Ask me about the Universe (stars, light, Sun, black hole)
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What I meant to ask is: why don't the star lights I see at night appear closer than they are? What keeps the lights from getting closer to us? It's the light that travels very fast. So why wouldn't some of those star lights shoot down at earth like some laser beam?
There are examples where the star light you see at night are closer to you than they appear. Such as the Andromeda galaxy in the Andromeda constellation. It is blue-shifted, meaning the galaxy is moving toward the Milky Way galaxy. What we see is where the Andromeda galaxy was 2.5 million years ago, not where it is today. Today it is much closer, and in ~3.75 billion years it will eventually collide with the Milky Way galaxy forming one huge elliptical galaxy.
That is just one example of many, but all those examples are in what is known as the "local group" of ~54 galaxies, counting dwarf galaxies. Beyond our local group, all the other galaxies are red-shifted, meaning the galaxy is moving away from us. The greater the red-shift, the further away they are and the faster they are traveling away from us and we from them.
The greater the red-shift, the further away they are and the faster they are traveling away from us and we from them.
Quick, tiny clarification:
The galaxies outside our local group arent really "moving away" from us, or us "away" from them. Its much deeper than that. The space between them is getting bigger by way of the Universes continued expansion/inflation. The Universe is expanding at a rate of approximately 150,000 MPH (or 70Km/sec). The speeds are a little more technically complex than these generalities but for here the numbers work. If we were getting a bit more technical we'd say it was 70Km/sec per Mpc That's 70 Kilometers per second, per Megaparsec. But the 150,000 MPH is the easiest to remember and makes the most sense here in the USA. :-)
I know Glitch knows that, as he's for certain one of the most articulate and capable members here on City-Data in the Space forum, but just wanted to clarify. :-)
The galaxies outside our local group arent really "moving away" from us, or us "away" from them. Its much deeper than that. The space between them is getting bigger by way of the Universes continued expansion/inflation. The Universe is expanding at a rate of approximately 150,000 MPH (or 70Km/sec). The speeds are a little more technically complex than these generalities but for here the numbers work. If we were getting a bit more technical we'd say it was 70Km/sec per Mpc That's 70 Kilometers per second, per Megaparsec. But the 150,000 MPH is the easiest to remember and makes the most sense here in the USA. :-)
I know Glitch knows that, as he's for certain one of the most articulate and capable members here on City-Data in the Space forum, but just wanted to clarify. :-)
The rate of expansion has been refined further. Based upon the latest Spitzer measurements of Cepheid variables, the universe is expanding at a rate of 74.3 ± 2.1 km/sec/Mpc.
Or 166,204 ± 4,698 mph every 3,261,633 light years. Therefore, the space between an object 32.6 million light years away (10 Mpc) and us would be expanding at a rate of 1,662,040 ± 46,980 mph, or ~0.24% the speed of light.
Here's one my nephew asked me. I understand the reason but I can't quite explain it well enough to make him understand. He's 7.
Explain Moon tilt. Why is the moon a crescent some times and a smiley other times?
I tried hard to explain it depends on where the sun is in relation to where you are on the planet and where the moon is and the season... but I couldn't get him to grasp that. He went on his first vacation to Mexico and he was blown away by the "Smiley Moon". Our moon (in Ohio) never gets THAT smiley.
Here's one my nephew asked me. I understand the reason but I can't quite explain it well enough to make him understand. He's 7.
Explain Moon tilt. Why is the moon a crescent some times and a smiley other times?
I tried hard to explain it depends on where the sun is in relation to where you are on the planet and where the moon is and the season... but I couldn't get him to grasp that. He went on his first vacation to Mexico and he was blown away by the "Smiley Moon". Our moon (in Ohio) never gets THAT smiley.
Good question!
The Moon orbits in roughly the same plane, an ecliptic plane, same as Earth. The ecliptic plane is tilted 23.5 degrees from the celestial equator. Or, better put, the Earths equator is tilted 23.5 degrees. When plotted on the sky, the ecliptic crosses the celestial equator at two points - our equinoxes! The ecliptic is oriented about 23 degrees above the equator at the September equinox and about 23 degrees below the equator at the March equinox. Because the Moon is close to the ecliptic throughout its orbit, the crescent Moon in the eastern sky before sunrise shows the "smiley" or upright crescent.
Do you think the Universe is finite or infinite and how would it ever matter either way to humans.
Your question allows me to speculate a little. I think our Universe is finite. If it's infinite, it means it could only happen once, and once everything decays back and the Universe is cold again, then what? But, alas, I also subscribe to the Multiverse theory. That would be where we're one of many Universes. We would call our Universe the "Observable Universe".
Will it ever matter to humans? Not with our current understanding of nature, no. With our observable Universe expanding still, it means eventually we wont even be able to see outside of our own Galaxy because the distance for light to reach us will be further than the light can travel to reach us. We'll look like we're alone with our local galaxies. If we find a way to accelerate humans faster than the speed of light, then it will matter. But, until then.......... There's plenty to explore in our own galaxy though! But it sure would be neat to try and travel to the "edge of the Universe".
Much as i'd like to imagine humans exploring the galaxy one day i keep getting the feeling its always going to be cost prohibitive and not really worth the effort,If our explorations are about the procurement of natural resources i think we have enough of what we need right here in our own little solar system.
The thought of how much it would cost to build an Enterprise type warp capable starship or build and sustain a whole fleet of them boggles the mind..
Watching StarTrek i never did see much return on investment from the fleet of Starships other than military applications which we may never have to deal with..
Hey Ben, have you heard of the new measurements relating to dark energy that put the cosmological constant solution into serious question? In terms of high energy theories beyond SM, does this help the situation by constraining the models or would this present even more serious theoretical challenges that would need to be addressed?
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