# All Questions

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### Two MOON's & One Earth?

Can any one explain to me What will happen to Earth if its Have 2 Moons Same Distance & 2 side of earth (North & south)? will it be good for Humans or bad?
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### How can black holes be sometimes so gaseous?

One of the most massive Supermassive Black Hole observed is the one at the centre of the galaxy NGC1600 with a mass of 17 billion suns. It would have a density of ∼0.01kg/m^3, or one part in 100,000 ...
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### a random distribution of RA&Dec

How to make random positions in Equatorial coordinate system? If I divide Dec between -90 and 90 evenly, the space distribution is not random.
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### Why is the CMB not simply travelling parallel to us?

When we look to the distant farthest reaches of the universe we see light that was emitted at the big bang 14 billion years ago. But the universe was tiny back then so that light, which is only ...
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### Eyepiece projection photography

Nothing is showing up in the viewfinder of camera when I try to do eyepiece projection photography.could I have something set up wrong?
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### Would a viewer see Earth from the rim of Shackleton Crater?

I've been researching this but so far have not found an answer. If you were standing on the top of the rim of Shackleton Crater at the lunar south pole, would you be able to see any of Earth? I can't ...
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### Question regarding the Milky Way when calculating galactic space velocities for galaxies

I have been calculating galaxy space velocities (where proper motions are known) in order to measure their orbits of the Milky Way using the method proposed in the appendix of http://www.aanda.org/...
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### How do astronomers distinguish the spectral lines?

As a black body a star emits a continuous spectrum of light and other radiation. I've learned they are capable of knowing of what elements the stars are made of because of the spectral lines. But how ...
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### Milky Way mass fraction breakdown review

I'd like to know a breakdown of the mass of the Milky Way, by the major categories. So, something like ...
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### How would seasons at the equator be if the Earth were tilted 90 degrees?

If Earth's axis of rotation were tilted 90 degrees, what type of seasons would be observed at the equator. My prediction is that there would be no seasons, as the orientation of the equator would be ...
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### How close would merging black holes have to be to feel gravitational waves?

Recently LIGO discovered gravitational waves caused by two black holes that were orbiting each other, and then collapsed into one black hole. A few months later, we find out that this actually happens ...
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### an exercise from Spherical Astronomy by Smart

I want to solve this exercise from Spherical Astronomy by Smart: Prove that, in latitude 45°, the interval between the moment at which a star's azimuth is 90° east and the moment of setting is ...
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### Unable to achieve focus

I feel like this is going to be a duplicate of this question, Astrophotography - Unable to achieve focus with current setup. However, the suggestions to go to a straight adapter doesn't apply in my ...
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### How could universe inflate itself out of the very dense and curved early spacetime? Could it happen in a black hole too?

Wasn't spacetime as much curved as a black hole directly after Big Bang, because mass was so densly packed? Wasn't everything like an event horizon and how could things expand across it? Could ...
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### Send a rocket against orbit around the sun

I presume it's a bit simplified, but ... What if we launch a rocket, the same speed but opposite direction of the orbit of our planet around the sun. Will that rocket fall into the sun?
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### Distance and orbital period for terrestrial binary planets

This article, http://phys.org/news/2014-12-binary-terrestrial-planets.html, suggests binary planets could orbit each other at a distance of only three planet radii. For two earth-like planets, that is ...
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### Black hole darkness a result of gravity or temporal distortion?

Please correct me if I am wrong as I may have made some incorrect assumptions. Okay so we know that at some stage of "nearness to a black hole", light is no longer reflected back at us from the black ...
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### Is it possible to build space elevators? [on hold]

Can we build an elevator so high that it goes out of the earth's atmosphere and can be easily used to launch satellites??
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### Precision of geocentric gravitational constant

I am looking for an answer as to why the geocentric gravitational constant, μ, defined as the product of the gravitational constant, G, and the mass of a body (earth in this case), M, can be ...
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### Having some weird issues with my tracking (Advanced VX)

I need your help! I am having some weird tracking issues with my tripod (Advanced VX). When I setup and calibrated my scope yesterday I took this picture of NGC6888 (90s exposure): As you can see ...
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### What is the Galactic Latitude and Galactic Longitude? How is different from the latitude and longitude we use on Earth?

It has to something with the positioning of sun and galactic center of the milky way but I wasn't able to understand how for a given star, its co-ordinates are calculated. Some explanation would be ...
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### How can there be 1,000 stellar ancestors before our Sun?

I've heard from a few sources recently that the Sun is a 1,000th generation star, meaning it had a thousand stars that came before it based on it's heavy element content. I understand that earlier ...
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### Is extraterrestrial mining more difficult or impractical for bodies without plate tectonics?

This article talks about the possibility of mining Uranium on the moon. Since the Moon lacks the geological forces that have created veins of concentrated minerals on Earth, would extraterrestrial ...
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### Black holes and material interaction

I was wondering about what happens when a black hole forms. I mean, a black hole forms when a star collapses, so when an enormous mass of protons, electrons, neutrons etc collapses together. But when ...
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### Why are stars so far apart?

So, this is mere musing, but it seems that stars are quite extremely far apart. I tried to determine the mean distance between nearest neighbors for stars (in just our galaxy) but I'm not sure what it ...
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### What would happen if Jupiter and Earth were at the same distance as the Moon is from Earth?

If Spock came with a super machine capable of moving planets, and placed Earth so close to Jupiter as the Earth's moon, the gravity of Jupiter would make us fall into it?
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### How to understand orbit definitions

I've been reading about satellite observations (such as this one). The writer uses terms such as these to define the orbit: ...
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### How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it?

How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it? We know the Sun is orbiting the galactic center every 225 million years. But how far are we from the ...
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### Blackhole Finding Techniques

I know of two methods for finding exoplanets: the transit method and the radial velocity method. These two methods work as follows: Transit: we observe stars and watch for when a planet obstructs ...
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### A phonecall inside a blackhole

I was wondering what a phone call would be like entering or falling t=into a black hole. Due to the massive density of the black hole and time would feel slower, how would that appear to the person on ...
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### Unknown moving objects

Last night, I used my new Sony WX500 camera to get long exposure pictures of the sky from my backyard. I used the "Heavens Above" app to find out when satellite flares would happen and I even got a ...
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### Protocol for establishing longitudinal meridians on other heavenly bodies

When we first observe a new heavenly body (it could be a new star, asteroid, etc.,or a minor planet in our own solar system), are there any procedures set in place for establishing a system of ...
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### What is the name of the cycle whereby the lunar azimuth and altitude recur on a given day?

Like the Metonic cycle, except for position in the sky, not phase. Original question: If I look up at the moon tonight, how long before it is in the same apparent position, and same phase, again? I ...
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### a math problem in Spherical astronomy [on hold]

this is an exercise from Spherical astronomy by Smart, which i want to solve: $\frac{d \eta}{d H}= -\cos(\phi) \cos (A) (\sin (z))^{-1}$ when $\phi$ is latitude, $\eta$ is parallax, $H$ is sidereal ...
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### How much magnification is needed to see planets of solar system?

I have a 3inch Newtonian reflector telescope with 300 mm focal length. I can use highest magnification of 75x using a 4mm eyepiece. But in 75x I can't see details of Jupiter what was expected. Instead ...
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### Why don't we have 2 Summers and 2 Winters?

Due to Earth's elliptical orbit, its distance from Sun varies by almost 5 million Kilometers (147 million Kilometers at closest point & 152 million Kilometers at farthest point, i.e. almost 3% of ...
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### Cluster of fast moving stars

We live in NW Tasmania in a country town and tonight out walking I pointed out a long cluster of stars to my sister as they made an unusual shape but then we realised they were moving really fast - we ...
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### A quick (elementary) check on arsecond conversion to sky distance in parsecs

I just wanted to double check I had something correct. If an object, say a nebula, is measured to roughly have a diameter or extent of, say, 250 arcseconds, would its diameter in parsec simply ...
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### Is it possible to move a planet out of its orbit? At least a lighter planet?

As observed by many researches our sun will be exhausted in the distant future. So does anyone think that driving our planet (or any planet) closer to the sun for more light and heat is a solution for ...
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### Warm and Hot dark matter density profiles

For cold dark matter, density profiles are well known and easy to find information about - eg. NFW, Burkert, Einasto, and others. But for some reason I couldn't find explicit expressions for the ...
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### Could the Sun's magnetosphere block extraterrestrial contact?

I was reading how certain strong magnetic fields can block or alter radio waves so bearing this in mind would it be possible for the Sun's magnetosphere to block attempts to establish radio contact ...
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### What (actually) is a radio “homology telescope” and will the 500m dish in China be one?

This question is about design aspects of large radio telescope dishes which allow them to flex under the influence of gravity as they change elevation angle, and still maintain good optical ...
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### How can the Sun burn without oxygen?

Allright I am a 17 year old student, that only just figured out that the universe is amazing! Thanks to Dr. Neil Degrasse Tyson I raised a lot of interest in the universe. Due to his latest show "...
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### Could this three moons system be stable?

In my fictional world I have selected all parameters to maximize the Hills Sphere of my planet. The planet has three times Earth's mass and it is located in 2 AU from its star that's 1.4 times more ...
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### What are the requirements to become a planet? [duplicate]

A planet is taught to us (at primary school) as a ball of rock that orbits around the Sun and is similar to our own planet, Earth (in as a ball of rock). But of course, humans have to be more specific ...
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### How many planets are there in this solar system?

So, in school (that's a long time age) they have been teaching us there are 9 planets in our solar system. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto But every now and then I ...
Suppose I have a large thin disk of rotating gas in a galaxy -- the disk has a maximum inclination-corrected $V_{max}$ and a maximum radial extent of $R_{max}$ corresponding to that $V_{max}$ ...