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29

The same reason (almost) all of them rotate in the same direction: because of the conservation of angular momentum. Before a star and its planets exist, there’s just a cloud of disorganized gas and small molecules. The Solar System formed from such a cloud around 4.6 billion years ago. On that scale, there is some small amount of rotation within the cloud....


15

The picture was so much cleaner 20 to 25 years ago. I'll present that nice clean picture first. Stars form from the gravitational collapse of huge clouds of interstellar gas. Those gas clouds inevitable have some net non-zero angular momentum. This forces the gas cloud to change shape from being more or less spherical to being disk-shaped. (Why? That's a ...


9

It is generally thought that Jupiter "formed" first via the core accretion process. An icy core forms first and then sweeps up the gas around it. This process is generally thought to take from a few million to ten million years. After that, the solar system gas was dissipated and Jupiter was basically as it is today, but larger and hotter. Earth formed on a ...


6

The sun is slowly losing mass, partly from the conversion of mass to energy (which then escapes as neutrinos and light) and partly from the solar wind (particularly in coronal mass ejections). Solar wind accounts for a loss of about 1.5 million tons per second, fusion accounts for 4 million tons per second. However compared to the mass of the sun (about 2 ...


5

I understand 'Sun rise' and 'Sun set' is caused by 'earth rotation'. I read 'Sun light' takes around 8 minutes to reach earth Every city in this world has its own 'Sun rise and sun set' timings. This is all correct. The apparent motion of the sun in the sky is mostly due to the rotation of the Earth. Lets assume 'sun arises' at 6 AM in 'City A'. ...


4

As the Sun's mass is reduced and it's gravitational attraction is thus reduced the Earth will slowly spiral out from the Sun and yes slow down (to preserve angular momentum). But the effect is ridiculously small (do the math yourself) it will not be measurable directly.


3

Sir Cumference's answer is great. Molecular clouds are generally thousands of times more massive than the Solar System, and since they're less dense they're much much larger in volume. We don't know where our Solar System originated from, and we don't know how many other stars were born in the same cloud, probably hundreds or even thousands (just recently 1 ...


3

Gravity does not repel, but there is another "force" at work here. The angular momentum of the original protoplanetary disk is conserved. In other words, just because the cloud condensed into planets doesn't mean it is going to stop spinning. When we orbit artificial objects, we speed them up until they reach a velocity that sustains orbit--so again there ...


3

I love Einstein's explanation of "events". Not the exact words but he stipulated that an event has not happened until the light of that event has reached you. So, the Sunrise time is when you actually see the disc of the Sun, not when it has actually been in your line of sight for a person who might be standing on the surface of Mercury observing you and ...


3

I think the answer to your question lies with Jupiter, be it directly or indirectly, the gas giant is now believed to have had a large influence on the way the inner planets formed. Many planetary scientists believe that the reason we only have 4 small inner planets today and not any "super-Earth" sized ones is because of Jupiter, and how it interacted ...


2

That's an interesting way to put it. Indeed, since bodies spend most od their time at the slow end of an eccentric orbit, the extended lobes will attract each other, torquing the orbits into a birdsnest shape. See this presentation by Dr. Madigan. I'm really disappointed that the more scientifically literate press (like SciAm) doesn't cover this idea, but ...


2

Earth used to be many, many asteroids and meteorites. The larger asteroids would pull meteorites and smaller asteroids, crash with them, and bundle into a bigger and bigger clump, that eventually became so heavy, that rock began behaving like liquid under the pressures, forming the neat sphere Earth is now. That all rubble was already orbiting the Sun when ...


2

It's simply that we are moving fast. It's that simple. The Earth is moving VERY fast around the sun, so it is not "dragged in". If for some bizarre reason the Earth slowed down ... it would move in closer to the Sun. If it stopped moving - it would fall directly in to the sun. It's that simple. Note that this is exactly how satellites work. (I mean ...


1

If you are calculating the angular distance between planets, as viewed from Earth, then of course you need to include the retrograde motion. The natural way of doing this would be to first use heliocentric coordinates to calculate the positions of both planets and the Earth relative to the sun (You could do this using Kepler's laws). Then change your ...


1

In our moving Earth-based point of view, retrograde apparent motion means a planet's geocentric ecliptic longitude is temporarily decreasing instead of increasing as usual. The word "apparent" avoids confusion with a retrograde orbit. All major planets' orbits are prograde, with heliocentric longitude increasing at all times1. Most retrograde-orbiting Solar ...


1

The tidal field of the Galaxy does lead to the oscillation of the plane of very wide binaries. The mechanism of this oscillation is identical to the Kozai-Lidov mechanism (the only difference is that in the case of KL oscillations the tidal field is generated by the averaged orbit of a tertiary stellar companion). However, if you run the numbers, the ...


1

The Nice theory of planetary formation: Created in Nice, France Also answers the not so pretty picture (except for Planet 9). In the beginning, the sun, as a protostar, sucked up mass from a nebula and became a rapidly spinning star. The matter flattened out into a disk (Why? See Why are some galaxies flat.) The Nice theory explains the Late Heavy ...


1

Planetary systems are formed from clouds of gas and dust. The gravity of the cloud's mass holds it together; the densest part at the center of the cloud collapses until it's dense enough to begin nuclear fusion, turning into a star. Things further out randomly collide and stick until a few of them become big enough to have significant gravity of their ...


1

Sunrise and sunset times are based on when an observer at the location in question would see the first or last limb of the sun appear or disappear; they do not take into consideration the light-speed delay between the Earth and the sun. They do, however, take into consideration the average refraction of the atmosphere, so sunrise occurs a bit earlier than ...



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