The Sun plus the collection of bodies in orbit around the Sun such as planets, dwarf planets, moons, asteroids, comets, etc.

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37
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4answers
2k views

How far ahead can we predict solar and lunar eclipses?

The solar system is non-integrable and has chaos. The sun-earth-moon three-body system might be chaotic. So, how far into the future can we predict solar eclipses and/or lunar eclipses? How about ...
36
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2answers
2k views

Why are our planets in the solar system all on the same disc/plane/layer?

I always see pictures of the solar system where our sun is in the middle and the planets surround the sun. All these planets move on orbits on the same layer. Why?
34
votes
4answers
4k views

Why is Earth's climate so stable?

Earth wasn't always the only water-world in the solar system. Mars also appear to have started out wet but, as conditions changed, Mars lost its oceans. So, how has Earth managed to avoid a ...
34
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7answers
4k views

“Falling upward” - how far you have to be from Earth to start falling to the Moon?

Talking about gravity with my 9 y/o she asked when do we start "falling upward" to the Moon. What is the distance at which the Moon's gravitational attraction is higher than that of the Earth and thus ...
34
votes
3answers
2k views

Can the solar system really fit in a thimble?

Almost every time somebody talks about atoms, at some point they mention something like this: If we remove the spaces between the atoms and atomic components, we can fit the solar system in a ...
27
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3answers
2k views

Why do the planets' orbital distances fall on an exponential curve?

Background: I was recently reading a book on the planets to my son and I noticed a pattern in the distributions of the planets. The planets' distances roughly follow an exponential distribution. ...
26
votes
9answers
3k views

What is the speed of the fastest moving body in our solar system?

On Wikipedia I saw that the average orbital speed of planet Earth around the Sun is a whopping $29 783\text{ m/s}$, and it made me wonder are there bodies (planets, meteorites, asteroids) that move ...
20
votes
4answers
3k views

How do you calculate the anomalous precession of Mercury?

One of the three classic tests of general relativity is the calculation of the precession of the perihelion of Mercury's orbit. This precession rate had been precisely measured using data collected ...
19
votes
2answers
8k views

Is Jupiter a failed star?

In my physics lessons, my teachers have always been keen to tell my class that Jupiter is considered a 'failed star' by scientists. Is this true? In my own effort I wondered if maybe this could just ...
18
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14answers
5k views

Why do we say that the earth moves around the sun?

In history we are taught that the Catholic Church was wrong, because the Sun does not move around the Earth, instead the Earth moves around the Sun. But then in physics we learn that movement is ...
18
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4answers
780 views

Staying in orbit - but doesn't any perturbation start a positive feedback?

I am not a physicist; I am a software engineer. While trying to fall asleep recently, I started thinking about the following. There are many explanations online of how any object stays in orbit. The ...
18
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4answers
2k views

Why doesn't dark matter affect planetary motion?

If the universe is made up of ~95% dark matter, and it interacts only gravitationally then why didn't Newton and Kepler discover it before ? Why does it show itself only in the radial velocity profile ...
18
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6answers
4k views

Why are the orbits of planets in the Solar System nearly circular?

Except for Mercury, the planets in the Solar System have very small eccentricities. Is this property special to the Solar System? Wikipedia states: Most exoplanets with orbital periods of 20 ...
17
votes
4answers
7k views

What did general relativity clarify about Mercury?

I frequently hear that Kepler, using his equations of orbital motion, could predict the orbits of all the planets to a high degree of accuracy -- except Mercury. I've heard that mercury's motion ...
17
votes
1answer
663 views

How fast is the Earth-Sun distance changing

This is inspired by Evidence that the Solar System is expanding like the Universe?, which referenced an article by G. A. Krasinsky and V. A. Brumberg, "Secular Increase of Astronomical Unit from ...
15
votes
7answers
8k views

What is the average distance between objects in our asteroid belt?

We've all seen sci-fi movies with asteroid belts that require "great skill" to fly through, but how dense is the asteroid belt really? How much of the belt could you see from the surface of a given ...
15
votes
3answers
787 views

Why is Uranus's axis of rotation tilted?

The poles of Uranus are 'in the wrong place', why is this? historically, do we have any evidence of its past? also, do we have an understanding of how its rotational axis might be evolving?
14
votes
2answers
2k views

Why Aren't Saturn's Rings Clumping into Moons?

While reading with my son about how a Mars-like planet collided with the early Earth that resulted in our current moon, it said the initial debris also formed a ring, but that ring ended up getting ...
14
votes
5answers
5k views

Why do we always see the same side of the Moon? [duplicate]

I am puzzled why we always see the same side of the Moon even though it is rotating around its own axis apart from revolving around the earth. Shouldn't this only be possible if the Moon is not ...
14
votes
2answers
739 views

What if our Sun were located in the middle of a globular cluster?

Say you took our current solar system and relocated it deep in the heart of a globular cluster such as Omega Centauri. What would the night sky look like? Would the starshine of nearby stars be enough ...
14
votes
3answers
4k views

Why are Saturn's rings so thin?

Take a look at this picture (from APOD http://apod.nasa.gov/apod/ap110308.html): I presume that rocks within rings smash each other. Below the picture there is a note which says that Saturn's rings ...
13
votes
3answers
339 views

Why were space physicists wrong about the location of the heliopause?

The heliopause is now estimated to be something around 100 AU (1 AU = Astronomical unit = about the earth sun distance). See the wikipedia article: http://en.wikipedia.org/wiki/Heliosphere From ...
12
votes
1answer
280 views

Relationship between Mars and Earth rotation

Is it by pure random chance that Mars and the Earth have nearly the same day duration (Mars day is barely 40 minutes longer, which is just 3% difference), or there is some causal relationship between ...
12
votes
2answers
323 views

What would we see if we looked at our Solar system from 2,000 light years away with our current technology?

Assuming the tables were turned and we would live in a system like Kepler-422/423/424, some 2,000 ly away. If we'd look at the Solar system with a telescope like Kepler and using techniques like ...
11
votes
3answers
304 views

Why did the ancients fail to discover that the Earth orbits the Sun?

The ancients observed that the Sun and the 'fixed' stars rotated about the Earth. They were also aware that the Earth was spherical. They performed many astronomical measurements on the planets - ...
11
votes
4answers
503 views

Is solar wind positively charged?

Many times I heared that the solar wind consists of protons and alpha particles. The both are positively charged, but are there electrons in solar wind?
11
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1answer
5k views

How does a comet form?

As the title explains, How does a comet form? What are the elements, what is a comet composed of? Why didn't they become part of planets, moons or asteroids?
10
votes
3answers
878 views

Planets and Pluto? Neptune?

If one of the rules to be a planet is that it needs to clear ALL objects from their orbit, does this also make Neptune a non-planet? Since it has thus far failed to clear Pluto from it's orbit. Or ...
10
votes
4answers
660 views

Why do all the planets of the solar system orbit in roughly the same 2D plane?

Most images you see of the solar system are 2D and all planets orbit in the same plane. In a 3D view, are really all planets orbiting in similar planes? Is there a reason for this? I'd expect that ...
10
votes
6answers
7k views

What is the simplest way to prove that the Earth orbits the Sun?

Assume you're talking to someone ignorant of the basic facts of astronomy. How would you prove to them that the Earth orbits the Sun? Similarly, how would you prove to them that the Moon orbits ...
10
votes
1answer
4k views

What are the facts that allow accepting the Oort cloud theory?

I admit without any fact that the Oort cloud (comet reservoir) should exist, and it seems to be accepted by far by the large majority of astronomers. But it is still a theory without any direct ...
10
votes
1answer
582 views

How is the Plane of the Solar System oriented to the Sun's motion through space?

How is the Plane of the Solar System oriented to the Sun's motion through space: parallel, perpendicular, or some other angle?
10
votes
2answers
2k views

Observing Jupiter's non-Galilean moons

What strength of telescope is required to observe some of the non-Galilean moons of Jupiter? My current telescope at 50 magnification resolves the Galilean moons well, but I'm guessing it's far ...
10
votes
2answers
133 views

When the Sun goes red giant, will it “vaporize” away a significant fraction of Jupiter and Saturn moons?

Since Jupiter and Saturn's moons are composed of a rock+ice mix. For example, Callisto is 50% rock and 50% ice. When the Sun finally goes red giant, could it melt a significant portion of the 50% of ...
9
votes
2answers
214 views

How big is the Solar System?

How big is the solar system? By "big", I guess I mean "wide", i.e. how far away from the Sun is the farthest object that is considered part of the Solar System? I've checked Wikipedia's pages on ...
9
votes
1answer
162 views

Are Uranus and Neptune too big for their location?

So I was watching some TV, and I heard Dr. Plait mention that the planets Uranus and Neptune are too big to be located so far out in our solar system. Now, I heard his explanation on the show as to ...
8
votes
8answers
3k views

How does the earth move?

My son who is 5 years old is asking me a question about how the earth moves around the sun. What answer should I give him?
8
votes
2answers
2k views

How did Halley calculate the distance to the Sun by measuring the transit of Venus?

What numbers did Halley, Cook, et al. have? What was the strategy by which they calculated the AU?
8
votes
1answer
413 views

Where will New Horizons go after sailing past Pluto?

The New Horizons Spacecraft is scheduled to whiz by Pluto around 2015, and my understanding is that it is going to do exactly that — whiz by it. Where will it go after that? Or what else can it do ...
8
votes
1answer
57 views

Why does the debris from comets and former comets hang around so long?

So tonight's Quatrantids shower got me thinking. Why does the debris from comets and former comets hang around so long? Each year the earth sweeps through the region of space that the comet went ...
8
votes
1answer
389 views

How did Eratosthenes know the suns rays are parallel?

Eratosthenes famously observed that the suns rays were perpendicular to the ground in one location, yet non-perpendicular to the ground at a location some miles to the north. On the assumption that ...
8
votes
1answer
338 views

What exactly is the composition of radiation in interplanetary space?

The articles I found on radiation in the solar system mostly dealt with solar wind, I wonder about other types. Is there a breakdown that tells me, withhin an order of magnitude, at least what ...
7
votes
3answers
1k views

Kepler's third law doesn't give earth's orbital period! Why? [closed]

I tried to calculate earth's orbital period using Kepler's third law, but I found 365.2075 days for the orbital period instead of 365.256363004 which is the correct value. I checked everything, and I ...
7
votes
6answers
1k views

Can any telescope be used for solar observing?

Can any telescope, such as a 8" reflector, that is normally used at night to look at planets be used or adapted for solar observing? What kind of adapters or filters are required or is it better to ...
7
votes
5answers
527 views

Why aren't all rocks in space orbiting bigger rocks?

Why do only big rocks (planets) have satellites, and not small ones? Why doesn't cosmic dust orbit rocks that are many times heavier than the dust grains? If dust is still too heavy then what about ...
7
votes
2answers
20 views

Predicting solar storms?

Quote from BBC "A strong solar storm is expected to hit Earth shortly, and experts warn it could disrupt power grids, satellite navigation and plane routes." How is it that we are aware of a massive ...
7
votes
2answers
865 views

Having trouble weighing the sun

So I gather the way you (and Vera Rubin) calculate a galaxy's mass is by measuring a star's orbital velocity $v$ and its distance $R$ from the galactic center, and then plugging them into this ...
7
votes
1answer
27 views

Meteorites from Mars?

So I've heard of meteorites "originating from Mars" (e.g. AH84001), but the phrase confuses me. I'm interested in what this means - have these rocks somehow escaped Mars' gravity and ended up here; or ...
7
votes
1answer
93 views

How plausible is a subsurface ocean on Pluto?

According to this article on physorg.com, it's likely that Pluto has a subsurface ocean of liquid water. It suggests that the ocean would be about 165 km deep, under an equally deep crust of solid ...
7
votes
1answer
194 views

When the sun's magnetic field reverses, how can “the north pole (have) already (…) reversed, and (we are) waiting for the south pole to catch-up”?

I was reading a popular news account of the sun's upcoming magnetic field reversal at http://www.csmonitor.com/Science/2013/0807/Sun-s-magnetic-reversal-means-big-changes-for-the-solar-system-video, ...