# Questions tagged [distances]

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

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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 ...
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 & =\...
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 ...
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 ...
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
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, ...
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 ...
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,...
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 ...
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.
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### 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 ...
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 ...
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 ...
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
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
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:...
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
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
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
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 (...
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 ...
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
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 ...
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 ...
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 ...
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 ...
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 = [<...
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.
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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.
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 ...
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)?
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 ...
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?
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?
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
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 $ds^2=0$ ...
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 ...
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.) ...
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 (...
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 "...
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{...
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### 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 ...