Wow, that's a stunning image!
However, me being me, I do have one nitpick. To show you, I have added some extra annotation to the already richly annotated APOD, to bring out the Pipe Nebula. And near the Pipe Nebula is one of my favorite stars, Theta Ophiuchi, whose lovely azure light is not given full justice in the APOD. Wait, I'll show you!
A furious sky over Mount Shasta. Image: Ralf Rohner.
Can you see the Pipe Nebula at left in the APOD, which I have marked in light brown? And can you see θ Oph, Theta Ophiuchi, very close to it? It hardly looks blue at all in the APOD.
But Theta Ophiuchi
really is a lovely blue star, as you can see in Jose Mtanos' image. Few stars in the sky have a bluer B-V index. The B-V index measures the proportion of blue light to the proportion of yellow-green light emitted by a star (or a galaxy), and the lower the B-V index is, the bluer is the star (or the galaxy).
The fact that Theta Ophiuchi has an unusually blue B-V index is certainly not to say that Theta Ophiuchi is the intrinsically bluest and hottest star in the heavens, even though it is
hot. Simbad Astronomical database calls it an OB star of the Beta Cephei type, which probably means it is of early spectral class B. But it is less affected by dust reddening than most O and early B stars in the sky and thus looks bluer than most stars to our eyes.
The only star in Ralf Rohner's superb image that has a bluer B-V index than Theta Ophiuchi is Shaula
, Lambda Scorpii, which can be seen in the lower left corner in Rohner's image. Interestingly, Shaula is a Beta Cephei star, too.
So what about the original Beta Cephei star, Beta Cephei
itself? Sure, it is a hot and blue star and it stands out - not strikingly so, but it does - in its own constellation.
And of course, the Cepheus constellation also contains one of the redder stars in the sky that is visible to the naked eye, Mu Cephei
, also known as the Garnet Star. It is an extremely swollen, cool and luminous star. Antares, you are so out-reddened and out-sized by Mu Cephei!
But I can feel that I'm veering off the topic of today's APOD, so I'm leaving here!
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