Astronomy and Cosmology

Is this a plausible scenario (?) — please comment Prof. Richard A. Muller has shown that the Lunar cratering rate actually increased, beginning about 400 Mya*: By extension, the cratering rates on the Earth, and even across the Inner Solar System, likely increased too, from ~400 Mya. * PBS Exploring Space — The Quest for Life (DVD) A.J. Meadows (The Future of the Universe, pp. 118-125) says that, as our Sun orbits around the Galaxy, it travels into, thru, and out of, our Galaxy's Spiral Arms; and, that these can cause close encounters with Star Forming Regions, on ~200-500 Myr time scales: The Sun is currently positioned near the edge of a …

Is this a physically plausible scenario (??) — please comment In the Lunar geologic [Lono-logic??] timescale, the "Early Imbrian Epoch" (3850 - 3800 million years ago*) is associated with the Late Heavy Bombardment, and the resulting huge impact basins, which would later fill w/ lava to form the Lunar Mare, during the ensuing Late Imbrian Epoch (3800 - 3200 million years ago). This happened when "the mantle below the lunar basins partially melted and filled them with basalt"**. * Early Imbrian - Wikipedia, the free encyclopedia ** Late Imbrian - Wikipedia, the free encyclopedia Now, it is well-known that the Moon first formed roughly 15 times closer to Earth th…

Hi Everyone, I'm wondering how many arcseconds the Sun "travels" in one Tropical Year. I think it travels 1296000 in one day. Mark Merged post follows: Consecutive posts mergedSo, this is from the reference point of someone standing on the solid Earth in one spot all year. We could say that the sun starts at 90 degrees, goes down and up and back to 90 degrees(of course as the seasons change, the angle changes but that doesn't effect the calculation of angle travelled, and it does this 365 times, eventually coming back to the same position in the sky. 360 degrees times 365 days. Here are my calculations: One year: 131400 degrees, which is …

According to Stephen Eales' Planets & Planetary Systems, pp. 73-75, earthquake longitudinal Compression Waves (P-Waves) travel w/ velocity: [math]v_{p}^{2} = \frac{\left( K + \frac{4 \; \mu}{3} \right)}{\rho}[/math] while transverse Shear Waves (S-Waves) travel w/ velocity: [math]v_{p}^{2} = \frac{\mu}{\rho}[/math] where "K is the bulk modulus of the rock, [math]\mu[/math] is its shear modulus, and [math]\rho[/math] is its density". His discussions seemingly suggest, that the bulk & shear moduli of rock remain roughly constant, across the range of conditions encountered in planetary interiors. Since earthquake wave velocities are inversely proport…

Hi,about the expanding universe: I have some questions that I do not get any answers for. Can somebody please help. 1. Why are the objects closer to earth(or our galxie) moving away slower than those far away? What do we have to do with the whole situation. 2. What force is eccelerating all that mass in space. If it is black matter, why are they evenly spread around the visible galaxy to achieve such even acceleration in all directions. 3. If you go backwards in time and reverse the expansion, then you end up with all matter in one heap, how do you start the expansion from there. Thanks, johana.

BACKGROUND: Scale-independent (Harrison-Zeldovich) Initial Curvature Fluctuations According to Prof. Martin Rees (New Perspectives in Astrophysical Cosmology, pp. 40-80), the most "natural" assumption, regarding the growth of density fluctuations in the early Universe, is that when any region becomes causally connected, it's density contrast ([math]\delta \rho / \rho[/math]) has become the same constant Q, for all regions across all scales at all times. (Of course, this argument is made solely in a statistical sense, and actually applies to the mean density contrast.) During the matter-dominated epoch, these causally-connected "Hubble Volumes" contain, at time t …

I was just thinking about this. Space is said to be "cold", but really, because space is a giant vacuum, is it not the case that there are no particles with low amounts of energy floating around to take away heat from a substance? Say you have a 1 kg aluminum block at 500 degrees inside the international space station. You then throw the block out into space through a special airlock door. Wouldn't the block stay at that temperature because there are no cold particles around the block that the block can give its heat to? I honestly have no basis for thought in this kind of environment. Would the above, as I have described it, occur?

I just learnt that the geometry of the universe has recently been measured. It turns out to be Euclidian after all (as opposed to spherical or saddle-shaped). I learnt it here, a course you can order on cosmology, taught by Mark Whittle. Whittle says this: "The geometry of the universe, as best we can measure, is Euclidian. Giant triangles do add up to 180 degrees. Giant sphere do have surface area 4(pi)r^2, and volumes (4/3)(pi)r^3. All the geometry you learnt in high school applies not only to surveying your property, but also to surveying billion light year galaxies maps." What are the implications of this? Thinking of the 3D universe as the surface of …

I saw a really cool article a few weeks ago about possible endings of the world. It made me think of some really scary things and one of them was quite argumentatively pleasing that I had to ask whether someone can prove that it cannot happen. Now, wormholes, blackholes and rips in timespace continuum can occur, and if I am not mistaken, they do so when there is releases of energy or something similar (don't hold it against me). Now imagine one of these rips occurring near a star and the other side of this rip is close to Earth itself. Could energy pass through a rip like this and literally boil earth. Uh and I also made a drawing of the whole concept to better ex…

The total context shows that there was no big bang. The distance problem is an example. Physicists claim the universe is about 15 billion years old. When they look at a galaxy which is 15 billion light years away, they say they see it shortly after the universe began. How did it get that far away in such a short amount of time? If it traveled at the speed of light, it would have taken 15 billion years to get that far away from the earth in addition to the 15 billion years for the light to get to earth. It doesn't add up. One tenth the speed of light would be a more realistic velocity for matter to travel. It would then have taken 150 billion years to get that far from the…

So, I saw a Youtube video of Michio Kaku (I don't know that he predicted this phenomenon first, its just where I learned of it first) predicting that, between a hole in earth's magnetic field and the sun's 11-year-cyclic release of radiation shock waves, we should all gear up for an impending global telecommunications failure? If this is TRUE: A.) Care to elaborate on the dynamics of this phenomenon? B.) Why isn't it BIGGER NEWS? If this is NOT TRUE; Why is Michio Kaku wrong?

The sun's surface temperature is about 5800 K. The sun's atmosphere (the corona) however is over 1000000 K. How does the corona stay so hot? I read the wikipedia article that I linked to, and that suggests that magnetic field of the sun heats the corona. In addition, the sun spots seem to occur from the sun's interior. Finally, "coronal loops" are very common in the corona (they're the "basic structure" according to wikipedia). It also mentions that (part of) the corona is always moving away from the sun due to the magnetic fluxes generating the solar wind. In addition to the magnetic field that heats the corona, could it be that the corona is also hea…

When it should be either 23 or 23.4, or 23.44 or some other appropriately rounded amount?

Hi, what exactly is the difference between dark matter and dark energy? Why does dark energy not send out em-waves? Why don't people use just the e=mc^2 for energy and matter equivalance? Thanks for help.

what is the entropy of a black hole ?

Hi! Question 1: Correct me if I'm wrong but it seems like its assumed that Dark Energy is now over powering Dark Matter so that Dark Energy is 'pushing' the universe outward rather then 'pulling' it outward. If this is so, why is the pushing (or, if I have it back wards, pulling) assumed? Question 2: I believe that current theory says that about 5 billion years ago (that time frame could be wrong) the clumpy dark matter's gravity, weakened by the expanding universe, was over powered by the constant dark energy and the accelerating runaway expansion began. One of the things that led to the discovery of dark matter was the way galaxies rotate -- the outer stars …

Where does Hawking's calculation fail?

This is just a super cool talk, on many levels. I personally found it rather interesting, and wanted to share it having just watched it myself... The universe came from nothing. Got an hour? Don't waste it. Watch this. Watch here --> 7ImvlS8PLIo From the talk: The universe must be flat. <...> It turns out, that in a flat universe the total energy of the universe is precisely zero...Because gravity can have negative energy. So, the negative energy of gravity balances out the positive energy of matter. What’s so beautiful about a universe with total energy of zero? Well, ONLY such a universe can begin from…

I read that a telescope's three main attributes were: 1. it's light collecting power 2. it's resolving power 3. it's magnification power The magnification power can be changed independently of the light collecting power by using different eyepieces with different focal lengths. But the resolving power is dependent on the diameter of the primary mirror/lens and is basically just a function of the light collecting power, no? So you could better summarise a telescope's attributes as: 1. light collecting power (from which resolving power is derived) 2. magnification power Just trying to clarify in my head as always.

I've been learning about the lunar phases and then came across this photograph of Mauna Kea. The photo seems to show sunrise in Hawaii throwing Mauna Kea's shadow over the atmosphere, so that we can see the moon through this shadow. What confused me is this: From the shadow of the mountain the Sun would appear to be low in the sky behind the viewer and the mountain and to the left. However from the phase of the moon (which appears to be a waxing crescent), the Sun should appear relatively near the Moon in the sky, seemingly below the horizon to the right of the picture in front of the viewer and the mountain... Can anyone set me straight? Merged pos…

see pseudo science/speculations

The Solar Storm of 1859 represents what some call a "perfect solar storm". Through the coincidental convergence of conditions it was so strong it set fire to telegraph lines and created auroras that could be seen as far from the poles as Rome. Could this happen again? If it did, what would become of our technologically dependent society?

Quick question to check I'm visualising this correctly: Over the course of a day/night cycle, from any point on the Earth you actually see as much of the celestial sphere as you are ever going to during the year (ignoring precession of equinoxes etc). The only thing that stops you seeing some stars is the inconvenience of the Sun; you have to wait for it to "move along" the ecliptic and stop blinding you with pesky daylight. Is that correct?

I was watching a documentary show on the History channel talking about the Sun and it said that nuclear fusion is the only thing known to man that could power the sun. Now I'm not saying that I don't think this is true; but I'm just wondering if we actually have definitive proof that it it fusion that powers it or is that just the only explanation that makes sense? P.S. I do think that nuclear fusion is the explanation; I'm just wondering if it's been proven.

Hi! Does this statement make any sense? New space is being created between the Milky Way and a galaxy in the Great Wall named X and that's why they are getting further apart. Regardless... (more questions...) = what exactly is this 'space' that is expanding? Just the distance between the MW and X and... The distance between the individual atoms between the MW and X? Just all the empty space available to hold all the matter and energy there is? I take it the matter and energy in the universe remains constant? = in this expansion, the MW and X are not getting larger or thinner, only the 'empty' space between them is…