biochemistry - Why does Rigor Mortis occur after death?

You are right that ATP is needed in relation to Rigor Mortis: This for ion pumps to maintain concentration gradients in cells. Without a constant supply of ATP to the pumps, calcium starts to diffuse from the extracellular matrix (and other intracellular compartments with high concerntations of calcium) into the sarcomere where it binds to troponin, a regulatory protein in skeletal muscles. This holds myosin the actin filaments together creating the effect of rigor mortis.

gravity - If the Universe is infinite, would heat death be impossible?

If the Universe is infinite, one would imagine that if we kept moving through space, we'd constantly find newer and newer galaxies and objects forever. This would imply that there is an infinite amount of matter in the Universe.

The heat death theory states that, eventually, there will be no free energy left in the Universe. Stars would no longer form, black holes would eventually evaporate, and the Universe would be effectively dead. But if there's an infinite amount of matter, won't there always be more gas clouds that haven't formed stars, more stars that have yet to become black holes, etc.? If there is an infinite amount matter and energy, shouldn't more activity be possible no matter how many stars go out or how many black holes evaporate?

One might say that with enough time, all matter in the Universe would still run dry. But if there is an infinite amount, there should always be areas in which activity is still going on...right?

Is what I'm saying correct? Does the heat death of the Universe contradict the theory that it is infinite?

observation - Do neutrinos have as much information as photons do?

If neutrino detectors keep improving so that a fair number of neutrinos can be observed, would they be as informative for astronomy as photons are?

They are of course a very valuable complement to photons, but I'm thinking about neutrinos in and of themselves. Photons have wavelength, spectral lines, redshift, diffraction, polarization which reveal their origin and interactions on the way to us. Do neutrinos say more than just what direction they come from?

neuroscience - How old does a baby have to be before it can retain memories?

Surely an important question. But there are different kinds of memory (classified mainly as declarative and procedural) which you don't specify exactly in your question. Wikipedia and Scholarpedia list here many known facts. I will give you some short hints and links for introduction and overview instead of pasting that stuff here.

You are probably referring to autobiographical or episodic memory, that is memorizing consciously particular events within one's own life within a context. And for this type of memory researchers agree that self-awareness seems to be a necessary precondition. The existence of this cognitive ability can be checked by the mirror test. Human infants pass this test normally around a age of 18 months (also some animals). The cognitive self develops between 21 and 24 months and marks the end of infantile amnesia.

Could an asteroid knock the moon out of its orbit?

Basically no and not by a long shot. The asteroid's measurements are pretty vague, but lets give it a nice clean 600 meters in diameter and the same density of the moon. The moon is 3,474 km in diameter or 3,474,000 meters. So the moon is nearly 5,790 times the diameter and that gives is 194 billion times the mass as that asteroid. Conservation of momentum, if the asteroid transfers all of it's 78,000 mph into the moon, with no energy going into angular momentum, 78,000 / 194,000,000,000 = .0000004 mph. That's roughly the speed your fingernails grow.

To knock the moon out of orbit, it's velocity would need to be increased by oh, very rough ballpark, maybe 400-500 mph. The additional velocity needed for the moon to reach escape velocity from the Earth is .414 x 2288 or about 947 mph, but given that it has an elongated orbit and that it would escape the Earth's sphere of influence well below escape velocity, maybe as little 400 extra MPH could knock the moon into a far enough orbit that it could escape the Earth.

Figuring 78,000 MPH, and you want to move the moon some 400 or more MPH with ah it just right, you'd need an object about a 5th or 6th the diameter of the moon or 600 KM in diameter give or take, assuming it was straight on impact as a glancing blow would lose a share of energy into angular momentum and assuming it hits the moon away from the Earth, not towards as towards would require even more energy.

This space pebble doesn't even come close. You'd need something the size of a small dwarf planet to have a chance at knocking the moon out of the Earth's orbit and that speed.

300-600 meters is huge, if it hits the Earth. That's probably a few square miles of earth practically leveled to the ground and broken windows and knocked down trees a good deal further than that. If it hits the moon it would leave a nice crater, maybe a miles or two across but that's about it.

It seems like you're only talking about the moon being kicked out into
space. Would the same amount of energy be needed to knock the moon out
of its orbit in towards Earth?

The mathematics of crashing is a bit more complicated. Escape Velocity vs Orbital Velocity is easy, just straight multiplication. More details here, and because the Moon wouldn't need to reach full escaple velocity, I cut the number in half - and it might be a bit less than that.

Moon's orbital Speed (2,288 MPH) x (Square root of 2 minus 1, or 0.414).

Crashing the Moon into the Earth - a bit harder. There's probably a simple enough formula, but I'm not sure what it is, but I believe that would take even more energy.

It's discussed here without math and here, with math. But it would take a huge amount of energy, probably 3 or 4 times more energy to push the Moon into the Earth than to push it out of orbit if I was to guess.

botany - Do plants produce any heat?

Plants will be respiring continuously, which is an exothermic process. Therefore the plants will be producing a small amount of heat. The protection from frost may be more a result of the vastly smaller convection current of the coat compared to the atmosphere rather than by reducing any conduction away of heat produced by the plant, however.

Keeping the plant out of the wind by 'dressing it' will reduce the rate of transpiration when the stomata are open. I would very tentatively suggest that, as water has a very high specific heat capacity, having a greater volume of water within the plant would help to retain any heat that was produced by respiration. However this is entirely speculation on my part.

Are there naturally radiation shielded areas on Mars? (shadowed by terrain formations)

If you want protection from radiation on Mars, you'd have to either live in caves, or else build some kind of thick dome overhead, or live behind thick walls/ceiling. Cosmic radiation will reach you anyway as long as the sky is visible, so deep valleys can only help you so much.

The only way to stop hard radiation is to place a lot of "stuff" (thick mass) between you and the source. A pile of dirt would suffice in many cases. The geologic layers on top of a cave would work well. I guess a dome could also work if it's thick enough. Habitats with thick ceilings (and walls) could also be an option. Have a large water reservoir? Put it on the roof of the habitat: voila, instant radiation shield.

The main concern is the stuff coming in from directly overhead; near horizon even Mars' atmosphere is thick enough to reduce radiation a little. So prioritize the ceiling.

I guess at the base of a hill with some overhang above your head you'd get some shielding, but again - is the sky visible? That's the main concern. Also, areas under an overhang may or may not be safe (stable) long term.

Find a very large boulder (the size of a house or bigger), much taller than your habitat, and place the habitat right next to it - you've cut 50% of radiation right there.

For a shorter term stay, a simple habitat with thin panels would be enough - not very different from the interplanetary vehicle after all.

gas giants - Types of Exoplanets

Any statement about the relative frequencies of exoplanets of different size, is limited to the parameter space over which they can detected.

I'll add a reference shortly, but I recall the that a recent analysis of the Kepler-discovered exoplanets, that takes account of observational selection biases, indicates that for planets orbiting with periods less than about 100 days, that Neptune-sized objects are more common than Earth-sized objects, which are in turn more common than Jupiter-sized objects.

Extending this comparison outside this range of orbital periods is not possible with present data.

stellar evolution - Temporal path through Hertzsprung-Russell diagram?

There are a number of illustrations of this on the Stellar evolution page of wikipedia.

Roughly a star begins as a large but cool ball of contracting gas, to the right of the main sequence until fusion starts in its core.

Once fusion starts it has reached the main sequence. It gradually moves up as it slowly brightens during its life, and then moves to the right and up as it expands into a red giant. There are then some significant movements as heavier elements begin to fuse. Sun-like stars undergo a significant change when the helium fuses in a matter of days (or less according to some models), called the Helium flash. As this occurs, the star moves significantly down and left, back towards the main sequence, before expanding again into an even larger red giant. The expelling its outer layers in a planetary nebula, and rapidly moving to the left and down.

Larger stars undergo other fluctuations, changing from red supergiants, to Luminous Blue Variables, and Wolf-Rayet stars, and ending in a supernova.

There are several illustrations of this on the wikipedia page, but noting the sometimes significant differences between the diagrams suggests that this is a topic in which the details are not certain, in part due to the difficulty in getting observational evidence of changes in stars, which occur over very long time scales.

human genetics - Is there any difference in terms of personal healthcare between complete DNA sequencing and SNPs genotyping?

This difference would have the greatest impact on treatment for cancer, in which a treatment protocol is based on genes deleted, amplified, altered in the tumor vs the reference genome for that patient.

In terms of health risks based on SNP genotypes, the data are far from complete. Sure, some level of risk can be assigned to a variant (SNP), say at certain markers within the FTO gene and risk of obesity. However, the complete list of risk alleles for this and numerous other complex traits is not fully described. Furthermore, the impact of environmental factors (EF), or lifestyle choices, on those genetic variants is only beginning to gain wider attention. For example, a risk allele may not show itself as risk until the EF, such as amount of physical activity or percent energy from dietary polyunsaturated fat, passes a certain threshold. Such gene-environment interactions are thought to contribute to the variance in traits (phenotypes), but to what degree is not known.

Added in edit 15 May 2012: Epistasis, or gene-gene interactions, also are important but far from being cataloged for humans. A situation could arise where one allele elevates risk for a certain condition, but compensatory alleles elsewhere in the genome decrease that risk. We don't know the full extent of epistasis in humans.

Thus, in terms of personal healthcare outside of something like cancer and monogenetic disorders, there may be little that is gained from genotyping or complete genome sequencing, little that is compared to other advice you already know. I carry risk alleles for certain conditions, but there is not really any advice one can give me that is specific for those alleles that I have, where that advice is different than or goes beyond general advice health care providers already have dispensed.

rotation - What is the accepted theory as to why Uranus' axis is tilted so severely?

The planet Uranus is another solar system anomaly, where according to the NASA profile has an axial tilt of 97.8 degrees, also considered to be retrograde. This NASA summary "Uranus" suggests the current theory of a large planet-sized impact earlier in its history.

Does the planet-impact theory still hold true or have new accepted theories come to light?

Most of all, are there any results from any simulations available?

A note, this is posted as a separate question to my other question "What is the current accepted theory as to why Venus has a slow retrograde rotation?" as the axial tilt is significantly different.

cosmology - How do we know that there is no border at the end of "infinite" space?

We do not know what lies beyond the limits of our instruments, by definition.

For all we know, there could be a big sign saying "This area under construction."

However, that doesn't seem very probable.

The most probable answer is "more of the same". After all, there is no reason the bit of the universe we can see should be different from other places.

If you keep adding "more of the same" to the universe, you get the infinite universe you have seen described.

It is just a theory, but it seems like a pretty probable one.

It is also easier to do calculations on. Having a border introduces all kinds of problems like galaxies near the border only getting gravitational forces from one side only. With an infinite universe these forces come from all directions and cancel each other.

It is still just a theory, but it is one that is (relatively) easy to work with.

cell biology - Do larger multicellular organisms have an increased risk of mutation and thus cancer?

As mentioned in the comments, this question is quite complicated. If the chance of a single cell from different organisms getting cancer was the same, then you would be correct, but this is not the case.

Different organisms have evolved to live different lengths of time. This is rather obvious when you think about it: mice have a maximum lifespan of ~3 years, humans ~80years (these figures are of course massive generalizations - but it doesn't really matter). Yet 'old' mice (> 2 years) still get age-related diseases such as cardiovascular disease, and cancer. It should be fairly clear that the risk of a 2 year old mouse getting (age-related) cancer is much higher than a 2 year old human.

The explanation for this isn't exactly concrete, but it goes something like this; mice invest a lot more resources in growing very fast and reaching a reproductive age very early, whereas humans develop much more slowly, and invest a higher proportion of their resources in maintaining tissue function, thereby reaching reproductive maturity much later than the mouse. The Hayflick limit for a mouse is about 10, whereas for humans this is closer to 60.

Thus the rate of aging in humans is much lower than that of the mouse, and it comes back to evolution: mortality in the wild is very high for the mouse, and thus mice that invest heavily in reaching early reproductive maturity are selected for - and those that invest in anti-cancer mechanisms take longer to reach reproductive maturity, and thus have less chance of actually doing it!

So to answer your question - smaller organisms tend to have higher risks of getting cancer because their lifespans are comparatively shorter, and thus they 'age' at a faster rate and invest less resources in maintaining function (e.g. genome integrity).

dark matter - How close are we to be able to detect and measure gravitational lensing inside the milky way?

Well, there are microlensing experiments, the results of which have largely removed MACHOs as a significant source of Dark Matter. The background field of stars is usually a nearby galaxy (a Magellanic cloud one or Andromeda, say), or the galactic bulge, and the experiment looks for lensing objects between us and there. In particular, they're pretty much always looking for the microlensing effect within our own Milky Way or its halo. These experiments have detected a number of microlensing events (and many, many more candidates that were due to other things), so, yes, this is not only possible, it is already done.

The wiki page I started with linking has this to say, in particular:

The first two microlensing events in the direction of the Large Magellanic Cloud that might be caused by dark matter were reported in back to back Nature papers by MACHO and EROS in 1993, and in the following years, events continued to be detected. The MACHO collaboration ended in 1999. Their data refuted the hypothesis that 100% of the dark halo comprises MACHOs, but they found a significant unexplained excess of roughly 20% of the halo mass, which might be due to MACHOs or to lenses within the Large Magellanic Cloud itself. EROS subsequently published even stronger upper limits on MACHOs, and it is currently uncertain as to whether there is any halo microlensing excess that could be due to dark matter at all. The SuperMACHO project currently underway seeks to locate the lenses responsible for MACHO's results.

Despite not solving the dark matter problem, microlensing has been shown to be a useful tool for many applications. Hundreds of microlensing events are detected per year toward the Galactic bulge, where the microlensing optical depth (due to stars in the Galactic disk) is about 20 times greater than through the Galactic halo. In 2007, the OGLE project identified 611 event candidates, and the MOA project (a Japan-New Zealand collaboration) identified 488 (although not all candidates turn out to be microlensing events, and there is a significant overlap between the two projects). In addition to these surveys, follow-up projects are underway to study in detail potentially interesting events in progress, primarily with the aim of detecting extrasolar planets. These include MiNDSTEp, RoboNet, MicroFUN and PLANET.

mycology - How do fairy rings propagate?

In addition, the mycelia (the underground mass of hyphae which constitutes the bulk of the fungus) expand outwards because they decompose organic matter in soil as they go, leaving very little organic matter in the soil in the interior of the ring. My Campbell & Reece textbook tells me that they can expand outwards at about 30 cm/yr. (1)

(1) Campbell, N.A., Reece, J.B. et al., Biology, 8th edition, Pearson, 2008

rna - Majority of transcripts are from sense strand?

From my understanding sense and anti sense is contextual. If you are looking at a gene from 5'->3'(which is convention) that strand is the sense strand and the complement to the gene is the anti sense strand.

However further along the DNA there could be a gene on the 'original' anti sense strand, if you are discussing this new gene, there is a new context and it is now on the sense strand (oriented 5'->3'), and it's complement on the anti sense strand.

I hope that's clear.

Why is beta-mercaptoethanol often added to cell culture media

2-me is a reducing agent necessary to be added to help keep free radical oxygen from affecting mouse cells. It is generally not necessary for human cells.

Also from S Bannai and Ishii et al., 2-mercaptoethanol improves tumor cell uptake of cystine by creating a reducing environment.

How many meteors hit the moon every day or in how many days does a new meteor hit the moon?

We generally like you to check google before posting questions here. I posed your question to google and amongst other links, I got these:

http://science.nasa.gov/science-news/science-at-nasa/2006/13jun_lunarsporadic/
http://www.slate.com/blogs/bad_astronomy/2014/02/24/lunar_impact_video_of_an_asteroid_hitting_the_moon.html

Per Bill cook in the top link:

No one knows exactly how many meteoroids hit the Moon every day. By monitoring the flashes, we can learn how often and how hard the Moon gets hit."

And in the second one:

The Moon is smaller and has less gravity than Earth, so it gets hit less often than we do.

Both articles mention MIDAS (the Moon Impacts Detection and Analysis System). Since the first link is from 2006, perhaps soon we will have a good estimate for you.

universe - Is the earth bombarded equally in all directions by neutrinos?

In addition to neutrinos from the Sun and other discrete sources in the Universe (see James's answer), there is also expected to be a cosmic neutrino background. Although this is yet to be detected (efforts are underway), its expected properties are reasonably well understood. The neutrinos "decoupled" from the universe seconds after the big bang at temperatures $>10^{10}$K. As the universe expands, the de Broglie wavelength of these neutrinos (which are not massless) lengthens with it, such that the neutrinos are expected to have a temperature of $<2$K today. There are 112 of these cosmic neutrinos per cubic centimetre per neutrino flavour (probably 3).

The C$nu$B is analogous to the cosmic microwave background in a number of ways, but (a) it hasn't been detected; (b) it is cooler; (c) because neutrinos have a small but non-zero mass, the C$nu$B neutrinos are likely non-relativistic today.

This latter point is important to your question. On large scales we expect the neutrino background to have an asymmetry due to the motion of the Earth through the universe with respect to the co-moving standard of rest. This is exactly the same global dipole asymmetry seen in the cosmic microwave background. However, non-relativistic neutrinos are also anisotropic because they are much more affected by gravitational fields. In particular they should be gravitationally focused by the Sun, such that the Earth receives more neutrino flux when the Earth is "leeward" of the Sun with respect to its motion with respect to the co-moving rest frame. This will produce an annual modulation in any non-directional neutrino flux amplitude of a few tenths of a per cent (Safdi et al. 2014) and might allow a dectection of the C$nu$B to be confirmed.

On top of this there may be other anisotropies caused by the acceleration of C$nu$B neutrinos by massive galaxies and clusters of galaxies, that should lead it to be much more inhomogeneous and anisotropic than the cosmic microwave background. Overdensities with respect to the average of factors of 10 or more are possible (see section 2.2 of Yanagisawa 2014), but it depends on exactly what the neutrino mass is.

early universe - What happened just before the Big bang?

Caveat: I'm not a cosmologist, so this answer may not reflect the forefront of scientific knowledge/accuracy, but I have some knowledge so thought I'd share it and hopefully someone can correct me if I'm wrong.

The Big Bang theory states that everything is moving away from everything else, so it must have started closer together. We know from the Cosmic Microwave Background that everything was very dense and hot and small.

You may have heard that the universe started in a singularity. This means one point at which all matter was in the same place. In this state, all information in matter is lost. No particle can be labelled as having a position or size or spin, because every particle is in the same state as every other particle. This means we lose all possibility of having any information about what happened before this. There are many theories of what could have been before this, but no matter how simple/beautiful/mathematically rigorous the theory, it is physically impossible to know anything about it so they are impossible to test. In some definitions this makes these theories not actually science, as the scientific method involves making testable predictions.

planet - Is Mercury's core liquid?

As detailed here,

To figure out whether Mercury's core was liquid or solid, a team of scientists led by Jean-Luc Margot at Cornell University measured small twists in the planet's rotation. They used a new technique that involved bouncing a radio signal sent from a ground telescope in California off the planet and then catching it again in West Virginia.

After 5 years and 21 such observations, the team realized their values were twice as large as what would be expected if Mercury's core was solid.

"The variations in Mercury's spin rate that we measured are best explained by a core that is at least partially molten," Margot said. "We have a 95 percent confidence level in this conclusion."

The NRAO has another article on it, which goes slightly more in-depth into the subject.

The official site of the Messenger mission is slightly more cautious:

However, these constraints are limited because of the low precision of current information on Mercury's gravity field from the Mariner 10 and MESSENGER flybys. Fundamental questions about Mercury's core remain to be explored, such as its composition. A core of pure iron would be completely solid today, due to the high melting point of iron. However, if other elements, such as sulfur, are also present in Mercury's core, even at a level of only a few percent, the melting point is lowered considerably, allowing Mercury's core to remain at least partially molten as the planet cooled. Constraining the composition of the core is intimately tied to understanding what fraction of the core is liquid and what fraction has solidified. Is there just a very thin layer of liquid over a mostly solid core or is the core completely molten? Addressing questions such as these can also provide insight into the current thermal state of Mercury's interior, which is very valuable information for determining the evolution of the planet.

At this point in time, though, all evidence indicates that Mercury has a molten core.

As userLTK pointed out, lower pressure inside Mercury makes it easier for the core to stay liquid at lower temperatures.

What's the proper terminology for nebula clouds?

The term "nebula" has been used historically for virtually any astronomical object that was fuzzier than stars. Specifically, galaxies which to the naked eye and in small telescopes looked like elongated clouds were called nebulae (e.g. the Andromeda Nebula), even though they definitely aren't clouds.

Nowadays, the term is mostly used in the context of planetary nebulae, which are the beautifully colored death breaths of low-mass stars, lighted up by a central white dwarf. These objects were originally thought to be planets, but has nothing to do with that.

Other types of nebulae are usually called by their more descriptive names, e.g. molecular clouds, HII regions, and supernova remnants. The only objects I can think of that are often called nebulae, are reflection nebulae, which are the clouds of dust and gas surrounding a young star cluster.

the moon - Why is the Color scheme of natural satellites in our solar system based of light shades of grey?

The colour of a natural satellite is almost entirely based off the atmosphere and surface of the satellite. The moon Io, of Jupiter is not grey and is coloured because of sulfur on its surface that create a colour. Io has a very thin atmosphere.

So that brings us to your question, why is the majority of natural satellites grey? We know that moon's colours are dependent on what they are made up of and if they have an atmosphere, so the basic answer is that the majority of moons are grey because they do not hold an atmosphere, and are made up of rock. Our moon is made out of basalts which are a grey rock. You can probably go out and research what certain moons are made of, and find out more about the rocks on them and how they affect the colour of the planet.

Does "Dark Matter" really exist?

The question seems to be based on some misconceptions, so I'll try to clear them up.

Dark matter and dark energy are two completely separate and unrelated concepts. It's unfortunate that many articles trying to entice readers with tales of the unexplored frontiers of astronomy tend to use the phrase "dark matter and dark energy" quite a lot, typically with the buzzwords "mysterious," "unknown," and even "spooky."

Obviously, the best introduction here is to read the Wikipedia articles on dark matter and dark energy. You can also see the dark-matter and dark-energy tags (and the questions that use them) for more information. Physics also has some good questions about these topics.

I'll give you the important points:

• Dark matter . . .

  
  
  



• Dark energy . . .

  
  
  
  • . . . is responsible for the acceleration of the expansion of the universe, though not the expansion of the universe
  
  
  • . . . can be represented by the cosmological constant
  
  

The one thing that the two share? We know very little about them.

In fact, it causes more problems than it solves.

You can come up with many different universes that begin with a Big Bang but don't have an accelerated expansion (not counting inflation, though you don't have to have that in a universe under some circumstances). They don't somehow suffer from any problems that universes with dark energy don't have. In fact, they're better because you don't have to somehow explain dark energy.

Courtesy of Rob Jeffries, here's one tidbit about the one fairly important role of dark energy in the Big Bang:

Our universe is close to flat (see the many papers by the WMAP team), and quite a lot of measurements have confirmed that we're not living on some wacky-shaped universe. The issue is that the measurements indicate that the universe isn't quite flat. Again, see the WMAP data. You can attribute part of the percentage offset from flatness to experimental error, or you can attribute it to the idea that perhaps the universe isn't so flat after all.

Dark energy provides an explanation for this inherent not-quite-flat-ness that characterizes our universe. In those other toy universes (without dark matter), you need to explain this near-flatness some other way. Not in our universe, it seems.

Well, sort of. Coming from someone like me (who is firmly on the "theorist" side of the scientific spectrum), that's quite a whopper. But from a certain point of view, it's completely accurate.

Dark matter is actually a theory. It's an explanation for some screwed-up galactic rotation curves, where some stars near the outer edges of a galaxy move much faster than they should.

So it's actually a theory to explain a phenomenon.

Dark energy, on the other hand, is an experimental phenomenon. We don't have a good theory to explain it. But it's a phenomenon responsible for many different problems. There's quite a lot of evidence that says, "Something odd is going on."

What I mean by all this is that there's a heck of a lot of evidence for them. Our theories of them were created to explain evidence, and not vice versa (evidence gathered to support or refute a theory).

---

I advise, once again, that you look at the Wikipedia articles on both concepts to start learning more (especially the sections on evidence). Physics and Astronomy have plenty of good information. arXiv has many pre-prints that may be helpful. And there are lots of books, magazines, and (reputable) web sites that can give you even more detailed information.

the sun - Calculating effective SSN (sunspot number)

I am doing research on SSN like parameters. As I can see effective SSN is a parameter that derived from SSN or may be using other parameters. Do anyone know how to calculate effective SSN.

i.e following file has some parameters ftp://ftp.swpc.noaa.gov/pub/latest/DSD.txt

ref http://spawx.nwra.com/spawx/ssne.html

Thanks

archaeology - How to read Babylonians' tablet that were used to track Jupiter's movements?

There is a science news article on how Babylonians used geometry to track Jupiter’s movements.

Here is an image of cuneiform tablet which shows Jupiter's movements.

From a layman's point of view, it looks like someone engraved gibberish on a tablet. How do we even know it was used to track Jupiter's movements.

Can anyone translate this? Thanks.

black hole - Blackhole Finding Techniques

I know of two methods for finding exoplanets: the transit method and the radial velocity method. These two methods work as follows:

1. Transit: we observe stars and watch for when a planet obstructs the light from the star.




2. Radial Velocity: detecting the planet by observing the motion of the star and using Kepler's law.

Are these methods also used for discovering black-holes? What are the pros and cons of these methods, I think that the con of transit is that it's difficult to see the black hole. A pro is that it doesn't matter how many stars there are around the black hole.

With the Radial Velocity method, a pro is that it's easy to detect but requires exactly one companion star (I used this source).

human biology - What actually happens when my leg 'falls asleep'?

The explanation in the link Polynomial posted is essentially correct.

Whenever there is a reduced or blocked blood supply (ischaemia) to your extremities, the 'five P's' can occur: pulselessness, pain, pallor (colour), paresthesia (numbness) and paralysis (or weakness).(1).

The numbness and weakness happen after the blood flow have been reduced for a particularly prolonged period.

Cells in our body require a blood supply to stay alive (think about a stroke or heart attack for example). So a reduced supply can cause them to function abnormally or after a time (depending on the cell or tissue type) die.

So with a 'sleeping leg', staying in an awkward or particular position where arterial blood supply is blocked or reduced to the leg, the muscle, nerve tissue etc all lack supply hence causing sensory disturbance and weakness.

The possible buildup of metabolites could also contribute to the symptoms (pain).

Hope that helps!

1. Miller's Anaesthesia - Miller.