# All Questions

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### If the hammer and feather move at the same speed why do comet and the tail particles move at different speeds?

From this exhibition by an astronaut on the moon dropping a hammer and a feather and showing they move at the same speed, why do the particles of the comets tail move away from the comet, slow down ...
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### Hypothetical beyond Neptune far away planets orbiting the Sun

The planet HD 106906 b was found at 650 AU from its home star, which is not a star much different from the Sun. Fomalhaut b is also a young planet that is orbiting very far away from its sun. These ...
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### How do we know that the intrinsic brightness of Cepheid variables corresponds to their period?

As I understand it, beyond parallax the next way of estimating the distance to astronomical objects is by using a relationship between the period and intrinsic luminosity of Cepheid variables. How do ...
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### What are some night sky objects I could see with my Celestron UpClose 20x50 Porro Binocular?

I bought this binocular because I've read countless times that one should start with a pair of binoculars before diving into telescopes. I've seen details of the moon and I can notice Venus round ...
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### Is the Jupiter-Sun system considered a binary system of some type?

Since Jupiter is very massive, it is the only planet (in our solar system) that has a center of mass with the Sun that lies outside the volume of the Sun. (Source) If Jupiter was a star, they would ...
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### How do we calculate the escape velocity of galaxies?

How do we calculate the escape velocity of galaxies? Do we have to know the total mass? What is the escape velocity for Milky Way?
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### Is there an orbit that could cause regular debris showers like in the movie Gravity?

[some spoilers] If you were in the ISS and orbiting the Earth roughly every 90 minutes, would it be possible for debris to be orbiting such that it passes you every 90 minutes? While Neil DeGrass ...
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### What theories are there in explaining the formation of the Pluto-Charon system?

After reading the question and answer to Effect of Charon on Pluto, a further question is this: how is the Pluto-Charon relationship explained? Specifically, what theories are there in how did the ...
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### What's the smallest scale at which dark matter has been measured?

What is the smallest scale at which we have detected "dark matter" (more kinetic energy than would be predicted)? If you don't mind indulging a follow-up: Would its detection on smaller scales be ...
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### What are the current observational constraints on the existence of Nemesis?

Nemesis is a hypothetical companion to the Sun on a very eccentric, long-period orbit. The star supposedly returns every few tens of millions years, driving comets into the inner solar system and ...
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### Calculate apsides without knowing eccentricity

How would one go about determining the apsides of an orbit, knowing only the current distance between the 2 bodies, the orbital velocity, and the period? Every formula I've seen requires eccentricity, ...
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### Why do the planets in the Solar system stay in the same orbital plane?

An earlier question addressed why all planets formed in the same orbital plane, but how is this angle maintained? What prevents the planets from taking on a different orbital plane?
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### Why are galaxies disk shaped?

I always see galaxies in "disk" shape in pictures. It is like, there is a rotational movement on a plane and the system is balanced by the pulling-in gravitational force which prevents the stars to ...
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### Where does the radiation in space come from and can we observe it?

I have recently been reading that space travel is strongly influenced by "space radiation" and how it poses a threat to human space exploration. Does this radiation originate from stars like our Sun, ...
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### What are some theories that explain the 11 year solar cycle?

The Sun exhibits a periodic cycle for solar activity as manifested by solar activity (e.g. sunspots, solar flares). This activity is related to magnetic fields which emerge from the interior of the ...
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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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### 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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### How can the Earth's rotation speed up? [closed]

It is known as a fact that Earth's rotation is slowing every year, that's why we sometimes have 61 seconds long minutes. In the Java documentation of Time : ...
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### Can protoplanetary disks form main-sequence stars?

As has been pointed out by @Envite in the context of a more general discussion (see Generalised planets?), there seems to be a moderate possibility for protoplanetary discs forming main-sequence stars ...
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### Brightest Radio Source In the Universe

I would have assumed that the brightest radio source in the Universe is a quasar of some kind (perhaps 3C 273) given that the average pulsar has luminosity of $~10^{40} \text{Watts}$ and this is 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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### Where did Mars water go?

Many sources indicate that there is ice water on Mars today, but it is mainly traces, here and there, but not that much. However, solid hypothesis state that there were oceans on Mars, see ...
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### Official registry of lunar placenames?

What's the definitive source for names of geographic objects on the moon? Reason: As a computer graphics project I've rendered a scene based on LROC terrain data. I want to know what I'm looking at. ...
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### How can absolute value of azimuth exceed distance from pole?

I'm sure I'm just doing something dumb, but: Yildun has a declination of approximately 86.5. This puts it 3.5 degrees from the celestial north pole. Per the snapshot below, Yildun's azimuth can ...
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### Source of T Tauri wind?

What particularly causes the T Tauri star to eject the strong bipolar wind which clears the gases around the star?
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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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### What is the formula to figure out how far away a star is? [duplicate]

I have tried to search for this but it won't show me the formula or "how to" figure out the formula. So what is the formula, and how do you figure it out? (The formula for stars within 400 light ...
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### How would we detect an Earth doppelganger planet?

With our current technology, or technology available in the near future (up to 2025), how would we detect a planet exactly like our own, and how close would it have to be to be detectable? Which ...
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### What are the current accepted theories of the formation of the Uranian moon Miranda?

Miranda, a moon of Uranus is unique in that it has a very fractured surface Source: University of Oregon The surface is said to be jagged and fractured, with comparatively large disjointed cliffs ...
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### Coordinate transformations between reference frames in spherical astronomy

Suppose there are two observational frames of reference with origins $O$ and $O'$, respectively, separated by some constant distance. A body located at point $P$ has Cartesian coordinates ...
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### How to measure the altitude and azimuth of a star?

Given that the star is crossing the local meridian line in a certain location, I've tried calculating the altitude of a star by finding the difference between the declination of the star and the ...
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### How do you figure out the magnitude of stars?

How do you figure out the star magnitude of a star? Do they just give it a guess or what? If not, how do they figure it out accurately?
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### Is there a pattern between the mass of a body and the mass of orbiting objects around it?

I was looking at Wikipedia's Solar system page, and it says that Sun represents 99.86% of the whole solar system mass. I found that pretty huge. So i calculated ratio of masses : Earth / (Earth + ...
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### How do scientists know there are about 300 billion stars in a galaxy and there are about 100 billion galaxies?

Just to think about this is mind boggling. But how do scientist get these numbers? What technology/system/theory do they they use?
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### How do people measure the distance between the earth and the moon?

How do people measure the distance between the earth and the moon? What methods were used? Where can I find the official data?
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### How to build a powerful home made telescope [closed]

Simple, I fell in love with the sky when my parents were constructing our new house I was a kid then and one day I ventured out on the terrace, to my amazement it was a full moon, ever since I've felt ...
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### Calculation of right ascension and declination

I am confused about this problem: If I see an object from Mount Teide (longitude is 16"30'E and latitude is 28"18'N) that passes the meridian (azimuth=0) at 5h (am) UTC, and I also know that the ...
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### Are there any alternative explanations for the gravitational force we attribute to dark matter?

It always seemed counter-intuitive to me that we observed an measured a gravitational force and since the universe has not enough mass to account for it, the conclusion was to say there's a different ...
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### Milky Way Galaxy from Earth

I've seen a lot of beautiful pictures of the Milky Way from Earth such as this: ...but I can't understand what the cloudy ribbon at the bottom the horizon is. Is it a super-large nebula? Or is it ...
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### Could any known, living organisms on Earth survive on Mars?

No life has been discovered outside of Earth (yet?), but do we know if anything that would be considered "living" on Earth could conquer Mars? (or maybe Venus?) With the Mars One project on the way, ...
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### Why don't Neutron Stars form event horizon?

Trying to compare density of Black Holes and Neutron Stars I came up with the following: A typical neutron star has a mass between about 1.4 and 3.2 solar masses1[3] (see Chandrasekhar Limit), ...
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### Find distance from star to star?

How do you find the distance from a star/planet/black hole to another? I know people can calculate the distance from Earth to a star, but what about from one to another?
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### Very bright star in the east at northern hemisphere. What it is ?

From some time now (few weeks as far as I can remember), there is a very bright star in the eastern sky. I first thought it was Venus, but according to this link, Venus is in the western sky and ...
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### iteration to cover the whole sky with right ascension, declination, angle

I am sure I get parts of the terminology wrong but if anyone can shed some light in the following: I understand that for a given right ascension (RA) and declination (DEC), one has defined a ray ...