Questions tagged [distances]

Questions regarding the amount of space between two objects, the units, or measurement thereof.

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What exactly is the estimated distance to a far-off object when they say '50 Mpc/h' or '50 Mpc h^-1'? Is it less than 50 Mpc? Do you ÷ by 67 or 74?

Several recent arxiv.org papers I read mention distances to very distant objects in Mpc (megaparsecs) divided by Hubble's 'constant'.... Does that mean we should divide the Mpc or Gpc (gigaparsecs) by ...
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The two channels of Type Ia SNe and their use as standard candles

As we know, Type Ia supernovae are used as standard candles since their absolute luminosities are expected to be roughly constant. The consensus model, as seen from the Wikipedia page, suggests this ...
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What is that stuff around Andromeda Galaxy

I know Andromeda Galaxy is one of the closest galaxies to our Milky Way, but there are photographs showing it to be surrounded by smaller bodies. Are there any that are closer, or are they all farther ...
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Horizontal and equatorial coordinate systems

What is the difference between horizontal and equatorial coordinate systems apart from the notations (azimuth, altitude) and (right ascension and declination angle)? Please provide some measurements ...
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1answer
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Calculating distance to High Redshift Galaxies based on observations

I am aware that we need to account for the expansion of the universe, changing $H$, the relativistic redshift eqn: $1+z=\sqrt{\frac{c+v}{c-v}}$ and so on, but can we accurately calculate velocity ...
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65 views

Radar technique for distant objects

If we want to detect the distance to an object using radar, we can do it only for objects inside the solar system, otherwise the returning signal would be too weak to detect. On the other hand, we are ...
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What is Saturn’s apparent magnitude at its brightest when viewed from Uranus?

Considering that the apparent magnitude scale is an inverted scale; what is the lowest apparent magnitude of Saturn that can be seen from Uranus. We are of course talking about when Saturn is viewed ...
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If we could fly off edge of observable universe what would happen? [closed]

If we could be at the edge of expanding universe in a fast space ship such that we could go beyond the edge, what does the science think we might experience? Would we still be floating in space? Would ...
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Why does apparent magnitudes get increased fourfold when distances get halved, instead of simply getting doubled?

This website explains: The apparent brightness of a star is proportional to 1 divided by its distance squared. That is, if you took a star and moved it twice as far away, it would appear 1/4 as ...
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Is it more accurate to measure distances from Mars?

I'm trying to figure out answer to this task: At a certain level of development of the Martian civilization, scientists of this planet began to measure distances. Will their measurements be more or ...
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Could Neptune be viewed with the naked eye from Uranus?

Which star or planet in our night sky can match what Neptune would look like when viewed from Uranus, or one of its moons? The answer would be for the most favourable condition, which is when Neptune ...
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Is saying that what we see of an object 1 light-year away happened 1 year "ago" in any a way useful view of the universe?

Since the speed of light is the speed of causality, the "now" state of the a faraway object for an observer should be the exact point at which its light reaches the observer, for literally ...
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Calculating the present comoving distance or light travel distance of distant objects when only one value is given?

I was wondering how to calculate either the present comoving distance or the light travel distance when the source material only gives one value? Is there and an online calculator or simple equation ...
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How exactly was Giovanni Cassini able to measure the distance to Mars?

Recently learned that Cassini was able to calculate the distance to Mars quite well using parallax in 1671. I was surprised, since even at opposition of Mars, the parallax (with respect to the Earth's ...
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305 views

How are SIMBAD's parallaxes calculated?

I've been trying to figure out how to convert parallax information from SIMBAD's database into parsecs. Looking at Wikipedia as well as many other sources, parallax is calculated as follows: ...
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Is the information about space we have old? [duplicate]

As we know light has a definite speed i.e. $c=299792458$ m/s so it takes some big time to travel from distant galaxies, right? So I always wonder about the big telescopes and big space companies ...
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How can eclipsing binaries be used to gauge distances?

I understand that we can infer much about the parameters, such as the radius and mass, of stars in eclipsing binary systems. But how can eclipsing binaries be used to gauge distances? The current ...
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Radius to which all hydrogen-burning stars are known?

For the purposes of this question, I wish to consider active, hydrogen-burning stars, not deuterium-burning brown dwarfs, or stellar remnants like black holes or neutron stars. (Though including ...
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Photometry templates -- what are the templates of?

Redshift measurements from photometric data can be determined using template-fitting (Cosmos website, SDSS photo-z). What does it mean to fit a template to determine redshift? What is the template of?
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How to find the scale factor on given time in the future if initial distance between source and destination is known

Assume the received redshift $z$ of a photon is known. We then can calculate the initial distance (when the received photon was emitted), the light Travel Distance, the current Distance (proper ...
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How to actually obtain the parallax angles that are used to determine distances of stars?

I’m trying to understand how to measure the distance to nearby stars using the parallax method. My question is: how do you get the value of the p angle?
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285 views

Comoving Volume Calculation

Suppose I have data from an astronomical survey at redshifts in the range $z = [2,3]$. Suppose that, on average in this range, the data covers an area on the sky of $A=1$ $\mathrm{Mpc}^2$. How would I ...
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109 views

Nearby galaxy distances

Type Ia supernovae are extremely useful in measuring the distance of remote galaxies. It is known that type Ia supernovae always reach the same brilliance at their peak. Like Cepheid variables, they ...
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How can I find the distance of the tower while standing at my roof?

Whenever someone starts telling about finding distances in astronomy, it all starts with a parallax. The example they give is straightening your hand and see how your thumb changes its location while ...
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What's the difference between minutes and arcminutes?

I read in trigonometry class that 1 minute is equal to 1/60 degrees. So, 'minute' is an angular unit. But also 'arcminutes' are used to measure seperation between celestial objects and also equals to ...
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Will the night sky ever be more stars than darkness? [duplicate]

Given enough time, will enough light from distant stars reach Earth so that our night sky will be more than 50% stars?
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Converting parsecs to light years in the dumbest way possible

I have to convert 132 parsecs to light years and I'm struggling to get the expected result. Here is my method: $132 \text{ pc} = 132'' = 2,2' = 0,03(6)°$ I have an equation for stellar parallax which ...
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111 views

How to compute for Distance Modulus' uncertainty/ies?

This is rather a short question. As we know of; Distance Modulus (DM) $\mu = 5 \log d - 5$ If $d = 168_{-14.9}^{+27.5}$ pc ($3\sigma$ value), how can I possibly compute for $\mu$'s uncertainty? P.S. ...
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166 views

How can you find the distance to a galaxy using right ascension and declination?

For example, Galaxy NGC 3689 has the right ascension of 11:28:11 and declination of +25:39:40.0. Using these values, how can we find the distance to the galaxy? If it helps, its radial velocity is ...
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Since Proxima Centauri orbits the other two Alpha Centauri stars, will it eventually be farther away from us than they are?

And, if so, will we have to change its name to Distal Centauri ;-) ? Granted, its orbital period around the other two is about 550,000 Earth years, so we have some time....
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Converting equatorial coordinates to Cartesian coordinates for extragalactic distances

I'm trying to search for galaxy clusters with the friends-of-friends (FoF) algorithm. I have the equatorial coordinates ($\alpha, \delta$) and redshifts ($0.5<z<2.5$) of galaxies that I wish to ...
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How do you calculate comoving distance and light's travel distance? According to the formulae below?

According to Wikipedia, Distance measures (cosmology), Comoving distance: $${\displaystyle d_{C}(z)=d_{H}\int _{0}^{z}{\frac {dz'}{E(z')}}}$$ Light-travel distance: $${\displaystyle d_{T}(z)=d_{H}\int ...
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How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?

After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-...
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How reliable is it to use globular cluster lumniosity function as a distance indicator?

I have seen many research suggesting that GCLF can be used as a secondary distance indicator for extragalactic objects. However, this method seems to be only reliable when the GCs in use come from say,...
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Which celestial body is able to come closest to Pluto?

Other than Pluto's moons (including Charon), which known body comes closest to Pluto, and how close? Neptune doesn't come closer than 16 au. What about Orcus, whose orbit is similar to Pluto's, or ...
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139 views

Approximate spectral type and luminosity given apparent magnitude and distance

I am looking at the data acquired from the Gaia DR2 survey. I found that most of the stars had their distance and apparent magnitude catalogued, but not their spectral type and luminosity class. Is ...
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165 views

What is the mean separation between a star and its closest neighbor in the Milky Way halo?

My question is inspired by this previous question, Are there any stars that orbit perpendicular to the Milky Way's galactic plane?. In the great answer posted by @ConnorGarcia, one commenter said he ...
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How do you correct the Period-Luminosity relationship for metallicity?

Refer to the link: https://www.astro.utoronto.ca/DDO/research/cepheids/cepheids.html Tha author has used the relationship $M_V=-2.902log(P)-1.203$. It is mentioned that this is not corrected for ...
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SIMBAD TAP queries seem to indicate there are no distance measurements for a great many nearby stars, including Alpha Centauri or Barnard's Star

I'm attempting to create a map of all objects within 50LY, including main-sequence stars, binaries, planemos, etc. As such, I'm trying to do it all from first principles, building a micro-ETL to ...
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How precisely we know the Gaia spacecraft baseline? [Question related to Planet 9 and the cosmic distance ladder]

The European Space Agency mission Gaia is performing an outstanding job by measuring the parallaxes of almost 2 billion stars, many of which are thousands of light years away from the Sun. For this ...
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277 views

How is it that Jupiter and Saturn appear the same size in the sky?

Saturn is twice as far as Jupiter is from Earth according to a quick Google search. But I needed to understand why do they appear as if they are the same size. I mean as if they are not far apart. For ...
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62 views

Computing the over-density of Lyman-alpha emitters

Let's assume that I have observations of $N$ galaxies in a projected area $A$, within a redshift range $\Delta z = z_{max} - z_{min}$. What is the correct way of computing their number volume density? ...
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593 views

Minimum distance between planets

In our solar system, MOIDs (minimum orbital intersection distance) of different planets reach a minimum of ~30 million miles (Mercury and Venus). However, other star systems have more compact planets. ...
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472 views

How to find the distance between two galaxies from ra and dec and redshift [duplicate]

I have ra and dec and corresponding redshift of galaxies. I would like to calculate the distance between two galaxies. I did like this to find the nearest neighbour galaxies. Suppose I am trying to ...
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1answer
111 views

Type II supernovae as a distance indicator

Could someone explain in brief exactly how type II supernovae could be used as distance indicators? as in simply the formulae used and how they are employed? I know there are certain methods based on ...
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56 views

How to improve the precision in a star's distance

When I use the Gaia star catalogue, the parallax values often have large uncertainties which, therefore, leads to a large uncertainty for the distances to the stars. If you were interested in the ...
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137 views

What's the farthest point humans have explored?

By using powerful telescopes on land and space, what's the farthest point humans have explored or viewed?
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51 views

How do you go from transit times to Earth-Sun distance?

In the early 18th century, Halley described a method to determine the value of the astronomical unit by observing a transit of Venus from multiple locations on Earth. How do you go from the transit ...
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230 views

How were the distances to stars measure before parallax?

A comment under When was the distance to a star measured for the first time without using parallax? mentions that the distance to stars was measured before parallax was possible. How was this done?
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How did we determine the distance of the CMB?

The cosmological microwave background (CMB) is the oldest electromagnetic radiation in the universe. How do we know how far away the CMB is?

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