# Tag Info

## Hot answers tagged sun

36

The sun does rotate. We can see the rotation of the sun by the doppler shift of the light we get from the sun. . (Image from this page.) Since we know the characteristic spectrum of light from a hot body of a given temperature, we can use the same effect to determine if other stars rotate as well. Note that this only gives the spread in velocities along ...

30

Briefly: Because the moon's orbit "wobbles" up and down, so it isn't always in the plane of the earth's orbit around the sun. There's a 2D plane you can form from the ellipse of the earth's orbit and the sun. This plane is known as the ecliptic. The moon's orbit is not exactly in the ecliptic at all times; see this (slightly overcomplicated) picture from ...

30

The Sun isn't "made of fire". It's made mostly of hydrogen and helium. Its heat and light come from nuclear fusion, a very different process that doesn't require oxygen. Ordinary fire is a chemical reaction; fusion merges hydrogen nuclei into helium, and produces much more energy. (Other nuclear reactions are possible.) As for rockets, they carry both ...

28

Yes, the sun and nearly all other stars do rotate. One can see the rotation of the sun by looking at the motion of sunspots on its surface. Over time, the sunspots will move across the sun's surface - proof of its rotation. Furthermore, the rate of the sun's rotation is not constant throughout the sun; it is higher near the equator and slower near the ...

26

This is from the Physics FAQ article that I wrote 15 years ago: If shorter wavelengths are scattered most strongly, then there is a puzzle as to why the sky does not appear violet, the colour with the shortest visible wavelength. The spectrum of light emission from the sun is not constant at all wavelengths, and additionally is absorbed by the high ...

19

It just happens to be a coincidence. The current popular theory for how the Moon formed was a glancing impact on the Earth, late in the planet buiding process, by a Mars sized object. This caused the break up of the impactor and debris from both the impactor and the proto-Earth was flung into orbit to later coallesce into the Moon. So the Moon's size just ...

18

The reason being closer to a heat source makes you warmer is the inverse square law. Think of it this way: If you have a $1~\mathrm{m}^2$ piece of material facing the Sun and located at Mercury's orbit, it will be quite hot. What does the shadow of this square look like at Earth's orbit (about $2.5$ times further away than Mercury)? Well, it will be $2.5$ ...

18

This is a really rough calculation that doesn't take into account the realistic direction of the bow shock, or calculation of the drag force. I just take the net momentum flow in the solar wind and direct it so as to produce the maximum decceleration and see what happens. Apparently the solar wind pressure is of the order of a nanoPascal. As I write this ...

13

No, there is not a solar eclipse whenever we see a new moon. The reason we do not have a solar eclipse at every new moon is mostly due to the angle of Earth's axis (and by extension, the Moon's orbital plane) to the Earth-Sun line. See the picture below for a visual explanation. In the picture, the Sun is to the left. The upper image shows the orbit of the ...

13

The Moon's orbit is inclined with respect to the Earth's orbit. In other words, if you imagine a Sun, Earth, and Moon model sitting on a tabletop, the Sun would sit approximately still and the Earth might slide around the desktop, while the Moon would orbit the Earth, hopping up off the table, and sinking back down into it. (I used to do this demonstration ...

13

@dmckee guessed correctly. From An excerpt from an address delivered before Section A of the American Association for the Advancement of Science, on August 23, 1882, by Prof. Win. Harkness, Chairman of the Section, and Vice President of the Association: (ref) He was destitute of what would now be regarded as the commonest instruments. The invention of ...

13

Great question. The electric field creates such a strong force that it would be very hard to move large amounts of just one type of charge. So astrophysical systems do generally eject equal numbers of protons and electrons. In particular, the solar wind is electrically neutral. So these cosmic rays are created in very nearly equal numbers, but by the ...

11

I believe the easiest way to do this would be empirical, rather than theoretical- Just mark out each hour, all day. It would be especially fascinating if you did this, say, every Saturday, starting with the upcoming Summer Solstice. The artistic possibilities are endless as well... different symbols, colors, outlines, etc., for different times of the year, ...

11

It is much more. During its core-burning phase, the Sun will burn about 10-15% of its hydrogen supply. The gas is about 70% hydrogen by mass, so that translates into about $0.07$ to $0.1\,M_\odot$ of hydrogen burned. The exhausted core then contracts while hydrogen is burned in a shell that gradually moves outwards (in terms of mass). Helium ignition starts ...

11

Placing the solar filter before sunlight hits the instrument is the correct way of doing it. You could put the filter after the instrument, provided you don't mind being blind - the concentrated energy from the Sun heats up the filter, which sooner or later melts (if it's plastic) or cracks or explodes (if it's glass), your eye(s) receive a full dose of that ...

11

Several points that need addressing: The seasons are due to the tilt of the Earth, but not because of the atmosphere. When the sunlight is grazing the ground at a low angle the same amount of heating is spread over a larger area than when the sun is directly overhead, so the temperature drops. The atmosphere has a negligible effect on absorbing radiation ...

11

Short answer, no. The Sun's orbit is non-Keplarian; there are many perturbations and a general unevenness in the motion of the Sun around the Galactic centre. This is a result of non-uniform mass distributions, the galaxy not being a point mass, and the impact the relative motions of neighbour stars has on measuring. Thus, giving a particular eccentricity ...

10

Moonlight is not almost as bright as mid-dawn. Moonlight is really fairly low illumination, and human eyes don't detect color well in low illumination. Moonlight is reflected sunlight. If there's enough of it, it produces color mostly the same way sunlight does. This page, found through a Google search, shows a spectrum of moonlight. All the colors are ...

10

Michael Luciuk's answer is right, but there's an even stronger reason for rejecting this hypothesis: refraction in the corona would be wavelength-dependent, but the gravitational bending due to the Sun has been measured over a wide range of wavelengths (at least from visible to radio) and has been found to be independent of wavelength. Clifford Will's ...

9

The reaction rate doesn't increase that quickly with temperature, but pressure does. If you perturb a solar model, making a zone near the core marginally hotter, the increased pressure will rapidly (at roughly the soundspeed divided by a characteristic length) cause it to expand. That lowers the pressure and temperature enough to substantially quench the ...

9

The ionized particles from mainly solar wind are caught and trapped by Earth magnetic field, which behaves like a magnetic bottle. (The region in which ions are trapped is called Van Allen radiation belts.) This trap is weaker in the polar regions, and there the ions are mainly released into the denser parts of atmosphere. There they collide with air ...

9

The thing is, the Moon's orbital plane is slightly tilted (about 5$^\circ$) with respect to Earth's which means from the Earth's perspective that the Moon's motion oscillates around the Sun's trajectory. On most new moons, then, the Moon is either north or south of the Sun and we don't see an eclipse. For eclipses to happen, new and full moons must occur ...

9

Both the moon and the earth's orbits are eccentric, and so the ratio between the sun's and moon's apparent diameter varies with the time of year. When the moon is at perigee, and the earth at aphelion, the moon will seem larger than the sun than when the moon is at apogee and earth at perihelion. However, the eccentricities of these orbits are low, and the ...

9

Any reasonably flat piece of sort-of reflective metal will function perfectly well as a heat collector, but would not be terribly suited to do astronomical observations with. In principle, you could probably pull it off. But it would require a lot more accurately shaped mirrors, with a lot better quality reflective surface. Also, there's good reasons ...

9

In theory, perhaps. It is possible, using multilayer dielectric coatings, to produce a surface which is reflective in very narrow bands (in this case, the Sun's dark lines)and transmissive (or absorptive) elsewhere. In practice, the spectral "blurring" caused by atmospheric transmission/absorption/re-emission effects would make this effect pretty much ...

8

There will not be any kind of "massive bombardment" and it won't "light up" things out there. However, using the Sun as a gravitational lens for a radio telescope is a real possibility. There was a lecture at the SETI Institute on 11/25/2009 titled "Deep Space Flight and Communications: SETI, KLT and Astronautics in a 2009 book" by Claudio Maccone, Co-Vice ...

8

From the Sun's center, always. When you deduce the equations of motion of planets, you're always calculating from the center. Plus, the results don't change when the Sun blows up as a red giant, or collapses as a dwarf. But even if you measure from the surface, in most cases it won't make a huge difference. In Earth's case, it's a 0.5% error. It would be a ...

8

What part of the sun? That would make a huge difference in your question. Overall, these types of hypothetical questions are rather non-nonsensical without really defining the parameters very clearly. That said, keep in mind, we have "released the power of the sun on the surface of the earth" a few times already. Not only that, we have even contained it! ...

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