# Questions tagged [distances]

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

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### Stability of this complex gas giant moon system

Let us consider this gas giant moon system: Gas giant: 7 Jupiter masses 1.37 Jupiter radii Moon 1 0.317 earth masses 775332 km semi-major axis 40 hrs orbital period Moon 2 0.2 earth masses ...
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### With 42 supernovae in 37 galaxies, how do we know SH0ES results is robust?

SH0ES is a collaboration that's anchoring the cosmic distance ladder by matching Cepheid data with Type 1a supernovae. Both of these are standard candles, so if we know the distance to a particular ...
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### Ancient Astronomy, Distances, and Parallax measurements

Andrew Michael Chuggs in his recent book The Pharos Lighthouse in Alexandria (Routledge 2024) goes into an excursus on the ancient astronomy of Eratosthenes. The author is a published historian whose ...
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### What are we misunderstanding about the scale factor-redshift relation? [closed]

If the scale factor as a function of time represents or is equal to the average distance between the galaxies, then it increases altogether with the CMB redshift $z$, but it also must be equal to the ...
61 views

### How to count observable number of galaxies at a given latitude considering interstellar extinction?

If galaxies are uniformly distributed in space, then in the absence of extinction, the number of galaxies per square degree brighter than magnitude m is given by $$\log_{N_0}(m) = 0.6m + C$$ How will ...
104 views

### Distance from Earth to Sun averaging method in AU definition

Historically, $1~\text{AU}$ is defined as $1/2(r_{min}+r_{max})$, but the problem is that this is not the average radius if Earth orbit would be transformed into circle, with Sun at the center and ...
92 views

### How to calculate moon's distance and parallax in it's altitude

I'm trying to calculate moon's parallax in it's altitude depending on the day I need and I followed this formula by geoastro.de Basics of Positional Astronomy and Ephemerides but I need to calculate ...
3k views

### How close will Pluto come to Earth this year (2024)?

For reasons associated with a 1943 story, I am keen to find how close Earth will come to Pluto in 2024. According to https://theskylive.com/pluto-tracker today (21-May-2024), Pluto is now slowly ...
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### Calculating lunar parallax based on a distance between two objects at certain latitude

I want to compute lunar parallax based on the distance between two points. In fact I know the formula, but I guess they're explained wrong. By looking at the image below we can see the polar radius, ...
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### Easy guideline for using JPL Horizons DE431 for planets in aphelion and perihelion from 11000 BC to 16000 AD?

Can someone give me a step by step Guide how to use JPL DE431 or DE441 as a Beginner. I tried the Horizons website app and Webgeocalc but it didn't showed understandable Information. This websites ...
79 views

### Closest/farthest point where the sun stops being the brightest star?

Which is the closest point to the Sun where it's not the brightest star anymore? My intuition is that this is either on a direct line between the Sun and Alpha Centauri, or between the Sun and Sirius ...
497 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 ...
22 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 & =\...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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,...
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### 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 ...
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### 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 ...
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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 ...
926 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 ...
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1 vote
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### 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 ...
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1 vote
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### 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
78 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/...
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1 vote
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### 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 (...
230 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
578 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 ...
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### 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 ...
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### 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 ...
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### 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.
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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### 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.
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### 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 ...
88 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 ...
130 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)?
191 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 ...
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 $ds^2=0$ ...
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### 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 ...
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### 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 (...
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### 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 "...
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### 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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### What would Betelgeuse look like from Earth if it was at the edge of the Solar System

If we parked Betelgeuse just outside the Solar System, how big would it look from Earth?
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### Distance from Earth to Mars at time of November 8, 2022 lunar eclipse maximum

I’m looking for the “exact” distance from the Earth to Mars, at the moment of the lunar eclipse maximum earlier this week (November 8, 2022). As many significant digits as you can muster. Between the ...
159 views

### How dark is the side of the Moon facing away from the Sun? ( I don't mean the far side)

Remember, the actual "dark side" of the Moon is not the far side, facing away from us that we can't see, but rather it's the side that faces away from the Sun that is illuminating it.​
617 views

### How can I convert a galaxy arcmin to light years?

https://en.wikipedia.org/wiki/List_of_largest_galaxies says galaxy ESO 383-76 has a MA diameter of 1,764,000 light years based on information from https://ned.ipac.caltech.edu/cgi-bin/objsearch?...
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