Hot answers tagged

104

You are correct that the axis of the Earth's rotation is tilted with respect to the plane of its orbit by 23 degrees. But it is incorrect that the direction that the axis points changes by a large amount (it should be 2*23 degrees) over a 6 month time span. Your assumption: If axis it pointed at Polaris at (1), then it should be pointed at a different star ...


101

The Sun is immensely loud. The surface generates thousands to tens of thousands of watts of sound power for every square meter. That's something like 10x to 100x the power flux through the speakers at a rock concert, or out the front of a police siren. Except the "speaker surface" in this case is the entire surface of the Sun, some 10,000 times larger than ...


65

The oldest light in the universe is the cosmic microwave background. Roughly 380,000 years after the Big Bang, protons and electrons "recombined"1 into hydrogen atoms. Before this, any photons scattered off the free electrons in the plasma filling space, and the universe was essentially opaque to light. Once recombination occurred, however, photons were able ...


46

Still new at stellarium but here are some quick capture gif lasting one month. Sorry about the quality- limited to 256 colors for smaller gifs. Date on lower left corner. By the way the sun is of course the brightest and i use it as reference for recording (start record when sun is in frame then stop when it appears again in the same position which is ...


42

You are correct. The Earth would always appear in approximately the same location in the sky, when viewed from a point on the lunar surface. And it would be seen to spin, the continents coming in and out of view over the course of an Earth day (24 hours). The sun would make it's way across the sky, from one horizon to the other over a period of about two ...


40

That's what it really would look like if you were there with DSCOVR. The albedo of the Moon is only about 0.136, about half of the Earth's average albedo. Of course the part with clouds is higher. I was shocked too, but it was explained in written copy that accompanied the release of the original image. Shouldn't the Moon appear as bright as a full ...


40

The answer is ironic: Without good instruments, there is no evidence. The people who thought that the Sun went around the Earth were perfectly correct as far as the actual evidence went until the early 1700s and mid-1800s when two lines of evidence opened up that showed that the Earth moved. Aberration of Starlight Wikipedia has a correct but over-...


38

There are a few incorrect assumptions in your post, so it is difficult to answer as asked. But I can address the misconceptions. 1. The seasons are not caused by our distance from the sun The seasons are caused by the 23.5° tilt in Earth's axis. When the Northern Hemisphere is tilted towards the sun (summer), the Southern Hemisphere is simultaneously tilted ...


37

They do, but due to the ratio of masses being vastly different, they seem like they would not to do so as moon seems to rotate just around (the centre of) Earth. The ratio of Earth and Moon's masses is $\frac{M_{Earth}}{M_{Moon}} = 81.3$ whereas for Pluto and Charon the same ratio is $\frac{M_{Pluto}}{M_{Charon}} = 8.09$. Because the ratio for Pluto and ...


37

It is a matter of exposure and dynamic range. A sensor like a camera can only handle inputs in a certain range of intensities, and much of photographic skill (or smart presets) is about mapping the outside light onto this range so the details you care about show up rather than turn into white or black. If you take a picture of a brightly lit scene, in order ...


31

The coincidence isn't so much that they appear very similar sizes from Earth, but that we are alive to see them at the point in time in which they appear very similar sizes. The moon is slowly moving away from the Earth, and at some point in the future the moon will be unable to totally eclipse the sun and conversely, if you could step far into prehistory, ...


31

First, we need to decide which definition of "day" to employ. There are several types of days: Apparent solar day: the time between two successive culminations of the Sun (apparent Noon) from an fixed Earth-based observer; Mean solar day: a more uniform, averaged solar day without seasonal variations; Stellar/Sidereal day: the time needed for the Earth to ...


30

We have "days" because the Earth is rotating. The shape of the orbit has little effect on the daily cycle of light and dark. The length of the day is determined by the tilt of Earth to the orbit of the Earth around the sun. When the Northern hemisphere is pointed away from the sun, then the sun is low in the sky and is below the horizon for longer. So the ...


28

As HDE 226868 noted in his answer, the Sun is not going to go supernova. That's something only large stars experience at the end of their main sequence life. Our Sun is a dwarf star. It's not big enough to do that. It will instead expand to be a red giant when it burns out the hydrogen at the very core of the Sun. It will continue burning hydrogen as a red ...


27

While Sir Cumference's post is a very intriguing answer, but I'm afraid it's wrong. The sun's surface is clearly in motion, but that does not necessarily result in the radiation of audible sound, even if the sun and earth where in a fluid medium (such as a air) that would allow sound transfer. To explain why, we can actually apply the same line of analysis ...


26

There is currently only one planet known to be capable of supporting human life, and you're on it. Several planets have been found in the region in which we expect water to be liquid on much of the planet. Of these, only one fits the criteria of being Earth-sized and well placed in the habitable zone: Kepler 186-f However we know nothing about it's ...


25

First up, the tilt is exactly 23.45 degrees. The reason for Earth's tilt is still not yet really proven, but scientists at Princeton stated on August 25, 2006 that planet Earth may have 'tilted' to keep its balance. Quote: By analyzing the magnetic composition of ancient sediments found in the remote Norwegian archipelago of Svalbard, Princeton University's ...


25

What you're asking, basically, is whether there are any proofs for the heliocentric model of the Solar System. A literal naked-eye observation of the Earth revolving around the Sun would be rather difficult, since human beings have never gone to another planet yet, and have only been to the Moon briefly, decades ago. Here are several proofs; some of them ...


25

Not strictly satellites/moons, but certainly companions are 2010 TK7 with a diameter of ~300 m, an Earth trojan at the L4 point, and the ~5 km 3753 Cruithne in a peculiar orbit locked to the Earth's.


23

The chance happenstance that Earth happened to be floating along and got captured is minuscule. How did Earth wind up floating through space? There's no established mechanism for terrestrial planets to form on their own. As far as we know, they need a host star to form around. So if our Sun captured Earth, it must've formed around another Star, got ejected ...


22

This is a bit more complicated than it seems. First off, the definition of a day that matters to us earthlings is the average amount of time from one solar noon to the next (or alternatively, the time it takes for the Sun to appear above the same meridian from day to day); it is called a solar day. The sidereal day, which is the time it takes for some given ...


21

Our atmosphere is only transparent to visible light, In most other wavelengths, some or all of the light is absorbed Image from Wikipedia, adapted from image by NASA Our eyes have evolved to take advantage of the transparency at these wavelengths. If we had evolved in an atmosphere with a very different mix of gases. One in which visible light was ...


21

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 ...


20

To add to Mark Bailey's answer; the Earth would indeed hang in the sky and rotate, but it would also wax and wane over the course of a lunar day (27.3 Earth-days). Starting at lunar dawn, the Earth would be half-full. The Earth would then wane (more shadow) towards lunar noon. At lunar noon, the Earth would be all in shadow (New Earth) and quite close to ...


20

No, we cannot. It's relatively simple math to show that we are a very long shot from changing Earth's orbit by anything significant at all: consider the kinetic energy of Earth in its current orbit, and do the same math for that in the desired orbit: $ E_{kin} = \frac{m_E}{2}v^2 \approx \frac{m_E}{2}\frac{GM_S}{a}$ where $m_E = 6\cdot 10^{24}$kg is Earth's ...


19

The Sun's luminosity is stable to 0.1% - it varies slightly in response to, or associated with, levels of solar magnetic activity (Solanki & Unruh 2012). This variation would not be perceptible and is completely outweighed by the $\pm 3.4$% variation caused by the non-circular orbit of the Earth (the Sun is closest in January). Obviously, if you live ...


19

Why doesn't the sun pull the moon away from earth? Short answer: Because the Moon is much closer to the Earth than it is to the Sun. This means the gravitational acceleration of the Earth toward the Sun is almost the same as is the gravitational acceleration of the Moon toward the Sun. The Moon's acceleration toward the Sun, $-GM_\odot\frac{\boldsymbol R+\...


19

You cannot prove that the Earth orbits the Sun rather than vice versa because this goes very much against the grain of all frames of reference being equally valid (but some make a lot more sense than others). For example, it makes much more sense to use an Earth-centered, Earth-fixed point of view rather than a non-rotating geocentric, heliocentric, ...


18

A moon is held together by its own gravity, and pulled apart by the tidal action of a planet. If a moon comes too close to a planet it will be ripped apart by the planet's gravity and become a ring. The closest a moon can come to a planet is known as the Roche limit, and it is dependent on the mass and density of the planet and moon. A large planet, such as ...


18

I realize this queston might be closed, and perhaps this should've been a comment, but it got too long: I was in a radio show last spring with a flat-earther. I really tried to understand him, rather than just ridicule him. We went to the beach with his 87x magnifying camera, to watch the coastline 19 km away. If my model of the geometry of Earth were right, ...


Only top voted, non community-wiki answers of a minimum length are eligible