What are the demographics of stars visible to the naked eye?

https://physics.stackexchange.com/questions/79954/what-are-the-demographics-of-stars-visible-to-the-naked-eye/105509#105509

by r721 • 3 years ago

54 41 3 years ago

physics.stackexchange.com

DoreenMichele3• 3 years ago

The actual question:

Of the stars that can be seen with the naked eye, what are the distributions of each type? For example, how many are main sequence? how many are Super Red giants/white dwarfs/neutron stars...etc. What's the distribution by mass and distance?

Posting it here because that's not what I thought was meant by demographics.

throwbadubadu3• 3 years ago

But what did you expect?

DoreenMichele3• 3 years ago

I thought it might be a question about light pollution. Like "Given the spread of light pollution, how many people can still see the stars and where are they?"

Something like that.

chongli2• 3 years ago

Demographics implies a study about people. The word comes from Greek: “demos” meaning “ordinary citizens or common people” and “graphia” meaning “writing, drawing, description.”

None of this relates whatsoever to populations of stars, which would more aptly be described as having a distribution. So a better way to write the title would’ve been:

“What is the distribution of stars visible to the naked eye?”

zokier• 3 years ago

Not OP, but I was thinking of question I was pondering few days ago: what is the distribution of people vs bortle scale, i.e. what percentage of population live in area where they can see X stars

dotancohen• 3 years ago

Thank you. Perhaps the term "Astrographics" would have been more fitting. This is _exactly_ how words are coined.

detrites2• 3 years ago

I've tried but cannot come up with another way to interpret it. Do you actually have one?

mc32• 3 years ago

Can’t they use ‘characteristics’?

kupopuffs• 3 years ago

Graphs of (quantitative) Qualities? Relationships? A thesaurus? A metaphor? Your imagination?

DoreenMichele3• 3 years ago

https://news.ycombinator.com/item?id=35118130

_a_a_a_• 3 years ago

-> What are the types (or categories) of stars visible to the naked eye?

layer82• 3 years ago

Number and size of alien civilizations around those stars. ;)

layer82• 3 years ago

We talk about “populations” of stars, so “demographics” isn’t entirely inappropriate. I agree the title is still a bit confusing.

sinuhe692• 3 years ago

Yeah, as a non-native speaker, I was a bit confused about “demographics” as well. What did I expect? Nothing. It’s only felt “off” with stars and demographics. A “characteristics” or distribution on the other hand would click immediately. (If we have to nitpick about the title ;) )

peyton• 3 years ago

Demographics means distribution of population characteristics. Made sense to me as a native speaker.

actually_a_dog• 3 years ago

That histogram is one of the most perfect real world lognormal distributions I've ever seen.

HervalFreire• 3 years ago

It tends to get more "perfect" as samples increase. For stars there are ALOT of samples.

delta_p_delta_x• 3 years ago

It's a fairly straightforward conclusion that most visible stars are more massive than the Sun. Star mass directly affects the fusion reaction rates at the core, which in turn directly affects the luminosity and the lifetime of the star.

The brightest stars can even shine through dust clouds (or simply emit enough radiation to ionise and dissipate them altogether).

(Space) telescopes can see far dimmer magnitudes than can the human eye at sea level, so more Sun-like stars and red dwarfs show up considerably more easily, given these star types (K and M types) emit strongly in the infrared, which the Earth itself blots out).

fsckboy• 3 years ago

It's a fairly straightforward conclusion that most visible stars are more massive than the Sun.

I can imagine that scientists have figured out accurate ways to measure the "actual" brightness of stars and including our sun, and maybe in retrospect using some simple insights and tricks, but it's not obviously straightforward at all.

Let's hypothesize that our sun is the most massive star in the galaxy, and what we look at in the sky are the rest of the stars in decreasing order of size, with the largest the most visible. How is it straightforward to conclude that that's not true? And are we declaring Newton's accomplishments straightforward?

kfrzcode2• 3 years ago

Mass spectrometry, classical physics, radio spectrum wizardry, and a whole lot of signals theory

bank-error3• 3 years ago

We don’t know. That’s the hypothesis aspect of Scientia.

Our current working hypothesis(es) and theories have not been invalidated so far and thus, they depict the most accurate model we have.

But it’s just a model: data that we get artists to turn into pretty “space” pictures.

If the public had a real understanding of astronomy and space exploration it would neither be seen as interesting or worth funding.

hotpotamus• 3 years ago

The work that made Hubble famous was built on a slightly earlier discovery by Henrietta Leavitt that variable stars had a relationship between their absolute brightness and their period[0]. These were the early "standard candles" that Hubble used to start sorting out distances to objects within our galaxy and when he first realized that the Andromeda Galaxy is not local to us, but its own separate galaxy. Things have gotten on a lot since then, but the basics of how it was done are extremely approachable, astronomy 101 stuff.

[0]https://en.wikipedia.org/wiki/Period-luminosity_relation

twawaaay• 3 years ago

I can imagine that scientists have figured out accurate ways to measure the "actual" brightness of stars

Sure. This is actually pretty simple.

Stars visible with naked eye are relatively close to us. We can measure parallax (https://en.wikipedia.org/wiki/Stellar_parallax) and this gives you the distance to the star directly. Once you know the apparent brightness and the distance you can calculate the actual brightness.

"The Hubble telescope WFC3 now has a precision of 20 to 40 microarcseconds, enabling reliable distance measurements up to 3,066 parsecs (10,000 ly) for a small number of stars."

Vast majority of visible stars fall within couple thousand light years, the only ones that are further are extremely bright, extremely rare and extremely short lived.

01acheru• 3 years ago

Anyone knows which stars are the "outliers" in the first diagram? (the ones in the top-left and far right of it)

sinuhe692• 3 years ago

On the first diagram, the y-axis is the absolute brightness of the stars in the visible spectrum (V) and the x-axis is the difference between magnitude in blue (B) and the entire magnitude of the star in visible spectrum (V).

Thus on the left-top we will see super bright stars, all in blue spectrum, super hot blue stars actually. One is R136a1, a super massive blue star with 200 M and a radius of 4.7 millions sun! Although 163000 ly away, it’s still visible because of its super brightness. Those super-hot blue stars are just a momentary capture of quick giants, who is about to transit to other states entirely.

On the right side, we will see bright red giants. A good candidate would be the Garnet Star.

Maursault• 3 years ago

One is R136a1, a super massive blue star with 200 M and a radius of 4.7 millions sun!

R136a1 has 196 solar masses, 42.7 solar radii, and its solar luminosity is 4.7M (4.677M), so it has a radiant flux of ~4.7M suns.

college_physics• 3 years ago

"Visible to the naked eye" is increasingly a fuzzy statement ranging from magnitude 4.0 to 6.0+[0]: Light pollution means that in the environments where most of humanity lives we can see fewer and fewer stars. Nowadays if you see a "star" and it is not visibly moving or blinking, its probably a planet (and those come with very different "demographics" :-)

[0] https://skyandtelescope.org/astronomy-resources/astronomy-qu...

User23• 3 years ago

Light pollution is a real problem that should be taken seriously and mitigated. Nevertheless, you are exaggerating. Many of the more famous constellations such as Orion are naked eye visible in every city I’ve visited.

xenophonf• 3 years ago

I'm surprised none of the answers mention the Bright Star Catalog:

http://tdc-www.harvard.edu/catalogs/bsc5.html

The BSC includes "positions, proper motions, magnitudes, and, usually, spectral types" of 9110 stars visible to the naked eye.

Equally interesting is the WCSTools package, which is a bunch of C code that can find or compute the motion of objects in a given catalog, like the BSC. There's even mention of Perl and Python wrappers for it.

http://tdc-www.harvard.edu/wcstools/index.html

If you search GitHub, you'll find a small handful of projects dedicated to working with WCSTools.