Dark Side of the Moon

That title sounds cool, but should be amended to read "Far Side of the Moon". The moon rotates around the earth and is "locked" so that we only see one face of it. My sister and bro-in-law were wondering what the explanation was for this. I took a crack at it, and had a tough time convincing them. So, I've studied up and am writing it here for them.

Why is the moon locked facing the earth? I looked this up years ago and learned that it is basically due to what's called "tidal locking". From the wikipedia article on tidal locking, "A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner." Tides basically cause an spherical body (like the moon and earth) to be stretched in the direction of it's orbital partner.

How is it that something related to tides could cause a celestial dance between giant objects like the earth and moon? Don't tides just make the oceans go up and down? The image below gives some idea of what's happening on earth.


Tidal bulges. Earth's oceans are stretched toward the moon on the side facing the moon and away from the moon on the opposite side. The diagram above also shows earth's rotation dragging the stretched shape slightly counterclockwise such that the bulge "leads" the moon.

The moon is also stretched like the earth, and the stretched direction always points to the earth. This is because when the stretched direction is not pointed at the earth, there is a correcting force that rotates the stretched direction to point at earth.

When the moon was liquid, it was bulged, and rotated "under the bulge" just like the earth does. As it cooled and froze, it's rotational energy must've tried to move the bulge from its orientation toward earth, but the corrective force mentioned won and we have our tidally locked moon.

Cool, huh? My dad asked the tough question of why the stretched shape is formed. For example, why doesn't earth just have a single bulge on the side facing the moon? Why another bulge on the opposite side? How the devil does this really work? Ike Newton was one of the first (if not the first) to understand this scientifically. The wikipedia page on tidal force is excellent. A summary follows.

Tidal forces diagram. Moon's gravitational forces (red arrows) are acting on the earth (the black sphere).

The red arrows in the top pane shows the moon's gravity which is weaker farther from the moon. The earth (the black sphere) is in free fall. Thus, it makes sense to subtract off the average gravitational force acting on the earth. This is done in the lower pane. Now you can see the forces that cause the tidal stretching.

Keep in mind that the tides are only ~10 feet. This is a tiny bulge for an object with a radius of 20 million feet.

Another cool thing I learned in the article is that the debris that makes up Saturn's rings would have condensed into moons if not for tidal forces exerted by Saturn.

Cassini image of Saturn.

Tidal forces are stronger closer to the source of gravity. Moons formed around Saturn when the debris was far enough away that tidal forces didn't disturb the formation.

windward side rain / orographic lifting

The issue of rain on the windward side of mountains arose in my trip last week. My dad attributed the phenomenon to cooling of the rising air mass. The reasoning is that air is cold at high elevation, so as the air gets higher, it cools, reaches dewpoint, and starts releasing water. After further study, fundamentally, it is correct that the air cools and reaches dewpoint. However, the cause for the cooling is kinda ... cool. It's called orographic lifting. Basically, the air expands as it goes to high altitude. As it expands, the air does work on the air that it displaces. The work energy had to come from somewhere. It came from the energy of the air molecules. Temperature is, basically, a measure of the average speed of the air molecules.

For further reference, see
http://en.wikipedia.org/wiki/Orographic_lift

On that page, there is a beautiful picture of clouds being formed at the crests of waves, called gravity waves. Orographic lifting can cause air at the crests of the waves to reach dewpoint and form clouds.

Clouds are created at the crests of gravity waves due to orographic lifting. These waves are created as air flows over an island in the southern Indian Ocean.

For more on gravity waves, see
http://en.wikipedia.org/wiki/Gravity_wave

plasma school

Down at UCLA, I enjoyed another 6-day plasma science winter school. (I previously attended in 2007.) Plasma science is mysterious, but when you couple good theory (pencil and paper work) with the enormous computing power that's we're developing. We covered several topics, listed below, but the funnest was probably the astrophysics.
* Learned something about how magnetic field is generated on large scales -- earth's magnetic field; galaxies' magnetic fields; magnetic fields in the universe in general.
* Learned some new stuff about turbulence and associated heat transfer in both astrophysics and in fusion devices.
* Learned more about shocks in fluids and in plasmas.

It's hard to convey how neat some of the computer simulations were, but here is a picture of one of the sims. The full sized movies (which I can't round up online right now) and images were more impressive.

Here's a picture of the aftermath of Tycho's supernova, the shell of which is a plasma shock wave:

Here are some pictures of the crab nebula. It has a pulsar at its core. Image in optical spectrum on left. Infrared (?) taken by Hubble on right.

Now the Crab nebula in xray:

Met lots of cool people. The U Wisc Madison crew was especially fun. We went out one night and ended up hanging out at one of the plasma labs where we drank a few beers and some British guys showed us how to play cricket -- the game seems quite strange to me.

Had an afternoon off on Wednesday. Went down to the beach to enjoy the 70 deg weather. I jogged from Santa Monica to Venice and back. At sunset, I took this photo of Ci using some rings. I'd never seen this kind of set of rings before. Some kids were doing some spectacular acrobatics on them...

Note the ferris wheel on the Santa Monica pier in the background. It was fun to ride that.

One evening Ci and I went to the nice outdoor track at UCLA. I ran a mile in 5:53. I was shooting for 6 min. I incorrectly calculated that I needed to run four laps at 1:20 per lap. Because I aimed for this pace (which would've given me a 5:20 mile), I managed to average 1:28 per lap... :) Then I did a 100 meter sprint to see how slow I am. On the first try, I set a new world record at 9.5 sec. Then we realized I hadn't run quite far enough. My time was 13.7 sec. Not bad.

At sunset that eve, I didn't see it, but some people saw a "green flash" at sunset. On my flight home, I looked for the flash, but evidently conditions weren't right. I did get this cool pic tho:

Nature, 1970: don't worry about co2

I’ve been doing some library research recently and saw issues of Nature dating back before 1900. I grabbed a random issue from ~1970 and browsed thru it. Found an article saying we shouldn’t worry about co2. Don’t worry, nuke power will be coming on strong by 2000. We’ll only have an 18% rise in co2 (rise to date has been ~15%, so they were on with this figure). Hell, we think the ocean will soak up all the co2 pretty quick anyway, but if it becomes a problem, we’ll just cut down on the fossil fuels. Cake. Wait.. reality check.. this ain’t so easy! Hard to figure how to slow down fossil fuel intake, either in booming nations like china and india or in addicted nations like US.

fusion as replacement for fossil fuels?

My grandfather (aka Uncle Bill) asked me if fusion power could replace fossil fuels. Here's my response....

Unk Bill,

You asked me if fusion can replace fossil fuel in our energy economy in the relatively near term (30 years). Below I’ll describe two candidate fusion machines. The first is a tokamak. It is unlikely to solve the problem because it’s too expensive. The other is the compact torus (CT). It is unlikely to solve the problem because a technological breakthrough is required. However, anything is possible, especially if enough research money is devoted to the challenge.

Tokamaks have received the vast majority of research effort in the past 50 years. With the tokamak, we have achieved “breakeven”, which that the ratio of fusion power out to electrical power in is one. For a commercial powerplant, this ratio should be about 10. If things go as planned, the International Thermonuclear Experimental Reactor (ITER) will achieve this desired factor of 10. However, tokamaks are incredibly complex and expensive engineering marvels. Superconducting magnets are required to produce the strong magnetic fields in tokamaks. Perhaps in 30-50 years, tokamaks can be made commercially competitive with coal plants, but not in the near term.

A sudden breakthrough in an innovative device called a compact torus (CT) is a long-shot possibility. The CT is similar to the tokamak, but is generally smaller and doesn’t require the superconducting magnets. One of the keys to the CT is that it allows the magnetic fields to relax naturally instead of using the high magnetic fields of a tokamak to force the plasma to behave. Consider bridge building: if an engineer wasn’t very crafty, he/she might just make the bridge deck very thick. However, a crafty engineer would use cables to suspend the bridge, thereby greatly reducing the cost of the bridge. The CT is the crafty engineer’s approach. CT development is far behind the tokamak in funding levels and in technological development. However, a breakthrough might yield a useful fusion powerplant in the next 20 years.

Now… if fusion can’t solve the problem alone, can it help somehow? Nuclear fission technology works, but has a radioactive waste problem. Nuclear fusion can help solve that problem. Fission produces radioactive isotopes. By bombarding the radioactive isotopes with neutrons, they can be transmuted into radioactively stabilized. Fusion produces lots of neutrons even if it doesn’t produce energy. With fission-fusion hybrid technology, we can employ those neutrons to deal with radioactive waste.

Many people don’t realize how much progress has been made in fusion! We routinely control plasmas and make fusion energy. Hydrogen (which can be obtained by splitting water) is the fuel for fusion. This is a technology that humanity will surely benefit from in the long run if not the short run.

Hope this sheds some light on the issue!

Eric

P.S. I’ve only talked here about magnetic confinement fusion which uses electromagnetic fields to trap plasma (hot charged particles). Another approach is to use lasers to compress a chunk of fuel. This idea also has some merit, but I think magnetic confinement is preferable, so I ignore laser compression here.

truth stalking -- Russian racehorses and speed vs. mpg

Have done a little truth stalking today on two subjects:

- What does it mean to have to piss like a Russian racehorse?
- And what are some experimental numbers on mpg vs. vehicle speed?

I has having chai tea with a friend this morning, and she bought me a grande. I knew it'd be way too much tea, but figured it couldn't hurt. We talked for an hour or so then I rode my bike home. Would've stopped in the bathroom but it was occupied. Eyeballs were floating upon arrival home. I thought to myself -- I have to piss like a Russian racehorse! But what does that even mean!? I found an interesting tidbit:

Apparently (and I don't have any solid info on this but it makes a good story and might be true [doubtful .. see comments below .. but maybe Russians were especially agressive in their methods somehow?]), in Russian horse racing, they used to tie off the (male) horses' penises. This way, they had to pee really bad once they started racing. Not very nice, and surprising to me that it was even effective. But that's where the saying comes from! You can go farther and say "like a Russian racehorse in winter." I guess in cold winter air, mammals generally offload water to contract blood vessels and avoid heat loss.

Now on to mpg. Found an interesting website. They show what one my dad told me long ago, that slower is better for mpg. For a typical car, it is empirically found that you get better gas mileage at 35 mph or even slower. See this chart from the website. I only looked briefly into this and this website isn't the word of god but it seems pretty good...

Stay tuned for more truthiness next time.

Stargazing -- Jupiter, M11 (Wild Duck Cluster), etc.

My 10" dobsonian reflector is really easy to take out onto the grass in front of my house. Did so this eve. Light pollution in Seattle is pretty bad, but you can still see some interesting things. Would've driven to a dark spot but moon was due to rise at 10 pm.

Jupiter is always amazing. Have looked at it several times in last month. Can see 4 satellites. Can easily see bands with my scope through either 32 mm lens (40x mag.) or 12.5 mm lens (100x mag.). Saw red spot on one occasion. Noted rapid movement (moved visibly over 1.5 hrs). Looked up Jupe's rotation period -- 9 hrs vs. Earth's 24 hrs!

Was going to look at M81 and M82. Looked hard at star charts and thru binocs. Had it nailed. Then clouds covered them. But now I know that part of the sky (NE of big dipper bowl) pretty well.

Scanned sky near jupe and saw nice blob. Looked up in star charts and saw that it is M11. Put scope on it. Nice view. Lots of stars in this "Wild Duck" cluster. Got to know Aquila constellation in which Altair shines brightest.

Moved to Ring Nebula in Lyra near Vega (Altair, Vega and Deneb form the summer triangle). Can make out ring with 100x mag. No doubt would be better in dark conditions.

Looked at Andromeda over by Cassiopeia. Maybe on a really dark night it'd be more exciting through this 10" scope. On a dark night with long film/digital exposure that you can really see Andromeda in detail, so here's a picture:

Image credit: Jason Ware, http://www.galaxyphoto.com/

Also looked at nebulas 884/869, and 654/653 which are near Cassiopeia. Seems easy to play with this dobsonian mounted scope as compared to typical tripod.

Constitutional authority for developing technology / health care / soc. security

[This post is a continuation of an email conversation between my dad Steve and friend Jason .. comments encouraged.]

Interesting discussion :) Long-winded. I'll contribute some more steam before we switch to nuclear.

Jason, your idea about the limitations of the constitution is quite interesting, particularly with regard to energy legislation. A quick read of the constitution reveals that there is no constitutional mandate for our government to develop/maintain/expand our transportation system except perhaps "To establish ... post Roads" -- Art. I, Sect 8. Yet the DoT is a pretty well-funded department. Likewise, the DoE gets a fair chunk of change. Why? It's a good question. Maybe private industry could handle it. Maybe not. For instance, could private industry have collaborated to put together our interstate freeway system? I seriously doubt it. Private industry did the work, but the government orchestrated it, and used taxpayer money to pay for it. Likewise, solving our energy problems will likely require government orchestration. We'll probably need some pretty nifty power and energy transmission infrastructure including conduits for electricity and for "portable power" for autos (e.g. hydrogen).

Sometimes nations/civilizations/organisms can get an upper hand by having big common projects. Think militaries. Think ocean exploration in the 14/15/16th centuries. Think space program (but don't think so hard that your start to wonder what the hell it's done for us so far... mostly i jest .. if you've considered it much, you recognize several crucial benefits that space has brought us). I think state-sponsored technology development is appropriate. How one would write a constitutional amendment to properly sanction it is another question!

In the opening passage of Common Sense, Paine says that government is a "necessary evil", negatively constraining society's vices. Meanwhile, society itself provides the positive influence, "uniting our affections". What you are suggesting (and I expanded on above) is that gov't should be in the business of "positive influence". We also obviously need to worry about gov't properly constraining society's vices. This is where we clearly need corruption control.

Medical care and social security (which is in desperate need of being renamed "managed savings" or being re-directed to being a safety net program) are in the same boat as energy technology when it comes down to it I guess.

On the sub-crime crisis: 1) if the gov't is going to bail out these lenders, they should regulate. 2) gov't shouldn't bail out the lenders. I think I'm with you Jason, voting for #2.

Who is this physicist who told you about the nuclear fuel problem? He/she is right that we have a problem if we don't effectively use fuel. As I recall, if we used all of the available energy in uranium ore, we'd have plenty of power for centuries even if energy consumption were to go up 10x. Using all available energy would involve something quite different than what the French do which is a joke compared to what i'll call true nuke fuel squeezing. French squeeze less than 5% of available energy in fuel. Standard US nukes get only 1%. You can squeeze out nearly 100% of energy with breeder reactor. Breeders are expensive because it's expensive to make them safe. Proliferation is another concern and is a concern for any squeezing operation. But you can squeeze in a safer way using fusion as a source of neutrons (there are other possible sources too) to maintain a sub-critical reaction that uses "fast" neutrons to squeeze energy out. Look for fission-fusion hybrids hitting news in next 5-10 yrs. (physics sidenote: when you don't moderate/slow neutrons [as we do in our current "slow" neutron reactors], the characteristic time of a critical system is very very fast, making it tough [expensive, uncertain] to design a control system with an appropriately small response time).

Oh -- Nanosolar -- i hope it works! But I question their ability to get materials cheap enough to power the globe.. maybe they can tho? I really have no facts on this matter.

astro party

Had a good time star gazing on Saturday night. I was impressed with the performance of my 10" scope. We bbq'ed at my place and watched Djokovic take out Nadal prior to heading up. Seemed likely to be clear so we headed up to Rattlesnake Lake. Ci, Monica and I drove up and met my roomies and some other friends up there. It was clear .. in a few spots .. for a little while. We got a nice view of the apparent double star in the handle of the dipper -- Mizar and Alcor -- and could clearly see the true binary system of which Mizar is part.


We got a quick look at M13, a globular cluster in Hercules.


By 11:30, cloud cover was quite thorough. So we hung out (Ci stayed warm by huddling like a homeless person in the telescope box) and hoped for clear skies for a while and chewed the fat. For instance, we talked about Starbucks, Shultz, and the Sonics. Kind of an interesting situation... We packed up at 1 am and headed down. Bhuvana called and reported that the skies cleared as they approached Seattle. So Ci, Monica and I stopped short of Seattle and did a bit more viewing. The highlight of that leg of the stargazing was Jupiter.

The image above is plagiarized from the internet. Though our viewing was not as spectacular as shown above, we could see the planet in breathtaking detail. Four of its moons were clearly visible.

We also viewed Andromeda which looked like a fuzzball. I think if it is extremely good viewing, one could make out the shape of the galaxy. Couldn't see the N. America Nebula at all (I assume was too light).

I tried to find M81 and M82 which are in Ursa Major. Couldn't get there. Need better star maps.