
If Andromeda Were Brighter, This is What You’d See (2014) - joubert
https://waitbutwhy.com/2014/06/andromeda-brighter-youd-see.html
======
tombh
I'm the one that made the original composite that set this whole thing off[1]!
By "whole thing" I mean it's been this amazing meme-like recurring wave that's
ebbed and flowed continuously in the 6 years since I made it. It's so
wonderful to see. I'm not even an astronomer, I just used to like looking at
Nasa's Astronomy Picture of the Day[2], which gave me the very simple idea to
paste Andromeda into a picture of the moon. I'd seen a composite of the moon
pasted next to Andromeda on APOD, and just wondered what it would be like the
other way round. Of course my original image has been corrected many times
since then by people with actual astronomy credentials. This is my favourite,
corrected for both size and to be in the true colour spectrum:
[https://i.imgur.com/2pbfvJa.jpg](https://i.imgur.com/2pbfvJa.jpg)

1\.
[https://www.reddit.com/r/spaceporn/comments/1u0dxs/andromeda...](https://www.reddit.com/r/spaceporn/comments/1u0dxs/andromedas_actual_size_if_it_was_brighter/)

2\.
[https://apod.nasa.gov/apod/astropix.html](https://apod.nasa.gov/apod/astropix.html)

~~~
TheOtherHobbes
I'm surprised no one has corrected for relative brightness. This photo would
only be realistic if Andromeda was an incredibly unusual super-bright galaxy,
or if we could see a lot more light.

The former is physically unlikely although we'd see a very bright core if we
lived next to a quasar. But the latter would turn the entire sky into a blaze
of stellar glory. Far more stars would be visible, and we'd also see more
nebulas between them. And other galaxies.

So the entire sky would be much busier. The Moon would be blindingly bright,
the Sun would be unbearable - unless we had HDR eyes and maybe protective
membranes for daylight - and Andromeda wouldn't stand out as much among all
the other sky candy.

~~~
ggus
but we do have HDR eyes, don't we? we perceive light in a logarithmic way, we
should just tune the exponent a bit more

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cthalupa
While the visuals would be stunning, what's interesting to me is how much our
knowledge of the cosmos has advanced in the past 6 years between that article
being written and now.

We now know the Milky Way is probably nearly 200,000 light years across[1].
And that it's not only much larger, but much more massive - probably larger
than Andromeda[2].

When we talk about these collisions being billions of years away, we're also
really only talking about the main portions of the galaxy - all of the
globular clusters are going to start interacting way sooner. We're already
seeing star formation in the Milky Way's globular clusters as a result of
interaction with the Large Magellanic Cloud, even though we're 2.4ish billion
years from the primary collision occurring [3].

Last year NASA also came out with a bunch of images on what the night sky will
look like as the Andromeda collision occurs: [https://kottke.org/19/10/behold-
our-dazzling-night-sky-when-...](https://kottke.org/19/10/behold-our-dazzling-
night-sky-when-the-milky-way-collides-with-andromeda-in-4-billion-years)

1\. [https://www.nbcnews.com/mach/science/milky-way-galaxy-may-
be...](https://www.nbcnews.com/mach/science/milky-way-galaxy-may-be-much-
bigger-we-thought-ncna876966) 2\. [https://www.businessinsider.com/milky-way-
is-much-more-massi...](https://www.businessinsider.com/milky-way-is-much-more-
massive-than-previously-thought-2019-3) 3\.
[https://www.universetoday.com/144556/an-upcoming-impact-
with...](https://www.universetoday.com/144556/an-upcoming-impact-with-the-
magellanic-clouds-is-already-causing-star-formation-in-the-milky-way/)

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nirui
This is one of the thing which made my really sad about been a human - our
lifespan is poorly short.

See, if my lifespan is 4.5 billion years, then I can just sit here and wait
until Andromeda become a daily light show when it finally got close enough.

Look through a live telescope yourself will give you a very VERY different
feeling when compare to look at a picture on NASA website.

I have an amateur telescope, 130EQ. I still remember the feeling it give to me
when the first time it brought Saturn into my view, and then again for
Jupiter, stars and clusters ...

For me, the best way to get over all the unhappiness, anger and depressions,
is to sit down in the pitch dark of the night, setup the telescope and hunting
for the stars.

Sadly I managed to broke it's tripod few years back :(

~~~
mmazing
I also remember the first time I managed to see Saturn through my own
telescope.

It took forever to get it in frame, and I wasn't even sure what I was looking
for until I finally centered it. I knew it was brighter than the other stars
and that it was probably a planet but not sure which one it was.

Finally got it in frame and focused, saw the rings and jumped up and down
exclaiming "it's Saturn, it's Saturn!". I was super excited and kept having to
readjust the telescope because of Earth's rotation as it moved out of frame.

It was great night with my family and they still remember it to this day.

~~~
nirui
I know, right? All that aiming and panning is part of the experience which
makes the fun.

To someone who don't have it before, we're basically looking at a blur dot
slightly larger than a peanut. But when you do it yourself, the memory you'll
receive is priceless.

I strongly recommend everybody try it out when they have chance.

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forgot_my_pwd
It's quite interesting how close galaxies are to one another relative to how
far stars are from one another.

The distance from the Milky Way to Andromeda is only about 25 Milky Ways, but
the distance from the Sun to Alpha Centauri is about 29 million Suns.

~~~
frickinLasers
I think a more apt comparison would be how many solar systems away we are. I
calculate we are only 143-4550 solar systems away, depending on how you define
the solar system (using the orbit of Sedna or Neptune as the radius).

~~~
s1artibartfast
I think you under by 50%.

Also 266,900 earth orbits away

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mmazing
Earth orbits != solar system diameters

~~~
KMag
That's implied by "Also".

Other interpretations of the GP would imply the GP thought 267,000 / 5,000 is
about 1.5. I'm pretty sure the GP isn't making that mistake.

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gdubs
The thing is so wide that light needs to travel 140,000 years (!) to get from
one side to the other. That’s just so hard to wrap my head around. I never
even really considered that our own galaxy is 100,000 light years across.

Think of all the human history that occurred over 100,000 years — that’s how
long it takes for light to go from one side of the Milky Way to another.

~~~
javajosh
Its cool to visualize a little bubble around the Solar System that represents
the 100 or so years we've been emitting radio waves into space. The signal
would be very faint (power falls as 1/r^2) but visually if you zoom out on the
milky way its a _tiny_ little bubble around our system that barely reaches
into our home galaxy. It's a humbling visualization.

~~~
solstice
This fact is used to great comedic effect in a Futurama episode. (S01E12)

~~~
EForEndeavour
And in the first artificial radio transmissions received from outer space in
Carl Sagan's _Contact_ (both the book and movie).

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robbrown451
"And given that it’s 2.5 million light years away, the surprising amount of
sky space Andromeda takes up speaks to just how ridiculously large a 140,000
light year diameter galaxy is."

Well, not really. I mean, that doesn't tell me anything about its hugeness,
because apparent size is based on a ratio. They're making a ratio with light
years on both sides, so they effectively cancel out. 2.5 million / 140,000 is
17.8. So Andromeda is only 17.8 times as far away from us as its diameter.
(which is, to me, a very interesting takeaway)

You could substitute "millimeters" for "light years" and it would appear the
same size, i.e. a 459 foot diameter object that is 8200 feet away would have
the same apparent size as Andromeda.

Not trying to criticize the article, but thought it was an interesting way
they put it.

~~~
unwind
That's of course true, but I think it's a pretty big part of the context that
"the object" is a galaxy, i.e. a collection of approximately 1 trillion
(1,000,000,000,000) _stars_.

It's more or less obvious that such an object cannot be very close, and thus
it's apparent size in our sky really does convey something about its size.

That was my interpretation, at least.

~~~
robbrown451
If you could see the galaxy as brightly as in the photos, there's nothing to
indicate its size, at least not directly. You are saying it can't be close
because it has a trillion stars, and we know stars are big, therefore it is
big, therefore it must be far away, and then back to therefore it is big.
Isn't that kind of circular?

I could imagine ancient people seeing a galaxy that size (if it was bright
enough), and guessing it was a few hundred miles away and under a hundred
miles across.

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henearkr
There should be devices to help make artificial occultation of bright stars...
maybe even glasses? Maybe could it be done with a LCD panel with really tiny
pixels?

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enriquto
Brightness is in the eye of the beholder. I'm sure that animals that have
better eyes than ours must see the whole thing at night.

~~~
mangamadaiyan
No, light pollution puts paid to that. The sight of M31 in truly dark skies -
with naked eyes - is truly awe-inspiring.

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chkaloon
Cool, but how does define the "whole galaxy"? I assume there's not a hard
defined edge. How do you decide what should be made brighter for the effect in
the photo?

~~~
SiempreViernes
It’s just a photoshop composite of some picture of the andromeda scaled to
match the size of the moon, not a well principled simulation of a wide field
survey telescope with otherworldly dynamic range. Don’t worry about it.

~~~
vl
The point of the article is that it’s not scaled, it’s brightened. Angular
sizes are correct.

~~~
mkl
It needed to be scaled to be correct. The moon and Andromeda images were taken
separately, scaled to match each other, and composited together.

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mehrdadn
When the Milky Way collides with Andromeda, approximately how far would the
stars overshoot? And how long would their overshoot distance take to peak?

~~~
dredmorbius
One computer simulation that should give a general notion:

[https://youtube.com/watch?v=4disyKG7XtU](https://youtube.com/watch?v=4disyKG7XtU)

Most stars and matter will become part of the fused galaxy, "Milkomeda" is one
proposed name. Some will be flung int intergallactic space.

The Sun will have entered its white dwarf phase. Earth will either be a
cinder, or have been subsumed by or possibly be nova ejecta of the Sun.

~~~
mehrdadn
Wow, thanks. That's such strange dynamics... their separation seems to follow
a square wave more than a sine wave! Any idea why?

~~~
htfu
This is an entirely uneducated guess, but look closer at the spin over time,
and consider the objects low density. Think timeline of a highly elliptical
orbit, but with energy and work concentrated on angular momentum.

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balnaphone
I believe what they're saying, but in some way it feels unbelievable. The vast
sizes and distances involved are frightening.

~~~
simonh
The scale is so big fo me it's not possible to actually comprehend it. The
distance to the nearest star is so vast I can't get a grip on it mentally.
just one lightyear is unimaginably huge.

So I can only think about interstellar and intergalactic distances relative to
this measure, which itself I can't comprehend.

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perl4ever
I wish they'd drawn an outline around the "fuzzy star" for scale.

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ggm
The history of astronomy, navigation, the Catholic church... Would have been
very different.

