# 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 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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### Virial coefficient when computing dynamical mass enclosed by a rotating galactic disk of gas

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 $V_{max}$ ...
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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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### 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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### 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 would Earth be like without the Moon?

If somehow our moon was destroyed (for example by an asteroid) what would happen to Earth? Would the Earth be affected by the absence of the moon? Would humans be able to live normal lives without ...
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### Is there always visible airglow from space? [migrated]

Looking at time lapses taken from the International Space Station, I discovered that earth atmosphere can glow at night, even when it seems that those pictures were taken far away from auroras. ...
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### What is Half-life of knowledge in Astronomy? [closed]

This question is inspired by this answer. About 16 years ago, we knew different numbers of stars in Polaris system than we do now. Even though we have come a long ...
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### Where can I find the DR12 SDSS dataset in their website

I have to cross-match the SDSS DR12 dataset with that of GALEX but apparently I cannot find the fits document which has the same field as that in GALEX. I have explored the website but I couldn't find ...
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### How many actual stars are Polaris?

I am getting conflicting accounts everywhere. I heard astronomers saying Polaris is a 3-star system. Some say they are binary but are optical-doubled with a 3rd. ...
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### Are a white hole's forces completely opposite of a black hole? [duplicate]

Would not all the forces of a black hole be opposite if the light is escaping from it? For example, rather than it attracting everything to it, would it repel everything?
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### How was Earth's “quasi-satellite” 2016 HO3 “first spotted” and it's orbit determined?

Under a question I asked a few days ago Have there been any documented mini-moons since 2006 RH120? @Hobbes mentioned the recent news about 2016 HO3 - a near-Earth asteroid that stays near Earth ...
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### How can I convolve a template spectrum with a photometric filter response spectrum?

Suppose I have a template stellar population spectrum (say, from Bruzual & Charlot 2003) which runs from like 1000 Angstroms to 160,000 Angstroms and which has x-axis wavelength units of Angstroms ...
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### Question on retrograde motion [duplicate]

I am a beginner Does planets exhibit retrograde motion (eg Mercury and Venus) only because of earth rotation? Or is there any other reason? Please clarify
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### What starting circumstances have to be for “grand tack” hypothesis to work, and why they are lacking in other planet systems(as far as we know)?

I recently read a bit about "grand tack" hypothesis. It was extremely interesting and it seems to reasonably well explain many features of our solar system. At the same time it supposedly is ...
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### How to find which part of the sky a photo contains?

I was taking some photo stacks yesterday, and I also took a plenty of random ones (pointed not at a specific object) too at 200mm. However, I've ended with a shot but I have no idea where I pointed ...
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### Could the word “multiple stars” include binary stars?

We are translating some illustrated book for kids about astronomy, and then have a question as in the title. Referring to Wikipedia etc., It appears that "binary stars" represents the star systems of ...
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### Survival on a rogue planet [closed]

Are there any planets not orbiting a celestial body which can support life despite the temperature? Also what is the absolute minimum temperature that life can survive in?
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### Negative Spectral Flux Density

I am working on a project and using some satellite images. In some of the images the Spectral Flux Density is negative. What does it indicate?
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### Can a rogue planet neither orbit around a star nor a galaxy?

As we know, rogue planets don't orbit around a star, how about galaxy? Can a rouge planet not orbit around a galaxy?
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### How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

Suppose I have a wavelength array for a spectrum in units of Angstroms. Suppose further that the wavelength has "uniform logarithmic spacing" such that if I just take the difference in Angstroms ...
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### How do I reduce planetary photometry to standard viewing geometry using phase angle?

I'm trying to make light curves for Pluto using old data. Most papers give magnitudes "reduced to standard viewing geometry" of r = 39.5 AU, Δ = 38.5 AU, and α = 1 degree, where r is ...
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### “Extinct Species” of meteorite - how quantitative is the statistical analysis?

This recent paper in Nature A new type of solar-system material recovered from Ordovician marine limestone is available to read on line, and Figure 3 is already widely publicized. Comparison of ...
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### why was the probability of one in 10 billion per planet considered highly pessimistic by a recent study on aliens? [closed]

A recent article about the existence of extraterrestrial life claimed that "unless the probability for evolving a civilization on a habitable-zone planet is less than one in 10 billion trillion, then ...