For Shakespeare: How Hot Is the Sun?

Shakespeare asked: How hot is the sun, how did it get this way, and how does it stay hot without burning up?

Good questions. First off, whenever I get a question about the solar system, I stop off first at Nineplanets.org. Great educational stuff about about the planets, their moons and, of course, the sun. Wikipedia's a good source, too. The temperature of the Sun is actually a tricky question. Like the gas giants, the sun isn't a solid mass but a tightly packed gaseous mass (though it is very very massive - 99.8% of the solar system mass is contained within it's "boundaries).

At the core, where the heat is generated, the temperature is 15.6 million degrees Kelvin (and about the same Centigrade - when you get that hot the 270 odd degree difference in scale really doesn't matter). I can't think of an analogy to tell you how hot that is, but it's hotter than anything we can make (or at least sustain) here on earth. The core is also under so much pressure (from the gravitational weight of all that mass) that the core of superheated hydrogen gas is actually 150 times denser than water. Think of that, gasses that weigh more than water.


Near the boundary's of the sun, the so called "surface of the sun" the heat and pressure are much less, 5800 degrees Kelvin (which is still unbearably hot) with sunspots that can be 2000 degrees cooler. However, above this level, there is another level, called the corona that extends far out from this solar "surface" and can be hotter than the surface itself, ~1 million degrees K. You can see the corona in this photograph during a solar eclipse.


Solar flares and limbs and also shove out streaks of fire from the surface. Is this a cool picture or what (taken by Hinode's Solar Optical Telescope)?

The way we understand things, the sun was formed when a dense molecular cloud of hydrogen collapsed. The weight of the mass caused tremendous pressure and heat in the core triggering a nuclear reaction. The heat and energy from the nuclear reaction keep the fire going. Now, that may not make much sense, so let me explain, step by step.

If you compress a gas suddenly, you will increase pressure and temperature. Release it, suddenly, the gas will cool and pressure drops. This is adiabatic heating and cooling and it happens from the work done on the gas without any additional heat added from the outside. There was a lot of pressure, a lot of compression and that meant a lot of heat, which is how the reaction was triggered.

Nuclear reactions aren't like burning the way most of us know it. When something is "burned" we are really breaking down the structure of a mass, combining some of it with oxygen (which is required for fire) and sending much of it into the air. The mass of an object if one could capture all the byproducts from combustion, is the same. Matter can't be created or destroyed without nuclear reactions.

For example, if you burn hydrogen gas in an oxygen atmosphere, you'll get water in return. But the hydrogen's still there, as part of the water, H2O. You can extract it back out because it can't be destroyed with simple combustion.

However, with nuclear reactions, elements are changed into other elements, combined or reduced, and the extra mass those elements shed are released as energy, a lot of energy: e=mc^2 which means the mass times the speed of light squared. That's a lot of energy for a little bit of mass. With fission, the extra mass comes from changing a heavy element, like uranium, into something less heavy like Xenon or Barium. However, even more powerful than a nuclear fission reaction is a nuclear fusion reaction, where hydrogen atoms (the smallest, lightest element) combines to form helium atoms (the second smallest lightest element). The extra mass from the two atoms to form the one larger atom is released as heat and radiation. A great deal of both.

That's what heats up the sun.

And, it is burning up its fuel. It just has so much of it that it takes a really really long time. The sun has used up a great deal of its hydrogen and has a great deal of helium from this reaction. In about another five billion years, it will use up all the hydrogen and start causing helium fusion which makes carbon. The sun will expand, out past where our planet is now, until it's used up all the helium, when it will throw off its outside layers and collapse into a little tiny star.

Fortunately, five billion years is quite a bit of time yet, so no nightmares.

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For Boris: What Would I Do?

Boris asked: If you had to choose your line of work again, would it still be the same, i.e. awesome rocketry with NASA (personal bias showing through)? What would be your second choice?

Good question, Boris. It should be one I can answer in a few short sentences. But I can't.

It's an excellent question because I'm not sure how much I "chose" this one. See, I am a rare beastie, an accidental engineer. I'd never had the slightest interest or inclination to do anything math related. Oh, science and math were fun and I enjoyed it, but only about as much as I enjoyed history and literature. I always intended to be a writer/novelist. The only thing in question was what would I do for a day job while I waited to get my book(s) written and sold. Stephanie likes eating.

I could do math, of course, in fact, it was so easy for me it was boring to me, which is likely one reason I never intended to pursue it. I think I'd always assumed I'd do foreign languages (which I enjoy great deal) or journalism or genetic engineering. I know, weird choices. Except, journalism, in high school, bored me silly. Writing the "truth" didn't hold any interest for me compared to fiction and I wasn't sure how to make money with foreign languages short of teaching. And genetic engineering wasn't offered at any of my immediate college choices.

But I wasn't set or picky. After all, I was going to write. So, since I was bright (and had excellent SAT and ACT scores - types of proficiency exams), I started applying for scholarships, a lot of them, anything. I figured wherever I had scholarships, I'd pursue.

Which is how I ended up with Engineering Physics - because I could get a scholarship from the Engineering department and a scholarship from the physics department. And, once I started in what I soon discovered was the "hardest" major on campus, I was too stubborn to get out. I wasn't going to let it beat me. I found my job with the same sort of muddling. I wanted to live somewhere "warm", didn't particularly want to do defense or quality assurance and definitely not petroleum. That left NASA.

Why did I tell you all that? Because, knowing what I know now and having an opportunity to get any major I wanted and work wherever I wanted, I think I'd do the same thing. I was exposed to all the science and every major type of engineering, and I like what I ended up with better than anything else. It's more real and practical that straight physics, more predictable than biology, smells better than chemistry, yet it's also far more versatile than any straight engineering field. But it also incorporates bits and pieces of all of it.

I used to think I would have been better off working for NASA directly (which I missed because I'd already accepted an offer with a contractor). Now, I'm glad that my background is more diverse (bioengineering, human factors, environmental science, robotics, calibration, safety, EVA, etc. etc.). And I love where I work now, more freedom, more variety.

So, honestly, if I could do it all over again, I probably wouldn't have changed anything. I wonder sometimes about genetic engineering. But I'm not unhappy, even with some of the frustrations I've run into along the way. I believe in what I do and believe I've made a difference.

So, call that I'd choose the same, with genetic engineering as a second choice.

However, I do have some regrets. I wish I'd pursued some singing training. I wish I'd pursued languages more so I was actually fluent. And I wish I'd pursued the writing itself more assiduously.

But, all in all, I'm good.

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For Flit: Lagrange Points

Flit asked: Lagrange points? should I know what those are? Suppose I could google but it's past my bedtime and I'm still not done the first (of 8) folders I wanted to get through...

Here’s the most simple explanation I can make: Lagrange points are the points in a two body system (like a celestial body and a large satellite) where the gravitational forces and centripetal forces effectively cancel out so that an object (which has a negligible mass relative to the other two bodies) moves such that it remains in place relative to the two bodies. That last part is important, because the object doesn’t “stop” – it’s moving with the two bodies but stays in the same location relative to their location (see second picture).



It’s often compared to geostationary and it’s a good analogy. Geostationary could sound like a “stationary satellite” – but it’s not. It’s moving quite briskly, orbiting the planet once a day so that it remains over the same area of the earth as it turns. Relative to the surface of the earth, it’s stationary. Note that geostationary satellites are only located over the equator. If you put them at a different inclination (even if the period is the same) it will veer above and below the equator during the course of the day.

In this case, the object is stationary relative to the center of gravity of both bodies, not the surfaces of the bodies, so it wouldn’t necessarily look to be in the same spot from the surface of either body. However, it would always be in the same spot, orbit-wise. Why is this exciting?

Couple of reasons. First, all the forces canceling out means that this location has a very low gravity gradient, true zero gravity. The orbit would be readily maintained with minimal effort unlike things in low earth orbit today.

The points are not all made equal. L1, which lies on the line between the two bodies, is the optimal place to enter orbit of either body with minimal energy. In theory, there perfect place to provide, say, a moon servicing station between the earth and the moon. The earth-sun L1 is the perfect place to get sun observations (without worrying about being blocked).

Conversely, the sun-earth L2 is the perfect place to get space observations without being blinded by the sun’s light (as long as you have a non-solar array dependent power system). It always has its view of the sun in eclipse by the earth. That’s where we intend to put the James Webb telescope (the successor to HST) and we have a couple there now with more to come.

The L3 point for the sun-earth interaction is actually on the far side of the Sun, as if in counterweight to our own planet in the same orbit. In this case, the earth would always be eclipsed by the sun. However, given that there are many other bodies in the solar system besides the earth and moon, the sun-earth L3 point is actually quite unstable. Ah, that imperfect universe. There’s also an earth-moon L3 where one would be facing the other side of the moon (which would eclipse the earth) all the time. I presume it’s more stable.

Actually, all three of the collinear Lagrange points are somewhat unstable. They’re stable in two directions, but nudged them toward one body or the other and they’ll go readily.

The last two Lagrange points, that are oddly triangular, are the most stable (assuming one of the massive objects is much larger than the other). This is the spot often discussed as an excellent place for a human space colony as the orbit is self-correcting and generally very stable.

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For The Mother: Retrograde Orbits/Spin

The Mother asked: How is it that Venus spins backward? Shouldn't the momentum that created the solar system keep everything spinning the same direction?

In theory, I believe you're right. Of the planets in the solar system, all of them orbit in the same direction so it makes sense that they'd rotate in that direction, too. The fact that so many planets rotate in the same direction (i.e. the same direction they're orbiting in) argues it, too.

But Venus doesn't and Uranus is tilted so far on it's axis (~98 degrees) that, depending on own's perspective, it can also be said to rotates backward. But really it's more lopsided.

So, why Venus and Venus only. Well, Venus is not the only item with retrograde motion. Several moons around Jupiter, Saturn and Neptune orbit in a retrograde way. Several of these items are believed to be captured Kuiper belt items. Kuiper belt items are items like comets and some very far flung planetary-type bodies that are far beyond the edge of the planets. Some objects, like comets, we see every so often because they have highly elliptical orbits and they can crash into planets (as happened to Jupiter a few years ago) or be captured, in theory, by the gravitational pull of a planet. As these items have their own spin and orbit (and will be going very fast as they get closer to the Sun), they can readily get caught by a planet, but not necessarily be in plane or going in the same direction when caught (it depends on whether it's incoming or out going and from what direction they approach the planet that captures them).

That, of course, doesn't apply to Venus. Venus is very similar in composition and characteristics to Earth and has a very circular orbit (which would be unlikely in a captured high speed body), in fact the most circular orbit in the solar system. So, why would it spin backwards even at a very slow rate?

The easy answer is, we don't know. There are speculations, of course. One is that the current year/day represents an equilibrium state between gravitational tidal locking by the Sun that tends to slow the rotation rate, and an atmospheric tide created by the solar heating of Venus' thick atmosphere. Ironically, in addition, the periods of Venus' rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. Whether this is a resonance effect or merely a coincidence is not known.

But there are other speculations. Alex Alemi and David Stevenson of the California Institute of Technology, using their models, believe that Venus once had a moon (it doesn't have one now) that had been formed from a cataclysmic impact event. Ironically, they believe the retrograde motion now is the result of another cataclysmic impact that changed the rotation and, ironically, pulled the moon back into the planet. This, they believe, happened billions of years ago. Since the surface of the moon is highly volcanic with a new surface, much like the Earth has, there's no indication of any such impacts on the planet's surface.

Just goes to show that there are many strange things going on in the big wide universe. And we've got a long ways to go before we get more than scratching the surface on figuring out how what we can see today happened. By then, of course, we'll likely have a whole new set of mysteries to figure out.

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For Shakespeare: What About Saturn?

Shakespeare said: That is too cool. And the picture! WOW! And think, I'd have forever to work every day, and I could get so much done in a year on that planet. Then again, my laptop would melt, and I would too, so the whole point is moot. Any details about Saturn? It's my personal favorite, after Earth (since Earth gives me an actual place to exist).


For any student of the solar system, I can't recommend Nine Planets website highly enough. It's always the first place I go when checking out another planet. Wikipedia has some good poop, too. So, what do they have to say about Saturn?

First, it's ironic that the arguably most beautiful planet in the solar system should be named after a God who is often used to personify old age. Not to mention Saturn's unsavory tendency to eat his own children.

Much of what we say about Saturn is comparing her to Jupiter, the titan of the gas giants. Both planets are composed primarily hydrogen (75%) and helium(25%), with traces of ammonia, methane, water and rock. Saturn is the least dense of the gas giants, at only 70% of the density of water. Like Jupiter, it is subject to visible storms (like the hexagonal storm to the left), generates it's own heat (though to a lesser extent), has a magnetic field (to a much lesser extent) and has a large number of moons. We used to say, categorically, that Saturn had the most moons actually, but they've discovered so many recently, I'm not sure we have a set number. Saturn has 34 named moons which would seem plenty, but apparently wasn't. About 200 moons have been observed, 61 in stable orbits.
Jupiter has a faint set of rings as well, but no planet in the solar system has rings as spectacular as Saturn. When astronomers first found her, she confused them as she looked oblate (and is, actually, more on that in a moment). When Earth is in plane with her rings, they "disappear" confusing those early astonomers even more.

She's quite luminous, perhaps more than her heat-generating processes can justify and her rings are particularly brilliant, presumed to be largely ice and ice-covered rocks. Saturn is not really spherical, rather a sort of flattened sphere because of her fluid state and rapid rotation (days are ~10.5 hours long, but not everything rotates at the same speed) pull her equatorial plane out a bit.

No one seems to be quite sure what creates Saturn's rings (or any other rings), but the consensus seems to be that they can't remain indefinitely, that they must be regenerated. It has also been noted that several moons are pivotal in maintaining and affecting the rings.

Really, there is so much good reading available on Saturn and her rings and her many fascinating moons. You should check out my links and learn more.

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Trivia Break: Venus

Since I'm not really here, I thought I'd take a day of trivia and, in the interest of the Apollo 11 anniversary, I thought I'd give you space trivia.

Since it's my favorite planet, I thought I'd start with Venus, one interesting little gem. Often described as Earth's twin she's slightly smaller and slightly closer to the sun with an atmosphere and continents hidden beneath her dense clouds. She has similar composition and density to the Earth, at 95% of Earth's diameter and 80% of her mass.

But she won't be ready for people to inhabit her any time soon - if ever. The clouds visible aren't water vapor but sulfur dioxide and sulfuric acid. Doesn't that sound fun. The pressure is 90 atmospheres, 90X higher than it is at sea level here. And it's hot. Not like Houston's hot, but hot enough, literally, to melt lead: 740K . Venus, though scientists think it once had water, and oxygen and all that good stuff - perhaps even life once - is now one of the least hospitable places in the solar systems. If there ever was life there, I doubt we'll ever know it.

There are active volcanos on Venus, large, flat volcanoes of the hotspot variety (as opposed to techtonic plates) that spew vast amount of lava. But I think one of the coolest things about Venus is the fact that it not only spins backwards (on of only two planets that do) but spins veeeeeeeery slooooooowly. In fact, the Venusian year is 224.7 years, but the Venusian day is 243 days long.

Space is fun.

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For Aron: AC on ISS

Aron asked: One a scale of 1 to 10, how bad would it be if the ISS lost it's AC?

The ISS doesn't have air conditioning the same way we have here on earth. On earth, air is moved in and out of homes here, but is just "conditioned" by being cooled and dehumidified.

On orbit, it's a bit more complicated.

The Environmental Control and Life Support System removes CO2, adds oxygen, regulates pressure and O2 partial pressure, removes trace contaminants, dehumidifies the air (while recycling the condensate into the water supply) and regulates temperature.

How important is each of these capabilities on the ISS on a scale of 1 to 10? - 10

If the system fails to remove CO2, the crew will die.
If the system fails to add sufficient oxygen, the crew will die.
If sufficient cabin pressure and partial pressure of oxygen, the crew will die.
If trace contaminants are not removed in the fully enclosed environment, the long term health of the crew can be at risk.
If the air is not maintained at the right humidity, condensation is a serious concern, especially in an environment with electronics everywhere, the electronics that keep the system oriented and powered and everything else - too much humidity and the crew and ISS is at risk. Many electronics systems are on cold plates for cooling - making condensation a real issue.
If the air is not at the right temperature, electronics can fail (we don't have any but forced convection on orbit since there's no gravity). Too hot, and systems overheat and fail. Too cold, and, again, you have condensation issues.

Most of these systems have redundant components and subsystems because they're so key.

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