Astronomy Stack Exchange
Astronomy Stack Exchange

Questions tagged [distances]

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

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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 all intents and purposes. My question is whether purporting…
DoltishNeuron
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Do we make predictions in our time, or local time?

I was scrolling idly through the Wikipedia article on Orion when I read: Orion will still be recognizable long after most of the other constellations—composed of relatively nearby stars—have distorted into new configurations, with the exception of…
hairboat
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Am I miscalculating distance to Moon?

The Moon's orbital period is generally given as 27.3 days, and the radius of Geostationary orbit as 26,200 miles. However, using Kepler's Third Law, if I raise 27.3 to the power of 2/3, and multiply the result by 26200, I get a value of a bit over…
Mike Stone
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Why has Moving Cluster Method been successful only for Hyades?

At all places where I have read of Moving Cluster Method for measuring distance to a cluster and once applied myself on data, I have been told that the method has been successfully applied only to Hyades cluster in Taurus. Question : What factor…
Cheeku
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What is the farthest object we've been able to bounce signals off of to date?

I know people bounced lasers off of Venus and Mercury in 1960s in order to test the Shapiro delay. Since then, we've developed higher power lasers and radio transmitters (Bolshakovo transmitter). Are there any farther objects where we've been able…
questionhang
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What's the furthest object observable by the naked eye from earth?

From XKCD: Caption: 'The light from those millions of stars you see is probably many thousands of years old' is a rare example of laypeople substantially OVERestimating astronomical numbers. So, what is the furthest object visible to the naked eye…
naught101
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Could you use luminosity changes over time to calculate distance?

More specifically: if you know your movement relative to a body, could you use the inverse square law to calculate distance? Since if you are distance $D$ away and you move $d$, $\Delta L \propto (D-d)^2-D^2=2dD-d^2$, I'm assuming you should be able…
Erez Israeli Miller
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How is the distance from Earth to distant celestial bodies calculated?

It's difficult for most people to grasp how distances between the Earth and distant celestial bodies are calculated. For example, when someone tells me that a given star is 100 light years away, how would I determine if that were accurate? I think…
Naftuli Kay
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What is the difference between the Synodic & the Sidereal Periods?

While studying Spherical Astronomy, I came to know the two terms: 'Synodic Period' & 'Sidereal Period'. Both were referring to the returning of a particular celestial body on the sky or the celestial sphere but I couldn't spot the difference between…
user47535
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Is the Alpha Centauri star system moving closer to us?

The closest star system after our sun is Alpha Centauri, a three star system with Proxima Centauri, a red dwarf, slightly closer to us than the other 2, around 4.3 light years. I tried Wikipedia and other articles that describe Alpha Centauri and…
0tyranny0poverty
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Function for current distance between in light-seconds between Mars and Earth

I'm looking for a function that given a time (for example Unix time) gives back the current distance between Mars and Earth in light-seconds. It can be a mathematical function or programming function (preferably in Python or pseudocode), but must…
Kevin
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Is it possible to get the distance to a star in the IPHAS DR2 catalog?

I'm looking at the IPHAS DR2 catalog. It has the Right Ascension and Declination but I'm not seeing any distance information (lightyears or parsecs). I'm wondering, given the columns in the dataset, if the distance can be calculated.
Justin808
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Are the distances between two celestial bodies the distance of their centers?

For example, the average Sun-Earth distance is 1 AU. Is this the distance between the center of the Sun and the center of the Earth the distance bewteen the surface of the Sun and the surface of the Earth, or something else?
AstroRP
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How close would quasars have been to each other?

My understanding is that quasars are the early phase of formation of galaxies. At the time quasars were forming, the universe would have been smaller and therefore things closer to each other. About how close would quasars have been to each other?
Duke Dougal
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How do we determine something is "x" light years away?

I always read/hear "This galaxy is X thousand light years away" or some similar statement (for example see this table). Please excuse the naivety of question. How do we determine that some astronomical body is "x" light years away. Surely we don't…
Pervy Sage
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