Questions tagged [velocity]

Questions regarding the movement of an object at a given speed and direction, often related to the concepts of orbital velocity and escape velocity.

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Determining the speed of meteor

How to determine the velocity of a meteor from two video data? I want to try to determine the orbit of the meteor, but before that I have to determine the meteor's entry velocity and apparent radiant ...
alphaaquilae's user avatar
8 votes
5 answers
2k views

Does the escape velocity formula take into account how a gravitationally bound object's distance to its primary increases before coming back down?

Confusing title, I know. Imagine a perfect, homogenous sphere with an exact radius of $1,000 \text{km}$ and an exact mass of $8 \times 10^{15} \text{kg} $. If you use the formula for escape velocity $...
user177107's user avatar
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1 vote
0 answers
91 views

Deriving the Tully-Fisher relation from the virial theorem

So I know this is a loose proof and a lot of assumptions are made, but I do not understand how these assumptions lead to the quantities we obtain so I will be asking questions at each step: start with ...
realanswers's user avatar
1 vote
1 answer
264 views

The preferred way of binning (classifying) data for galaxy snapshots in Python

Let's say I have a galaxy snapshot that I load with some package (pynbody etc) and I store my spatial coordinates of stars in the galaxy in x, y, z arrays and also velocity in array vz. Now I want to ...
Jerome's user avatar
  • 155
1 vote
0 answers
117 views

How are CMB frame redshifts of galaxies corrected for coherent flows?

Say, if I downloaded the CMB frame redshifts of some galaxies from NED database, then what is the procedure to correct it for coherent flows? I'm using the SNooPy(snpy) Python package to analyze some ...
gautam bhuyan's user avatar
2 votes
0 answers
57 views

How long is the sunrise (or sunset) on North (or South) Pole? [duplicate]

I wonder how to calculate the duration of the Sun crossing the line of the horizon on equinox on Pole. For equator I used this formula: $t = \frac{2 \times p}{\cos(\phi) \times u}$, where $u$ - is ...
ALiCe P.'s user avatar
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27 votes
5 answers
6k views

Can a planet with no atmosphere be orbited at extremely low altitudes?

Can a planet that has absolutely no atmosphere be orbited by a spacecraft at extremely low "altitudes" (if you'd even call it altitude at such a low orbit. For instance, if this planet's ...
veezy_101's user avatar
  • 379
2 votes
0 answers
356 views

How to calculate orbital velocity of binary star?

I am trying to simulate the Alpha Centauri AB System. I built the simulation, it works flawlessly when trying to simulate our solar system, and I am now trying to simulate the AB System. I found all ...
Marc Klemm's user avatar
3 votes
0 answers
30 views

How to find x-values of fourier-transformed correlation functions in velocity space?

I am trying to extract the kinematic parameters (rotation velocity, velocity dispersion, ...) of an elliptical galaxy by extracting the kinematical broadening function using the FCQ-Algortihm first ...
trynerror's user avatar
  • 849
4 votes
1 answer
252 views

How to calculate mean line of sight velocity of stars after rotation of galaxy?

I am trying to calculate the mean line of sight velocity from a simulation snapshot of a galaxy after the galaxy is inclined by a certain angle, theta. I am coding it in python. What I have done so ...
Jerome's user avatar
  • 155
31 votes
6 answers
10k views

Why does light accelerate instantaneously to c, while no other phenomena do it? [closed]

In physics, it always takes some time for a particle to move from rest to some speed. However, photons (light particles) accelerate instantly from zero to c. How? (A visualization would be helpful.)
AnnexRemotelearn's user avatar
2 votes
1 answer
329 views

Flux vs. Velocity representation of spectra?

I'm looking for a basic explanation of the flux vs. velocity representation of a spectrum and how it's obtained from the regular flux vs. wavelength representation. A good example of this is in Arav ...
Erik's user avatar
  • 121
-1 votes
2 answers
109 views

Why collisions between earth orbiting satelites do occur?

According to Kepler laws all earth orbiting satellites should have the same velocity. So how can they collide?
JCRCAN's user avatar
  • 21
0 votes
1 answer
141 views

can i use heliocentric velocity as a rotation speed? [closed]

In the research of the galaxies, does heliocentric velocity involves space's expanding velocity? and can i use heliocentric velocity by galaxy's rotation speed?
INHYUK PARK's user avatar
7 votes
1 answer
984 views

How to find the shape of an orbit

What is the minimum information I need to be able to draw the shape of an orbit of a body that orbits the sun? With this information how can I figure out the shape of its orbit?
Bartley's user avatar
  • 173
0 votes
1 answer
1k views

How to convert Proper Motion in RA & Dec to Galactic Coordinates

I'm trying to parse stellar data in the GAIA 2 release to galactic coordinates and am struggling with the velocity component. I've tried following online documentation and papers, but end up with ...
Borborbor's user avatar
1 vote
1 answer
69 views

Do planets have effect on velocity of Earth?

There is method for finding extrasolar planets called Transit-timing variation. If I understood correctly, exoplanets accelerate or decelerate each other (according on their position), so we can ...
Michal's user avatar
  • 323
4 votes
1 answer
447 views

What does "unremarkable transverse peculiar velocity" mean exactly, and how is it calculated here?

The abstract of A magnetar parallax (also in MNRAS) contains the following: Combining our new observations with two archival observations from 2006, we have refined the proper motion and reference ...
uhoh's user avatar
  • 30.7k
4 votes
2 answers
531 views

Binary Star Initial Speed

I am writing a 2D simulation for binary stars orbiting each other. Currently, the initial position of the stars are on opposite sides of the screen with the left star having a velocity up the page and ...
Tyler Smith's user avatar
1 vote
1 answer
165 views

can we calculate the velocity of galaxies at the edge of the observable universe?

I read this post Does the edge of the Universe travel faster than the speed of light? but there was no calculation, so I tried it thusly: The observable universe is 28.5 Gpc (gigaparsecs) = 28500 ...
aquagremlin's user avatar
4 votes
2 answers
8k views

Calculating object velocity at perihelion

I would like to calculate the velocity of an asteroid orbiting around a star (Sun) at the perihelion of its orbit. I know the excentricity of the ellipse and its semimajor axis. I have found that the ...
A.D's user avatar
  • 183
2 votes
0 answers
54 views

Find x,y,z velocity component of a star? [closed]

I am trying to find the initial x,y,z velocity components of the Epsilon Lyrae stars. How might I go about doing this? The radial velocities are available on Wikipedia, but I am not sure how to use ...
Stephane Hatgis-Kessell's user avatar
1 vote
1 answer
71 views

How to identify component of velocity of a star from its red shift? [duplicate]

When a telescope observes a distant star, all it sees is the light being emitted by the star. Observing the wavelength of this light, we determine the velocity of the star. If the wavelength is red-...
yathish's user avatar
  • 131
0 votes
1 answer
73 views

Where a database of different z values of redshift can be found?

I was working on reshift details for various galaxies but do not know any database to find the z values given to redshift galaxies. Can anyone help?
Pedro de Oliveira's user avatar
0 votes
2 answers
284 views

How can we calculate velocity of an object given the distance from an object in parsecs?

If you had the distance from a celestial object, in parsecs, how would you calculate the velocity of the said object? Edit: I'm sorry I don't have more context, the specific questions is: "A galaxy ...
Ganlas's user avatar
  • 11
2 votes
2 answers
300 views

Is blue light not traveling faster then red light in space?

I just can't understand why light and other massless particles are not traveling at different speeds? Gravity effects anything with a mass but light has no mass but a black hole, and weak lensing ...
Muze's user avatar
  • 1
5 votes
1 answer
1k views

How to determine the mass of a galaxy?

I am having a slight disagreement with my professor. We can measure the mass of a distant star cluster from: A.Its color B.Its radius C.Its metallicity D.Smearing of lines in its total spectrum My ...
Jim's user avatar
  • 67
8 votes
2 answers
311 views

Can "rogue" supermassive black holes be made this way?

Could two galaxies (one big and one small)intersect at a velocity to allow the smaller black hole to escape but not the galaxy around it?
Muze's user avatar
  • 1
1 vote
2 answers
1k views

What is the fastest a galaxy or other body has been measured to (or can) travel?

Our solar system travels at an average speed of 515,000 mph and our galaxy at 1.3 million mph through space. What is the fastest moving body in space recorded and the fastest can a black hole or ...
Muze's user avatar
  • 1
6 votes
1 answer
1k views

Calculating obital velocity from radial velocity

I'm not really a physicist so I don't know if it's possible to get the real orbital velocity of a star from its radial velocity. I'm working on a paper for school and I want to get the mean velocity ...
Camila Pazmino's user avatar
2 votes
1 answer
94 views

How is interstellar gas density mapped from GAIA data?

I found the image below in Space.com's article This 3D Color Map of 1.7 Billion Stars in the Milky Way Is the Best Ever Made. The caption for this image reads: The Gaia spacecraft gathered ...
uhoh's user avatar
  • 30.7k
6 votes
2 answers
726 views

Is there a rough analytical expression for the Milky Way's radial mass distribution?

I found the image below in Space.com's article This 3D Color Map of 1.7 Billion Stars in the Milky Way Is the Best Ever Made, although it is not the map mentioned in the title. The caption for this ...
uhoh's user avatar
  • 30.7k
3 votes
0 answers
719 views

How do I determine the velocity of Pluto at aphelion and perihelion?

I am a college astronomy student and I have to find the velocity of Pluto at aphelion and perihelion. I have found the distance of perihelion to be $1.96\times10^9$ km. Aphelion has a distance of $3....
Cerenkov's user avatar
6 votes
2 answers
1k views

Why most planets don't spin retrograde? [duplicate]

Edit: just found duplicate Since orbital velocity is greater on small orbits, and smaller on large orbits, why don't planets spin retrograde around their own axis? One portion of planet's mass is ...
user avatar
2 votes
2 answers
493 views

Circular velocity in axisymmetrici potential [duplicate]

If a matter distribution is spherically symmetric, the circular velocity is straightforwardly related to the mass via: $v_{circ} = \sqrt{GM/r}$ In an axisymmetric potential, on the other hand hand, ...
user1991's user avatar
  • 834
6 votes
3 answers
3k views

Does Absolute Velocity Exist?

It seems everyone is on the same page about there being no "absolute velocity" due to the fact that everything is relativistic. However, this leaves me confused. This seems to be disconnected with the ...
Chris Allen'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
-2 votes
1 answer
80 views

If velocity is relative, why mass (inertia) is increasing absolutely? [closed]

Would inertia not grow if we took out the reference frame?
s1w_'s user avatar
  • 1
8 votes
1 answer
567 views

Which celestial object in the solar system has the fastest tangential velocity at its surface?

Consider all of the naturally-occurring objects in the solar system : in the reference frame of the object's center (ie, ignoring the orbital velocity around the sun or, in the case of satellites, ...
Bruce Becker's user avatar
11 votes
1 answer
8k views

What does the velocity dispersion of a galaxy mean?

Also, what is the advantage of getting information about the velocity dispersion of a galaxy?
J. H. Azeez's user avatar
2 votes
1 answer
171 views

Why does the neutral hydrogen velocity have this characteristic behavior in the galactic plane?

The recently released map of galactic neutral hydrogen density and velocity is really beautiful. The work has been relased by the HI4PI collaboration (HI = neutral hydrogen, $4\pi$ = complete ...
uhoh's user avatar
  • 30.7k
9 votes
3 answers
856 views

Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

I was reading this overview article about the Gaia spacecraft and I saw the following statement: These spectra provide radial velocity information that are used to study the kinematic and dynamic ...
uhoh's user avatar
  • 30.7k
10 votes
2 answers
2k views

What (actually) is the " deprojected half-light radius" of this almost-all-dark-matter Galaxy?

The recent news of the Ultra Diffuse Galaxy (UDG) Dragonfly 44 is an excellent example of what could be termed 'observe different' thinking. The dragonfly telescope is noted not for the size of its ...
uhoh's user avatar
  • 30.7k
0 votes
1 answer
98 views

How to calculate a phase shift in the process of deriving Baade-Wesselinke distance?

The above is the equation used in the Baade-Wesselink method to independently get distances to Cepheid variables (in the process of deriving Period-Luminosity relation). According to the paper New ...
7_G.S.N's user avatar
  • 173
0 votes
1 answer
162 views

Which software is appropriate to integrate radial velocity with respect to time [closed]

I'm a high school student and currently I'm trying to use Baade-Wesselink method to independently derive period-luminosity relation of Cepheid variables. I noticed that to get the linear radius ...
7_G.S.N's user avatar
  • 173
1 vote
0 answers
183 views

Integrating radial velocity with respect to time

I'm a highschool student who is writing a research paper about plotting Period-Luminosity graph of the Cepheid variables by deriving distance through independent method such as trigonometric parallax ...
7_G.S.N's user avatar
  • 173
2 votes
1 answer
429 views

How was the acceleration calculated for this CME (Coronal Mass Ejection)?

I am looking at data used in a project to get the velocity and acceleration of a CME (Coronal Mass Ejection). I understand how the velocity was calculated, and for the acceleration, I get the v2-v1 ...
John Michaels's user avatar
3 votes
1 answer
319 views

Is the radius used in the formula for the escape velocity the average radius of the celestial object or the radius at the starting location?

I learnt that the escape velocity is given by $$v_e = \sqrt{\frac{2GM}{r}}$$ Say I want to launch a rocket from the earth into space and want to calculate the escape velocity $v_e$ (I guess without ...
Kevin's user avatar
  • 183
3 votes
1 answer
2k views

How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

Suppose I have a wavelength array for a spectrum in units of Angstroms. Suppose further that the wavelength has "uniform logarithmic spacing" such that if I just take the difference in Angstroms ...
quantumflash's user avatar
1 vote
1 answer
245 views

Question regarding the Milky Way when calculating galactic space velocities for galaxies

I have been calculating galaxy space velocities (where proper motions are known) in order to measure their orbits of the Milky Way using the method proposed in the appendix of http://www.aanda.org/...
R Thompson's user avatar