Here's a question for you that I could not find already answered on your very impressive and very useful web site.
Where can we find some actual (normal visible light) photographs of the sun taken from outside the near-earth environment? There seem to be no photos of the sun available, taken, for example, from a point half-way between the earth and the sun, or taken from the vicinity of Saturn, Jupiter, Uranus, Neptune or Pluto. Voyager 1 and 2, Pioneer 10 and 11, and numerous other deep-space spacecraft, from the USA as well as from Russia and from the ESA, surely must have taken some photos of the sun. Where can we find them? Why has NASA never released them?
Thank you very much.
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There is no advantage in taking pictures of the Sun from a different distance. You get the same result from a telescope.
What makes the sun shine so brightly?
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What makes the Sun shine? Its heat, because all hot objects shine--like filaments in lightbulbs.
What makes the Sun hot? Energy is released in the core of
the Sun by nuclear processes, which combine atoms of hydrogen
into atoms of helium. Four hydrogen nuclei (aka protons)
combine to form one of helium, with some energy left over, and
that energy provides the heat.
Many chemical reactions require a higher temperature (boiling an egg, for instance), and so do nuclear reactions. The temperature required for the solar energy release is enormous, and creates enormous pressure. Only near the center of the Sun can these conditions exist, with the weight of the higher layers of the Sun keeping the energy-release region confined. If that confinement did not exist and it had the
chance to expand, it would cool down and all nuclear energy release would end.
I'm trying to figure out lofting capacity for various gases on Mars, so I can more realistically visualize a lighter-than-martian-atmosphere-craft. What with the different gravity, different atmospheric pressure, and different atmospheric composition, I figure that the lofting capacity of various gasses would be different.
Unfortunately, I'm getting hung up on that lifting gas. I suspect that Helium will be in short supply on Mars. On earth, it is a byproduct of natural gas, but on Mars, there should be little, or no natural gas, and helium would have to be mined by itself.
My idea however, is that since the atmosphere is mostly CO2, blimps with much heavier gasses could be used. I would expect hydrogen, oxygen, and nitrogen blimps to be common, since these three gasses are highly useful commodities in their own right on a world with little water, and no breathable atmosphere.
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Flying a balloon on Mars is not easy. The ground-level atmosphere is (I believe) 1/140 times as dense as ours, and even with 1/3 of the gravity, it may be equivalent to flying a balloon at 25,000 meters on Earth or at 80,000 feet. It can be done, but takes a big balloon. With the fierce storms of Mars, one also wonders how long such a balloon would last.
About the lifting power--it equals to the weight of the displaced atmosphere, minus the weight of the gas inside the balloon, required to keep it inflated. Whether that is hydrogen or helium should make little difference, because either gas weighs much less than the air (or on Mars, carbon dioxide) which is displaces. Hydrogen should be available on Mars, if only a little water can be extracted there, which seems likely. Hydrogen was of course used in all the Zeppelins in WW-I and with proper caution is quite usable.
Oxygen and nitrogen are rather heavy, cutting the lifting power by a factor of about 4: considering how marginal any balloon is on Mars, they are clearly unsuitable..
Is there a terrestrial phenomenon occurring this month with Mars? I've heard form a few "wannabe" astrologers that the planet Mars will be "huge" is the sky and look as big as the moon with the naked eye. This is an event that has happened every 5000 years or so. Mars is to come within 34,649,589 miles to Earth. I have not seen any television reports on this (maybe due to the recent NASA landing). Could you expound upon this for me ?
Thanks,
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[Note: The above turned out to be a false rumor, which had quite wide circulation. The reply below was written before the new media reported on it.]
Beats me. The average Mars-Earth separation is 0.5237 AU, and with 1 AU equal approximately to 150,000,000 km or 93,000,000 miles, this comes to 48.8 million miles. The actual closest approach may be larger or smaller, because of the ellipticity of the orbits (mainly the one of Mars),
In any case, Mars seen by the unaided eye is never as big as the Moon. It is true, though, that viewed through a telescope, Mars appears to be about as big as the Moon seen by the unaided eye (although, unless seeing conditions are very good, the image may shimmer and distort).
Having looked at the elementary school texts my children have been assigned, I have been disappointed. Some of the most enthusiasm they have shown recently toward learning more about the physical world and doing a bit of thinking, is during a recent discussion of "how to point a telescope." But they do not get those kind of examples, or anything that seems remotely stimulating from their textbooks. Unfortunately, that kind of motivation seems only to come from strictly extracurricular activities.
If they do continue to show interest more than a few days in the telescope project, then I hope to help them build (instead of buy) a set of telescope drive controls. So far their enthusiasm has not waned, and they are asking a lot of questions about how to find objects in the sky and point the scope. My experience doing some controls engineering will help, but I want to let them do some of the programming to make the telescope follow the right target. My challenge will be to keep their challenges at the right level.
Your pages provide a nice balance. Appropriate examples, and reasonable approximations that make some of the fundamental calculations of motion of celestial objects trackable. I think if I can learn that art of finding and sharing simple examples, then the telescope project will generate several fun and useful lessons. Otherwise, it will become just another project.
Thanks for your contributions in making physics, astronomy and earth sciences fun for non-scientists.
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I do not know your children--what ages, what interests, what school. Nor do I know the limits of your budget.
As for telescopes, I might have a different philosophy here--give the kids an instrument with minimal hassles, to let them go right away and observe. For our son's birthday (32nd, I think) we gave him a Meade 3.5" telescope. We scrimped and did not buy the computer controlled model, and that was a mistake--I think he would have used it more if he had the one with built-in star catalog. On advice we also bought for it a 90-degree elbow eyepiece (easier to look at objects high in the sky), a better eyepiece and a subscription for "Sky and Telescope" (he had a tripod already, and he crafted his own camera attachment).
If your kids are not yet in that league, they have plenty to read in my web pages. I can also send you solutions to the problems, if you want to teach them that way. They should keep in mind, though, that no one will care as much about their own education as they themselves. If they want it, it's theirs for the taking.
Your site claims the particles in the solar wind are leaving the Sun at about 400 km/s. This is less than the escape velocity which is about 600 km/s. Does it mean many of these particles will eventually fall back to the Sun? Is there any evidence of such as behaviour?
Also, what are the leading "hot" topics on Solar Physics now?
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The solar wind starts not from the Sun's surface, but from the corona, and is accelerated somewhat gradually. Obviously, it has to overcome solar gravity, which I suspect is one of the conditions needed for accelerating the solar wind--maybe like a lid on a pressure cooker, holding down the hot corona until it can just barely escape.
Incidentally. NASA has been toying for years with the idea of a solar probe, approaching the Sun within 4 solar radii--following boost from a "hairpin" orbit around Jupiter (mentioned briefly here
and in the page following it). It would be shielded from the Sun's intense heat by an "umbrella" of tungsten or similar material, and would study the solar wind in its source region. How can it do so with a metal barrier between it and the Sun? Simple: at closest approach is moves at about 300 km/s, perpendicular to the line to the Sun, so in its own frame of reference, solar wind particles (unlike sunlight) would seem to arrive from the side, at an angle. They would seem to have the vector sum of their own velocity and that of the corona relative to the fast-moving probe.
"The leading hot topics"? I am only slightly involved in solar research, but the big question there seems to be what happens beneath the surface--where do sunspots originate and how, what are they, and what creates the uneven rotation of the Sun (which drives sunspots and magnetic fields). When I got into the space research, it was proposed all these were shallow phenomena, in the outermost layers of the Sun, but current study suggests they actually extend to appreciable depth. If you have a science library nearby, try to find