Astronomy and Cosmology

this thread can be for stashing links to webpages with good explanations of astronomy stuff in Cosmology forum I just saw where aman asked about the slingshot effect (used a lot to save fuel on missions to the outer planets) and swansont gave this link: http://www.mathpages.com/home/kmath114.htm explaining clearly how the slingshot maneuver gains energy and angular momentum (taking away from the planet being used) and then Jenab confirmed having seen slingshotting in simulations he'd run http://www.scienceforums.net/forums/showthread.php?p=30823#post30823 I'm thinking of adding other good links i see to this thread, to have them handy. like link-answe…

Before posting on cosmo topics consider getting squared away on the conventional standard version. There are several great tutorials, for which I'll post link. And the standard model universe is embodied in some online calculators---playing around with them gives you some hands-on experience with redshifts, recession speeds, distances and so forth. Here's the authoritative up-to-date Einstein-Online tutorial on cosmology, written in understandable non-mathy language. http://www.einstein-online.info/en/spotlights/cosmology/index.html It is the cosmology part of a broad outreach site maintained by the Albert Enstein Institute, a worldclass science outfit in German…

In my spare time I will be writing a series of useful articles to help answer common questions. As these are being designed for forum reference I feel strongly on cooperative review. Here is the first. Please look over and feel free to make suggestions. Any solid contributions will be accorded credit at the end of the final product. (Key note all articles MUST comply with textbook descriptives, they are being designed as teaching aids) [latex]\textbf{The Cosmological principle}[/latex] is defined as "at sufficiently large scales, the universe appears as homogeneous and isotropic." [latex]\underline{Homogenous}[/latex] is oft defined as " no prefer…

Just a reminder that there is a Team SFN on the BOINC network, which you can join if you are running programs such as Seti@home. Blike set it up a while ago but I don't think it was ever advertised http://setiathome.berkeley.edu/team_display.php?teamid=134923

Is there a "GOD" out there? Maybe I should drag this to a different forum, but I just can't get it done without fudging. With a lot of people wondering, in all honesty what do you think? Is there, or isn't there?

Hi! It is said that as we look deeper into space we look in the past...we see younger galaxies and objects, which formed at an early stage of development of our universe...and here is my question... Does it mean that we could see "ourselves", our own galaxy when it was young...or follow its formation back in time?

A new Edgeworth-Kuiper Belt object has caused astronomers a headache. This scattered disk object seems too distant to have a purely resonant orbit with Neptune, but theories used to explain its high angular tilt with respect to the ecliptic run into trouble. This is because its orbit is almost circular, and the available theoretical mechanisms would require its orbit to have become more eccentric. This is anomalous and has led to speculation by Hal Levison that another factor may be at play...perhaps the one-time presence of a binary object orbiting the Sun. http://www.newscientist.com/article.ns?id=dn8455 Just what exactly is going on out there???

According to John Archibald Wheeler (Journey into Gravity & Space-time): matter tells space-time how to curve; and, curved space-time tells matter how to move Now, beginning about 7 Gya, galaxies had 'clumped' together; and, evacuated inter-galactic deep-space; so that they stopped accreting new, fresh, primordial gas. Thus, galaxy growth has stalled; galaxies today have 10x less gas than 5 Gya; and, galaxies are forming stars 10-30x less rapidly, than 5 Gya (ABC AU 2011). So, if, beginning about 7 Gya, inter-galactic 'voids' had been largely evacuated; and, if local matter-density determines local space-time curvature; then, c.7 Gya, would not most of…

fig. 1 -- HR Diagram one-zone approximation for star-core pressures Assuming spherical-symmetry, and hydro-static equilibrium, w.h.t. [math]\frac{dP}{dr} = -g® \rho®[/math]. Then, discretizing that differential equation, and taking solely a single 'step', from star surface to star core (one-zone approximation), w.h.t. [math]-\frac{P_c}{R} \approx - \frac{G M}{R^2} \frac{3 M}{4 \pi R^3}[/math], or (ideal gas law) [math]\frac{\rho_c T_c}{\bar{m}} \approx \frac{3 G}{4 \pi k_B} \frac{M^2}{R^4}[/math]. PP [math]\left( 1/2 - 2 M_{\odot} \right)[/math] Observationally (from fig.1), the luminosities, of 'intermediate mass' stars ([math]1/2 - 2 M_{\odot}…

Exactly how do we define a 'killer' asteroid? Asteroids currently zipping past Earth range around one to two kilometers in size. Is this large enough to prompt the mass extinction events that have occurred periodically? Or is a larger body required?

Milky Way Is Warped, Like a Beer Bottle Cap - Technology Review COMMENT: The authors link the arm around to the Scutum-Centaurus arm, but I wonder whether it links around, instead, to the Perseus arm ??

If Neutrinos have a non-zero rest-mass, perhaps of roughly 1.5 eV, then couldn't Neutrinos exist... at rest ?? And, if so, couldn't they "clump", into "Neutrino planets" and "Neutrino stars" (as it were) ?? Could that explain Dark Matter ? At only ~1 eV per particle, the self-gravity of Neutrinos might be so weak, they their distribution would be continuously "stirred up", by the motions of planets & stars in galaxies. Could Earth, or our Solar System, be passing through a "thick fog" of cold, and nearly uniformly distributed, Neutrinos ??

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?

Let’s suppose that Big Bang was prepared and initiated by some “Creator” in other Universe and that our Universe is located within it being a smaller part of it. Is it theoretically possible to “create” in such a way several completely identical Universes with identical future and evolution? I mean is it theoretically possible that aeons ago somewhere existed the same Universe as ours with the same creatures and living beings and with the same events? Thanks in advance.

"Optically Cloaked" dark cloud in Virgo Virgo-HI-21 (VH21) seems to be a "dark spiral galaxy", with a "dark disc" spanning some 50 thousand light-years across. VH21 resides in the Virgo galaxy cluster, about 50 million light-years away: VH21 appears to possess a flattened, rotating galactic disc, typical of spiral galaxies (jb). Seemingly seen from the side, or 'edge-on', that disc is full of the diffuse, cold-and-un-ionized Hydrogen gas, otherwise common in the discs of ordinary, luminous, star-spangled spiral galaxies (register). But, sans stars, VH21 is only observable, from the faint, radio-frequency emissions (with a wave-length of 21 cm), of those c…

http://science.nasa.gov/headlines/y2005/28jun_deepimpact.htm?list45222 "The target: a 10-mile wide comet named Tempel 1. ...Deep Impact is going to shoot an 820-pound projectile into the rocky, icy nucleus of Comet Tempel 1. The 23,000 mph collision will form a big crater, and Deep impact will observe the stages of its development, how deep it gets and how wide it becomes. Researchers expect a plume of gas and dust to spray out of the crater..." the comet will be near the bright star Spica in the constellation Virgo here is a star map for 11PM Pacific Daylight Time on July 3, when virgo will be near setting in the west http://science.nasa.gov/headlines…

http://en.wikipedia.org/wiki/Harmonices_Mundi Why is this? The angular velocities vary in accordance to the distance to the sun, moving faster at perihelion, but what of it? The planets were formed of the same elliptical proplanetary disk, which explains why the ratios correspond so well, but I'm assuming that the approximation to musical harmonies can't be coincidental.

[math]T^4® = \frac{3 G M \dot{M}}{8 \pi \sigma r^3} \left[1 - \sqrt{\frac{R}{r}} \right][/math] [math]C_S^2 \approx \frac{k_B T}{\bar{m}}[/math] [math]v_K^2 \equiv \frac{G M}{r}[/math] [math]\dot{M}_{Edd} \equiv \frac{4 \pi c}{\sigma_T} \bar{m} R[/math] Defining [math]\dot{M} \equiv \mu \dot{M}_{Edd}[/math], then w.h.t.: [math]\therefore \left(\frac{C_S}{v_K}\right)^8 \approx \mu \left( \frac{k_B}{G M \bar{m}} \right)^3 \left( \frac{3 k_B c R}{2 \sigma \sigma_T} \right) r \left[1 - \sqrt{\frac{R}{r}} \right][/math] [math] \approx 2 \times 10^{-10} \left( \frac{\bar{m}}{m_H} \right)^{-3} \left( \frac{M}{M_{\odot}} \right)^{-3} \left( \frac{R}{R_{\o…

The title of this thread is the title of chapter 6-3 in the Richard Feynman's book, Six Not-So-Easy Pieces (1963). (This post is related to the discussion in one other recent thread, but not to its OP.) Here is the quote (pp.125-126):

Can anyone tell me if I am reading these guys wrong or if the writers got it wrong? http://news.yahoo.com/s/space/20070109/sc_space/pillarsofcreationtoppledbystellarblast The part I have trouble with is: What I don't get....if the light of the nova has hit our sky 1k-2k years ago, wouldn't the light the hubble uses to take these images build photos of that nebula 1k-2k post-explosion? If the light of the nova-event has passed us, then all light containing images of pre-nova conditions has passed by us - by a long time apparently. If we can still see the pillars even through they are gone, then the bright flash of the nova should be in the future right b…

Dividing the Planck Density (5e96), by the current Cosmic Critical Density (1e-26), and taking the cube-root, yields ~e41. Thus, at a red-shift of z ~ 1041, our Observable Universe would have been compacted to Planck Density. Is that when/where current physical theory breaks down?

According to Howell 2007: Now, WDs, which were "several Gyr" old, at time of SNIa, would be considerably older, colder & dimmer, lying lower, and to the right, on the HR-Diagram. Thus, could initial WD age / temperature, conceivably determine, the ensuing "luminosity trajectories", across the HR-diagram ?? Again, and conversely, younger, hotter (bluer) WDs, initially lying higher & and to the left on the HR-diagram, would presumably generate the brighter, longer-lasting SNIa's; whereas, colder & older WDs would, presumably, generate the dimmer & faster-fading SNIa's. To make an engine analogy, younger hotter WD "cores" could, conceivably, "comb…

what do you think of this? http://bitsofnews.com/modules.php?name=News&file=article&sid=3255 how possible is this? a long way off?

The observatory of Lisbon has published a video of Comet ISON, causing panic. The comet will be visible DURING THE DAY on all the planet on November 29 2013. See the shocking video here: http://third-secret.pro-forum.co.uk/h51-comet-ison ps :enable java-script if you have problems to load the video The 10 km wide core of comet will practically touch the surface of the sun, if the comet survives its orbit will be changed irreversibly, and it will be a Russian roulette for earth. If we believe their calculations ISON WILL BE ON COLLISION COURSE WITH EARTH, WITH IMPACT IN DECEMBER.

Please ponder the following "beta-decay" reaction: [math]p^{+} + \bar{\nu}_e \rightarrow n^0 + e^{+}[/math] So, if you propelled a powerful beam, of anti-neutrinos [math]\bar{\nu}_e[/math], into a star, then would you convert protons to neutrons? And, then, would those neutrons not fuse, with remaining protons, ultimately into helium nuclei?? So, could you not "stimulate" fusion, inside stars, and produce powerful "pulses" of helium production, i.e. generating an artificially-induced super-novae explosion (possibly powered by positron-electron annihilations too) ??