Questions tagged [distances]

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

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3 votes
1 answer
473 views

Measure the radius of the earth using the sun?

Can someone tell me why this would or would not work? I have a sun spotter device that projects an image of the sun onto a piece of paper using a lens and some mirrors. When you use the device it’s ...
0 votes
0 answers
21 views

Luminosity distance in a FRW Universe

In the following presentation: https://www.slac.stanford.edu/econf/C0307282/lec_notes/pinto/pinto.pdf we have the relation for the luminosity distance in a FRW universe: \begin{aligned} D_L & =\...
6 votes
2 answers
463 views

Calculating Earth-Sun distance only using trigonometry and terrestrial measurements

I have an interest in mathematics and astronomy, and my curiosity was piqued by the methodologies employed in contemporary solar distance measurement. Current practices use sophisticated instruments ...
11 votes
1 answer
1k views

Why was the standard distance set to 10 parsec and not simply to 1 parsec?

On closer inspection of the absolute visual magnitude and the apparent visual magnitude of the sun, I noticed that their magnitude range (4.83 + 26.74 = 31.57) exactly matches the human eye. The ...
3 votes
1 answer
307 views

Redshift distance proportionality at high Z and need for "mighty mouse" galaxies?

Allegedly supported by some evidence from the new James Webb space telescope physicist Eric Lerner has written an article that have garnered some attention. He writes that: "Put another way, the ...
1 vote
3 answers
870 views

Is our universe flat?

I heard our universe is flat. Then one question is puzzling in my mind. If our universe is really flat, why we measure distance from any point across in a spherical way. In other words, why we say, ...
7 votes
3 answers
2k views

How do we work out the light travel time on a cosmic scale?

I just read this article in the AUSTRALIAN SKY & TELESCOPE magazine, Nov/Dec 2022 Issue 140, on P16, KEEP YOUR DISTANCE: How far away are the objects we see in the universe? And on P23: "And ...
3 votes
2 answers
183 views

What is Hubble's parameter/constant H0 supposed to mean, exactly? [duplicate]

Surely it must mean that every second each Mpc expands by that much. Well what else, could it be. So if the expansion is accelerating, then how can H0 be decreasing!? Let's look at Hubble's law: v=H0D,...
2 votes
1 answer
130 views

Why are distant type Ia supernovae dimmer than expected?

Why are the (extremely) distant type Ia supernovae dimmer than expected? Relative to what? Their cosmological red shift? Well, what else. Please don't just say "Because the expansion is ...
4 votes
2 answers
4k views

Distance between stars Epsilon Eridani and Tau Ceti?

I am working on a story. It would be helpful if someone could provide the distance in light years between star Epsilon Eridani and star Tau Ceti.
7 votes
3 answers
3k views

Distance of the Crab nebula and the speed of light

I am watching a youtube video that says that, there is plenty of historic records that shows that the star, that turned into the Crab nebula, blew up in 1054. According to the video, it is located ...
0 votes
1 answer
212 views

What is the distance between Stephenson 2-18 and Earth?

The distance between Earth and Stephenson 2-18 is 19,570 light years (1.15×10¹⁷ miles). The thing that makes this reasonable is because the Earth is in the Milky Way Galaxy and Stephenson 2-18 is in ...
43 votes
6 answers
7k views

In this image taken by Voyager 1, which is closer: the earth or the moon?

NASA reports this photo was taken 19 Sep 1977 by Voyager 1: It doesn't strike me as obvious how to determine which celestial body is closer to Voyager 1 as the photo was taken. My (not very ...
3 votes
3 answers
788 views

Orion stars distance from Earth

For a textbook I'm creating a figure depicting the distances of Orion constellation's stars from Earth. However i wasn't able to found an Official Scientific catalog of most recent stars distance ...
1 vote
1 answer
148 views

How did scientists decide the boundary of the Milky Way at Edwin Hubble times?

I know Edwin Hubble used Cepheid variables to prove the Andromeda Galaxy is not part of the Milky Way. But how did scientists at that time decide the boundary of the Milky Way? And how did they find ...
1 vote
1 answer
199 views

Is luminosity distance related to both heliocentric redshift and CMB restframe redshift?

The luminosity distance $$d_l=(1+z)r(z)\ ,$$ where $r(z)$ is given by $$r(z)=cH^{-1}_0\int_{0}^{z}\frac{dz'}{E(z')}\ .$$ When I use the SNe dataset "Pantheon", I find there are two redshifts:...
18 votes
2 answers
8k views

Understanding The Turnover Point of Angular Diameter Distance

I am trying to get a better understanding of cosmological distances, in particular the angular diameter distance which I have also seen referred to as angular size distance. What I am looking for is ...
1 vote
1 answer
100 views

Finding an expression for the rate of change of Comoving volume with respect to redshift

I am trying to find the expression for the rate of change of comoving volume with respect to redshift, that is $\frac{\mathrm{d}V_c}{\mathrm{d}z}$. In this paper (Hogg, David W.), the comoving volume ...
1 vote
0 answers
54 views

Large dataset of galaxies redshift, mass, and metallicity?

I'm curious if there is a standard dataset for redshift-mass or redshift-metallicity like there is for redshift-distance with Pantheon+SH0ES. https://github.com/PantheonPlusSH0ES/DataRelease/tree/main/...
1 vote
0 answers
45 views

Where to find data about as many stars as possible?

I need computer-readable data about as many stars as possible, with their: distance to the Earth (or Sun), their masses, and if possible: coordinates, age, brightness distance to the center (...
3 votes
1 answer
657 views

Is there a physical limit to how far we can go?

Is there a physical limit to how far we can go? I am thinking there could be based on the following: 1: There are parts of the universe expanding faster than the speed of light that we will never be ...
-2 votes
1 answer
192 views

Planets revolving counter clockwise around the Sun

Planets revolving around the Sun Hypothetical case: What could have been or no impact if the planets viz Earth, Jupiter, Saturn, Mercury, Venus, Mars, Pluto, Uranus, Neptune in different orbits ...
1 vote
1 answer
464 views

How to find the distance between stars

I wanted to calculate the distance between the end points of the Orion's belt (Alnitak and Mintaka). I searched in the internet and I found out their angular separation to be 2.736°. Then I searched ...
8 votes
1 answer
2k views

Is Webb or any near-future telescopes like ELT capable of observing redshift changes to confirm General Relativity?

The (Davis and Lineweaver (2003)) "Expanding Confusion" paper states that "the expected change in redshift due to cosmological acceleration or deceleration is only ∆z ∼ 10^(−8) over 100 ...
4 votes
2 answers
322 views

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 ...
3 votes
1 answer
104 views

How can we estimate distance of galaxies by only redshift when there are other several factors other than distance to cause redshift

There are different factors for red appearance of different objects in the night sky. Two reasons which I know are Star red by nature Example: red supergiants They emit red light because of their ...
5 votes
2 answers
834 views

Comoving distance between two points [(RA1, Dec1, z1) and (RA2, Dec2, z2)]

I have Redshift (z), RA and Dec positions for two points in a galaxy catalogue (say P1 = [<...
-1 votes
2 answers
178 views

Why is a megaparsec considered to be a useful distance in astronomy?

Is the megaparsec fundamental or man made? I have read that galaxy clusters are megaparsecs wide for example.
21 votes
2 answers
4k views

What equation tells you how far in space you can go from a point and return?

We know that hubble expansion increases the distance between points in space, and that the cosmological event horizon represents the distance from the observer at which objects are receding faster ...
4 votes
2 answers
403 views

Before the 1761 transit, what was our best estimate of the distance to the Sun?

In 1761, many expeditions were launched to determine the distance to the Sun using parallax during the transit of Venus. Prior to the 1761 transit, what was the best estimate for the Earth-Sun ...
3 votes
1 answer
198 views

How can I get a list of the closest x stars and their distances from the Gaia ESA Archive using Python?

I've been trying to find this out for a while now, but I'm making zero progress. I really struggle to find good documentation for the query language, and even in the astroquery library I can't find ...
2 votes
0 answers
35 views

Which value of the apparent magnitude do I use from a Supernova light curve

I am trying to get the distance modulus from a light curve of a supernova and obviously the apparent magnitude changes with time. Not only that but there are so many filters with different mags. So my ...
0 votes
1 answer
75 views

Calculate the distance between two planets eliptical orbit point

What is the distance between Saturn's moons Polydeuces and Dione, Looking for Kilometers if one was to travel Nearest and farthest based on orbit. Best I can find: "Polydeuces can get as close ...
2 votes
3 answers
476 views

How to calculate distance between stars?

I have data on nearby stars, including galactic coordinates and distance from Sun. And I have a dilemma. In a story I'm writing, I have two starfaring alien civilisations. One originates from a planet ...
3 votes
1 answer
97 views

How to obtain luminosity distance from a light curve

I have some light curve data of a SN Ia from which I want to find the luminosity distance $D_L$. How can I do it mathematically? I'll then try to implement the answer using Python.
2 votes
1 answer
118 views

How to calculate the distance from earth and Vega in 1000 years?

Hello I read that Vega is getting closer to earth. I would like to learn how to calculate its displacement and calculate the galactic coordinates that it will have next year or in 1000 years. Knowing ...
4 votes
1 answer
126 views

See Venus in daylight

At what distance (in angular degrees) from the Sun, could we see Venus, in mid daylight, with a pair of binoculars (7x50)?
3 votes
0 answers
172 views

Determining the distance to the Moon from parallax using the following information

How could I determine the distance from the Earth to the moon by using the method of simultaneous parallax? I know the right ascension and declination as seen from two different points on earth. I ...
4 votes
2 answers
3k views

How do astronomers measure the size of celestial objects?

What techniques and tools are available to astronomers in order to measure the size of celestial objects, such as stars or perhaps black holes that don't emit light or reflect starlight?
4 votes
4 answers
15k views

How do you calculate the lookback time distance to a given galaxy?

By lookback time distance I mean the same as light-travel distance. Can it be calculated from just knowing the redshift?
3 votes
1 answer
194 views

Space travel to distant stars

This is more of a hypothetical question. Say space travel at near light speed was possible, and I wanted to travel in my spaceship to some distant star many light years away. At the time and location ...
1 vote
1 answer
37 views

How can a time-like trajectory be calculated using the Friedmann-Robertson-Walker metric?

Using the following FRW metric, $$ds^2=-c^2dt^2+R^2(t)(d\chi^2+f(\chi)d\Omega)$$ and considering $d\Omega=0$ from now on, it is clear that for a light-like trajectory, the equation must read $ds^2=0$ ...
6 votes
3 answers
3k views

What is the apparent size of Earth from the Sun?

Heatwaves have been in the news in recent years. I found it amazing to consider that the energy from the Sun is enough to kill you, when only a tiny fraction of its radiation reaches Earth. Then I ...
4 votes
4 answers
4k views

What would Jupiter look like from a Galilean moon?

If I were on a Galilean moon of Jupiter, like Europa or Ganymede, what would the planet look like? (Let's say I'm on a space station that provides atmosphere to make it slightly less unrealistic.) ...
2 votes
1 answer
256 views

3d distance between the Galaxies inside the galaxy cluster

I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z (...
11 votes
1 answer
225 views

Farthest distance two objects are "gravitationally bounded", considering expansion of the Universe

The narrative is: "on greater scales the expansion of the Universe dominates, but on smaller scales gravitationally bounded objects still stay bounded". But how small is meant by "...
10 votes
2 answers
2k views

Exact measurement of a light year

What is the exact measurement of a light year? I searched google for the answer in meters and came up with $9.461\cdot 10^{15}$ meters. When I calculated the answer considering $299\,792\,458 \;\text{...
10 votes
1 answer
112 views

How do astronomers distinguish between Cepheids and other types of variable stars?

So my understanding of how Cepheid is used as standard candle to determine distance of galaxies is like this: Astronomers observe a galaxy, notice an object within that galaxy whose brightness ...
86 votes
12 answers
23k views

Why don't astronomers use meters to measure astronomical distances?

In astronomy distances are generally expressed in non-metric units like: light-years, astronomical units (AU), parsecs, etc. Why don't they use meters (or multiples thereof) to measure distances, as ...
9 votes
4 answers
2k views

Does stellar parallax only occur parallel to the ecliptic?

Does stellar parallax only occur parallel to the ecliptic, or has it been observed in other directions, too?

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