APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

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APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

Post by APOD Robot » Thu Oct 31, 2024 4:06 am

Image Rigel and the Witch Head Nebula

Explanation: By starlight, this eerie visage shines in the dark with a crooked profile evoking its popular name, the Witch Head Nebula. In fact, this entrancing telescopic portrait gives the impression that a witch has fixed her gaze on Orion's bright supergiant star Rigel. More formally known as IC 2118, the Witch Head Nebula spans about 50 light-years and is composed of interstellar dust grains reflecting Rigel's starlight. The color of the Witch Head Nebula is caused not only by Rigel's intense blue light, but because the dust grains scatter blue light more efficiently than red. The same physical process causes Earth's daytime sky to appear blue, although the scatterers in Earth's atmosphere are molecules of nitrogen and oxygen. Rigel and this dusty cosmic crone are about 800 light-years away. You may still see a few witches in your neighborhood tonight though, so have a safe and Happy Halloween!

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alex555

Re: APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

Post by alex555 » Thu Oct 31, 2024 10:46 am

What is the estimated distance between IC 2118 and Rigel? It's amazing that a star can illuminate an object even very far away.

Alex

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Re: APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

Post by Christian G. » Thu Oct 31, 2024 12:07 pm

That witch seems bewitched by the beauty of Rigel!

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Re: APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

Post by Ann » Thu Oct 31, 2024 4:11 pm

alex555 wrote: Thu Oct 31, 2024 10:46 am What is the estimated distance between IC 2118 and Rigel? It's amazing that a star can illuminate an object even very far away.

Alex
That is a difficult question, and one problem is that we don't know how far away Rigel actually is! :shock:

The European Space Agency (ESA) has launched two space telescopes specifically designed for measuring distances in space. The first one was Hipparcos, which is now retired. Hipparcos performed well enough for its time, but its measurements really weren't reliable for distances larger than, say, 400 light-years. Astronomers are sure that Rigel is more distant than that.

ESA's other telescope for measuring distances in space, Gaia, is still busy doing observations. Gaia is much, much more sensitive than Hipparcos ever was, but the problem is that Gaia simply can't observe stars that are "too bright", or it will become "blinded". And since Rigel is a first-magnitude star, one of the brightest in the night sky, it is impossible for Gaia to measure the distance to it.

So what we have for Rigel is its Hipparcos parallax of 3.78 ± 0.34 milliarcseconds, corresponding to a distance of 863 ± 78 light-years. Is that reliable? Who knows. This is what Wikipedia said about the distance to Rigel:

Wikipedia wrote:

Rigel's distance from the Sun is somewhat uncertain, different estimates being obtained by different methods. Old estimates placed it 166 parsecs (or 541 light years) away from the Sun. The 2007 Hipparcos new reduction of Rigel's parallax is 3.78±0.34 mas, giving a distance of 863 light-years (265 parsecs) with a margin of error of about 9%. Rigel B, usually considered to be physically associated with Rigel and at the same distance, has a Gaia Data Release 3 parallax of 3.2352±0.0553 mas, suggesting a distance around 1,000 light-years (310 parsecs). However, the measurements for this object may be unreliable.

Indirect distance estimation methods have also been employed. For example, Rigel is believed to be in a region of nebulosity, its radiation illuminating several nearby clouds. Most notable of these is the 5°-long IC 2118 (Witch Head Nebula), located at an angular separation of 2.5° from the star, or a projected distance of 39 light-years (12 parsecs) away. From measures of other nebula-embedded stars, IC 2118's distance is estimated to be 949 ± 7 light-years (291 ± 2 parsecs).[58]
So the Witch Head Nebula may be some 39 light-years from Rigel. If you are looking for bright star at about that distance from the Earth, there is Denebola, the "end star" of Leo, and Arcturus, the bright luminary of Bootes.

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Re: APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

Post by Chris Peterson » Thu Oct 31, 2024 4:15 pm

alex555 wrote: Thu Oct 31, 2024 10:46 am What is the estimated distance between IC 2118 and Rigel? It's amazing that a star can illuminate an object even very far away.

Alex
This nebula is extremely dim. Don't be fooled by an image exposed for hours. If Rigel were the only star in the sky it would do just fine to light up a nighttime landscape given a long enough exposure.
Chris

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Re: APOD: Rigel and the Witch Head Nebula (2024 Oct 31)

Post by caleb665 » Thu Oct 31, 2024 11:24 pm

Amazing photo of Rigel and the Witch Head Nebula. And you wonder how that nebula produces such an eerie shape while Rigel’s light bounces off it! Perfect timing, with Halloween feels cliché – kind of gives you the creeps. Space simply always have that unique ability of mixing beauty and mystery.

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