# All Questions

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### On analogies between gas and stellar systems

Analogies between (typically) ideal gas and stellar systems are not only intuitively valid to some extent, but have been established and used in the studies of stellar clusters and galactic systems, ...
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### What is the ultimate fate of a cluster of galaxies?

We're fairly aware clusters of galaxies drift apart due to space expansion, which will drive them out of each other's cosmic event horizon eventually, leaving them separate, alone, each a single ...
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### How do scientists determine the age of stars?

I was Googling about the oldest galaxies in the Universe. Everywhere is written that their age is known by the light. Referring to this line "Since light travels at a set speed, if you look at a star ...
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### How would I measure that I'm at a pole?

How would a person measure that he is at a planetary pole? My first inclination is to use a sextant to ensure that the Sun remains at a constant inclination. However, due to the orbit around the Sun ...
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### Does a planet's mass or gravity affect the height of it's mountains?

According to this Wikipedia page, the top five highest mountains on Mars (and the highest on Venus) are all taller than Mount Everest (and Mauna Kea as measured from the ocean floor). Does a planet's ...
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### Why is the interstellar medium so hot?

On this link, it states the following: "large assemblies of galaxies that are permeated by even larger amounts of diffuse gas. With temperatures of 10 million degrees or more". How are these ...
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### Generalised planets?

There is somewhat of an abstract way of generalising the notion of planets. Standard definition of planets is, obviously: "planets are the objects formed from the residual material surrounding a ...
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### Does our universe have to be embedded in a higher dimensional space?

I've heard that our universe may be open or closed. If it's closed it might have a toroid shape. If this is the case, would that imply that our 3 spatial dimensions have to be embedded in a higher ...
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### What's the fastest moving object in the universe?

We know that nothing can have proper velocities larger than the speed of light in vacuum. But are there any objects in space that get close to it? Any comets, or other objects thrown by gravity or ...
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### What do we know about the lifecycle of the Milky Way (or any other spiral galaxy)?

I know that the Milky Way will collide with Andromeda in the distant future but based on what we know so far there is a supermassive black hole in the center of each galaxy and thus the Milky Way will ...
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### How can only 1 magnetic pole of the Sun change at a time?

I read some news stories about the current Solar maximum and the flipping of the magnetic poles. They say that one of the magnetic poles has switched polarity and the other will switch in about a ...
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### Can I see comet ISON from Saudi Arabia?

I live in western Saudi Arabia, I am trying to see the comet ISON, reading here and there tells that I can see it by naked eye somewhere next to the constellation leo, I used an app to tells me where ...
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### Inflation cosmology: slow-roll inflation versus tunneling between two vacua

In slow-roll inflation models, the early inflation of the universe is driven by the flat non-zero part of the inflaton potential, and it ends as the ball rolls down the cliff and the potential energy ...
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### How can the equation of state for cosmic strings and domain walls be derived?

In this article which nicely explains why it is really the quantity $\rho + 3p$ which is relevant to determine if the expansion of the universe is accelerating or decelerating by making use of the for ...
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### Why is there billowing dust in nebulae?

Why do some nebulae look like the billowing clouds? Wouldn't that require something like a viscosity in empty space?
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### What is the distance that the Moon travels during one orbit around the Earth?

What is the distance that the Moon covers in one orbit around the Earth, and does it always take the same amount of time, or does it fractionally differ on each revolution?
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### Calculate Distance To Stars

I was just watching a lecture from Carl Sagan. He talked about figuring out the distance to the stars; it got me interested in learning more about the subject. As far as I know, the Inverse square ...
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### Will Neptune be visible with the naked eye if I am standing on its satellite

Assume that I am standing on one of the many satellites of Neptune. Will I be able to see the planet with my naked eyes (without any sort of visual aid). If I was to stand on Moon I would be able to ...
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### How does a Bahtinov mask work?

For focusing the image of a telescope, one can use a Bahtinov mask. How does this mask work, and how did Mr Bahtinov get the idea to cut such a peculiar shape? Is it possible for me to design my own ...
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### Crab Nebula Time Period

I've learned that the time period for a rotating neutron star, i.e., a pulsar is very accurate and can be used as an interstellar clock. But according to Walter Lewin's 8.01 Lec 19 on classical ...
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### How are the newly discovered Janus/Epimetheus rings different from the other rings of Saturn?

What are the newly discovered ring systems of Saturn, and the circumstances relating to the discovery? Is there something that makes them different from the old well-known rings, like their formation? ...
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### Open data for satellites positions

Is there a site / service where I can get the data for the positions of satellites (I mean artificial satellite, ISS, etc.)? I know that some sites provide a visualization of these positions, but I'm ...
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### Solar maximum and minimum

What are solar maximum and solar minimum? Is there a relation between sun spots and solar maximum and minimum? Thank you!
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### How can we be sure that we have identified very distant stars correctly?

From reading this question on calculating distance to stars and from a bit of background reading on the standard candle theory I still don't see how we can confirm that a star we see at one distance ...
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### Can the supernova remnant SN 1572 be observed by amateur astronomers?

The SN 1572 remnant, also called Tycho's supernova remnant, is beautiful in X-ray images. It seems to be rather dim in visible light. Are there any amateur photographs of this object? How long are the ...
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### Reference material [migrated]

I am interested in learning about astronomy from a rigorously mathematical perspective (astrophysics textbooks) whilst enjoying the subtleties of observations and pictures like a Dorling Kindersley ...
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### Day and night temperature on an earthlike planet with longer rotational period [closed]

I'm trying to understand the climatic effects of the far future scenario of an Earth-like planet with a reduced rotational speed caused by tidal locking with the moon (day-night period of 28 days, one ...
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### Earth and ferromagnetism [closed]

Earth's core is a giant liquid iron ball actually. If I know well, the magnetic field of our planet (that protects the surface from some particles comes from the Sun) can exist because as Earth ...
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### Why is the Earth's center still hot after millions of years? [closed]

Why didn't the center of the earth cool after millions or billions of years? What keeps it hot?
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### Why isn't Earth a perfect sphere? [closed]

In general, almost everyone describes Earth as an perfect sphere, but in reality it isn't a perfect sphere. Is there any specific reason why Earth is not perfect sphere ?
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### How would Earth's climate differ if it's axis were tilted around 90 degrees like Uranus? [closed]

As the title states, what would the effect on Earth's climate be if it's axis were tilted approximately 90 degrees like Uranus? I'm specifically wondering about the effects on seasons, temperature, ...
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### What effect does the Earth's rotation have on plate tectonics? [closed]

I've been reading up on plate tectonics and found that there are several different driving forces involved. One of the main categories of driving force mentioned on Wikipedia is forces related to the ...
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### What does it mean for a star to go nova or supernova? Can I safely observe these?

What does it mean for a star when people say it goes 'nova' or super nova, what are the differences? More importantly, can I safely observe these with an amateur telescope? I imagine they would be ...
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### What's the largest non-spherical object in the universe?

Some asteroids and comets are non-spherical. But is the nature of big things and gravity so that large things in the universe are always spherical? What is the biggest object in terms of volume out ...
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### Why do black holes have jets and accretion disks?

If supermassive black holes possess the gravity required to prevent the escape of photons and other mass particles, why do jets and accretion disks form? They seem to indicate that something is ...
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### Might Oort cloud comets be exchanged between solar systems?

Considering their distance from their parent stars, might Oort cloud object such as comets be exchanged between passing stars (assuming that other stars have similar Oort clouds)?
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### How can I calculate moon phase and height?

How could I know what phase the moon is in when it's high in the sky during sunrise? How could I tell in general what its height in the sky will be at any given time?
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### Do we live in a galactic bubble?

I have heard a certain statement, which can be summarized succinctly into "we live in a local bubble", implying that solar system is located in an intestrellar dust underdensity region. This region ...
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### How can I measure the mass of eclipsing binary stars?

Is there any method to measure the mass of eclipsing binaries without using Doppler shift effect?
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### Colossus telescope, trying to outsmart aliens?

I was listening to Jeff Kuhn's talk on SETI's Colossus telescope project. Background: He explains his theory that a civilization living somewhere the galaxy would want to hide, and thus would ...
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### Stars at near break-up rotation rates

Accretion discs are ubiquitous in astrophisics. As a direct corollary, they are important for the following question. Consider the following model, representing one of the most simple models for ...
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### Planned telescope to detect alien waste-heat

I remember watching a talk by someone who designed a telescope to view a single star at a time. The purpose of the telescope was to detect waste-heat which would presumably be emitted by any ...
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### What is the most extreme weather found on another planet?

On Venus, there is really inhospitable weather, as well as within the gas giants in our solar system. Are there examples of even more extreme weather on planets found in other solar systems than ours? ...
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### Two species of dark matter?

At this point in time, evidence for the existence of dark matter has accumulated in many ways: it affects galactic rotation curves plays a major role in cosmology, and the evolution of structure in ...
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### What Causes the Large Radiation Fields Around Jupiter?

I had heard that the large radiation belts around Jupiter may be formed by liquid metallic hydrogen in (or around) Jupiter's core (which Wikipedia says haven't been observed in labs yet due to the ...
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### How exactly is the Initial Mass Function (IMF) calculated?

The Initial Mass Function (IMF) is the empirical function which describes the initial masses of a population of stars. My questions are, 1) What are the various IMF's which are used? 2) For each, ...
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### How many sun-like stars are there in the universe?

After yesterday's announcement of the Kepler telescope finding a huge amount of newly observed exoplanets, i saw a headline claiming that as much as 22% of sun like stars in the universe have planets ...
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### Is there a upper limit to the number of planets orbiting a star?

Our sun has 8 planets orbiting as well as a number of dwarf planets. Are there any calculations that hint as to whether this number is close to some theoretical maximum value or are we simply an ...
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### What are the differences between a Black Hole and a Supermassive Black Hole

From what I understand, the mass of a black hole should be nearly infinite, how much more massive can something get? Is the name to be literally interpreted such that a Supermassive Black Hole just ...
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### What happens to a star after it has become a red giant?

When our sun reaches the end of its lifetime , it will turn into a red giant. How long will it be a red giant, and what happens after a star has been a red giant? Does it turn into a planet after a ...

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