Starship Asterisk*

Jim Kaler wrote about Tau Canis Majoris (Tau CMa):
Almost fifth magnitude (4.40), and needing reasonably dark conditions to see, it is one of the sky's rare very hot and blue class O (O9) supergiants, its modest apparent brightness the result of its huge distance of 4800 light years, the light you see having left the star around 2800 BC!

It is so far away that we would not have a good handle on its distance at all except for the fact that Tau is the premier member (or so most believe) of a star cluster called NGC (for New General Catalogue) 2362. Since we can easily compare the brightnesses of stars within such a cluster with those of clusters whose distances we do know, we can find NGC 2362's distance quite accurately.

More important, Tau CMa is a massive multiple star, having at least five components...

The brilliance of these stars reveals their huge masses, the inner four together shining with the light of half a million Suns, which suggests average masses around 20 times solar...

We speculate that the stars were not born in this configuration, but that the bright quartet was formed when two doubles within the cluster passed too close together and merged to create this remarkable system.

orin stepanek wrote: ↑Sun Feb 16, 2020 12:03 pm NGC2392_HubbleSchmidt_960.jpg

Wasn't this nebula referred to as the eskimo a while back? Or do I have it mixed up with some other nebula?

Tszabeau wrote: ↑Sun Feb 16, 2020 2:24 pm
Beautiful and interesting composition. It reminds me more of a Portuguese man-of-war than fur hooded head. I do have to wonder how they stuffed light year long filaments into a one-third light year wide nebula, though.

• It helps a little to be a TWO-thirds light year wide nebula:

https://en.wikipedia.org/wiki/Eskimo_Nebula wrote:
Radius = distance × sin(angular size / 2) = ≥2900 ly * sin(48″ / 2) = ≥0.34 ly

https://en.wikipedia.org/wiki/Portuguese_man_o%27_war wrote:

Portuguese man o' war in Tayrona National Natural Park, Colombia

---

<<The Portuguese man o' war (Physalia physalis) is a marine hydrozoan found in the Atlantic, Indian and Pacific Oceans. It is one of two species in the genus Physalia, along with the Pacific man o' war (or Australian blue bottle), Physalia utriculus. Its long tentacles deliver a painful sting, which is venomous and powerful enough to kill fish and even humans. Despite its appearance, the Portuguese man o' war is not a true jellyfish but a siphonophore, which is not an individual multicellular organism (true jellyfishes are single organisms), but a colonial organism made up of many specialized animals of the same species, called zooids or polyps. These polyps are attached to one another and physiologically integrated, to the extent that they cannot survive independently, creating a symbiotic relationship, requiring each polyp to work together and function like an individual animal.>>

Tszabeau wrote: ↑Sun Feb 16, 2020 2:24 pm Beautiful and interesting composition. It reminds me more of a Portuguese man-of-war than fur hooded head. I do have to wonder how they stuffed light year long filaments into a one-third light year wide nebula, though.

ta152h0 wrote: ↑Mon Feb 17, 2020 12:51 am Would the Solar System be just a speck in this picture?

MarkBour wrote: ↑Mon Feb 17, 2020 5:11 pm

ta152h0 wrote: ↑Mon Feb 17, 2020 12:51 am
Would the Solar System be just a speck in this picture?

The diameter of our solar system can be characterized in very different ways. If you use Neptune's orbit as a very conservative measure, it's within about 9 x 10^9 km. So, 1/3 light year, at about (1/3) * 9 * 10^12 km, is around 330 times as large.

Our solar system out to Neptune would be pretty small in this image, about 1/330th of the diameter of the outer shell shown.

neufer wrote: ↑Mon Feb 17, 2020 7:14 pm [The distance from the Oort cloud to the interior of the Solar System, and two of the nearest stars, is measured in astronomical units. The scale is logarithmic. The red arrow indicates the location of the space probe Voyager 1, which will reach the Oort cloud in about 300 years.]

MarkBour wrote: ↑Mon Feb 17, 2020 5:11 pm

ta152h0 wrote: ↑Mon Feb 17, 2020 12:51 am
Would the Solar System be just a speck in this picture?

The diameter of our solar system can be characterized in very different ways. If you use Neptune's orbit as a very conservative measure, it's within about 9 x 10^9 km. So, 1/3 light year, at about (1/3) * 9 * 10^12 km, is around 330 times as large.

Our solar system out to Neptune would be pretty small in this image, about 1/330th of the diameter of the outer shell shown.

However, the diameter of the outer shell shown is 2/3 of a light year.

Oort Neuendorffer

MarkBour wrote: ↑Tue Feb 18, 2020 4:34 pm
I took the APOD caption:

"The NGC 2392 Nebula spans about 1/3 of a light year" to mean diameter,

but Wikipedia agrees with you that 1/3 ly is the radius for the Eskimo nebula.

https://www.etymonline.com/search?q=span wrote:
span (n.1) "distance between two objects," from Old English span "distance between the thumb and little finger of an extended hand" (as a measure of length, roughly nine inches), probably related to Middle Dutch spannen "to join, fasten." The Germanic word was borrowed into Medieval Latin as spannus, hence Italian spanna, Old French espan "hand's width, span as a unit of measure," French empan. As a measure of volume (early 14c.), "what can be held in two cupped hands." Meaning "length of time" first attested 1590s; that of "space between abutments of an arch, etc." is from 1725.>>

neufer wrote: ↑Tue Feb 18, 2020 5:20 pm When the ship hits the span