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Comment by soheil | Hacker News Reader

I pick the Milky Way since it's likely no human has ever seen it.

You jest, but the percentage of humans have never seen the Milky Way with their naked eyes, since they live in or around some sort of city. Light pollution is so widespread that most people alive today have never experienced a truly clear sky.

Anecdotally, the first time I saw the Milky Way with my bare eyes was almost a religious experience.

Isn’t that exaggerated? I mean, light pollution is a thing, but you can easily escape it if you go at reasonable distance from most towns. It doesn’t require to go into the middle of a desert nor demand an excessive cost.

I think the expression you might be looking for is "a contemplative state".

I don’t think it’s exaggerated at all. Many urban dwellers in the US have never overnighted outside city limits. Camping trips and boy/girl scouts and such aren’t even on the radar. I would say that a significant number of people don’t even understand what the night sky looks like—to them, it’s always been a gray/orange fog with a few dozen faint stars. So there’s not even a concept of what they’re missing.

You're so right. I grew up a couple of miles outside a small Midwest city, and then that was enough to hide a lot of the dim stars. Being in the middle of the Pacific ocean at night, and caught been the phosphorescent bacteria churned up behind us and the Milky Way above us was the most spiritual experience of my life. It was so beautiful that I cried.

I took my kid camping in Joshua Tree last year and we spent a lot of time just taking in all the stars and waving at the occasional satellite zipping overhead. If someone's never done this, I cannot possibly over-recommend it.

Something that's been on my mind forever is, given the amount of photos and other data that's been gathered, if we put it all together with a really powerful computer/algorithm, could we generate a simulated picture of the Milky Way as if seen face on, at a few million light years above? Without it just being a generic galaxy.

I think I remember reading about the latest and greatest direct measurement of stellar distances, and how it's a huge number of stars but a very small radius relative to our whole galaxy. And of course there's all the dust and stuff in the way of viewing. So my belief is that what I want is impossible, but I think I have heard that we're fairly certain our galaxy is a barred spiral?

The latest and greatest survey at that range is probably GAIA, which has a very important data release coming soon I think. (Unless it came out and I missed it)

I have no sense of how much of the Galaxy it maps, but I know it's crucial for distance ladder measures because it will constrain the distance to the large Magellanic cloud better than ever before, so I think it's measuring individual stars at that range

Doing astrometry and proper motion measurements for more stars than ever before, very cool

We've had the early data release 3 from Gaia, There are several others incoming. The distances are good up to ~ few kpc which is ~ 1% of the size of the galaxy. And it sees ~1% of stars in the Galaxy

A few kpc is much more than 1% the size of the Milky Way. For reference, the Sun is about 8 kpc from the Galactic Center.

For bright stars, Gaia can measure parallaxes (and therefore distances) throughout a sizeable fraction of the Milky Way. But the fainter the star is, the closer it has to be for Gaia to measure its parallax. The other issue is that there's dust that obscures much of the Galaxy, limiting the range that Gaia can see to. If you take all these effects into account, you find that Gaia can "only" measure parallaxes for about 1% of the stars in the Milky Way. Still, that's orders of magnitude more stars than had parallaxes just a few years ago.

1. Can we create a sufficiently powerful telescope that allows us to see our own reflection perhaps from a body of water on a distant planet or at least our image from millions of lightyears ago?

2. Can gravitation lensing work in a daisy chain fashion by having multiple galaxies positioned ever so precisely to cause the light from our galaxy to travel in a semi-circle arc back to us?

1) No

2) Kinda maybe https://physics.stackexchange.com/questions/52167/since-ther...

1. No. We haven’t found large scale curvature of the universe yet. If it’s curved such that you could eventually see yourself from behind, it’s way more than 13 billion light years around.

2. See 1.

I think you answered 2 first. Someone mentioned this link so I just wanted to post it again [0].

Regarding the first question why can't there be a planet let's say in Andromeda with a lake that would reflect back the light from our galaxy? That's only 2.5 million lightyears x 2.

[0] https://physics.stackexchange.com/questions/52167/since-ther...

Oh, oops. I somehow managed to completely misread that question.

Didn't do the calculation, but I don't think you would get any meaningful light back.

I think the problem with doing that is that we've only seen the milky way from one angle (earth + rounding error). The smartest algorithms like the ones that make 3D images from pictures need a lot of pictures from different angles to stitch things together. Maybe if we sent out some deep space probes we could do it, but even then the dust in the Milky way makes it a problem.

It turns out many properties of the Milky Way are still poorly known. We can take what we do know and find galaxies that may match, though.

An early version of this work with a gallery of objects that might match what the Milky Way looks like (given all the observational uncertainties) is discussed at https://www.news.pitt.edu/milkywaycolor .

A couple of the resulting scientific papers are at https://ui.adsabs.harvard.edu/abs/2015ApJ...809...96L/abstra... and https://ui.adsabs.harvard.edu/abs/2016ApJ...833..220L/abstra... and

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