Questions tagged [doppler-effect]

Questions about the change in frequency and wavelength of an electromagnetic wave caused by a non-zero relative velocity of a source relative to the observer.

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Will a circular orbit cause doppler shift?

In a circular orbit, the orbiting body is the same distance from the central body at all times. But since the body is moving, will doppler shift occur from the perspective of the central body?
Astrovis's user avatar
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7 votes
3 answers
647 views

What would be the doppler effect in the a 2.42GHz signal coming from a satellite in orbit around Mars, received on Earth ground station

Say there is a satellite in orbit around Mars, and it sends a signal at such a time that it is more or less behind the Sun. In that case, Mars would be "Occulted" by the Sun. That signal is ...
Astroquest123's user avatar
2 votes
1 answer
86 views

How does doppler shift work for distant stars [duplicate]

I dont understand how you can look at the light from a star and say that it has been doppler shifted. For example a star emits a photon in the wavelength of 500nm and by the time it reaches earth it ...
Moiz khokhar's user avatar
2 votes
1 answer
91 views

Measuring Expansion Rate of Crab Nebula with Radio Spectrum Scan

I am a high school student who is into radio astronomy, and I have the opportunity to use Green Bank’s 20m radio telescope for a practice research project. I would like to use my observations to very ...
Myra's user avatar
  • 21
1 vote
0 answers
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Time average of radial velocities of multiple galaxies

Equation (34) in this paper shows an average radial velocity. The author wrote that the value was obtained by measuring the radial velocities of many galaxies in the cluster of galaxy and by averaging ...
Nownuri's user avatar
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1 answer
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CMB dipole anisotropy maping to earth visualization

I do not see how this dipole anisotropy is due to the motion of the earth (and thus a doppler effect). Does anyone have a visualization of how this maps onto the earth and the motion of the earth such ...
realanswers's user avatar
3 votes
1 answer
123 views

Radial velocity stability to spectrum shift calculation

I am engineer new to Astronomy and am trying to understand spec of an spectrograph (RV stability = 2m/s). There is a note in document saying "RV shift of 2 m/s is equivalent to a shift of the ...
Nirmala's user avatar
  • 33
2 votes
0 answers
173 views

How do I find thermal doppler line broadening for a K Ca II line in a star at 3000K? [closed]

If the wavelength of K Ca II is 393,4 nm and the weight of a calcium atom is 6.66e-26 kg, then how do I find Δλ? This is what I've tried so far:
Samuel Adámek's user avatar
3 votes
1 answer
223 views

Why is cosmological redshift treated as a different phenomenon to doppler redshift? [duplicate]

I understand that the expansion of the universe causes unbound structures to move apart from each other. This means that unbound structures have negative relative momentum due to universal expansion. ...
Alan Gee's user avatar
  • 211
1 vote
0 answers
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Any examples of a gas object temperature from Doppler broadening along one axis turning out to be wrong because velocity spread was not isotropic?

Discussions under Mass of the stellar cluster (not the whole galaxy) lead me to mention that when an actual temperature is inferred from a Doppler-broadened line profile (rather than just a linewidth ...
uhoh's user avatar
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2 votes
0 answers
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How to remove radial velocity effects of an exoplanet from the host star spectra?

I have a spectra of an M dwarf and I would like to remove the Doppler shift effects due to a known exoplanet, with known planetary parameters, from the whole spectra of the star. I have shifted/...
Mukul Kumar's user avatar
8 votes
1 answer
1k views

Why is there no color shift on the photo of the M87 black hole?

Last year, the first photo of a black hole in Messier 87 was published: (Source: EHT) It is quite obvious that about the lower half of the accretion disk is brighter. This question (or rather, the ...
jng224's user avatar
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2 votes
1 answer
145 views

Is there any way to distinguish the doppler redshift from a distant galaxy from the probably much greater cosmological redshift? [duplicate]

Is there any way to distinguish the doppler redshift from a distant galaxy, caused by its initial recessional velocity relative to this galaxy, from the probably much greater, cosmological redshift, ...
ParityViolator's user avatar
1 vote
1 answer
216 views

Intuitive explanation for why the Doppler effect (and red-shift) happens?

I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought: -Waves emitted travel at a constant speed -The source emits a wave -If ...
XXb8's user avatar
  • 201
0 votes
1 answer
74 views

Which redshift is used to determine the Hubbleconstant?

I think they measure cosmological redshift to use in the Law of Hubble-Lemaître together with the distance to calculate $H_0$. Is this correct, or do they use Doppler shift (too)? $H_0$ indicates how ...
PrincepsMaximus's user avatar
2 votes
2 answers
629 views

Is there still a red shift when moving perpendicular to the direction of incidence?

This answer suggests that when there is zero radial velocity... there will be no Doppler shift but it's not likely to be intended as precise and absolute. I remember reading about something like this ...
uhoh's user avatar
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2 votes
1 answer
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Universe expansion

I'm reading the book "The theory of everything". In the second chapter it says the Universe is expanding, and we know this because the measurements made using the Doppler effect of other ...
Juan's user avatar
  • 31
10 votes
3 answers
3k views

Cosmological redshift vs doppler redshift

I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift. He ...
user120112's user avatar
5 votes
3 answers
866 views

How to Distinguish between Temperature and Doppler effect using Black-body radiation?

I understand that the radiation of a body can be described using the curve for black-body radiation. In the sense that a hotter body will be blue shifted and a cooler body will be red shifted. The ...
Marcelo Fonseca's user avatar
0 votes
1 answer
474 views

Doppler Spectroscopy - Finding mass of an exoplanet

An astronomer, T observed the spectrum of a distant star X. The spectral lines were observed to have tiny blueshifts and redshifts regularly with a period of 1.27 years. T concluded that the star is ...
Kunal Gupta's user avatar
5 votes
1 answer
139 views

How are exoplanets with 10,000 day periods discovered with the radial velocity method?

The radial velocity technique has apparently been used to discover exoplanets with extremely long orbital periods of ~10,000 days. For example, see this link: https://exoplanetarchive.ipac.caltech....
user4437416's user avatar
4 votes
1 answer
470 views

Are there any examples where the transverse doppler effect is applied in astronomy?

Are there any astronomical examples where the transverse doppler effect(Horizontal doppler effect) is applied (Derives a meaningful result)?
YYJ's user avatar
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18 votes
3 answers
3k views

Energy loss from Doppler effect

The energy of electromagnetic radiation is related to frequency; higher the frequency, higher the energy level. If electromagnetic waves have lower frequency when they arrive on Earth than originally ...
Dilettanter's user avatar
1 vote
2 answers
178 views

Would you expect this planet to be hotter or colder than earth?

I have a lab where given the mass of a star being $1.23$ times the math of our sun, some planets wobble of central start is $273$ days, and the velocity of 79 m/s. I found that the mass of the planet ...
Wolfy's user avatar
  • 113
1 vote
1 answer
152 views

What are evidences of stationarity of rotation of galaxies

Recently I have found the article Does There Really Exist the Problem of the Dark Matter in Spiral Galaxies? which states that dark matter does not exist because astronomers are wrong assuming ...
Truffaldino's user avatar
1 vote
1 answer
339 views

How strong is the gravitational stretch we experience from the edge of the universe?

How much gravitational effect do we experience (e.g. maybe -.00001 G or smaller) from the edge of the visible universe? By edge of the visible universe, I am talking about the region of the cosmic ...
Jonathan's user avatar
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1 vote
1 answer
480 views

Question about Hubble parameter (Hubble constant) and measuring it

I see this question in "An introduction to modern cosmology - Andrew Liddle - Wiley Publication": In the real Universe the expansion is not completely uniform. Rather, galaxies exhibit some ...
titansarus's user avatar
2 votes
1 answer
391 views

Question about doppler effect

We know that we can use Doppler effect to determine equatorial velocity of a planet. We send a electromagnetic wave with wavelength $\lambda_0$ to an equatorial edge of planet and we get wavelength $\...
titansarus's user avatar
10 votes
1 answer
4k views

How do scientists determine if a star's color is due to Doppler shift vs the star's composition vs temperature?

When looking at visible light coming from, say a star, scientists can determine by the shifting of the light towards the red or the blue end of the spectrum to determine if it is moving towards or ...
iMerchant's user avatar
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1 vote
2 answers
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Can we tell how fast bodies are moving away by measuring their frequency?

It's clear the universe is expanding because light from distant bodies, like galaxies, are shifted towards the red side of the spectrum. In other words, the light measured is more red than it should ...
Michael Lee's user avatar
3 votes
1 answer
781 views

How do we know galaxy GN-z11 is as far away as it is?

The news media recently reported that galaxy GN-z11, formed just 400 million years after the big bang, is much further away than originally thought at perhaps 13.2 billion light years. They say, ...
Michael Lee's user avatar
4 votes
2 answers
2k views

Gravitational red shift vs Doppler redshift: Is the universe really expanding?

Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted? What I think I know thus far is this: Redshift ...
Ska's user avatar
  • 479
4 votes
2 answers
289 views

How to disentangle a very distant star's relative velocity vs. redshift distance

We measure a star's relative velocity towards or away from us via its Doppler-shifted spectrum. This is also how we measure the distance of very distant stars: measuring the shifts in the spectrum ...
jvriesem's user avatar
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3 votes
1 answer
3k views

How do we know that light is redshifted/blueshifted and not the original light of a star/galaxy? [duplicate]

If a star/galaxy is moving towards us, then its light is blueshifted, and if it is moving away from us, then its light is redshifted. How do we exactly know that the color we are seeing is not part of ...
Madeyedexter's user avatar