# All Questions

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### When did the Moon stop?

According to various theories the Moon was created around 4.5 billion years ago. About all of these theories suggest that it was rotating around its axis at that time though. Currently, Moon is at ...
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### What is Event Horizon of a Black Hole? [closed]

The boundary of a black hole is said to be surrounded by event horizon - the point of no return! What is its significance in terms of general relativity?
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### regarding curvature of earth [closed]

i am having one doubt in earth's curvature.....this question may be dumb... How much we need to travel on earth to feel the curvature of earth. hypothetical case: for ex we are building a vehicle ...
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### Why do objects burn when they enter earth's atmosphere?

Why do all objects burn when they enter our atmosphere? is this because of our atmosphere composition? and does this happen on other planets as well?
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### What's the estimated remaining life of Halley's Comet?

I know that Halley's comet is seen from Earth every 76 years or so since a couple centuries. As it travels, and particularly when it comes near the sun, it loses some of its material (ice). Someday, ...
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### Time after sunset until star can be seen

Given a star's apparent location and apparent magnitude, how how many degrees below the horizon must the sun be for the star to be visible to the naked eye for an observer on Earth at a specified ...
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### Beta profile fit of Virgo cluster gas?

I'm looking for the parameters $r_c$, $\rho_0$ and $\beta$ in a $\beta$-profile fit of the Virgo cluster's ICM density. I just can't find a reference for it. Unlike for Coma (Abell 1656) where it's in ...
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### Weight of a celestial body

How do astronomers find out the correct weight of a planet tough there isn't any direct means to weigh them?What technique do they use?Just curious!
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### What is CMB radiation doing to the universe?

It is said that due to CMB radiation our universe has been expanding? Firstly what lead the universe to expand? What do scientists mean by dark energy? Will energy convert into matter?
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### Visibility of Apollo 11 module

I wasn't around when man landed on the moon in 1969. When I see the moon, I always wonder, were people able to see the rocket? Yesterday, I looked at the moon in daylight and wondered again. My ...
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### seasons elongating and shortening

I have heard of years with longer summers and winters and shorter springs and falls and vice versa because of a change in the earths axis. Is this from the procession that causes the season switch ...
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### Metallicity: What are the metallicity values of various galaxies?

What are the various values of metallicity of various known galaxies, like Milky Way, Large Magellanic Cloud, Small Magellanic Cloud, Andromeda and so on?
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### If an object with mass were to somehow go the speed of light, would it destroy the whole universe?

Would an object with mass traveling the speed of light destroy the whole universe because it would have infinite energy / mass? According to ...
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### How many stars are visible to naked eyes around Equator area?

In the best sky conditions, we can see about 44,000 stars in the sky. But what if I am located around Equator area? How many stars I can see? From what I know, the number of stars I can see should ...
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### Average amount of annual daylight at any place on earth

If this is the wrong group please direct me to the correct one. It seems intuitively obvious that the amount of daylight per annum should be the same for any latitude on earth. For example, 12 hours ...
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### What is the optimal escape trajectory from near a black hole?

Consider a space ship that is being drawn closer to a black hole. The crew begins to notice the effects, and discovers that they are nearing the black hole. They then manage to halt their ...
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### Why are spacecraft not air-launched from airplanes

I searched on the subject, thinking it could probably be cheaper to fly the spacecraft aboard a plane and then launch it from altitude. The only thing I found was this Wikipedia page, but it only ...
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### how to know the nature of the companion in a neutron star binary?

The companion could be a main sequence star, white dwarf, neutron star or black hole. We detected pulsar-pulsar binaryhere several decades ago. But if one of the pulsar does not radiate towards us, ...
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### Does Doppler shift affect apparent pulsar frequency?

We know that redshift and blueshift is the result of the frequency of light waves reflected or emitted by an object lengthening or shortening due to the relative velocity of the observer moving away ...
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### Choosing a diffraction grating

I am interested in doing some solar spectroscopy on my own for fun. How do I go about choosing the appropriate diffraction grating?
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### Satellite/Planetary Orbits

All planetary orbits contain 5 unusually stable points. These points are particularly important because they allow man-made satellites to orbit the Sun with a period equal to that of Earth’s. 3 of ...
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### What is the connection between moons, rings, and gaps?

I was watching this video and they said that the rock probably has a moon. Is the reason they assume it has a moon is because there is a gap between the rings created by the moon's orbit around the ...
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### Question about the formation of elements

So, elements such as iron, gold, etc. are formed from different types of supernovas, whether it's type 1A or 2. My question is, is it possible that there are elements that are formed that we never ...
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### What is the speed of light relative to (in space)?

From what I understand the universe is expanding faster than the speed of light and accelerating so that it's possible that a given galaxy: $A$ will no longer be visible to another given galaxy: $B$. ...
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### How can I calculate the orbital periods in a binary star system?

I have two stars, with known masses and known orbital radius. How do I calculate the orbital periods of both stars?
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### What would the sky have looked like when galaxies first started to form?

If I stood on a theoretical earth at the time that galaxies were just starting to form, what would the sky have looked like? Due to the smaller size of the universe would it have been densely packed ...
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### Absolute magnitudes of stars

Where to find comprehensive list of absolute magnitudes for stars of different spectral types? I need published paper or web page with data and reference to the source.
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### if the big bang only expanded the universe when and how did it originate? [duplicate]

If the big bang expanded the universe from a singularity point, that means that there was matter before, so where and how did matter form for the first time if it's even possible to know such a thing? ...
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### If oxygen was abundant in Neptune, would there be combustion?

Since Neptune/Uranus have high percentages of methane, wouldn't it be highly likely that there will be combustion (triggered by the lightning storms or any other factor) if oxygen was abundant? And ...
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### If the tilt of the Earth changed, would the tropics latitude change too? [closed]

I wanted to know if the tilt of the earth were changed to 30 degrees would the tropics of cancer and Capricorn also both change to 30 degrees?
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### the most accurate system that can show the positions of planets at my birthday [closed]

My birthday : 4 December 1982 If you have such astronomical calculator on your computer please send me the result ! Alternatively if you know an online astronomical service for my purpose please ...
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### How do kepler orbits account for planetary migration?

This article got me thinking if kepler orbits explain how a planet moves in a solar system how can a planet migrate as explained in the article. At some point don't the kepler orbits must need some ...
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### Can we conclude with reasonable certainty that there is/are no Type 3 Civilizations in our galaxy?

As per the Kardashev Scale, type-3 civilizations are defined as "civilization(s) in possession of energy on the scale of its own galaxy, with energy consumption at ~ 4 x 10^44 erg/sec". Considering ...
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### Data for red-shifting

I am looking for basic data regarding red-shifting that comes with reliable measure of distance of the emitting star.
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### Collimator for Dobsonian, same as Newtonian?

I have been looking on line for Collimator for my Meade Dobsonian. The only Collimators I can find are made for Newtonian Lenses. It's a 8" mirror with a 1.25" lens. Will this work for my telescope?
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### Why do the rings around the Gas Giants get their 'ring' shape?

In our Solar System, all the gas giants have ring systems. However, why do these rings form rings and not a cloud of debris around the planet?
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### how does Kepler stop exposure after a 5 minuate or 30 minute cadence time?

There are two kinds of cadence time for Kepler, 5 minutes and 30 minutes. I just know there is no shutter and the CCDs of Kepler can be locked after exposure. handbook But how to realize that? ...
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### Date and time system on moons

Supposedly, if humans were to establish a colony on one of the moons of a planet (such as gas giants in our own solar system), how could we possibly design date and time system? On Earth, we define ...
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### How did the reionization epoch make the universe “transparent”?

I've been reading about the reionization epoch of the universe, and it isn't entirely clear to me. As I understand it, very shortly after the big bang the universe was ionized, with the electrons ...
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### Compute Planet's Apparent Visual Magnitude

In a hypothetical solar system there exist: a sun of radius $r_s$ and absolute visual magnitude $V$ the Earth, with radius $r_e$ and distance from the sun of $1\,AU$ another planet, wit radius ...
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### how does redshift prove expansion is accelerating?

My astronomy teachers never would answer this for me... Redshift obviously indicates an object (such as another galaxy) is moving away, but how do we know its acceleration from this? It's my ...
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### Help in determining the features of an unusual, fictional star system

(Hope this is the right Stack-exchange site for this question) I'm working on a sci-fi RPG campaign, set on a very atypical location. Since this is a work of fiction, there's enough room for ...
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### Does mass create space?

Imagine two cubes each with the side 1 light year. One of the cubes is empty of any matter. The other cube contains a massive star. Does the cube which contains the massive star have a larger volume ...
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### Does Tobler's First Law of Geography Apply to Star Composition?

There is a principle in Geography called Tobler's First Law of Geography which states that "Everything is related to everything else, but near things are more related than distant things." Does this ...
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### How does solar activity (e.g. flares, coronal mass ejections) change over the life cycle of a Sun-like star?

As a Sun-like star is born from a collapsed nebula and generates energy by nuclear fusion some of that energy is converted to magnetic fields which fuel solar activity. How does that activity evolve ...
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### Instrument aperture sizes on Hubble Telescope

When looking at the diagram of the focal plane of the Hubble Space Telescope I noticed that the aperture sizes of most of the scientific instruments are very small. They occupy a very tiny fraction of ...
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### Meaningful theories of the shape of the universe

Normally, when people say "the universe is infinite" they generally mean something like "the observable universe is locally flat, it is easy to assume that it is flat way beyond the observable ...
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### Hamiltonian of general three body problem

i try to extend my analysis from planar restricted three body problem to the general one. Is there anyone that can help me to find out the Hamiltonian for this prolem in cartesian coordinates? I ...