Gaia space telescope plots a billion stars | Hacker News Reader

Gaia space telescope plots a billion stars

bbc.com

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The Gaia Data Release 1 Archive: http://gea.esac.esa.int/archive/

Some information about the archive: http://www.cosmos.esa.int/web/gaia/dr1

Press conference from earlier today: https://www.youtube.com/watch?v=5pAjvQ5uu7I

Gaia's first sky map (incl. downloads up to 15360×7831): http://sci.esa.int/gaia/58209-gaia-s-first-sky-map/

Visualization of the data: http://gea.esac.esa.int/visualization/index.html

Seems like there are two smaller galaxies in the bottom right. Does anybody know what those are?

I had the same question, found the answer here: http://sci.esa.int/gaia/58209-gaia-s-first-sky-map/ it says > The two bright objects in the lower right of the image are the Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way. Other nearby galaxies are also visible, most notably Andromeda (also known as M31), the largest galactic neighbour to the Milky Way, in the lower left of the image. Below Andromeda is its satellite, the Triangulum galaxy (M33).

T'was back in December 2008, I applied for a university sideways move to a job analysing the data from the yet to be launched Gaia probe. Turns out I was over-qualified (which was their way of saying that the university was already paying me more than they were willing to pay for that position), and they recommended I apply for a position analysing data for the Planck probe instead. Went to that interview too, where I was told I was underqualified. Every time either of those two probes turns up in the news is a nice trip down memory lane. The engineering involved in building them was quite remarkable, and sifting through the data would have been fun.

I wonder why they couldn't be honest with you? What bad things would happen if they simply told you "we're only able to pay X for this position, take it or leave it"?

Because it was a sideways move (in other words, I was already working for the same university) it would have been illegal for them to lower my pay.

Ironically, them telling me I was underqualified (specifically, I didn't have doctorate) spurred me on to go and get one. I had basically hit the ceiling for a Mr. in a university.

Even if we're talking private companies, many hiring managers prefer to not hire someone who'd be underpaid -- increased turnover is one issue, and there are others.

"There may be 2-3 times more stars in the Milky Way Galaxy than we thought"

Looks like they found the dark matter.

400 Million "new" ones or so. That's absolutely a fantastic result.

> The one billion to be catalogued by Gaia is still only 1% of the Milky Way's total

I mean, wow. We are so tiny.

> The called-for specification was to get to know the brightest objects' coordinates down to an error of just seven micro-arcseconds. This angle is equivalent to the size of a euro coin on the Moon as seen from Earth.

This is quite an impressive feat of engineering!

It's amazing, and completely depressing at the same time. 1% of the stars in 0.00000000001% of all galaxies.

Totally out there thought of the day. I'm hoping some day my atoms are reformed into another human in the much distant future, where we are technologically advanced to get something meaningful out of all of it.

Why don't you see that it's meaningful now? We didn't know about the galaxies only some 100 years ago. Now we know a lot even about how the universe started, read as an example, we will never see most of the first 500 million years, except on some places where the reionization process ended sooner:

https://medium.com/starts-with-a-bang/why-hubble-will-never-...

But we already see in the past all the billions of years: the further the object from us, the older is what we see.

And we see the glow of the Big Bang. In the distant future, much less will be observable.

https://medium.com/starts-with-a-bang/throw-forward-thursday...

"Instead of clusters and superclusters of galaxies, there will be… nothing. Dark energy will take care of that, driving all the other galaxies in the Universe, everything that isn’t bound to our local group, our beyond our visible horizon. Even the closest galaxies to us beyond the local group, like the Virgo Cluster, the Leo triplet, and even the extremely nearby M81 group will have redded out, and will leave no measurable signature behind."

"Even the leftover glow from the Big Bang would be undetectable! What appears now as a 2.725 Kelvin afterglow, with a relatively dense 411 photons-per-cubic centimeter, will look nothing like that 100 billion years from now."

Unfortunately the distance to even the nearest stars, makes travel to them unrealistic in any of our lifetimes. Sure we're getting new observational knowledge, but it's still depressing to think about the scale of the universe.

It would be a lot more depressing if we had already found all there was to find and knew there wasn't anything more...

Considering the Universe is debatably infinite. I don't think we have to worry about that scenario.

There are known limits, "the Limits Of How Far Humanity Can Go In The Universe" no matter which technologies it possesses:

https://medium.com/starts-with-a-bang/the-limits-of-how-far-...

https://www.youtube.com/watch?v=ZL4yYHdDSWs

"Appreciate the view we have today; it’s the greatest one any living creature will ever have of our Universe, exactly as it is."

This isn't new, either. In the early Iron Age we knew a lot about how the universe started, "B'reshit bara elohim..."

And there are more galaxies in the known universe then there are stars in our galaxy.

Yes, there may be more galaxies than stars in our milky way. But almost all of them are extremely far away and we will never have a chance to interact, or even visit them. Worse, the rate they are moving away from our galaxy/local cluster is accelerating. We have a bit time to study those galaxies before they fade into the eternal redshift, but the real interesting stuff, what at least has a decent chance to matter beyond pure curiosity is what Gaia observes.

> We have a bit time to study those galaxies before they fade into the eternal redshift

Just want to point that we do receive light from galaxies that are receding from us faster than the speed of light and always have been.

Until they are so far redshifted that they fade into background noise. And the expansion of the universe is accelerating. We have a bit time to watch this spectacle, but the fate seems it is just our local cluster that will matter, for most of the time while stars generate heat. That is why I am not so keen on emphasising the billions and billions of galaxies. It's only a nice good-bye firework.

Edit: I still think there are much more galaxies in our universe than stars in our milky way: The universe must be bigger than our observable part and there is no reason to believe that it is much different there (read less or no galaxies) than where we happen to be. So the "eternal redshift" already happened for many galaxies (from mutual perspective).

The number of stars in the Milky Way galaxy is about as the same as the number of galaxies - 1e11 to 1e12: http://www.esa.int/Our_Activities/Space_Science/Herschel/How... .

Double-checking: https://en.wikipedia.org/wiki/Milky_Way says 2.5e11 ±1.5e11 stars in the Milky Way. https://en.wikipedia.org/wiki/Galaxy says about 1.25e11 galaxies in the observable universe.

That's nearly a mole of stars in total.

I have some questions on the "stellar parallax" illustration.

If I remember correctly the speed of Sun around the milky way is much bigger than the speed of earth around the Sun. So the position of the earth is completely different in June and December, because the sun has moved. So

-> Do the parallax computation works only in one direction ? (perpendicularly to the sun trajectory ?)

-> Does it works for nearest stars because they have roughly the same speed and direction than Sun ?

> they have roughly the same speed and direction than Sun

Are you sure about that?

https://en.wikipedia.org/wiki/Barnard%27s_Star : "The proper motion of Barnard's Star corresponds to a relative lateral speed of 90 km/s. The 10.3 seconds of arc it travels annually amount to a quarter of a degree in a human lifetime, roughly half the angular diameter of the full Moon."

https://en.wikipedia.org/wiki/Alpha_Centauri "All components of Alpha Centauri display significant proper motions against the background sky, similar to the first-magnitude stars Sirius and Arcturus. Over the centuries, this causes the apparent stellar positions to slowly change. Such motions define the high-proper-motion stars"

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