Apparent size of Andromeda galaxy compared to the Moon | Hacker News Reader

Apparent size of Andromeda galaxy compared to the Moon

astronomy.stackexchange.com

348 pointssieste128 comments

I made that image![1]. And this is not the first time it's been on the front page of HN either[2]. So I'd like to share some context that I've not mentioned elsewhere before.

My father died from alcoholism in 2004. He made his living writing software (hence why I do too, and why I enjoy HN). But he also, for a short time, taught Astronomy evening classes. I've always felt short-changed by the emotional absence and traumatic passing of my male parent. But the continued virality of this image has been some sort of magical glimmer from the depths of the universe that it was still his shoulders that I stood on in order to reach where I am today. Maybe it was the glint in his eyes every time he showed me the latest APOD image[3], and the deep love with which he would explain their contexts. I made this composite image of Andromeda and the moon precisely because of that extra commentary, or rather I should say, extra love, of the night sky that my father gave me. Seeing it here, sparkling in the "night sky" of the HN front page stirs the same kind of wonder I sometimes feel catching those million year old specks of light above my head. Reminding me that though the universe is mostly cold and dark that doesn't diminish its warmth and brightness.

1. https://www.reddit.com/r/spaceporn/comments/1u0dxs/andromeda...

2. https://news.ycombinator.com/item?id=22992384

3. https://apod.nasa.gov/apod/astropix.html

Thank you! For making the image, and sharing story behind it

Very good image, thanks for sharing it out there. Not even JWST could do that ha ha :-)

Do you mind if I ask: is that image CC licensed at all?

Thank you :-)

The base image is indeed public domain: https://www.flickr.com/photos/srahn/9013096528 But I don't remember where I got the image of Andromeda from. Not that I believe I have any power to claim rights over it, but I've always considered it to be affectively CC licensed.

touching back story, thanks for sharing.

> You should read Nightfall by Isaac Asimov. It's a short story about a planet that has four suns so it is always daytime, except for one night every thousand years.

>> If the stars should appear one night in a thousand years, how would men believe and adore, and preserve for many generations the remembrance of the city of God!

Love that Reddit comment.

https://old.reddit.com/r/spaceporn/comments/1u0dxs/andromeda...

And sadly with 4 suns the orbit would be chaotic and no periodic pattern would exist to be found. Which ruins the premise of the story.

Foundation also fails because human society is chaotic so his psychohistory would never work.

Sometimes it's best just to enjoy the fiction and not over think it too much. I think you have to give them some artistic license.

He wrote both before there was general public awareness that a thing called chaos existed.

True, Poincaré had already worked out that gravity was chaotic. But Asimov was a chemist and so was unlikely to be familiar with that work.

I suspect that Asimov was a better physicist than you.

Someone can be both a better physicist and have a poorer understanding of physics. We have the luxury of time. We can learn about the great discoveries that the great physicist developed from scratch. Just imagine the type of discoveries he would have made if he was born in the late 20th century.

Probably less than he did in this reality.

We haven't discovered much, really.

Relevant to this discussion is that between then and now we have discovered a lot about the ubiquity of chaotic systems, and their practical consequences for forecasting.

Chaotic systems were well-known and had been studied in great detail before Asimov was born. He knew about chaotic systems, as anyone with a high-school level mathematics or physics education would have.

Reference needed supporting your claim that it was so widely understood.

My strong impression is that it wasn't until James Gleick published Chaos: Making a New Science in the 1980s that there was a popular treatment available to the lay public. And that book lays out many examples from the early 1960s at people like Edward Lorenz and Yoshisuke Ueda being surprised at extreme sensitivity to initial conditions, and having their discoveries met by doubt and disbelief. Which indicates pre-1960, only a fairly niche audience was strongly aware of chaos theory among either the lay public or scientists.

Okay, have you heard of Henri Poincaré? Because he studied chaos in the 1880s, and anyone with a high-school level grasp of mathematics would know that.

Hinged pendulums which exhibit chaotic behaviour have been a popular demonstration for about 100 years.

Just because the first pop-sci glossy coffee table book to mention chaos wasn't published until the 1980s, it doesn't mean that anyone who studied maths or physics - particularly at a level that would allow them to teach at a university - would not have even heard of chaos theory.

Given that I pointed out Poincaré in https://news.ycombinator.com/item?id=33285644 I clearly have heard of him.

The double pendulum actually goes back further. It was studied in the 1700s. But what could be done with them was limited until computer simulations were available - in the 1960s. The same time that chaos as a subject became a thing.

And your claim that chaos was something that anyone with a high-school grasp of mathematics would have known about in the 1940s is supported on nothing more than your say-so. And directly contradicts multiple reports of working scientists in the 1960s. For example from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202497/ you find:

Lorenz considered, as did many mathematicians of his time, that a small variation at the start of a calculation would Induce a small difference In the result, of the order of magnitude of the initial variation. This was obviously not the case, and all scientists are now familiar with this fact.

In other words people with PhD in directly relevant fields in the 1960s actually were ignorant of basic facts about chaos theory that are now known to every high school student. Even the phrase we all have heard to capture it, namely "the butterfly effect", dates from the 1970s.

And with that, I'm done. You're providing assertions that run counter to my citations, and are refusing to accept information that I cited about what was and was not general knowledge. There is no point in continuing.

That (and the other comments) just seems pointlessly argumentative.

> Asimov was a chemist and so was unlikely to be familiar with that work.

The premise is true but the conclusion does not follow. Asimov was one of the most prolific authors of popular science books including astronomy, cosmology, physics, etc. It's entirely plausible that he was familiar with chaos.

When the book was written in 1941, he was a graduate student. His attempts to popularize science were many years in the future. Lorenz's work with chaos and powerful enough computers to enable it were still 20 years in the future. Terms such as "the butterfly effect" did not get introduced for another decade.

It was unlikely that he was unfamiliar with chaos. Doubly so given that the first prediction of what we now call chaos theory is that we won't see the periodic behavior that is a fundamental premise of the story.

You must be fun at sci-fi conventions afterparties

Sounds like you would enjoy the Three Body Problem, if you haven't already read it (which I expect you have).

First book was great. Lost my ability to keep track of names as a non-Chinese speaker on the second one, for some reason.

same here. Not just the names, but IMO even the storylines get pretty convoluted by the second book. Game of thrones number of story branches, but French New Wave thickness of plots.

For me its even the plot. I mean scientific parts are very fine, but human parts are meh at best.

[minor spoilers below] It is practically a racist book where everybody non-chinese is evil, conspires to harm chinese in a comical villain fashion, should be killed, and is killed eventually. I get that 100 years ago similar literature was OK in the west too, but we moved our societies quite a bit since then.

> I get that 100 years ago similar literature was OK in the west too, but we moved our societies quite a bit since then.

100 years ago? Today, the ratio of militaristic "America F** Yeah!" sci-fi vs every other language is probably 100/1 and the amount of times the Chinese and Russian are the ones portrayed as evil in that literature is literally orders of magnitude greater. Are those also racist books?

> Chinese and Russian are the ones portrayed as evil in that literature

I've not noticed that. OTOH as a brit, the number of times I see us portrayed in American films as cold, unemotion, untrustworthy, manipulative, I could go on...

Edit: on reflection that does seem to have died down a bit in recent years.

I don’t think this is true at all. Especially the parts about the cultural revolution made me wonder how this was ever published in China at all.

It was kind of refreshing to have someone else be the villain for once.

Glad I’m not alone. I really want to love this series of books but I’m never excited about reading it because i find it too hard to follow.

It's called science fiction for a reason ;)

Sure, but the science is also there for a reason

Akshually...

> with 4 suns the orbit would be chaotic and no periodic pattern would exist to be found

This is only true for certain configurations of N-body systems. The solar system is an N-body system with periodic patterns, at least at a human timescale.

This is true as long as at least 3 of the bodies have comparable masses, or the timescale is long enough.

The periodic behavior of the Solar System is because 99.86% of its mass is in the Sun. So every other interaction is a small rounding error. And therefore the Solar System is chaotic but with a long Lyapunov time - estimated at about 5 million years.

The Wikipedia page on three body problem shows many periodic patterns.

There appear to be stable configurations for the 4 body problem too, even if the 4 masses are similar.

Its not fair to say there's no periodic pattern possible with 4 suns, then, even though most initial configurations might lead to chaotic behavior.

Don't worry, XKCD has you covered!

https://xkcd.com/2623/

A few details might need to be tweaked, but neither the story nor chaos theory is fundamentally incompatible with a solar system where night happens every few thousand years on average, is unpredictable over long timescales but can be predicted years or decades in advance using 20th century technology.

The idea of the story? Of course.

But the actual story as told? The regularity of civilization collapse was rather central to the people in the story.

> Foundation also fails because ...

The Mule shows Asimov knew psychohistory would never work on its own.

The recorded prediction of the crisis with the independent traders didn't happen, because of The Mule. This was the Era of Deviations, and it took centuries for the Second Foundation to manipulate things back to the Sheldon Plan.

And of course, the influence of R. Daneel Olivaw across nearly 20,000 years, guided by the Zeroth Law of Robotics.

> Foundation also fails because human society is chaotic so his psychohistory would never work.

Ant's are also chaotic as individuals, but if you get enough of them you can model them easily. We can already semi-predict global human behaviour; population graphs, economic charts, actions of specific demographics. When enough humans walk down a street, you can model their flow with fluid dynamics.

Psychohistory wasn't a study of the intricacies of the human condition, it was an iterative model that follows general trends. It just happened to be sophisticated enough to predict thousands of years into the future and to allow for outliers.

The whole weather vs climate argument.

However when you look back over the last 200 years, one of the striking features is that every 10 years or so people are concerned about something very different than they were before, and which was often a result of a crisis that few were ready for. For example nobody in the Clinton era would have predicted 9/11. The 2008 financial crisis caught most of us by surprise. COVID was on nobody's radar. Nor did we expect Russia to launch a full-scale invasion of Ukraine (nor to lose if they did). And so on.

I can't tell you what we'll all be worried about in 2030. It won't be COVID or Ukraine. My guesses include financial collapse, climate change, the collapse of Russia, the invasion of Taiwan, and so on. But odds are that it will be none of those things.

     COVID was on nobody's radar

Pandemics have absolutely been on the radar. We already had plenty of hints: SARS, swine flu, heck the great influenza pandemics of the past. Increasing total population, increasing population density, and increased travel have been obvious risk factors for as long as anybody has talked about this stuff.

    one of the striking features is that every 10 years or so

There are multiple things every decade. In the past 10 years we've had the pandemic, something resembling a coup in America, war in Europe, a nuclear disaster, accelerated global warming, and so on.

Trying to fit it into a shallow truism like "every 10 years, it's something!" is some kind of magical lazy thinking, right up with "it takes 10,000 hours to master a thing!" and "celebrities always die in threes!"

It wasn't stated as a truism. It was stated as a practical limit to our ability to naively project the future forward. And therefore the centuries long sweep of Foundation fails.

This is lampshaded a bit in the novel length version of the story, where the theory of universal gravitation was invented only recently because the complexity of motion of the bodies involved made it incredibly non-obvious.

Also, there are six suns.

> a planet that has four suns

I remembered five; Wikipedia says six, two of which form a binary star system (https://en.wikipedia.org/wiki/Nightfall_(Asimov_novelette_an...)

I also remember reading that such a system can exist, but can’t find a reference. It’s probably not that surprising, though, given that the proposed system has one large star and five minor ones, making it similar to a system with one star and five giant planets. Putting a planet in in such a way that it only has a night every 2000 years may be the only tricky part (giving it a much smaller orbit than the minor stars would help avoiding nights, but giving it a single moon that can cause nights once every 2000 years?)

A bit tangential, but here we go.

A place where there's daytime all the time, except every once in a while is quite close to us. It's the Moon.

If you live on the near side of the Moon, then you always see the Earth hanging there in the sky in the same spot every day. It does not rise and it does not set, it just stays in place. But it goes through phases. New Earth, Crescent Earth, Half Earth, etc.

The Sun does rise and set. A "day" on the moon is half a month long. When the Sun is in the sky, the Earth is at most in "half Earth" phase. When it's nighttime though, the Earth is at least "half Earth".

And seen from the Moon, the Earth is big. Very big. Just take the Andromeda in the picture, and make it a disk. That's how big. (Actually about 15% bigger).

The Earth is also bright. Much brighter than we see the Moon on a bright night. Earth's albedo is about 3 times higher than Moon's. All in all, at "full Earth", you would receive about 40 times more light that we get here from the Moon when it's full.

In other words, when the Sun is not in the sky, you get enough light from the Earth to see around. The closer to "midnight" the more light you get, because the Earth is closer to "full Earth" phase.

Of course, when you have a solar eclipse, you stop seeing light from either the Sun or the Earth. Here on Earth, solar eclipses are quite short. The moment of full eclipse is fleeting, generally it's 3 minutes or less. On the Moon, because the Earth is so much bigger in the sky, the eclipse is long. Of course, we knew that from here: when it's a solar eclipse on the Moon, it's a lunar eclipse on Earth, and that takes hours.

It's not completely dark on the Moon when there's a solar eclipse.

It's not completely dark here either. Because of the Sun's corona. The apparent diameter of the sun is virtually identical with the diameter of the Moon as seen from the Earth, but the Sun's corona extends a bit further, so we get to see it during total eclipse.

But on the Moon, the Earth is so large that the Sun and the corona are fully obscured during total solar eclipse. What you will see instead is the Earth atmosphere. Very thin, impossibly thin, you will not be able to perceive its thikness. It will just look like a one-dimensional line. A part of it will be very, very bright. And very red. It will be a very bright, very large and very red circle in the sky.

You will also see the inner planets, Mercury and Venus. Normally you can't see them on the Moon, but during a full solar eclipse they'll be quite close to that bright circle, and they'll be very bright themselves.

And what a glory the Milky Way will be at that time. And if you are lucky, you'll see that very oblong shape that's the Andromeda. Somewhat faint, but still, much brighter than any of us here on Earth would perceive it.

I am personally convinced that the close correlation of the perceived sizes of the Sun and Moon, and the spectacularity of eclipses, drove mankind to study them and thence to measure intangible things. Next step: progress!

What a coincidence! I'm currently reading Nightfall.

I've used this photo to show friends the size comparison at star-parties! It's a great educational photo but also just beautiful.

Beautiful (and well written) story, thanks for sharing.

A small counterpoint. The pain of losing someone is the cost of having someone decent and good, for the time you had with them. Some of us have never felt that because we've never had someone decent to lose (though I will be glad; feel the world a better place; when one of my parents dies, and mainly indifferent when the other goes, reflecting his apparent indifference to me. Sometimes being left alone is the better option).

To all those with normal lives, make sure you count your blessings now, now when it's too late.

Sorry for weird post, but I had to say it.

Perhaps though, people should not go through life always acutely aware of what they've got. Perhaps in some ways it's better to feel your loved ones' presence but not think about it, sort of take it for granted, feel the warmth of their presence but not think about it. I don't know. Anyway, I'm glad you had him.

BTW absolutely love the pic! I just wish I had the eyesight to see it. In fact In london, I wish I could just see the stars at all...

Saying "enjoy it while it lasts" serves no purpose other than to blunt a person's enjoyment of the the thing. They will already suffer when the the thing goes away...why remind them of their future suffering, causing double the suffering? If one person has a pleasant 15 minute call with their father as a result of reading this thread, but 30 people get depressed or anxious about not having visited their parents for too long due to the normal circumstances of life, there is a net loss.

> Saying "enjoy it while it lasts" serves no purpose other than to blunt a person's enjoyment of the the thing

Does it blunt it, or make you realise what you have while you have it, and value it the more? Or are you right and I acknowledged that possibility in my pentultimate paragraph?

I hear a lot of regrets about people no longer there, I hear very little of people saying how lucky they are with their partner/parents/others. I just don't know.

If you're concerned about net misery, you probably should have refrained from posting like this.

Your awesome, thank you for sharing this comment and the image you created with the world. As someone who has struggled with a similar family history with my own father, I appreciate and am thankful for the humanity you have shared. We are all better for it. Thank you.

Thank you. I'm very glad to know that it resonated with somebody else with a similar family history <3

This (or some sort of very similar comparison) prompted me to figure out how to locate Andromeda. And I could not see anything, So I bought a nice pair of binoculars, and perhaps I could see something, but it was impossible to tell for sure. until I went camping in Arizona, I was looking at the stars, I remembered how to find Andromeda, remembered my binoculars. everything had came together and there it was! it looked like a blue mist.

But really it was a nearly spiritual experience. Out in the cold Arizona desert, more stars than I have ever seen in my life and you bring up a pair of binoculars to what looks like an empty area of sky and it too is full of stars, And there is this blue mist, the furthest thing you can see with the naked eye(at least with better eyes than mine) with billions and billions of stars contained within. I don't know, but you feel stuff under those circumstances.

I often recommend to beginning sky-watchers that they try looking at the night sky with a large pair of binoculars (look for large objective-lenses and not too much magnification) rather than a telescope.

The nebulae and larger Messier objects are beautiful and approachable with bright handheld optics.

A small bit of advice from me: consider the weight of the binoculars when buying them. They can be too heavy to hold for more than a minute - especially large ones made for astronomy. You will either want a tripod (which is inconvenient to carry around and set up), or you’d want the binoculars to be smaller in size.

Or you can buy image stabilizing binoculars which mechanically keep the image steady in your view despite the slight motion of your hands.

I didn't know this was a thing.

https://en.m.wikipedia.org/wiki/Image-stabilized_binoculars

For any practical viewing with binoculars you do need a good tripod - otherwise instead of stars you’ll see shaky lines. Unlike daytime viewing your eye/brain doesn’t eliminate small shakes, or maybe it’s just harder to stabilize binoculars when looking up.

There's something special about the actual photons hitting your eyeball, instead of just looking at a picture.

I just about fell on my arse the first time I saw Saturn through my telescope, actually looking at it and seeing the rings. Rings, right around a planet, right there. I couldn't see a lot of of detail because it's a fairly small refractor but there it was, a planet with rings.

Rings. Right around a whole fucking planet. Right there for everyone with a couple of hundred quid's worth of glass and aluminium and a reasonable view of the night sky to see. Just, right there in the sky, bright and clear.

I know exactly what you mean. I saw it with a £40 amazon telescope.

You know that weird feeling when you, for whatever reason, take another route from somewhere you know well, find you've arrived at an unusual end of another place you know well. The moment of connection, realisation that these two places are linked in this way.

I felt that, but on a huge level seeing Saturn's rings for the first time. For years outerspace, without me realising, occupied a place in my encyclopedias, books, internet images from NASA. Maybe subconscious me didn't really 'believe' it was actually just above my head this whole time.

Great analogy. Lovely way of thinking about it.

How amazing would it be if it were as bright as in the photo though? We'd probably take it for granted, but at the same time, maybe not always. I'll sometimes marvel at the moon when you can really see its details and three-dimensionality, and that's just a moon. I expect being able to look up and see a whole galaxy with your naked eyes like that would be a pretty incredible experience.

I mean, in Southern Hemisphere you can see ie Large Magellanic Cloud with naked eye, and its by definition another (albeit smaller) galaxy.

I do love astronomy and can stare at starry skies on top of mountains for half a night, but you don't need to buy some crazy equipment to see similar things, just travel a bit (or not if you live there).

I believe mankind would be mentally in a bit better place of all folks that want enjoyed starry nights more often, and maybe grokked a bit what they actually see. Humility and all.

> billions and billions of stars contained within. I don't know, but you feel stuff under those circumstances.

Obligatory link to Gigapixels of Andromeda[1]. There are other Gigapixels of Andromeda videos out there but this one also has the perfect background music.

Crazy how "billions and billions" might be an understatement, looking at how many stars appear after the 2min mark alone. And Andromeda is not even a huge galaxy[2].

1. https://www.youtube.com/watch?v=udAL48P5NJU

2. https://en.wikipedia.org/wiki/List_of_largest_galaxies

If you have good eyesight (or good glasses/contacts prescription), you can see it without binoculars (at least the brighter core of the galaxy). Just don't look directly at it or it disappears, because you don't have rod cells in the middle of your field of view.

It may be obvious and this may be a bit pedantic, but the “actual size” and “size compared to the moon” part is confusing, as comparing the size of two objects is usually comparing two objects at the same scale.

If someone was completely clueless, they would think Andromeda is a teeny tiny galaxy. But it’s actually 110,000 light years wide — quite a bit bigger than the moon. :)

The title show just be something along the lines of “Andromeda in the sky if it were brighter, next to the moon”. Or just “Andromeda if it were brighter”.

I say this because I’ve seen other “X compared to Y” articles on HN (one compared planets and the sun to the moon, where the moon was a pixel), and these are all at-scale comparisons. So I was expecting something similar here from the title.

Andromeda Galaxy is visible at its actual brightness, but it appears much smaller than in that image because only the central area is bright enough to be seen. Thus the "actual size" part. I don't think anyone was going to demand a 100,000 light-year wide image based on that phrasing.

Ok, we've consed "apparent" onto the title above.

Thank you for your cons-cientious moderation!

> as comparing the size of two objects is usually comparing two objects at the same scale.

It is actually quite common to hear that something in the night sky is xFullMoons distant/apart. Of course, that is a relative measurement of area of sky covered from a human's viewpoint while standing on terra firma. It's just a size/distance that is understandable by most people. Telling someone that one object is 3° from another object means nothing. Knowing that the width of the moon is roughly 0.5° means that it is the distance of 6 full moons is more relatable. So in this case, the width of the full moon is the scale

Slight tangent, there are other measurements that make things easier to navigate[0]. The width of your index finger ~1°, the width of 3 fingers ~5°, the full fist ~10°, the width of thumb/pinky fully extended ~25°. Knowing these helps find other objects.

[0]https://www.timeanddate.com/astronomy/measuring-the-sky-by-h...

You'd have no trouble understanding that andromeda is a large number of magnitudes bigger than the moon even if your entire astronomical education was from that Star Wars intro scroller. It's a total non-issue.

What I find surprising (really unexpected!) is how close this "appears bigger than the moon" observation makes our neighbor galaxy: considerably less than 100 "galaxy diameters"! My intuitive understanding of the vastness of space would have expected far more emptiness. (objectively, that's certainly more than made up by the insane amounts of emptiness we already have within each galaxy, but still, so close!)

It's even bigger than that: the diameter of the main galactic disk of Andromeda is 152 000 light years. There are additional stars orbiting the galaxy in a halo with a total diameter 220 000 light years.

In comparison, Earth's moon is very much smaller, with a diameter of less than 1 light year.

For some reason I really enjoy the way you describe the moon as having "a diameter of less than 1 light year.", which is also true of my cat and the shoe I am wearing. And everything else I have ever seen or will experience in my life.

Yeah, I realized that after it was too late to edit. I posted that after a quick Google search — I originally had no idea how big it was, but new it was more the 2x the moon :) — and of course the big “110,000 light years” it returned at the top was the radius, not the diameter.

I once tried to observe Andromeda on a clear night with simple binoculars. The hardest thing was not to shake too much, to get a good view. In the binoculars it was clearly larger than the moon. It appeared like a smudge with a very soft eliptic halo. I was surprised by its size.

Just want to point out that it was only about 100 years ago humans discovered that galaxies exist. Good old Edwin Hubble doing observations from Palomar in a Southern California sky that was still good for seeing.

I believe it was Lemaître who first discovered that! Just in case it matters.

Apparently, there was lively debate prior to it being settle by Lemaître and Hubble. I like the original name of 'island universes'

https://physicsworld.com/a/shapley-curtis-and-the-island-uni...

To be clear, people have discovered galaxies earlier, but didn’t understand their true nature. Hence, the discussed galaxy was first known as “Andromeda Nebula”.

And anyone to anyone sailing on one of those first ships to Australia, the SMC and LMC would have been really obvious in the sky. Sure, they're only dwarf galaxies, but still.

Oh man, if only we could see the deep sky like the cameras do (with long exposures/filters/etc). Space looks so underwhelming in comparison with plain human eyesight -- though it's still cool to see the stars from a dark site. Andromeda is a tiny fuzzy smudge in our eyes.

"I saw a star explode and send out the building blocks of the Universe. Other stars, other planets and eventually other life. A supernova! Creation itself! I was there. I wanted to see it and be part of the moment. And you know how I perceived one of the most glorious events in the universe? With these ridiculous gelatinous orbs in my skull! With eyes designed to perceive only a tiny fraction of the EM spectrum. With ears designed only to hear vibrations in the air. ...

I don't want to be human! I want to see gamma rays! I want to hear X-rays! And I want to - I want to smell dark matter! Do you see the absurdity of what I am? I can't even express these things properly because I have to - I have to conceptualize complex ideas in this stupid limiting spoken language! But I know I want to reach out with something other than these prehensile paws! And feel the wind of a supernova flowing over me!"

That's beautiful. Forgive my ignorance -- what's that from?

Ahh, great quote from Battlestar Galactica.

Please no one offer any more context! Anything else might end up being a spoiler for folks who haven’t had the chance to enjoy it yet :)

Precisely why I left it un-referenced :).

Is it a book, or TV show, or?

It’s from the reboot of the TV show in the early 2000s. An incredible show.

Thanks! Is it similar to Expanse?

If you like anything in the spacefaring sci-fi genre and haven't yet watched the 2000's iteration of Battlestar Galactica, you're in for one hell of a treat.

Be forewarned. It is very difficult to avoid binge-watching the show.

I did like Expanse, but I tried to watch a few of the older Star Trek and/or Star Wars movies (don't remember the difference), and I didn't like them at all.

Looks like you can stream the whole series on Peacock.

Warning! Peacock bizarrely separates the 3 hour long pilot episode (referred to as a 'mini series') from the rest of the series.

Start here: https://www.peacocktv.com/watch-online/tv/battlestar-galacti...

Then go here: https://www.peacocktv.com/watch-online/tv/battlestar-galacti...

It's at the hard sci fi end of the spectrum, compared to Star Trek and Star Wars, but not as hard edged as TE, but get close. They have FTL and artificial gravity, but the space combat portrays pretty decent zero-g manoeuvring and combat tactics. Some of the space battles are among the best ever committed to screen, and the most realistic before TE anyway although some Babylon 5 fans might argue. The CGI was a good generation or two better than B5 though and still looks great.

There is some science fudging for sure, and I have to warn you later on it gets more and more metaphysical and ambiguous. The last season turned some fans off, but it really didn't bother me. I'd have rather is stayed more grounded, but even right to the end the characters and the storytelling carried me through. Some of it's tough watching, a few of the characters really go through the grinder.

I'd highly advise checking some clips on Youtube, and maybe check out the Spacedock channel's analysis of some of the battles.

Arc fleet ship b

The first series or the remake?

> And feel the wind of a supernova flowing over me!"

The wind of a supernova flowing over you would be the end of you and everything around you.

The wind you feel today probably has a meaningful supernova component.

Even the neutrinos from a supernova would be enough. https://what-if.xkcd.com/73/

> How close would you have to be to a supernova to get a lethal dose of neutrino radiation?

> The phrase "lethal dose of neutrino radiation" is a weird one. I had to turn it over in my head a few times after I heard it.

> Only one neutrino will hit you every few years

Ah, the excuse I’ve been looking for.

“Can’t come into work today, was hit by a neutrino this morning. Need to rest up.”

An even better one is proton decay.

Proton decay is theoretically possible but has never been observed. and perhaps somewhere in the vast universe one might have done so... maybe.

So I like to blame it on many of life's unexpected events.

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

"there are about a trillion neutrinos from the Sun passing through it every second."

That's exactly the point, isn't it?

It depends on your physical form and how close you got. With forms like ours yes that’s the point he’s making. In context it makes sense he’s pissed off.

I relate so much to every bit of it. Being a human is not a blessing, but a curse truly absurd one for a conscious being.

I think humans would relate to each other very differently if the stars (Milky Way) were normally visible.

Likewise magnification for bright objects like Saturn. Saturn is usually one of the brightest "stars" in the sky, but it's just a point of light without magnification. Once you add some magnification, it looks like all those photos you've seen of Saturn with the rings. It blows your mind the first time you see it.

If it's less real to see something with an instrument-- are people who need glasses to see blind? :D

It's too bad it isn't brighter. I managed to see most of it one time when I was in an place with 'good seeing' and a very dark sky (150 miles from the nearest city).

I'd been looking at that part of the sky for a long time, and was astonished that something that big had always been there!

These maps may help you to find the nearest dark spots.

US: https://www.go-astronomy.com/dark-sky-sites.php

World: https://blue-marble.de/nightlights/2019

I would like to know if there's estimates for how long it should be before Andromeda gets near enough to be as visible as the moon in plain daylight. (All else being equal.)

A nitpick on the image Andromeda image: when viewed with telescope and in most images you can find online, the core of the galaxy and the region around the core is much brighter than the outer branches, while on the composite image it looks like the core is dimmed to make the outer branches stand out more.

So the actual bright part of the Andromeda, seen with naked eye under dark skies, is much smaller.

I’ve heard it said that the angular size of many astronomical targets is not so small — that the real limit to seeing them is the overall amount of light collected.

But then some basic sense of scale eludes me: 1) isn’t most astronomical stuff insanely far away, to the point that it would have to be cosmically large to take up a medium angular size? 2) the angular “real estate” in the sky is severely limited (4pi solid angle) so wouldn’t this get quickly used up such that we could only see a small collection of such objects? (Andromeda is already taking up a huge patch of the night sky!)

Of course these are quantitative questions that can be settled by calculation, but does anyone have relevant intuition to offer?

A 200mm telephoto lens on a DSLR/mirrorless on a tripod can take a passable photo of Andromeda from the bay area with a bit of technical technique (well perhaps not in the most light polluted parts,...).

The key to doing it with nothing other than a tripod is merging a lot of relatively short exposures (e.g. a half second) to avoid blurring the image.

Likewise, a fast telephoto w/ live view on a modern camera is an interesting alternative to binoculars-- especially because image stabilization is common on such devices while IS binoculars are a pretty niche thing. (Obviously binoculars are less expensive, but if you already have an expensive camera...)

The apparent size of the Andromeda galaxy (M31) is 3.167 square degrees [1], and the angular diameter of Moon ranges from 29.3 to 34.1 arcminutes [2]. Using area = πr², the apparent size of Moon ranges from 0.1873 to 0.2537 square degrees. Hence M31 should appear to be roughly 12.5 to 16.9 times the size of Moon.

[1] https://en.wikipedia.org/wiki/Andromeda_Galaxy

[2] https://en.wikipedia.org/wiki/Moon

> Hence M31 should appear...

I don't think square degrees should be used here. People don't visually approximate that way when fitting round objects into a space.

Andromeda 3.167° across its longest length. Moon 0.518°. That's about 6 moons across the longest length.

Andromeda is 1° across the shorter axis. Approximately 2 moons.

So, appearing about 10-12 moons in area maximum, shaving some off at the corners.

I should have mentioned that area = π r² is only an approximation for the moon’s apparent size in square degrees. What we really want to calculate is the surface area of the spherical cap (on a unit sphere) with the same angular diameter as the moon. A formula for that is 2π(1 – cos r) [1], where r again is the radius of the moon in degrees. In this case, the two formulas give the same result to four significant digits (e.g. [2]).

[1] https://en.m.wikipedia.org/wiki/Spherical_cap

[2] http://www.wolframalpha.com/input/?i=2pi%281-cos%5B%2834.1%2...

Fun classics for star lovers:

- The three body problem

- The hitchhiker’s guide to the galaxy

Aahh, it's coming right at us!!

The image of M31 in the sky reminded me of that StarTrek DS9 wormwhole. How's going there, Cmdr Sisko?

I do agree that without the myriad of stars from our Milky Way the M31 looks very much pasted in.

ignoring actual size, what is the APPARENT size of the object from the same observers point of view, if they could "see" all the fainter magnitude stars which make it up?

thats what this shows. the arc of vision the moon covers, against the arc of vision the galaxy covers, for the same observer, if they are drawn "together"

its right there in the title. Apparent size, is about what things "appear" to be to you, the observer.

Begs the question - if everything was brighter what would be the biggest object - excluding solar system and milky way.

Quasar, Pulsars, Filaments...

Which animal has eyes best biologically tuned to star gaze? And when cam I get that transplant.

i saw a similar image in a documentary video. i was so impressed by it that i took a screenshot, intending to look up more about that some time. looks like i don't have to do that anymore because HN brought it to me.

I got confused with the term "size compared to moon".

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