Astronomy and Cosmology

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?

So I've been looking up the holographic principle for a while and I'm having trouble understanding somthing that I feel is obvious that I'm missing. I understand that a volume of space will have the same information as it's surface area, but is it the same information? What I mean is if I drop Alice into a black hole, from her view inside the black hole she will see everything 3-dimensionally. Bob, who is outside of the black hole, will see Alice's information 2-dimensionally on the event horizon. The part I'm having trouble with is are they looking at the same Alice? Is the Alice on the inside a clone of the one on the surface, or is she in a sense in both places…

Here is the question At the Big Bang, the universe were created and started expanding. The universe includes us, the Earth, the Milky way galaxy, and also the CMB. So the question is: how is it possible for us to observe a radiation that was emitted at the time we were born? It looks like the archer running faster and being killed by its own arrow.

I posted this as a sort of answer to another thread about where does space stop, but the thread was quite old and so I thought I might create a new thread just to see what you all might think, hope that's ok. Hi Everyone, this is my first time on here, but I love the subject and so would like to share my thoughts, although I'm not sure it's going to answer the question, "Where does space stop". It depends on whether you believe in the multiverse theory or not. Personally I do. I think it's more than likely that the big bang happened many many times before and after the one that created our own universe and is still happening over and over again like bubble…

hello. sorry about this question here, but so which direction we have to look to see the moment of BB of our universe?

Hi there, First Light Magazine is lauching an Astrophotography Contest. The competition is ending on December the 15th. The winners will be published and get a one year free subscription! As it's a digital magazine, animated pictures and time-lapse are allowed! Rules are written in FB page

As it is shown by Hawking the area of the events horizon never decreases, but it depends only on the mass of the black hole and it's rotation speed. But when the hole evaporates it's mass decreases until in won't become a Plank's black hole. What happens to it's events horizon while such evaporation? Does it's rotation speed increase so it becomes more and more flat ellipsoid looking like a pancake with same area? The evaporation is a quantum process, but the Hawking's explanation with two light rays going on the events horizon is unlikely to be violated even in quantum mechanics.

I'm impressed at this great feat of European cooperation. I wonder what this also means in view of the possibilities of in the future being able to divert these objects, and thus prevent them from hitting earth? For I guess one this size would constitute a wee problem when its remains hit Amsterdam?

Thought this was cool. http://arstechnica.com/science/2014/11/new-telescope-array-captures-planet-forming-disk-orbiting-distant-star/

Do you guys think that the dark matter and dark energy is related each other? Such as Dark Energy is a form of dark matter's momentum energy, or dark matter is zero momentum state of dark energy. What you guys think?

Does the dark matter increasing its existing ratio? What I mean is Dark Energy: 73% Atoms 4% Dark Matter 29%, and I need a fact information that the dark matter had been increased for a long time. I just thought a unsense, in hawking radiation, only negative particle (generated from quantum flactation anti-particle and particle pair) sucks into the blackhole and positive particle flies away. Is that 'lonely' particle Dark Matter? Literally, positive in physics, it means 'having mass' and 'existing'.

1. Do you accept the singularity of the Big Bang Theory and other ideas on the beginning of the world? 2. Do you think String Theory is valid? I've seen things that says it's invalid like this new study http://www.wired.com/2014/08/multiverse/ 3. This world will end and time itself will end in the Big Rip correct? Accurate estimates on when this will occur yet? 4. You think that there can be another world once this one ceases to exist?

Excuse my ignorance but what evidence have we that 10 billion years ago the CMB was measured more than it is measured today?

So many crackpots try and defend that idea, it is a bit cliched. We need someone to revive phlogiston. I can't revive every idea but if dephlogisticated air was good enough for Priestley it's good enough for me... Monday was rather optimistic.... A brief preemptive defense... This post Steady state cosmology, proposed by Sir James Jeans and later revised by Fred Hoyle, Thomas Gold, Hermann Bondi and others, postulated an eternal, exponentially expanding universe with matter creation such that the average matter density was always constant. This theory was effectively refuted observationally by the discovery of cosmic microwave background radiation …

Action of gravitation reminds me light refraction in transparent substances.For example,violet beams refract in glass more strongly red,we will present index of refrection increases, beams will stsrt being bent as in a cycloid.Action of gravitation is similar, but it is more difficult,it is necessary to consider the particles creating the weight which sticks at the movement of particles and the and the final result the Solar system and galaxy will turn out.Of course space not empty,space particles the which create gravitation at the movement are involved in the movement.Also,between magnetism and gravitation similarity is found, at a piece of a magnet the movement of its …

I had read an article on the web a while ago mentioning how neutrinos may construct dark matter, I have done little research and would prefer a fuller explanation on the possibility. My question is if anyone is knowledgable on this particular idea and can explain this in more depth as I would really appreciate it. I am currently making a presentation/poster on dark matter and am considering opinions and theories of all sorts. Thanks

The Sun's mass is decreasing all of the time, because of nuclear fusion and the solar wind and coronal mass ejections. How much has this altered the Earth's orbit over the last 10,000 years?

Hi all. What is the delay from a lunar noon (moon at 90 degrees azimuth observed from earth) at a given meridian to the high tide maximum at that meridian ? Is that delay constant for the same location ? Does that delay changes for different locations ? I suppose yes, due to geographic and topographic sorroundings of coastal shores. Does that delay changes by the elevation of the moon when at lunar noon ? [ *Perhaps zenith is the wrong term as would imply 90 degrees elevation. I mean lunar noon when moon azimuth is coincidental with the meridian of observer. Should I say 90 degrees azimuth instead of zenith ? ]

If the moon is observed at 30 degrees azimuth seen from -say meridian 77 in New York- Is the moon said to be also at 30 degrees azimuth at meridian 77 for an observer in Lima ? Sorry, not a subject of my expertise.

Having recently chanced upon the Bortle Scale, I'm intrigued to know just how much increase there would be in stellar luminosity as observed from space - say, from the ISS. For the sake of argument, I'm discounting the effects of spacesuit visors etc. Many thanks. http://en.wikipedia.org/wiki/Bortle_scale

I know there are large collections of electrons in the Van Allen belts 2 to 3 rings, Are these in a coherent state within these magnetic fields? Or is this just about plasma the waves? http://www.spacenewsfeed.co.uk/index.php/news/218-van-allen-probes-shed-light-on-decades-old-mystery

Hi everybody, The calculations of the normal rotation period of the galaxies we observe depends on their observed mass, but it also depends on the doppler effect from their recession. The more they speed away from us, the more their period is stretched. When we calculate this period, thus when we calculate their rotational speed, we have to include doppler effect in the calculations, which increases that speed. Has anybody thought of not including the doppler effect in the calculations? If not, can somebody do these calculations for a couple of galaxies and tell me if their rotational speed is still too fast to account for their observable mass?

Hi All, Does anyone know how the new Gaia telescope measures distances e.g. parallax to the distant stars ? I am just interested in the basic principle. It would be easy to use the Gaia - Earth distance as the baseline for the traingle and then for Gaia and an observatory on Earth to measure the two angles to the star at the same time. That would enable the Parallax angle and the distance to be calculated. BUT, is this how it is done? I have looked at the Gaia ETSA site but there is no explanation that I can find. George

A mysterious explosion that rocked Nicaragua on Saturday night, creating a 39ft-wide (12 metre) crater, appears to have been caused by a small meteorite. And authorities in the region believe the meteorite was in fact a shard of rock from the 2014 RC ‘pitbull’ asteroid that soared past Earth over the weekend. link deleted by mod

I have participated SETI@Home recently. I want to ask one question: Are there any members in this forum are members of the SETI@Home project? Also, any opinions/improvements/suggestion about SETI@Home project?