agate_ t1_jdl7rpf wrote

Yes, the STEREO mission (Solar Terrestrial Relations Observatory) was a pair of satellites launched into solar orbit in 2006, one going slightly faster than the Earth, one slightly slower, so that over years they move to the opposite side of the Earth's orbit from us and are able to see the "back side" of the Sun. STEREO-B (Behind) died in 2014, STEREO-A (Ahead) is still operational.

By a funny coincidence, as you're asking this question now, STEREO-A has almost completed its first "lap", and is coming back past the Earth this summer. So it can't currently see what's going on on the other side of the Sun because it's got almost the same view we do.

There's also the Parker Solar Probe and the ESA Solar Orbiter, which are currently making tight elliptical orbits close to the sun, which bring them to the "back side" once every few months. Right now the Parker probe is pretty close to the far side of the Sun from us, and the Solar Orbiter is between us and the Sun.


agate_ t1_jaxebva wrote

If /u/LadyLaLas and /u/CrustalTrudger are willing, there’s another way to answer the question: share a photo of your rock, and I bet /u/CrustalTrudger could narrow down the range of places it might be from.

Depending on what it looks like the answer could be “damn near anywhere” or very specific. And keep in mind that this is very difficult to do with just one photo, and I don’t think /u/CrustalTrudger is a specialist in rock identification or the geology of Ireland. But they’ll do a better job than I would and I bet it will be interesting!

For best results take a photo in bright light with a white background and a ruler or other common object to give the scale. Crustal I apologize for asking you to do geology tricks.


agate_ t1_jasl2w2 wrote

The rock types of the inner planets — Mercury through Mars — are basically the same. Earth has more variety because it’s got plate tectonics and water on the surface, but most of the minerals on these worlds are stuff we recognize from Earth, and the major components of the bulk planets are the same.

You mentioned Titan though. The moons of many of the outer planets are largely made of water ice. Out there, water is just a type of rock. (You could argue water is a mineral here on Earth too, especially if you live up north, but if it is it’s a weird one.)

Two other types of “minerals” appear in the outer solar system that are nothing like what we see on Earth. First, many of the outer moons’ surfaces are covered with dark or reddish materials that we can’t identify precisely but seem to be organic carbon compounds of some sort. Second, many of the larger moons have water ice layers so thick that exotic new types of ice form in the high pressure interior.

And in the extreme outer solar system (beyond Neptune), nitrogen becomes a solid ice that could be considered a mineral as well.

Titan in particular has probably has a lot of organic schmoo on top of a water ice crust, a liquid water layer under that a high pressure ice layer under that, and then a core of traditional rocky minerals at the center.


agate_ t1_jacx53k wrote

It’s really simple. The sign on the right is for people who look like customers, the sign in the left is for people who look like shoplifters.

And I’ll give you two guesses how they decide which one you look like.


agate_ t1_ja6xblq wrote

The best bit is that nobody is giving the right answer, and even the article only hints at it:

There are a few places in Antarctica where ice slowly evaporates due to very low snowfall and high winds. This forms regions of clear blue ice, and the ice sheet flows toward these regions. Any meteorites that fall elsewhere on the ice sheet get carried to the blue ice zones where the ice evaporates leaving the meteorites behind on the surface. The meteorites build up to very high concentrations over thousands and thousands of years.

So the Antarctic meteorite hunters aren’t just going there because fresh meteorites are easy to spot, they’re there because all the meteorites that fell over a huge area for thousands of years are concentrated in one spot.


agate_ t1_j921et4 wrote

This is a neat answer, but I hope someone will tackle what I think is the most interesting part of OP’s question: why is iodine biochemistry apparently localized in the thyroid? It’s not like we have specific organs for zinc or manganese chemistry. (Or do we?)

What animals have a thyroid? Is iodine chemistry localized in a different organ in the ones that don’t?


agate_ t1_j8igwtp wrote

Re “dosage compensation”, is it generally true that more copies of a gene means more gene expression? Aren’t most genes regulated by homeostatic feedback systems?

And what about the many, many plant species that get along just fine with duplicates or triplicates of their entire genome?


agate_ t1_j7ut646 wrote

We're interested in seeing what's in our solar system because we're curious about it. Some solar system discoveries may have important things to tell us about the formation of the Earth and the development of life on it and beyond, but frankly the number of small moons of Jupiter isn't "important", except that it satisfies our curiosity.

Which is the most important thing of all.


agate_ t1_j7u1wsk wrote

If they didn’t, the control device would heat up as much as the hob.

Using the “water analogy” for electricity, voltage is like water pressure inside a pipe, current is like water flow. The power consumed by an electrical device is the voltage change across it times the current through it.

If a switch is turned off, it holds back the full voltage from the mains, but no current flows through it, so the switch consumes no power, because anything times zero is zero. If it’s turned on, the current is high but it doesn’t hold back the voltage at all, so again no power consumed by the switch.

But if you turn the switch on “halfway”, so it blocks half the mains voltage and lets the other half pass through to the hob, then hob and switch carry the same current across the same voltage change, so the switch consumes as much power as the hob. This is wasteful, but more importantly it’s dangerous, because the switch will produce as much heat as the hob.

This technique is called “pulse modulation”, and it’s incredibly common, not just in stoves. Any time a digital device is controlling a smooth variation of something, the device is usually just switching it on and off. Often the switching happens too fast for humans to notice (like dimmable lighting) or the signal goes through a filter that smooths out the pulses.


agate_ t1_j7f6jdb wrote

Not by much. Thermal conductivity in gases happens by molecules gaining thermal energy and moving to a colder place. Adding more molecules gives you more energy carriers, but they can’t move as far before bumping in to each other. So the thermal conductivity of most gases increases only slightly with pressure.

If you get near the boiling point, or the pressure is so low the molecules fly the length of your chamber without bumping into anything, the situation is different.


agate_ t1_j6nidr1 wrote

One way to think about the fact that “the mantle is a solid but it flows” is to think about ice. Ice is a solid, just look at an ice cube, and yet a kilometer-thick glacier flows.

Like ice, the mantle isn’t perfectly solid. But if you compare it’s viscosity to that of a glacier, you find that the mantle is roughly a million times more solid than ice.

(Ice is also a non-Newtonian fluid, so a precise comparison isn’t possible.)


agate_ t1_j6mi3f9 wrote

In the US, towns get their authority from their charter, which is approved by the state legislature when they are formed. The charter will describe and authorize a town police department; the local police get their authority from that.


agate_ t1_j6a7c2x wrote

Neat, I hadn’t seen the data presented that way before. Your graph also shows an important difference between land and sea: because the sea surface is usually smoother than the land (no trees and hills), there’s less turbulent mixing and the boundary layer is usually thinner. So the neutral point you’re talking about is much lower at sea.

The weaker, thinner boundary layer also means the overall wind speed is much higher at sea, which is why people go to the trouble of building offshore wind turbines.


agate_ t1_j66q62p wrote

This engineering question needs a meteorologist! The answer lies in the turbulent mixing of the lower atmosphere.

The planetary boundary layer is the turbulent layer of air near the ground. Turbulence in this layer mixes air near the ground with air higher up. This mixes all sorts of air properties from top to bottom of the layer: for example, humid air near the ground is mixed with drier air higher up, making the ground-level air less humid and the upper air more humid.

The layer also mixes momentum, or air speed. The air at ground level -- down among the grass blades -- isn't moving at all, but it's moving very fast several kilometers up. Turbulent mixing transfers momentum across the planetary boundary layer just like humidity, making the ground-level air go faster and slowing down the air higher up.

And now for the kicker: the amount of turbulence in the layer depends on solar heating. When the ground is heated by the sun, hot air rises. The rising plumes of air increase the turbulent mixing in the planetary boundary layer and cause it to extend higher up.

So, during the day, mixing in the boundary layer is more intense, so more slow-moving air at ground level is stirred up to the height of the wind turbine blades, so they experience slower wind speeds. At night, the PBL doesn't carry slow-moving air up to the turbines, so they get the full force of the upper-level winds.

You may have noticed that for you as a human, nights seem to be calmer, and it's windier during the day, which is the opposite of what wind turbines feel. This is the same effect in reverse! You're so close to the ground that you don't feel much wind unless turbulence in the planetary boundary layer brings it down to your height.


agate_ t1_j5b7f4e wrote

No. The ring particles are in orbit, and orbits that are closer to the planet always go faster. So the inner particles are always moving faster than the outer particles, and can’t stick together.

If you took Saturn’s rings and added more ice particles to them, they would not weld together. Instead, collisions between particles would knock more of them into higher orbits and more into lower orbits. The ring would get wider, and a lot of the mass you add would fall into Saturn.

Even if you tried to build a solid structure shaped like Saturn’s rings from scratch out of steel, the difference in gravity between inside and outside would create tremendous forces that would rip it apart.


agate_ t1_j2dz8m3 wrote

Many ocean organisms live only at specific depths. For example, the coral Acropora palmata only grows within a few meters of the sea surface, where it can get the most sunlight.

Suppose you drill a core into a coral reef using a floating drill, and find some of this coral that's 10,000 years old at a depth of 100 meters below the surface. How could this happen? Either the sea level must have risen, or the island the coral is growing on must have sunk.

You can figure out whether the island has sunk by looking for very old corals of the same type. For example, if you find corals dating back to a previous warm period 120,000 years ago at or above sea level, you can be sure that the land isn't sinking very fast.

You can repeat this analysis for other corals that live at greater depth, you can repeat the analysis in coral reefs all around the world, and repeat it for other types of organisms that live near the water surface in colder climates, and you find a consistent pattern of sea level change over time.

> Is someone who denies the historic sea level graph equivalent to a Flat Earther?

There aren't many people who deny that sea level has changed. Most often climate change deniers use the past sea level graph to show that sea levels are not stable, and thus -- they say -- the current sea level rise is nothing special, and a natural process. Some people argue that the ages of the changes are wrong, and the sea level changes actually represent the biblical flood.


agate_ t1_j2dl4o5 wrote

American history is a constant re-definition of what "West" means. In the 1700s and early 1800s, the northwesternmost extent of the US was the Northwest Territory, which included the modern states of Ohio, Indiana, Illinois, Michigan, Wisconsin, and Minnesota.

A number of things in this area are still called "northwest", including Northwestern University near Chicago, and Northwest Airlines, which was based in Minnesota.

Of course, after the Louisiana Purchase in 1803 and the gain of the Oregon Territory in 1846, the old Northwest wasn't very northwest anymore, and so "Pacific Northwest" came to be used for the new northwest corner of the contiguous US.