Celestial body that orbits following an elliptical path around a star or stellar remnant.

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2answers
144 views

How does gravity behave outside the geoid?

I was watching a program about the geoid recently and the relative "height" of the Himalayan plateau gave me an idea. It makes sense for the geoid to be "highest" (is that the correct term?) there as ...
2
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2answers
261 views

Why do we orbit around the sun instead of one the other stars?

I am still very new to many physics theories, however while sat in class today, a thought came to mind that I have not been able to answer from simple googling. What is so specific about our sun ...
2
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1answer
325 views

Presence of planets in Milky Way and other galaxies

Are there only planets in the Milky Way galaxy, or are there other planets in other galaxies? If planets are only in the Milky Way, why aren't there planets in others?
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3answers
19 views

Does anybody actually do astrometry in the 21st century?

I mean the nitty-gritty measurements of positions of stars and planets using transit circles. The transit instruments I've seen are mostly in national observatories and are essentially museum pieces: ...
2
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3answers
418 views

The theory of moon creation when a Mars size planet hit Earth

As we know the predominant theory where does the moon come from is that a Mars size planet hit the earth and took a chunk out of it which eventually materialized into moon. My question is that if a ...
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1answer
5k views

How long does it take for radio or light waves to travel from Earth to Jupiter, Saturn, Uranus, Neptune and Pluto?

I know it roughly takes 20 minutes from Earth to Mars, and 8 minutes from the Sun to Earth, but don't know how long for the other planets on my list.
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2answers
586 views

How can I visualize a gas giant?

From wikipedia Gas giants are commonly said to lack solid surfaces, but it is closer to the truth to say that they lack surfaces altogether since the gases that make them up simply become ...
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2answers
108 views

Does gravity affect radiation incident on the planet?

Just curious ... Known facts: When outside the atmosphere levels of radiation are higher Typically such radiation is CBR, Solar Radiation Question: If the matter of the atmosphere and ...
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2answers
209 views

The size of the planets

What calculations were done to discover the size of all the planets?
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1answer
196 views

When Venus is the brightest when viewed from Earth?

Nowadays Venus is very bright. I can spot it during broad daylight without problem. It's because it's near Earth and appear as a crescent. This made me think: as it's reaching the inferior ...
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2answers
130 views

Would a magnetic rod through Mars shield it from solar wind?

Would a magnetic rod going all the way through Mars shield it from solar wind?
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2answers
142 views

Does Planet revolution time is always greater the more it's getting away from the center?

The entire question is in the title . It's the case for the solar system but is it always the case ? Can a planet do a revolution faster than another that is closer to the center ? As far as I ...
2
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1answer
125 views

How should I be thinking about tides?

I am working on a project for physics that involves tides. This is my current mind set when thinking about tides: The earth applies a gravitational force on some mass ...
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3answers
1k views

Moment of inertia of a planet

Is there a good way to directly measure a moment of inertia of the Earth, or say, other planet?
2
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1answer
211 views

Motion of mercury [duplicate]

I studied that mercury motion around the sun slightly displace by a certain value in each year. But, this is not predicted by kepler until general theory of relativity. What does general theory does ...
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2answers
2k views

Artificial planetary magnetic field

I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need? The question is inspired by thinking about possible colonization of ...
2
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3answers
654 views

Would a Helium powered balloon vehicle work on Mars?

Would a Helium powered balloon vehicle work on Mars? Things that might need to be answered: How much liquidHelium would you need to pack in order to fill a balloon with enough helium gas to travel ...
2
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1answer
121 views

Are the inner planets on planar orbits because there was more dust in the inner solar system (early on in planetary accretion)?

Question inspired by a question thread here. So when there's lots of dust in a galaxy, the galaxy tends to collapse into a spiral galaxy (to maintain angular momentum and to minimize gravitational ...
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2answers
135 views

Saturn's polar versus equatorial gravity

Wikipedia's reference for Saturn's gravity gives $10.44 m/s^2$ at the equator, but this conflicts with Britannica, which gives $8.96 m/s^2$ at the equator and $12.14 m/s^2$ at the poles. All values ...
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1answer
748 views

What causes the collapse of a Magnetic Field?

It's theorized that Mars once had a magnetic field which collapsed at some point. There's also lots of speculation that a similar process will eventually happen to Earth. More recently has been the ...
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1answer
994 views

Where to find the current positions and velocities of the planets?

I've written a program which simulates the motions of planets and other bodies. I'd like to run it on our own solar system, but to do so I need to know the current positions (preferably in ...
2
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1answer
98 views

Synchronising the Earth's rotation via mass redistribution

How much material would have to be moved per year from mountain-tops to valleys in order to keep the Earth's rotation synchronised with UTC, thus removing the need for leap seconds to be periodically ...
2
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1answer
56 views

Help understanding centre of mass

So basically the question I posed myself a few days ago was for a torus shaped planet, what would the gravitational field be like inside the torus? After viewing some answers on the internet, (Gravity ...
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2answers
135 views

Interstellar bodies

As a solar system evolves the planets interact, and in trying to achieve a harmonious state some bodies are ejected. Space is big, but I have heard that some meteorites have been found with anomalous ...
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2answers
247 views

Solar System Capture of Orphan Planets

NASA recently announced (http://www.nasa.gov/topics/universe/features/planet20110518.html) that orphan planets, planets no longer orbiting a star, may be more numerous than the stars in our galaxy. ...
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2answers
83 views

Stability of planet-enclosing shell supported by atmosphere

I understand that a hollow spherical shell of uniform density gives net zero gravitational attraction to objects inside it. So in vacuum, a ball at the centre of a spherical shell would not be stable ...
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2answers
56 views

What is the value of $g$ at centre? [duplicate]

What is the value of $g$ at the centre of the Earth? Is it zero or infinity? My attempt: I know it's zero but applying law made me on fused.
2
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2answers
83 views

Is the Earth round?

Imagine you are a common man and want to prove that the Earth is Round, how would you prove it without any mathematical derivation or without the theory of the ships.
2
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1answer
80 views

What properties are used to quantify the odds of a star harboring earth-like life?

Say you start with a list of stars. What properties do we believe to be critical in the present existence or future formation of earth-like life in those star systems? How can one reasonably pare down ...
2
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1answer
122 views

Magnetic field line length

If I had a magnetic bar in space that was 2cm wide and 2cm high and was one Earth diameter long and had the same magnetic strength as the Earth, would the distribution of field lines be the same ...
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2answers
640 views

How does one measure Earth's speed of revolution around the sun?

I know that there are several formulae that one can plug numbers into to arrive an estimate of Earth's speed around the sun (Kepler's third law for instance), but I'm wondering how these things are ...
2
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1answer
240 views

What is the critical mass of a planet to have an atmosphere like Earth's? [closed]

Small planets/orbits like Moon cannot have atmosphere because of their masses. They don't have enough gravity to hold an atmosphere. Then what is the critical mass that makes enough gravity to keep an ...
2
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1answer
2k views

Why are the orbits of the planets in our solar system along the same basic plane? [duplicate]

Possible Duplicate: Why are our planets in the solar system all on the same disc/plane/layer? After watching this video I realized that the orbits of the planets in our solar system ...
2
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1answer
463 views

Metallic Hydrogen and Gaseous Planets

Jupiter has about twice the density of Saturn (1.33 versus 0.69 g/cm^3) because it apparently has a higher mass percentage of rocky core and of metallic hydrogen in its interior. Available density ...
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0answers
58 views

What would the collision between a (large) solid planet and a gas giant be like?

Assuming a Jupiter-like planet and an Earth-like planet (Except, say... half the mass of Jupiter), what would happen when the two collide? For clarification: What would the actual collision be like? ...
2
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0answers
102 views

Only gravitation and Newton's $2^{\mathrm{nd}}$ law needed to derive Kepler's laws?

It is known that Kepler's laws of planetary motion can be derived from Newton's laws of motion and his law of universal gravitation. However, are all of Newton's laws of motion necessary? According ...
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0answers
48 views

What speed should have an alone planet to have a habitable zone due to relic radiation?

What speed should have an alone planet to have a habitable zone due to relic radiation, without any star involvement? How much time the planet will be able to remain in the habitable zone before the ...
2
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0answers
55 views

Stable planetary rotation states

In reading an article about theories as to how the slow retrograde rotation of Venus may have come into being, the article Why Venus Spins the Wrong Way (Franzen, 2001) stated that it is bound to ...
2
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0answers
278 views

For two planets in a 2:1 mean motion resonance , where will their periastron and apastron points be?

I want to animate the changing orbits of planets when they enter a mean motion resonance. Using a 2:1 resonance, I want to show a low-mass inner planet and a low-mass outer planet being tugged by a ...
2
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0answers
462 views

How do I find equations for the distance of the planets relative to one another?

I know I should be able to piece together some basic Newtonian equations for this, but I'm not sure where to start. I want to be able to choose one planet as the center and calculate its distance ...
2
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1answer
75 views

Single plane Ring system [duplicate]

Possible Duplicate: Why are our planets in the solar system all on the same disc/plane/layer? I've noticed this in many pictures, Planets are shown with a single ring around them (in some ...
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vote
1answer
2k views

Why does the moon or the earth revolve anti-clockwise?

The question is very simple: Why does the moon or the earth or any another planet revolve anti-clockwise? And can any planet (or satellite) revolve clockwise? What is the physical law for this ...
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6answers
2k views

Why does the moon not revolve around the sun directly?

The sun pulls on the moon with a force that is more than twice the magnitude of the force with which the earth attracts the moon. Why, then, doesn’t the sun take the moon away from the earth?
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1answer
95 views

Is it possible for a solar system to have planets orbiting the star(s) in a spherical pattern?

By the question I mean that the planets spin in their ellipse but all ellipses describe the surface of a near-sphere shape around a star. Same question but for a solar system with 2 stars of ...
1
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2answers
193 views

What's the weight of the earth?

What's the weight of the earth? That is, what's the weight of the earth in the gravitational field of the sun? I imagine it's either $0$, because there's no net fall toward the sun, so the downward ...
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5answers
301 views

Age of universe estimates

I was recently involved in a discussion on a sister site regarding how tightly coupled Physics is with the age of the Universe (and Earth). I believe that the Earth and the Universe are both billions ...
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2answers
649 views

Will a spinning object come to rest?

Will a sphere spinning on its own axis come to rest given enough time, provided no other forces act upon it? I know that if you have two spinning spheres in the depths of space and orbiting each ...
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2answers
149 views

Elements of a Planet reveals nearby supernova remnant?

During a random reading through this site, I found this one: Origin of elements heavier than Iron (Fe)... The answer was "The formation of many elements in earth was due to Supernova nucleosynthesis" ...
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1answer
600 views

Atmospheric Escape of Gas Molecules

Most of the Bodies and Objects in space are likely to have an atmosphere. Since the space is empty, the gases in atmosphere should have either dissolved or emptied into space. But, Why doesn't this ...
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1answer
383 views

Why do larger planets cool more slowly than smaller ones?

I learned it during my environment class. My professor introduced the concept--- ratio of surface area and volume. The numerator has connections with the radiative loss, while the denominator is ...