionis (arrow).
Source: https://astro.swarthmore.edu/~emartel1/sigoriab.htm






The star responsible for carving out the dust pillar that is the Horsehead Nebula is Sigma Orionis, an O-type, multiple star system slightly similar to the Trapezium (in a picture by Theofanis Matsopoulos) in the Orion Nebula. The large Hα nebula surrounding Sigma Orionis is one of the reddest parts of the entire Orion constellation, and this Hα nebula is the backdrop against which we are seeing the Horsehead Nebula. You can see another picture of the full extent of the Sigma Orionis Hα nebula here, in a picture by Rogelio Bernal Andreo.






The Flame Nebula in infrared light and X-rays.
Photo: Chandra Space Telescope and Spitzer Space Telescope.


The next nebula we should take a closer look at is the large yellow Flame Nebula. My guess is that the yellow color is caused by dust reddening of the blue stars being born inside. As you can see in the picture at right, a cluster of stars is being born inside, hid from optical view by a thick dust lane in front of it.

Note the structural similarity between the Flame Nebula and the star forming region S106, in a picture by NASA, ESA, and the Hubble Heritage Team (STScI/AURA).




The Horsehead Nebula and reflection nebula NGC 2023.
Photo: Ken Crawford.













Finally, take a look at the picture at left of the Horsehead Nebula and the blue reflection nebula at the "foot" of it. NGC 2023 is lit up by the blue light of a B-type star being born inside it.

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by Antony Rawlinson » Sun Oct 06, 2019 7:59 am

Does the red emission nebula that makes the Horsehead visible, have a name?

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by Boomer12k » Sun Oct 06, 2019 10:27 am

The large photo looks like a red sunset, over a Ridge that has cloud cover, with CITY LIGHTS shining up through them... awesome...

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by orin stepanek » Sun Oct 06, 2019 12:19 pm

:thumb_up: Nice rendering of the Horsehead & Flame Nebulae! 8-)
HorseFlame_Priego_960.jpg
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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by dzsobacsi » Sun Oct 06, 2019 12:41 pm

or APOD: The Horsehead Nebula (2015 Dec 16) ???

https://apod.nasa.gov/apod/ap151216.html

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by De58te » Sun Oct 06, 2019 12:50 pm

Antony Rawlinson wrote:
Sun Oct 06, 2019 7:59 am
Does the red emission nebula that makes the Horsehead visible, have a name?
Yes it does. IC 434 But note, I am just an interested layman. I could be wrong. Wait for confirmation from an authority.

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by neufer » Sun Oct 06, 2019 1:28 pm

APOD Robot wrote:
Sun Oct 06, 2019 4:06 am
Image The Horsehead Nebula

Explanation: Just to the lower left of the Horsehead nebula featured picture
is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars.
You couldn't just name NGC 2023 or point to its APODs:

https://apod.nasa.gov/apod/ap180329.html
https://apod.nasa.gov/apod/ap180309.html
https://apod.nasa.gov/apod/ap161225.html
https://apod.nasa.gov/apod/ap010224.html
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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by Ann » Sun Oct 06, 2019 1:50 pm

neufer wrote:
Sun Oct 06, 2019 1:28 pm
APOD Robot wrote:
Sun Oct 06, 2019 4:06 am
Image The Horsehead Nebula

Explanation: Just to the lower left of the Horsehead nebula featured picture
is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars.
You couldn't just name NGC 2023 or point to its APODs:

https://apod.nasa.gov/apod/ap180329.html
https://apod.nasa.gov/apod/ap180309.html
https://apod.nasa.gov/apod/ap161225.html
https://apod.nasa.gov/apod/ap010224.html
At least I posted a picture of it and named it, didn't I?

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by neufer » Sun Oct 06, 2019 2:58 pm

Ann wrote:
Sun Oct 06, 2019 1:50 pm
neufer wrote:
Sun Oct 06, 2019 1:28 pm
APOD Robot wrote:
Sun Oct 06, 2019 4:06 am
Image The Horsehead Nebula

Explanation: Just to the lower left of the Horsehead nebula featured picture
is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars.
You couldn't just name NGC 2023 or point to its APODs:

https://apod.nasa.gov/apod/ap180329.html
https://apod.nasa.gov/apod/ap180309.html
https://apod.nasa.gov/apod/ap161225.html
https://apod.nasa.gov/apod/ap010224.html
At least I posted a picture of it and named it, didn't I?
Sort of as a footnote in an extensive posting
(& only because it is the blue member of the group).

However, I was talking mano a robo to Otto.
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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by RCompassi » Sun Oct 06, 2019 3:07 pm


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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by Ann » Sun Oct 06, 2019 3:25 pm

neufer wrote:
Sun Oct 06, 2019 2:58 pm
Ann wrote:
Sun Oct 06, 2019 1:50 pm
At least I posted a picture of it and named it, didn't I?
Sort of as a footnote in an extensive posting
(& only because it is the blue member of the group).
Hey hey hey, I also posted pictures of the red Sigma Orionis Nebula and the yellow Flame Nebula!!! :evil:
However, I was talking mano a robo to Otto.
Okay. That was funny! :lol2: :D

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by rj rl » Sun Oct 06, 2019 5:30 pm

Older APOD entries of the Horsehead Nebula have the same text except for one word, now it says:
After many thousands of years, the internal motions of the cloud will surely alter its appearance
and before it said:
After many thousands of years, the internal motions of the cloud will alter its appearance
I'm curious, why the correction? I can't see how it could possibly retain its shape.

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by neufer » Sun Oct 06, 2019 5:54 pm

rj rl wrote:
Sun Oct 06, 2019 5:30 pm

Older APOD entries of the Horsehead Nebula have the same text except for one word, now it says:
After many thousands of years, the internal motions of the cloud will surely alter its appearance
and before it said:
After many thousands of years, the internal motions of the cloud will alter its appearance
I'm curious, why the correction?

I can't see how it could possibly retain its shape.
  • By wearing a nylon web halter :?:

    (Shirley, it's an "alternative fact" as compared with prior APODs.)
https://en.wikipedia.org/wiki/Alternative_facts wrote:
<<"Alternative facts" was a phrase used by U.S. Counselor to the President Kellyanne Conway during a Meet the Press interview on January 22, 2017, in which she defended White House Press Secretary Sean Spicer's false statement about the attendance numbers of Donald Trump's inauguration as President of the United States. When pressed during the interview with Chuck Todd to explain why Spicer would "utter a provable falsehood", Conway stated that Spicer was giving "alternative facts". Todd responded, "Look, alternative facts are not facts. They're falsehoods." Conway's use of the phrase "alternative facts" for demonstrable falsehoods was widely mocked on social media and sharply criticized by journalists and media organizations, including Dan Rather, Jill Abramson, and the Public Relations Society of America. The phrase was extensively described as Orwellian. Within four days of the interview, sales of George Orwell's novel Nineteen Eighty-Four had increased by 9,500%, which The New York Times and others attributed to Conway's use of the phrase, making it the number-one bestseller on Amazon.com. Conway later defended her choice of words, defining "alternative facts" as "additional facts and alternative information">>
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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by bystander » Mon Oct 07, 2019 1:09 am

dzsobacsi wrote:
Sun Oct 06, 2019 12:41 pm
or APOD: The Horsehead Nebula (2015 Dec 16) ???

https://apod.nasa.gov/apod/ap151216.html
RCompassi wrote:
Sun Oct 06, 2019 3:07 pm
Why reuse a 2015 image?

https://apod.nasa.gov/apod/ap151216.html
New around here? Sunday APODs are often repeats. Search any Sunday APOD and more times than not you'll find that the image, text, or both are repeats of a previous APOD.
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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by dzsobacsi » Mon Oct 07, 2019 2:09 pm

bystander wrote:
Mon Oct 07, 2019 1:09 am

New around here? Sunday APODs are often repeats. Search any Sunday APOD and more times than not you'll find that the image, text, or both are repeats of a previous APOD.
Thank you for the info!

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Re: APOD: The Horsehead Nebula (2019 Oct 06)

Post by Antony Rawlinson » Tue Oct 08, 2019 6:55 am

De58te wrote:
Sun Oct 06, 2019 12:50 pm
Antony Rawlinson wrote:
Sun Oct 06, 2019 7:59 am
Does the red emission nebula that makes the Horsehead visible, have a name?
Yes it does. IC 434 But note, I am just an interested layman. I could be wrong. Wait for confirmation from an authority.
Thanks for the info - although IC 434 seems more like a catalogue number than a name.

I was just a little disappointed that the write-up for the APOD image didn't have anything much to say about it - even though, as I say, the Horsehead would be far less spectacular without it, or maybe not even visible.

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Post by neufer » Tue Oct 08, 2019 4:30 pm

Antony Rawlinson wrote:
Tue Oct 08, 2019 6:55 am
De58te wrote:
Sun Oct 06, 2019 12:50 pm
Antony Rawlinson wrote:
Sun Oct 06, 2019 7:59 am

Does the red emission nebula that makes the Horsehead visible, have a name?
Yes it does. IC 434 But note, I am just an interested layman. I could be wrong. Wait for confirmation from an authority.
Thanks for the info - although IC 434 seems more like a catalogue number than a name.

I was just a little disappointed that the write-up for the APOD image didn't have anything much to say about it - even though, as I say, the Horsehead would be far less spectacular without it, or maybe not even visible.
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