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Why do some electromagnetic waves continue travelling while others disappear?

Electromagnetic radiation will continue to travel until it is absorbed. Some of your wifi signal is escaping to space where it may continue traveling for a very long time. However, the strength of ...
Connor Garcia's user avatar
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17 votes

Why are wavelengths shorter than visible light neglected by new telescopes?

There are some technological issues to solve with putting any large telescope into space - and a space telescope is required at UV wavelengths. It is not possible to optimise such an instrument to ...
ProfRob's user avatar
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15 votes

Why are wavelengths shorter than visible light neglected by new telescopes?

You're correct in that the sharp dropoff is simply because there are very few planned major telescopes operating in the UV range, whereas there are a substantial number planned in the infrared range. ...
HDE 226868's user avatar
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14 votes

Why do some electromagnetic waves continue travelling while others disappear?

Signal-to-noise ratio In addition to what others have said, it is very important to understand the difference between just detecting something and decoding a useful signal from it. The CMB is ...
JohannesD's user avatar
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11 votes

Why do some electromagnetic waves continue travelling while others disappear?

There's higher quantity of atoms in your 20cm wall than there is in the 13.8 billion light-years travelling to the CMB, so the wifi waves hit atoms on their travel. Space has an average density of 5.9 ...
bandybabboon's user avatar
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8 votes
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What objects in the night sky have the narrowest range of visible light

...the narrowest spectrum of visible light... is tough because most process that make electromagnetic radiation either result in broad continua or multiple emission lines. I originally wanted to ...
uhoh's user avatar
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8 votes

Does a gravitational wave loses energy over distance?

tl;dr: Yes. Feynman's beads on a string argument The other answers skirt what I think is the issue that the OP is asking about. In a lossless medium a spherical wave packet itself, caused by a ...
uhoh's user avatar
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5 votes
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Does wavelength affect redshift caused by the metric expansion of space?

Standard cosmological models predicts that the cosmological redshift and the speed of light are wavelength-independent. This result is confirmed observationally e.g. by Ferreras & Trujillo (2016), ...
pela's user avatar
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5 votes

At what wavelengths can black hole Sagittarius A* be observed from Earth?

From Genzel et al. (2010), here's part of Fig. 7.7.1: This is part of the spectral energy distribution of Sagittarius A*, a flot of $\nu$ (frequency) vs. $\nu L_{\nu}$ (frequency times luminosity). ...
HDE 226868's user avatar
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4 votes
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Question about doppler effect

Before I start, let me just say that this topic is vastly more complicated than you've presented and what I will be showing. The trouble here is that ultimately, everything you've done and I will do (...
zephyr's user avatar
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4 votes
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How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

If you have bins of equal log wavelength increment then a velocity shift corresponds directly to a pixel shift. That is the reason for binning in equal log wavelength increments. See this question ...
ProfRob's user avatar
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4 votes

Using emission lines to determine redshift of a quasar

So the two observed lines must be two of the three suggested lines, red-shifted by the same amount. That means the ratio of their wavelengths will be unchanged, so we need two of the suggested lines ...
Steve Linton's user avatar
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4 votes

How to listen to our world from 10,000 light years away?

For more fun, let's posit an experiment 10 000 years from now. I found some forum which provided this data for a transmitter: The Taldom transmitter is a large facility for longwave and shortwave ...
Carl Witthoft's user avatar
4 votes

How to listen to our world from 10,000 light years away?

As the above commentator says, our technology isn't sufficiently sensitive to pick up everyday radio broadcasts from so far away, and even if we could it wouldn't be worth sending them a message. The ...
Michael Walsby's user avatar
4 votes

Can the motion of the phenomena of supermoons be modelled by an harmonic wavefunction?

No. Because gravity is a long range force and everything pulls on everything, whenever you have more than two bodies involved you don't really have simple harmonic motion. In the end, celestial ...
uhoh's user avatar
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4 votes
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Why do we call radio images "maps"? Is it because it is not optical, so therefore not an "image", strictly speaking?

There is no distinction. No matter which wavelength regime you consider, "image" is an adequate and frequently used description. Also for radio, microwaves, sub-mm, IR, UV, and X-rays. The ...
pela's user avatar
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3 votes
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Wien's law gives two different results?

The frequency at which the flux per unit frequency is maximised and the wavelength at which the flux per unit wavelength is maximised do not agree, in the sense that $$\lambda_{\rm max} f_{\rm max,} \...
ProfRob's user avatar
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3 votes

Deep space radiation distribution

If you were in deep space, i,e., a spot somewhere between galaxies, then the night sky would look a lot like the sky seen by astronauts in the ISS, when they look away from both the ecliptic plane ...
eshaya's user avatar
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3 votes
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Wavelengths for observed objects -- emitted or observed?

If the redshift is $z$, then the wavelength of light you observe is at a wavelength that is $1+z$ times longer than the wavelength emitted in the frame of reference of the galaxy. In this case $z=0....
ProfRob's user avatar
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2 votes

Wavelengths for observed objects -- emitted or observed?

The WISE craft (Widefield Infrared Survey Explorer) surveys the sky in 4 wavelength bands; 3.4, 4.6, 12, and 22 $\mu$m. They are only using 3.4 and 4.6 since the coolant ran out. Source: FAQ "...
Rob's user avatar
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2 votes

What wavelengths are used to search for distant solar system objects like KBOs and Oort cloud members?

Virtually all KBO searches use mosaic CCD cameras operating in the visible part of the spectrum, usually with a red filter like SDSS-r' (centered at approx. 622nm SDSS filters) on big (~4m telescopes)....
astrosnapper's user avatar
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2 votes

Wavelengths and bounderies

It would be easier if you could include an example of the kind of image you mean, but I can guess that you're thinking of those drawings where there's a sine wave drawn in space and suggesting that ...
uhoh's user avatar
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2 votes
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Wavelength and radial velocity

$$v_r = c\left( \frac{\lambda - \lambda_0}{\lambda_0}\right),$$ where $\lambda$ is the observed wavelength and $\lambda_0$ is the wavelength at rest. This gives an equivalent velocity with respect to ...
ProfRob's user avatar
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2 votes

How to listen to our world from 10,000 light years away?

The book of Yosif Shklovskii and Carls Sagan, "Inteligent life in the universe" gives a formula for how far a signal could travel and still be detectable by an antenna, which is influenced ...
Alexander Cska's user avatar
2 votes
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Using emission lines to determine redshift of a quasar

Steve Linton answers correctly that the line ratios must be (nearly) identical and hence identifies the two lines as Lyman $\alpha$ and C IV, but it's not true that the two obtained redshifts are ...
pela's user avatar
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2 votes

What are the applications of cross matching astronomical catalogues?

I did work in the 90s on cross-matching optical catalogues with catalogues of X-ray emitting sources. The main reason for doing this was to figure out which object was responsible for the X-ray ...
ProfRob's user avatar
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2 votes

Does a gravitational wave loses energy over distance?

In empty space, just like a light wave, they spread out, becoming less intense as they get further from their source, but never vanishing completely. At some stage the waves from a distant event might ...
Steve Linton's user avatar
  • 10.3k
1 vote

Betelgeuse, placing light bulb so that its apparent brightness is similar to that of Betelgeuse; wavelength where it shines brightest?

The necessary distance for the light bulb depends on the brightness of the light bulb. The necessary brightness of the light bulb depends on the distance to the light bulb. Part One: Only Visible in ...
M. A. Golding's user avatar
1 vote

What are the applications of cross matching astronomical catalogues?

If I’m understanding what you’re asking, then it boils down to two things: resource management and different physics. Let’s say you’re looking at a given variable star. Maybe you just started ...
Justin T's user avatar
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1 vote

Calculate speed of a galaxy with redshift

Redshift: $z=\frac{41}{656}=0.0625$ Speed $v\approx c\cdot z=299792458\cdot 0.0625=1.9\cdot 10^7\ {\rm m/s}$ Best regards.
Albert's user avatar
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