General Question

mattbrowne's avatar

When was the first time you asked yourself why it's dark at night despite all the trillions of stars out there?

Asked by mattbrowne (31588points) June 6th, 2009

From Wikipedia: In astrophysics and physical cosmology, Olbers’ paradox, is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe.

Watch this wonderfully animated GIF file:

http://en.wikipedia.org/wiki/File:Olber%27s_Paradox_-_All_Points.gif

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17 Answers

gailcalled's avatar

Have you ever seen a total eclipse of the sun? For a few magical moments the wind picks up, the birds squawk and the stars come out.

I always felt comfortable with Galileo’s discovery and then the issue of the stellar distances. They are points of light because of distance to us and the amount of non-stellar universe between them. Even the nearest galaxy (M 31) is undifferentiated rather than blinding.

Therefore, I never questioned that.

(Link doesn’t work; but thank you for posing the question and then the link, rather than the masses of Wikipedia text.)

mattbrowne's avatar

@gailcalled – Hmm. Could you try this link:

http://en.wikipedia.org/wiki/Olber%27s_paradox

No, I missed the total eclipse of the sun in 1999 and here’s the irony: I live in Germany and it was supposed to be visible, but we were in the US at the time visiting friends. However, later we found out that it was too cloudy in most regions in Germany anyway including the one where we live.

gailcalled's avatar

Nope, still the same “bad title” on the Wikipedia page.

I certainly know about hauling myself to distance places for solar eclipses only to watch it rain.

The one I saw was perfect…rising over the ocean in VA. beach and then becoming eclipsed..March 7, 1970.

mattbrowne's avatar

@gailcalled – Can you type Olbers’ paradox into the Wikipedia search box?

Lupin's avatar

@gailcalled My roommate and I went to Nantucket island to see that one. When it reached totality everyone got quiet and some dogs began barking in the distance. Eerie. It still give me chills. I recently found the 8mm movie I took of the event.

ragingloli's avatar

i don’t see how it is a paradox at all.
take an electric torch and shine on another person. then slowly move away. the person will gradually be less illuminated. light loses intensity with distance, because it spreads out.

hungryhungryhortence's avatar

I’ve never questioned it before (that I can remember). My grandfather used to take me up onto rooftops at night to look at the sky, sometimes we’d drive out into open country or during our road trips we’d lie on the hood of the car and compare how the sky without the distraction of town or city lights.

mattbrowne's avatar

@ragingloli – Trouble is there are other persons with torches as well.

backinflow's avatar

the first time was 5 seconds ago

ragingloli's avatar

@mattbrowne
all that means is that they have to be farther away to achieve the same lack of illumination.
and stars are very very very far away.
If you were to look at the sun from pluto, you would have trouble distinguishing the sun from any other star in the sky.

Lupin's avatar

Doesn’t dust and other absorbent media out there also reduce the light in addition to the 1/d^2 power drop?

cyn's avatar

the stars are far far away….

Bluefreedom's avatar

I’ve never asked myself that question actually. Instead, whenever I see the first star of each night, I have an overwhelming and undeniable urge to recite poetry:

Star Light Star bright,
The first star I see tonight,
I wish I may, I wish I might,
Have the wish I wish tonight.

mattbrowne's avatar

@ragingloli – Sorry, but this doesn’t explain it. There are more and more stars the further you go. So maybe you’ve never asked yourself this question. Try again and wait for the wow effect!

gailcalled's avatar

First star at night is often Venus.

The sun from Pluto would be less bright than from earth but still much brighter than Sirius, the brightest star.

mattbrowne's avatar

@gailcalled – It’d be interesting to calculate how far out we’d have to go for the Sun to be equally bright as Sirius seen from Earth. Eris? Beyond the Kuiper Belt?

gailcalled's avatar

@mattbrowne : Let me think for a moment. (You do the math, please.;>) Apparent magnitude of -20 is really bright.

Source

…. for someone on Pluto, the Sun would only be about 1/1400 as bright as the Sun when viewed from Earth. It would seem that an astronaut would need a good pair of binoculars just to see old Sol.

But even something 1/1400 as bright as the Sun is still pretty darn bright. Celestial objects are assigned apparent magnitudes that give us a relative sense of their brightness…. A magnitude difference of 15 amounts to a difference in brightness of 1 million. Using this scale, from Pluto the Sun would have a magnitude of approximately -20.

From Earth, the Sun has a magnitude of -26.7, whereas, the brightest star we can see in the Northern Hemisphere, Sirius, has a magnitude of -1.4 and Venus can attain a magnitude of -4. Thus, the Sun from Pluto would be more than a million times brighter than Venus looks like from Earth and 1,000 times brighter than our full moon!”

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