Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Webb captures iconic Horsehead Nebula in unprecedented detail

esa.int

Post reply on HN
Print view View original

91–100 of 310 posts

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#91

Post by sandworm101 »

causal wrote: post #82
sandworm101 wrote: post #71

Earlier quoted context omitted.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

Replying to the other replies here - this regards the observable universe. Speed of light limits and all that. Of course we have no reason to believe the universe just stops at the point where we happen to lack the ability to observe.

Well, no. The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. The size of that universe is extrapolated from the rate of expansion and the time since the big bang.

The size and shape of the observable universe also changes. A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another. Accelerate quickly enough and the "dark" side of your custom observable universe might catch up with you, causing all sorts of havoc.

https://en.wikipedia.org/wiki/Unruh_effect

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#92

Post by dheera »

itg wrote: post #38
bloopernova wrote: post #12

Gorgeous and upsetting that I'll never be able to visit it. 13 billion years before me, potentially trillions of years after me. Seems like such a waste of the spark of awareness that I can't take that awareness and experience the galaxy in all its glory.

Isn't a nebula a cloud of dust? I'm not sure how dense it gets, but would someone even notice if they were inside of the nebula?

There are multiple types of nebulae. Absorption nebula (or dark nebula) and reflection nebula are clouds of "dust" (more likely lots of rocks).

There are also emission nebula which are clouds of ionized gases that emit light.

The horsehead nebula is an absorption nebula that sits in front of light-emitting emission nebula. It's fairly easy to image the horsehead with a star tracker and DSLR, though not to this level of detail.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#93

Post by digging »

usrusr wrote: post #60
Maxion wrote: post #24

Earlier quoted context omitted.

Nature is very fractal, the same pattern occurs on multiple levels. You even see the same thing in human constructs.

But what's giving it it's seemingly clear cutoff boundary? I have trouble imagining anything in the nothingness of space taking the role of the forces that shape our atmospheric clouds. It feels a bit as if it was some arbitrary artistic decision like that 2001 slit scan or the Solaris ocean. Then on the other hand of course it's amongst the few most "artistic" ones picked from all those super tiny projection viewpor…

There are lots of forces at play! The article mentions some of them. Structures are shaped not just by gravity, but by electromagnetism, starlight, supernovae, and more.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#94

Post by floxy »

kibwen wrote: post #8
qwertox wrote: post #6

It's so very unlikely that there aren't millions of other lifeforms out there. Sometimes I think that life could well have been just my soul and no one else, but here I am sharing this world with billions of other people, trillions of other lifeforms on this planet alone. So it is possible that more than one lifeform exists, that they share this universe and communicate in it. Why shouldn't this also be possible on m…

Of course there are other lifeforms out there, it's statistically implausible for it to be otherwise. What's also implausible is that, given the impossible vastness and hostility of interstellar space, that any will ever manage to contact us, specifically. Fortunately, we've got lots of crazy lifeforms here on Earth to keep us occupied, if we can take a moment to stop extincting them as fast as we possibly can.

"Dissolving the Fermi Paradox"

https://arxiv.org/abs/1806.02404

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#97

Post by dheera »

For a size comparison, here's a stacked, partially star-tracked image I took fully shot at 85mm on a full frame camera to show the perspective. The vertical 3 bright stars to the center/left are the belt of Orion.

The small black notch in the red nebula to the bottom right of the belt is the horse head.

https://www.instagram.com/p/CZp_R1npsT-/?img_index=1

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#98

Post by layer8 »

afterburner wrote: post #67
HumblyTossed wrote: post #59

Earlier quoted context omitted.

Crazy how many galaxies are in that one photo (in the background).

Number of stars in the Milky Way: 100 billion Number of galaxies in the universe: 200 billion to 2,000 billion

*observable universe

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#100

Post by layer8 »

sandworm101 wrote: post #91
causal wrote: post #82

Earlier quoted context omitted.

Replying to the other replies here - this regards the observable universe. Speed of light limits and all that. Of course we have no reason to believe the universe just stops at the point where we happen to lack the ability to observe.

Well, no. The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. The size of that universe is extrapolated from the rate of expansion and the time since the big bang. The size and shape of the observable universe also changes. A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another. Accelerate quickly enough and t…

As far as we know, the total universe may have infinite size, and thus contain infinitely many galaxies.
Post reply on HN