# All Questions

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### Galaxy Cluster Temperature

I've read once in an article that the temperature of the medium between the galaxy superclusters is extremely high. What does that temperature really mean? particles' velocity? Why is that so? Is ...
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### Are there any Stars we know don't have planets?

We have been looking for planets around other stars for a while (see related Are there any other Earth-like planets in the universe? ) and we are finding lots of planets, some of them are Earth like ...
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### why does pluto have a high orbital inclination

Pluto has a high orbital inclination compared to the planets in our solar system. What has caused Pluto to have such a different orbit -- was it always like this, or did something happen to make it ...
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### Can we see Earth by looking into space?

It is known that spacetime is curved,so I am wandering to know if its possible to look into space and we see earth (light from earth long long ago). Did I understood spacetime correctly and if its ...
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### Any freely available large stellar spectra catalog?

For a non-astronomy personal project I would like to have a large set of optical stellar spectra combined with absolute magnitude when available. I search for a dataset that contains 10k - 10M ...
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### Linear motion in the equatorial frame

I would like to calculate how the RA/Dec changes when an object has an apparent linear motionin the equatorial sphere. For example, more or less what an artificial satellite would do in a circular ...
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### First time visit to dark sky stargazing site: what do I need?

Complete newbie here. I have an opportunity to visit one of the few designated dark sky sites here in Pennsylvania, Cherry Springs State Park. I plan on camping out over night, but I have never gone ...
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### Massive Nearby Stars

Is there a possibility that I will find records of stars with masses around 25-30 solar masses within 30 parsecs of solar system. If not, how far do I need to look?
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### Lack of planets in the Oort Cloud

With the current news about the possibility of a planet in the Oort cloud, I was thinking, why is the matter in the Oort cloud distributed so? It makes sense that inside the planet region there is not ...
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### Can a galaxy splits into multiple galaxies?

Is there any naturally occurring event powerful enough that can cause a galaxy regardless of shape and size to divide itself into two or more smaller galaxies?
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### Shall we say now that Pluto is “larger than Mercury” ?

http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20150717-3 "Scientists working with NASA’s New Horizons spacecraft have observed Pluto’s atmosphere as far as 1,000 miles (1,600 kilometers) ...
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### How significant is a planet's density to the formation of life?

I'm doing some writing set on a fictional earthlike planet that for reasons needs to be substantially larger than Earth but can't have substantially higher gravity. I've been able to compromise with a ...
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### why do peple think the most energetic events in the universe are GRBs?

Recently people have found supermassive black hole binaries with very short orbital period. link They should be more energetic than GRBs when they merge, right? It seems people do not talk about ...
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### How did our ancestors discover the Solar System?

I wonder, how did our ancestors discover the Solar System? They did not have any telescopes to see distant objects, right? Even a planet looks like a star from a distance. They discovered the ...
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### about H$_\alpha$ and H$_\beta$ lines in astronomical objects' spectra

Generally there may be some line ratio between the two lines. If H$\alpha$ is strong, it is quite possible we can see H$_\beta$ too. Is it possible we can see H$_\beta$, but can not see H$_\alpha$? ...
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### Was the Universe expanding before the beginning of inflation?

My point of view is that first there was the Big Bang singularity, and then the period of inflation which resulted in the observable Universe becoming many times bigger. But was the Universe expanding ...
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### Why do we observe spectral lines of specific energy?

The basis of my confusion is that atomic orbitals, even when described accurately by quantum numbers, have definite energies, meaning they represent energy eigenstates of the wave function. They're ...
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### How do we know Milky Way is a 'barred' spiral galaxy?

In reference to the question, "How can we tell that the milky way is a spiral galaxy?" The answers there clearly sum up the question asked. But Milky Way is not just a spiral galaxy. It is further ...
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### How do we know the universe's expansion is speeding up?

Please forgive my ignorance, I am not an astronomer, just an interested layman. The further away a galaxy is from us, the faster it is moving away from us. But the galaxies we see exist in the ...
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### Is the Tombaugh Regio on Pluto visible from Earth?

Is the Tombaugh Regio on Pluto discernably visible from Earth ground based or Earth orbiting telescopes? And more generally, can surface features seen in Hubble images be matched with images from New ...
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### Are lunar occultations visible to the naked eye?

The Moon occults a lot of stars. But are these events visible to the naked eye? Won't it be blinded out by the crescent even at its thinnest just before sunrise? Did ancient astronomers actually ...
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### Whats to be gained from the New Horizons mission once its beyond the Kuiper Belt?

Now that we have seen what Pluto has to offer and New Horizons is headed to the Kuiper Belt, is there anything we can gain from the mission in interstellar space after it travels beyond the Kuiper ...
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### Why are radio telescopes shaped so differently than optical telescopes?

Why are radio telescopes typically only a dish with a receiver above it, while optical telescopes have a primary, plus secondary and sometimes even a tertiary mirror? In other words, why do radio ...
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### Real images (not “artist concept”) by NASA

Does NASA make publicly available real images of missions in an organized manner? What I mean is: Say I'm looking for the images taken by New Horizons - a simple list of the images in chronological ...
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### which pulsar has the longest spin period so far?

Vela X-1 has a 283s spin period, while this one may have a 2.7hr spin period. However neither of them is included in ATNF catalog. They are not included in $p-\dot{p}$ diagram either. The longest ...
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### How can they tell no asteriods will hit earth in the next hundreds years?

It has come to my mind this interrogation : How can they tell no asteroids (big enough to create damage) will hit earth in the next hundreds years? Because, so far, we were unable to get a clear ...
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### How many nested stable (1 Mio years) orbits are theoretically possible?

If we look at our solar system we have the sun which has planet orbits and planets have moon orbits. If we look at the possible size difference from hypergiants to small asteroids why shouldn't it be ...
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### Official Definition of Satellite?

So I had an argument with a friend, which was about whether the Moon is a planet or a satellite. IAU 2006 Resolution B5 gives definitions on what it is to be a planet, but there is a vagueness, as I ...
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### Speed of light through the ISM and Wavelength

Articles written about fast radio bursts describe the signal's short-wavelength components arriving before its longer-wavelength components, suggesting energy-dependent time delays in the interstellar ...
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Regarding solar system dynamics, i.e. planets in stellar systems and moons in planetary systems, this is often mentioned in the literature, but it is difficult to find a good analysis/explanation of ...
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### Can stellar black holes cancel each other?

Hypothetical question: when a pair of identical stellar black holes are very close to one another wouldn't the side facing each other experience lower gravitational force? How is this logic un/sound?
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### Planets and moons positions in cartesian coordinates?

Is there freely available and reliable source, where one can find positions of planets and moons of the Solar system at given time in cartesian coordinates? (I am writing a simple gravity simulator ...
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### Historical astronomical lunar tables

I hope this is the right place to ask this question, and I apologise if not. I've come across a date written in an old book, but it is written using what seems to be a lunar/zodiac system. Below is a ...
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### Is the Universe really expanding at an increasing rate?

Here's what I just read from Wikipedia's page on the Hubble Space Telescope: While Hubble helped to refine estimates of the age of the universe, it also cast doubt on theories about its future. ...
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### If Venus and Mars changed places, would we then have 3 habitable planets?

This is the supposition: Venus is too hot, Mars is too cold. If they switched places then Solar energy would change to make both more Earth like. We might as well have had three instead of just one ...
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### Which kind of properties can we get for cosmic ray particles hitting on an optical ccd?

It is very common that we meet cosmic ray particles in optical images recorded by CCDs. You can see the "snowflakes" in the hubble images below: Generally we should remove them in order to get ...
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### Energy required for light speed [closed]

It is said that in order for us to travel at the speed of light, there has to be an infinite amount of energy. Light is made up of photons but photons themselves do not have an infinite amount of ...
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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 ...
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### Can you see man-made lights on the dark side of the Earth from the surface of the moon with the naked eye?

This question is prompted from a comment on this answer: Could a person on the surface of the moon see man-made lights on the dark side of the Earth with the naked eye? If not, how much magnification ...
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### How significant and accessible is modern Chinese astronomy?

Is China fully integrated in the international astronomical community, or does military secrecy and language problems and sanctions (ITAR) or something else stand in the way? Does China have valuable ...
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### Is there a mechanism that makes small moons more rounded than comets?

67P/Churyumov–Gerasimenko has a highly irregular dumbbell shape. But the sample of comet shapes observed is very small, so I wonder if irregular shape is the norm for comets and for small moons. Many ...
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### what planet is the most radioactive?

So as I understand it the source of most geothermal energy on Earth is due to radioactive decay. Jupiter is the most massive planet but if the bulk of it's mass comes from gaseous elements instead of ...