Astronomy Stack Exchange
Astronomy Stack Exchange

Questions tagged [light]

Questions regarding electromagnetic radiation in the visible spectrum.

342 questions
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Can you see the starting and the ending of a light beam passing in the distance?

This question arose to me when I saw a SciFi movie where they shot with laser guns and you clearly could see the dashes of light beams travelling from the shooter to the target. Nonsense of course, reality is much more boring. But I wondered if you…
Pathfinder
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Is there a place in the known universe that there would be no visible light from other stars/galaxies?

Is there a place in the universe where, with the naked eye, you wouldn't see any stars, galaxies or light emitting phenomena? From what I understand at some point into the far future in Earth's location, we wouldn't be able to see anything. Is there…
iMerchant
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Huge galaxies seen from earth

How do we see whole galaxies or even the whole sun? The photons of light travelling from the sun cover a vast distance, so shouldn't we only see the bit that hits the earth and the rest would be missing? The earth is many times smaller than the sun…
Dusia
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Can Doppler shift make colors of two stars at same distance different?

As you know, Doppler effect can change the wavelength of the light. Suppose there are two stars at same distance and same temperature. If one star is receding and the other star is approaching, their colors would look different. What I want to know…
user36437
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What is the farthest point of light that is emitted by a torch?

If I focus my torch into the night sky,what would be the farthest point the light can reach? Recently I looked at the night sky and noticed a light spark moving around the clouds for about 15 min.After observation I jumped into a conclusion that its…
Praveen Kadambari
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Do all stars of a given age and mass have relatively the same emission spectrum?

My understanding is that much of the visible light that we see during the day is given off from the Sun, and that means that most of the colors that we see are dictated by (with the exception of atmospheric effects) the particular wavelengths of…
one stevy boi
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What's the difference of the oldest light and newest light?

Excuse an amateur question, as inspired by this question: "How old is the oldest light visible from Earth?", how to determine the age of light? Does light get old? Does light have characteristic therefore we know this light "A" is different from…
Mishu 米殊
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Light From Sirius

I would like to know how large a telescope's mirror aperture would need to be, that is pointed squarely at Sirius to equal the light intensity at the focus of a 5 inch glass lens of our Sun? I well know that such a telescope is impossible. I am…
Roger H.
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Darkness in Outer Space

I am trying to imagine how dark outer space is. Looking at images of cosmonauts in space proved not very useful, as the exposure makes space look completely dark. Thinking about it, I would imagine an object would be quite well illuminated, being…
user14607
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how did James Bradley discover light aberration?

I do not understand his timing method. James The magnitude of the aberration could be v/c? The speed of earth is about 30km/s. That means the deviation from the real position of a star is about 30/300000 rad =180*3600/3.14159/10000…
questionhang
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Why can't we see the far rims of our galaxy by ordinary light?

I mean what is the relationship between the empty space between stars such that it contains sparse distribution of gas and our our inability to see the rims of our galaxy. I searched too long time to get an answer but I did not get any thing.
yh_2004
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how to assess a periodical signal?

After folding a light curve, we may get some kind of shape. How to tell whether there is a real periodical signal quantifiably? The fluctuation may be small, and the folded shape may not be perfect.
questionhang
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How much photon is still in flight?

Since space is mostly empty, one might first think that the majority of the photons, e.g. emissions from the stars since the beginning of the universe, are still in flight and not absorbed by anything. Is this true? Is there any estimates that the…
user3528438
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Is light bending around my finger?

I was hoping that astronomy enthusiasts/scientists would help me out with a simple question about light. Hold your outstretched hand up to any bright light source (the sun, or even a light bulb) so that the light is completely blocked by at least…
Keith
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Is the colour of a wave from a far galaxy the same for us as for a galaxy which lies between?

Because of the expansion of the universe, light from a far galaxy is redshifted. The expansion of the universe will make the wavelength of light longer. But is the colour of such light the same for us, as for an galaxy which is between us and the…
Marijn
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