# All Questions

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### State of the stars

This question may sound silly but I'm really not pretty sure whether the stars are rotating or stationary.If they are not rotating what makes them to be stable?
415 views

### Do meteorites streak across the sky in the same direction?

Once while camping with my family as a child we all watched a meteor shower in the summer (in the month of August). All the meteorites streaked across the sky in the same direction. Obviously, this ...
145 views

### How fast is the universe expanding?

I've hear several theories stating that the universe is expanding faster than the speed of light, others claim that the universe expands faster the further away you measure it. Which of this is ...
595 views

### 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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### How to get the longitude/latitude from solar zenith/azimuth?

How do I get the longitude/latitude from zenith/azimuth? Or how can I position my sun in a 3d application? code extracted from here ...
681 views

### Can an amateur astronomer bounce a laser off the moon?

In the TV show "Big Bang Theory" episode "The Lunar Excitation", the gang fires a laser from their rooftop, bounces it off mirrors on the moon, and measures the laser coming back on a computer. Is ...
129 views

### Why is a meteorite impact on the moon visible as white light?

You can watch a video of a meteorite impacting the moon at the npr.org website. Why does the impact produce white light? I understand that the impact is like an explosion, but there is no air on ...
267 views

### Why are most lunar maria on the visible side?

Is there any reason why the Earth side of the Moon has enormous plains and mountains, while the far side contains just few small ones inside largest craters?
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### Spotting the International Space Station (ISS)

Recently, I visited the NASA website which provides sighting locations to see the International Space Station (ISS). As we all know, we can even see ISS with the naked eye in a clear sky as a passing ...
211 views

### 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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### How far apart can two people watch the moon simultaneously?

Obviously there's a limited part of earths surface where the moon is visible at any given time. I imagine the area of this surface would be a lot smaller than the area where the sun is visible at any ...
281 views

### Why does e.g. Hubble's secondary mirror not block part of the picture?

The SOHO observatory has an opaque object in the light path that blocks the direct light from the sun making it possible to observe the corona. Hubble and many other telescopes have a big primary ...
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### Do planetary surface temperatures change in unison in a solar system?

Are there any known correlations between the changes in planetary surface temperatures in a solar system? If so, do the farthest planets have smaller albeit correlated changes?
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### How would light from a blue or red star affect the way we see?

How would things look if we saw them through the light of a blue or red star? Would there be any changes?
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### What is the maximum number of planets in the habitable zone?

At present, it seems like we are alone in our solar system. How many earth-like planets would fit into the habitable zone of the solar system? The orbits should be stable for quite a time, i.e. for ...
150 views

### Black Hole, Object or Portal? [closed]

Some say that a black hole is a rip in space-time, a portal linking two points in the universe as one. How sound is this? I've read that when a giant star collapses, what is left behind (a massive ...
155 views

### Age of the universe

A Galactic year is estimated to be around 250 million "terrestrial" years. That means there will be about 4 rotations per billion years. And age of the universe is estimated to be near 13.8 billion ...
166 views

### If we lived in a multiverse, what would our universe most likely then be named? [closed]

For instance, we live in the Milky Way Galaxy. We don't just call it "The Galaxy", because we know there are multiple different galaxies. So if we lived in a multiverse, it wouldn't make much sense to ...
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### Is light bending around my finger? [closed]

I was hoping that astronomy enthusiasts/scientists would help me out with a simple question about light. Hold your outstretched hand up to any bright light source (the sun, or even a light bulb) so ...
48 views

### Heavy bombardment - Why has things cooled?

I was always taught and lead to believe that at the beginning of our solar system, there was a period of heavy bombardment, which is conceivable. Why has it just stopped and we are at peace from ...
2k views

### 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 ...
2k views

### 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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### What is that void that the universe is growing into? [duplicate]

We understand that this is the universe and it is essentially full of space and time, but what is on the outside of the universe, and isn't that nothing, something, and how far does that reach. I.e. ...
846 views

### Why does the darkening of the Moon go from left-to-right during an eclipse?

In anticipation of the upcoming April 2014 lunar eclipse, I decided to use the 3D virtual planetarium software Stellarium to simulate what it is supposed look like where I live, since I've never ...
68 views

### How close would quasars have been to each other?

My understanding is that quasars are the early phase of formation of galaxies. At the time quasars were forming, the universe would have been smaller and therefore things closer to each other. About ...
238 views

### 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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### Are many exoplanets synchronously tidally locked like Mercury?

The only tidally locked planet in the Solar system i Mercury. But it is synchronously tidally locked 3:2, because of the relatively high eccentricity of its orbit, so doesn't turn the same side ...
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### Why doesn't the earth's surface collapse onto itself? [closed]

From what I know the sun (or any other star) nuclear fission keeps it from collapsing under its own gravity until the fuel runs out, if that's so why doesn't the earth surface like the tectonic plates ...
303 views

### Location on (or in) the celestial sphere

First off, I apologize if I am breaking any site-etiquitte. Secondly, this is probably extremely elementary. For a lab, I was given the question: When we are sitting in a planetarium, where are ...
75 views

### 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 ...
117 views

### What method is used to calculate the 'quality' of a solar/planetary image?

What sort of algorithm is used to calculate the relative quality of an image, such as is performed by PIPP, Registax, or Avistack? Such applications take planetary or solar images and prior to ...
107 views

### 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? ...
2k views

### 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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### How can we infer the mass of SMBH in galaxies that are not active anymore?

I know it is possible to infer the mass of a supermassive black hole (SMBH) by many methods, i.e., stellar orbits for out Galaxy, Iron line profile from the accretion disk, and probably other methods ...
8k views

### Did atoms in human body indeed come from stars?

I think I am not alone who saw videos about that we (humans) are made of same atoms which someday were in stars. In other words, some atoms in our bodies are from stars which exploded billions of ...
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### If NASA is going to capture an asteroid with a spacecraft, wouldn't a UFO be able to manuever a celestial body? [closed]

This article got me thinking If NASA is going to use our primitive space exploration technology to capture an asteroid wouldn't an Extra Terrestrial species have used UFO's to maneuver celestial ...
327 views

### Can someone explain a Geostationary Orbit in a simpler way?

According to Wikipedia (link), a geostationary orbit, geostationary Earth orbit or geosynchronous equatorial orbit (GEO), is a circular orbit 35,786 kilometres (22,236 mi) above the Earth's equator ...
123 views

### strange moonset around 10 pm (3.2 2014, NZ) - explanation?

during a visit to New Zealand we observed (on 3.2 2014) a strange moonset in Te Anau. Around 10 pm, shortly after sunset, the moon appeared, but then quickly began to go down, and about 1 hour or ...
408 views

### Do black holes die?

I know of stars actually dying (exploding as a supernova) but I have never heard of what happen to black holes. Do they continue to live forever, waiting there for more matter to absorb? Do they ...
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### Could I create a staircase to the moon and walk to it? [closed]

Assuming one could create a staircase and walk to the moon, would escape velocity still be a factor in leaving the Earth's gravitational pull? I'm not a physicist but am just curious to know.
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### Can we only see the past of the universe? [duplicate]

So I was reading some interesting stuff about universe and Big Bang and wanted to make sure one thing. As far as I understand everything we can see about universe is the past, right? I mean all the ...
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### What would happen if we put a small part of White Dwarf or Neutron Star on Earth?

I would know what would happen if we put a small part (let me assume 1 cm$^3$) of White Dwarf or Neutron Star on ...
494 views

### Why haven't Earth and Venus got any tiny moons? Or have they?

Why haven't some meteoroids gotten caught in Earth's or Venus' orbit? AFAIK most meteors are tiny fragments from comets. Shouldn't some comet tail sometime have passed Earth orbit at velocities ...
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### What are the concrete technical arguments supporting the idea that the wave function of the universe can be written as partition function?

In this talk, the not yet settled down idea that the wave function of the universe could potentially be written as the partition function of a scale invariant statistical field theory is mentioned: ...
840 views

### Is everything quantum entangled?

So, I am learning about quantum entanglement in my quantum course and had a thought. If the Big Bang is the creation of everything - time included, and this came from a single "source". Would it not ...
280 views

### What are the masses of the two stars (given the information provided)?

If anyone would at least be willing to point me in the direction of finding the answer, or help me solve it I'd appreciate it. I don't know how to go about this, and need to know how to solve this on ...
120 views

### What does black hole evaporation correspond to in the accelerating universe / black hole analogy?

In the same way, as a black hole emits Hawking radiation corresponding to its temperature $$T = \frac{\hbar}{r_{BH}}$$ the accelerating universe can be described as all of the stuff falling ...