tony873004

Was it low on the horizon? It can appear red for the same reason that the setting sun appears red. I wish you had a camera too. Moonsets make very cool pictures.

If you want a realistic scenerio, rather than a vanishing Sun, a rogue planet or brown dwarf could pass through the solar system. It's gravity could eject Earth from the solar system. It's highly unlikely, but more likely than the Sun simply vanishing. I imagine ocean currents would be able to keep some islands habitable for months.

As Jacques says, sunlight is 27 times fainter than on Earth. But that's still very bright. Consider that the sunlit ground is over 1000 times brighter than your living room at night with the lights turned on. When you're outside on a bright sunny day, your pupils contract to their smallest size. They'd just open up a bit more, and you wouldn't be able to tell the difference.

The Sun's luminosity is 3.85e26 W At a distance of 150,000,000,000 meters (~1AU), the solar flux is 1362 W / m^2 3.85e26 W / (4 * pi * 150,000,000,000^2) = 1362 W / m^2 The Earth presents a 2-d disk r=6371km to the Sun. So it will intercept pi * r^2 = pi * 150,000,000,000^2 = 127516117977447 square meters of sunlight. 127516117977447 m^2 * 1362 W/m^2 = 1.73676952685283E+17 W So the Earth receives 1.73676952685283E+17 Joules of energy per second from the Sun. If it absorbs 70% of this energy then it absorbs 1.21573866879698E+17 Joules of energy per second. I got the same answer as Severian.

The odds are 100%. The fact that Pluto has never been captured as any planet's moon means that it is an uncaptured moon. But things in the solar system aren't classified as "destined to be a moon one day". The capture hypothesis has its weaknesses. But for Pluto and Charon to independently be on the verge of a Neptunian capture, and escape the situation orbiting each other is a virtual nill. Not impossible, but the odds are so slim that you might as well call them 0.

If an object's current distance and its semi-major axis are significantly different, then the object has high eccentricity. I'm under the impression that objects in the galaxy's disk are in very circular orbits, while the objects in the galaxy's halo have high eccentricities as well as high inclinations.

Imagine if the Earth were a cube. The only places where you could feel like you were on level ground is in the middle of each face of the cube. The farther you travelled from the center of the face, the steeper your ground seemed. The corners would be very tall mountains. Things would want to erode downhill, with the center of the faces as the bottoms of valleys. Basically, the Earth would be eroding into a sphere. Asteroids don't have enough gravity to make this happen, at least not in reasonable timescales, and probably never.

Even if the capture theory were true, the Moon wouldn't have to be captured in such a way that the same side would always face Earth. It could begin with a spin, but tidal forces would lock it to the Earth eventually. I have a guess as to why the Moon has more large impact basins than Mercury. Assuming the giant impactor theory, as the debris cloud in orbit around Earth condensed into moonlets and the moonlets joined to form larger moonlets, eventually one of them was larger than the rest. This is the one that becomes the Moon. When it reaches almost is present size it has enough gravitational influence to eject many of the remaining moonlets out of the Earth / Moon system. This would include several sizeable ones in the 10s of km in diameter. What would be the fate of the escaped moonlets? They would orbit the Sun in Earth-crossing orbits. They'd probably orbit for 100,000s of thousands - low millions of years before slamming into Earth or the Moon. This gave the Moon enough time for a surface to solidify and hence record the impact. Mercury didn't have large collision that littered its orbit with timebombs, hence it has very few impact basins compared to the Moon. Any thoughts?...

It doesn't have more gravitational pull then before. It depends on how far the other star is. If the companion star expands and fills its Roche Lobe, then it will lose matter to the other star, whether it is a black hole or not. Its Roche Lobe is small when the stars are close to each other, and large when they are far.

With some basic math and some faulty logic I should have said that in 40-50K years, the Earth's rotational period will be 1 second less. We'll need to add 1 leap second per day.

Luminosity of the Sun = 4 * 10 26 watts The formula for the surface area of a sphere is: 4 pi r^2 A sphere with a radius equal to the Earth / Sun distance would have a surface area of: 4*3.14*150000000000^2= 2.81E+23 square meters. So each square meter on Earth receives 4e26 / 2.81e23 = 1442 watts of energy. Just Google for more accurate values for Solar Luminosity and Earth / Sun distance. Earth is a little closer to the Sun in Winter, so you could take this into account too. Then for latitude and time of day, you have to figure out the Sun's altitude in the sky. If it is overhead, at 90 degrees, then sin(90) = 1. A square meter at this point would receive 100% of the 1442 watts. But if the Sun were only 45 degrees high, then it would receive sin(45)=0.707 or 70.7% of 1442 watts. If the Sun were setting on the horizon, then sin(0) = 0, it would receive 0% of the 1442 Watts. There's a free program called Stellarium (Google to find the download page) that will tell you the Sun's altitude in the sky as well as the Earth / Sun distance for any given instant. Then you could feed these numbers into the above formulas.

A leap second due to the Moon slowing the Earth is only necessary about every 40,000 - 50,000 years. The Sun is not tidally locked to Mercury. And Mercury is not tidally locked to the Sun. Mercury's day is 2/3 the length of its year. It would be more correct to call this a resonance. Many of our solar system's outer moons are tidally locked to their planet, including all 4 Galilean Moons of Jupiter. As a general statement, yes. But there's lots of exceptions. The Earth can't tidally lock to the Sun and the Moon at the same time. Bodies can spiral inward and collide with the planet. That is theorized to be the fate of Mars' moon, Phobos. Bodies that spiral outward can exceed the Hill Sphere and get stripped away from their planets without ever tidally locking.