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Why don't astronomers use meters to measure astronomical distances?
In addition to the answer provided by @HDE226868, there are historical reasons. Before the advent of using radar ranging to find distances in the solar system, we had to use other clever methods for ...
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Is the Earth-Sun distance 1.012 AU?
As of this moment (2016 May 18, 13:15 UTC), the Earth is 1.0116 astronomical units from the Sun. WA is smart enough to know that "Sun Earth distance in AU" is a time-dependent question.
Update: The ...
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Why don't astronomers use meters to measure astronomical distances?
I would suggest it also makes the material more reachable for the human mind.
I just can't work with insanely large or small numbers. They convey no meaning.
But 1 AU is easy, even if I don;t know ...
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A "strange" unit radio astronomy
I would expect the authors to be talking about the signal in terms of janskys, the now-commonly-used units of flux density. The typical definition is
$$1\text{ Jansky}=10^{-26}\text{ Watts meters}^{-2}...
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11
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Does the age of the universe take into account General Relativity / Special Relativity?
Rob Jeffries gives a good response to this question, but I wanted to go through the basic outline of how the age of the universe is calculated, just so you can see how it works more or less. Be warned ...
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Does the age of the universe take into account General Relativity / Special Relativity?
This is a confusing question - your title mentions GR, but of course the age of the universe is entirely derived as a result of using GR to solve for the dynamics of the expanding universe.
The text ...
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Astropy units issue
In Astropy, u.G represents a Gauss, not the gravitational constant. That's why you get the "A" in one of the error messages; it represents an ampere. To ...
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11
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What does par. lines mean in relation to a telescope aperture in 19th century German astronomical publications?
I think it means a Paris line, or ligne.
In Klinkerfues (1867) it seems the author uses Paris inches, which was a common unit in particular for lenses. One Paris inch is equal to 1.0657 "modern&...
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Why don't astronomers use meters to measure astronomical distances?
Along with the other answers, there is one other reason, specifically when measuring the distances to other galaxies.
When stating the distance to other galaxies, Astronomers rarely ever state the ...
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How to convert density from physical unit to comoving unit?
You're asking two different, but somewhat related questions: One has to do with a practical way of describing the expansion of the Universe; the other has to do with a way of dealing with our ...
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8
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What does using these units (c=G=M=1) in MHD simulations mean?
It just means you choose a set of units where $M=1$. What those units are would then depend on what the mass of the object is.
For example, in geometrised units, the Schwarzschild radius is $2M$. In $...
- 115k
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Why don't astronomers use meters to measure astronomical distances?
Another not yet mentioned reason:
There were no usable SI prefixes for such distances.
If you want to use an unit, you need something which allows to express
a specific quantity without too many ...
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What does BJD-2450000 mean?
Julian dates offer one nice feature: All astronomical observations recorded by humankind have a positive timestamp. A key downside of Julian dates is that current timestamps on computers that use 64 ...
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Converting from $\mathrm{W \: m^{-2}}$ to $\mathrm{Jy \: km \: s^{-1}}$
You are essentially correct, but here's a more in-depth explanation:
Both units are a measure of the total flux $F$ of a light source in some interval, e.g. a spectral line or a broader region given ...
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6
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How are people converting intensities in Janskys to Kelvin?
This is, indeed, a result of how we measure things in radio astronomy. It's not just interferometry, but radio astronomy in general. The thing they're referring to is a concept called "brightness ...
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Units and some equations
The Hubble constant effectively has a unit of inverse time only: ${\rm s}^{-1}$:
It is usually given as ${\rm km}\cdot{\rm s}^{-1}{\rm Mpc}^{-1}$. Yet looking at it, km and Mpc are both units of ...
- 11k
5
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Why levels of radio contours maps are given in mJy/beam and what does it mean?
Jansky is defined as $1 Jy= 10^{-23}erg/s/cm^2/Hz$. So all the energy coming from a given solid angle per time, per frequency bin and per detector area.
This is convenient for sources of small ...
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Why don't astronomers use meters to measure astronomical distances?
Perhaps one needs to go back in time and think about why the cubit (length of forearm), league (distance walked in one hour), foot, (metre - one ten-millionth of a quadrant of the Earth?? and so ...
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How often and over what period is Earth’s rotation averaged to compute UT1?
Conceptually, the average is over an average year. Practically, that's not what's done anymore.
Sidereal time is much more readily measured than is solar time. Radio astronomy can measure the ...
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5
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What is projected separation and how can I make sense of its unit (h^-1 kpc)?
It means the separation between the two objects if they were both at the same distance away. This separation is found by multiplying the angular separation (in radians) by the distance to the objects.
...
- 115k
5
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Converting Jy/beam to Jy?
Actually to convert from Jy/beam to Jy/pixel you need to divide by the beam size.
Let's say you have a quantity of 1 Jy/beam, then
$\frac{Jy}{beam} \frac{beam}{\Omega}$, then to go from Jy/beam to ...
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How to convert from FELO-HEL to Km/s?
The axis type ‘FELO’ is regularly gridded in frequency but expressed in velocity units in the optical convention. The unit here is $m/s$.
This means that the wavelength/frequency has already been ...
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What does BJD-2450000 mean?
That is a simple offset in order to work with smaller numbers. Add that number (2450000) again to each value in the day column and you have the unmodified value of BJD.
- 11k
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How to scale down solar system data to simulatable values
As barrycarter mentioned in his comment, you should be more concerned with units and less with scale.
Generally, it's best to stick to conventional units that people recognize. (It will keep your ...
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Why don't astronomers use meters to measure astronomical distances?
I do not know how it is in your country, but here in Russia, astronomical articles and news very often report astronomical distances in kilometers, million kilometers, billion kilometers, trillion ...
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Why don't astronomers use meters to measure astronomical distances?
Several excellent answers have already been given. But no one has talked about logarithmic perception. (https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law)
We perceive everything logarithmic-ally....
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wavelength-based IFU data cubes VS velocity-based IFU data cubes
Your logic seems entirely correct. Whatever you do is an approximation, the difference between a Gaussian profile in cube B and what it "should" look like will be small for any sensible resolution. By ...
- 115k
4
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Finding the radius of a star in arcsec
Using basic circular maths: where $d$ is the distance of the star from the observer in AU, and $r$ is the star's radius in AU, and $a$ is the angle encompassed by the radius of the star in degrees:
$
...
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Units in optical and radio spectral data cubes: Flux vs Brightness
The answer is partially historically and partially scientifically. Flux, i.e. energy of radiation integrated across a solid angle (steradian) is basically counting all photons coming from a solid ...
- 284
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Flux density from brightness map
This expression is valid for low frequencies, including the case of the 1420 MHz hydrogen line. It arises from treating the source as a black body with temperature $T(\theta,\phi)$$^{\dagger}$, and ...
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