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…

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…

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…

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

Ever since I was a young boy, I have wrestled with trying to understand space. In particular, I have never really understood how space is supposed to never end. I really don't see how that's possible. Everything ends somewhere. Where one thing ends the next begins. Can people please provide thoughts on this?

I keep hearing gravity waves described as ripples in space time. Does this suggest that space time is a substance like the discredited notion of the aether? It seems to me that if space time can be said to ripple then a preferred reference frame is suggested by this "ripple" I know I must be off base here but how am I mistaken?

Is the Universe infinite or just really, really big?

Does anyone have an idea of the most efficient and expedient way to deflect, redirect, or slow an impending asteroid impact? Obviously, if it is a solid block of metal or rock, just hitting it with a large mass going at a fast enough speed, may change its' velocity enough. Here's my idea I haven't heard about yet. Since asteroids can be a solid block of metal, or rock, or a fragile rubble pile or fluff, or anything in between, catch it with a giant net. Launch a rocket towards the asteroid, and at the correct moment the rocket turns around and decelerates to zero, then accelerates the opposite direction to match the velocity of the asteroid. Then the rocket l…

wouldn't we have to see stars from everywhere during night? Shouldn't the space be so full of light that there is no darkness? Isn't that what they mean by no end to space? Infinite numbers of stars as well? OR do they mean space has no end but there are limited number of stars?

Just a fun game to play; Rules: State a word related to astronomy/astrophysics/cosmology. The next person states a word that starts with the letter the previous word ends on. Then state an interesting fact about that word. I'll start Pluto - Named after the Roman god of the underworld.

Do you think that SpaceX and Elon Musk can get us to Mars by 2024?

SPACE ENDS Space ends, space does not go on forever and ever it ends. The difference between space ending or not ending is if space does not end then space does not have a shape but once you understand that space ends then space can take a shape and that shape can move from one shape to another shape. Yes space ends and moves.

A star exploded 2 millions years ago. This star is at a distance of 1 million Light Years from us. Can we see the explosion?

Is here a good reference that gives me the periods involved in the formation of the Sun? I'm finding the various sites talk of when the Sun "formed" but I'm not sure what stage they are describing. We start off with a nebula, how long to the stage where the Sun goes Alpha Tauri (if it did)? Then how long before it becomes a main sequence star? I once tried to calculate how long matter would take to free fall into the Sun from an estimate of the size of the nebula and from memory it was about 150,000 years and that was if each particle did not collide with any other particle or have any angular motion, so it was a direct "straight line". So I suppose that is an …

Once again, I have some (maybe unusual) questions for the scientific community. I hope you can easily refute my ideas with good arguments. But first I want to mention again what we are currently supposing: 1. The limit of the visible universe is somewhere close to 13.5 billion light years away. (I am using this limit just to make my calculations easier). 2. The universe is expanding, and this expansion is pulling galaxies away from us according to the Hubble constant. 3. Whenever a galaxy is at a distance of almost 13.5 billion light years, this galaxy is moving away from us almost at the speed of light. 4. Objects that are very close to us (for exampl…

What created Big Bang? What created the thing that created Big Bang? And why is there something rather than nothing?

Just a fun question: what state of energy/matter, could it be argued, that a gravitational singularity is in? I would say that, it broke down to the most fundamental form of energy. Could it be said that, it is an extremely exotic form of atom?

Do we orbit the center of mass of the solar system or just the center of mass between the Sun and The Earth? It was discussed on another thread on the forum but I've lost track of it. So if the two biggest objects in our Solar System have a Barycenter outside of the radius of the Sun then would Mercury be orbiting this center of mass as well? Maybe that is the solution to the 3 body problems - do we have to go back to the combined Center of mass and orbit that. Even if we say that Mercury orbits the center of the Sun, and the Sun orbits around the barycenter (between it and Jupiter) that would mean Mercury is orbiting in some unusual way too. How does that start off? …

So I have noticed it’s about a week now everyday there is a new article from a different source about this. Not sure why it keeps making the news day after day as though there is something up with it we should know about. From what I have been told the constant of 1/137 may have changed and if it fell below 1 it can put the universe in universe in a vacuum decay state https://www.google.ca/amp/s/www.sciencealert.com/astronomers-have-found-an-ancient-galaxy-that-grew-fast-then-died-suddenly/amp

If the universe is expanding, what are we filling up. It cant be space beacuse the universe is space right?

I have a small question that has been teasing me of late. If the universe is expanding, and total energy can neither be created nor destroyed, and every inch of the universe is a field (eg magnetic field), then why doesn't field strength weaken as the universe expands?

An asteroid of a similar size to a rock that exploded above Siberia in 1908 with the force of a thousand atomic bombs whizzed close past Earth on Monday, astronomers said on Tuesday. 2009 DD45, estimated to be between 21 and 47 meters (68 and 152 feet) across, raced by at 1344 GMT on Monday, the Planetary Society and astronomers' blogs reported. The gap was just 72,000 kilometers (44,750 miles), or a fifth of the distance between Earth and the Moon and only twice the height of satellites in geosynchronous orbit, the website space.com said. The estimated size is similar to that of an asteroid or comet that exploded above Tunguska, Siberia, on June 30 1908, flat…

I recently started a topic called "The Speed of Light" and one of the responces said "You're going to have to unlearn this common misconception if you want to actually understand cosmology. The big bang happened literally everywhere and was never a 'point', and there is no rushing of material from a point into 'empty space' so to speak." So Imust be reading the following wrong... The Big Bang was the moment 13.8 billion years ago when the universe began as a tiny, dense, fireball that exploded. Most astronomers use the Big Bang theory to explain how the universe began. But what caused this explosion in the first place is still a mystery. A sphere exploded but…

http://arxiv.org/abs/0907.3432 This is a 39 page article that delves into a dozen or so different answers to the Fermi question/paradox that have been proposed over the past half century. The author is a Belgrade astronomer/SETI expert/future generalist. He seems to know a lot and reason carefully, like a credible academic. Well, that's my first impression. Maybe you can find some flaws, if so please let the rest of us know where you think he is wrong. I don't think he has any preferred answer, he compares and weighs them all. Maybe he ends up throwing out some as relatively improbable, and narrowing down to the ones he thinks are better. But on the whole it…

This is a question: Suppose that I am looking in my telescope to a distant star 1 million light years away. Around this star is a planet. On this planet I see an alien observatory and an alien scientist looking in my direction. Can he see me?