# All Questions

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### How can I determine line luminosities from equivalent width measurements?

I have a set of equivalent width measurements for different emission lines. How can I use them in order to determine the corresponding line luminosities?
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### Why does hydrogen ionization happen in HII regions?

Why does hydrogen ionization happen in HII regions? Why is the hydrogen there ionized?
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### Does Dark Matter affect the motion of the Solar System?

Would dark matter have a similar effect on the Solar System as it does on the Milky Way? I'd imagine it could help hold together some of the Solar System bodies or at least affect their motion, right? ...
144 views

### Does the mass of the Earth change?

Every day, babies are born and people grow, which makes their respective masses greater. However, this change in mass (should) come out of the food that they consume - it is used as energy and thus ...
64 views

### Looking back in time by looking further away

I have been pondering the question of how we can look back to the state of the early universe for some time. So I came here and found, to my delight, that several such questions have been asked, such ...
757 views

### When was the term “orbit” (in the modern sense) first used and by whom?

Wikipedia coyly suggests that some notions and views kept circulating (apparently since Adam and Eve) until finally Kepler, of all people, ... etc. I find this hard to believe. Please elucidate.
369 views

### Does this black hole magnetohydrodynamics equation even superficially make sense?

My question is about the journal paper mentioned in an Academia Stack Exchange post. Please understand that this paper has never been posted on arXiv, and I can provide only a link whose content is ...
121 views

### why hasn't Nasa gone back to our Moon? [closed]

why has not Nasa gone back to our Moon since the first landing on the moon
3k views

### How can we focus radio telescopes on a star when the earth is spinning?

Reading about the Star KIC 8462852, it has been said that the SETI project turned its radio telescopes towards the star to search for extra terrestrial radio signals as the star had strange ...
95 views

### Is time itself speeding up universally?

Time moves more slowly near a mass than in relatively empty space. For example, I get that an observer would see someone falling into a black hole to appear to move more slowly and get "stuck" on the ...
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### What's the difference between the apparent horizon and event horizon of a black hole?

The Wikipedia page for apparent horizon is pretty sketchy and requires some GR knowledge. Is there any simple definition?
144 views

### Need help with the math in Python program to flag Jovian radio emissions

A few days ago I decided to take on the little project of converting a Qbasic program into Python (as a side project to my Radio Jove project), and I've managed to get it to run, but the math is ...
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### Has the most luminous object in the universe been found?

It's hard to search through the entire (observable) universe, but the most luminous thing there is must on the other hand be easy to find. Can we now say that the most luminous quasar we know, is the (...
193 views

### How does the appearance of the analemma vary with latitude

How does the appearance of an analemma vary with latitude? This what I take to be a definition of an analemma: If the position of the sun is plotted or photographed at noon clock time (say UTC) every ...
145 views

### Is the mechanism of solar flares on red dwarfs and brown dwarfs the same as that on the Sun?

The Sun has solar flares that are caused when there is a magnetic reconnection in the Sun's atmosphere, causing a loop of magnetic field to be ejected at high energy, along with a large number of ...
138 views

### What you would see in a wormhole?

Science fiction seems to depict the experience of traveling through wormholes (if possible of course) as seeing psychedelic colors or lines of light where stars once were (ie. 2001 or Contact). I ...
36 views

### Extra dimensions [closed]

String theory, Kaluza Klein theory etc. need extra-dimensions. For string theory these are compactified. My feeling is that these extra dimensions are not of our 4-D space, but are only of the space ...
54 views

### Diameter of Astronomical Object Using Magnification

I took a picture of Jupiter through my telescope, using an iPhone. I know the magnification of the telescope lens I used, and can Google to get the magnification of the iPhone lens (the magnification ...
227 views

### How can an infinite universe expand?

I understand the expansion of the universe as actually an increase in the ratio of space to matter. Is this a correct understanding? Otherwise, I don't understand how an infinite structure can expand....
53 views

### can we use connect a long pipe with space station and use vacuum for fuel transfer? [closed]

We all know that we need a lot of fuel to escape from earth. Even 90% fuel of an spaceship is wasted in escaping the earth which definitely affect our power to explore the universe. we have to do a ...
60 views

### Luminosity of black hole accretion disc

The luminosity of a black hole accretion disc gaining mass at a rate $dM\over dt$ can be estimated as ${1\over 12}{dM\over dt}c^2$ That is a substantial proportion of the rest mass of the in-falling ...
168 views

### If the Universe is infinite, would heat death be impossible?

If the Universe is infinite, one would imagine that if we kept moving through space, we'd constantly find newer and newer galaxies and objects forever. This would imply that there is an infinite ...
84 views

### Is there an upper limit to the mass of terrestrial planets

The exo-planet Kepler-10c has a mass between 15 and 19 times the mass of the Earth (making it comparable in mass to Neptune), and yet is thought to have a density of about 7g/cm^3 and to be a ...
63 views

### Why does spectral class and U-V colour correlate slightly differently for main sequence, giant and supergiant stars?

In this diagram the $x$-axis is spectral type for stars and the $y$-axis is B-V colour. Taking Series 1 as the Main Sequence, Series 2 as Giants and Series 3 as Super-giants. Why the spectral class ...
148 views

### Could a star revolve around a planet? [duplicate]

They actually do, but let's set Relativity aside for a moment. And the whole barycenter thing too. Here's the scenario: Somewhere in the backwaters of a galaxy there is this huge planet. It is NOT a ...
53 views

### Age of Occator Crater

Has any official information been published regarding the estimated age of the Occator crater on Ceres? I ran some quick searches but couldn't find anything putting a definitive (or even speculative) ...
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### Formation of a magnetosphere for gas giants / small stars

This question got me thinking about this. Jupiter has, and presumably super-Jupiters can have a strong magnetospheres. A solid metallic core and rotating material around the core, creates a magnetic ...
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### Orion Constellation request

This isn't a question so much as a request. I'm looking for an image of the Orion constalletion I could use, but I would like to have a very high resolution HD image, whereby a lot of the deep sky ...
116 views

### How small a star can provide Sun-level illumination to its planets?

...or how small can a solar system be, to sustain an Earth-like planet? Sun is not really small, and 1AU is pretty far when you look at orbital radii of exoplanets and size of their stars. How small ...
130 views

### Conversion of magnitudes to Jansky and MAGPHYS?

I'm a bit puzzled and not an observer, so please bear with me if I'm being stupid here. The code MAGPHYS specifies Jansky (Jy) as the input unit for flux through ...
70 views

### What are the best candidates for solar lensing of exoplanets, and what would the results be?

If we were able to send a probe to 550AU from the Sun, which exoplanets could be examined, to what resolution, and what form would the examination take? It is radio telescopy only, or would it be ...
186 views

### Is there any hard evidence that rogue planets exist?

A rogue planet (or a rogue anything, for that matter: a celestial body other than a star) is something that's drifting through space without being attached by gravity to any star. They're just out ...
129 views

### How do we know which elements are in a galaxy spectra?

I know that each element has it's own distinct spectra (this is a good site that lists them: Periodic Table) but when looking at a spectra of a galaxy (or even a star) how do we match those elements ...
2k views

### Is Earth unique in its fairly clear atmosphere?

So, we have surface pictures from two alien planets, Venus (captured by the Venera 13), and Mars (captured by the rover). Both of these pictures appear to be very dusty. For Venus we see strong ...
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### Divide a star catalogue to optimize star search

I'm continue working on my Planetarium software and I have a doubt. At this moment my star catalogue is very small, but I'm planning to use a bigger one. To optimize the search inside this catalogue ...
62 views

### Is the size and heat of a star important in the development of a solar system?

How do the size and heat of stars affect development of solar systems and what kinds of planets can develop? Is it possible to orbit supermassive stars? Furthermore, would star's unleashing violent ...
456 views

### Equation to find distance between objective and eyepiece

I have a home made astronomical telescope with 100 cm objective lens and 5 cm eyepiece.when viewing an object in infinity the distance between eyepiece and objective is 105 cm. So how could I ...
177 views

### Can we have a second moon?

This question sounds like silly and rather fantasy filled. But can our earth's gravity capture a sizable asteroid and make it rotate around our earth like our moon which become visible from ground. Is ...
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### Is it plausible that Mars could have been one of Jupiter's natural satellites at one time?

Would more questions regarding the planet be answered if this was the case?
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### What is Color Index?

I found this Wikipedia page on this property called color index. Unfortunately, I could not find a source that explains this property well. My interpretation is that color index is the brightness ...
133 views

### Does the Sun orbit the Milky way in a (kind of) flat or inclined orbit or more of a sine wave? [duplicate]

I know it can't be a perfect ellipse or smooth orbit due to all the matter in every direction, and our Sun could be affected by a gravity assist of sorts if it passes close enough to another massive ...
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### Notable differences if all stars would disappear except the Sun

I am not an astronomy expert, but as of today, all other stars than the Sun have little to no effect on life on Earth. So I was thinking, would there be any differences for the Earth at all if all ...
240 views

### Can a gas moon exist?

Could a gaseous moon exist in the same way as a giant gas planet? All the moons in the solar system are rocky, or icy. Why shouldn't gas planets have gas moons?
187 views

### Is a black hole heavier than the star from which it was created?

I did some googling around and couldn't get answer to a simple question of black hole mass compared to the star from which it was created. It is well known that giant stars burn very bright and ...
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### Visibility of human activity on the moon

In this video the host of Test Tube Plus states that you can go out a buy a laser, point it at the moon, and see the retroreflector left by the astronauts. When you point at the right spot you'll ...
115 views

### Where did everything come from?

Where did all the material and gas contained in our universe come from? If it was the size of a "coin," then it could not have contained all the matter that is in our universe today before the Big ...
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### How bright can white dwarf stars glow as they accrue matter?

I realize this is kind of general as it would depend on the size of the white dwarf and the rate of accrual. The general idea I got thinking about is what would happen if a white dwarf star - lets ...
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### How do we know that our galaxy is a spiral galaxy?

I know that our galaxy is spiral in shape, but I'm wondering how the scientists found out that our galaxy has a spiral shape. I don't think we can see the entire galaxy from telescopes on Earth, ...