I was watching Jack Horkheimer last night and something he said about the star Vega got me worried.
Granted, it won’t be in my lifetime, but 500,000,000 years is not a very long time compared to the sun’s lifetime.
A few questions [list=1][li]Will Vega still be there waiting for us when we get there?[/li][li]If so, how close will the two stars approach?[/li][li]Will this be the closest approach of the sun to any star over its entire lifetime (i.e., before it burns out)?[/li][li]If not, what will be (or what was) the closest approach?[/li]How will life on Earth be affected by close approaches between the sun and other stars?[/list=1]
Hi, bibliophage, it’s me again. I’m not following you around, it’s just that your posts are the only ones I seem to find interesting today.
I don’t think we’ve got anything to worry about. If I understand the current thinking on this correctly, all space is expanding and therefore all the stars are getting further from each other.
Imagine that 2 cars are on a road. The one in front is a Chevy Vega and it’s travelling at 55 mph. The one behind is a Toyota Solara and it’s travelling at 54 mph. They’re both going the same direction, but the Solara will never catch up with the Vega because it’s pulling away too fast.
On the other hand, I’m keeping my “Viva Las Vega” sign from Contact handy.
Just a WAG, but I don’t think that neccesarily applies to this. I think if the estimates are correct, they imply they willl come close together. The expansion doesn’t really change the acceleration towards another body does it? Anyway, what’s to stop them from colliding. You talk about a close approach, but if Vega’s big enough, might we not be headed right into it?
I’d like to hear the opinions of the people who actually know about this tuff, so excuse the WAG and consider it a bump.
We don’t have anything to worry about, but not for that reason. Gravitationally bound objects such as galaxies (and also clusters of galaxies) do not expand with the universe. Since Vega is a star within the galaxy, we’re not getting further away from it because of the expansion.
The thing is, Vega, like all stars, has what is called proper motion. Proper motion is that component of movement that’s at right angles to the direct line between us and the star. In other words, we measure how far it moves across the sky by comparing is position over several years (using distant stars and galaxies as reference points). So besides moving toward us, Vega is also moving off to the side. By the time we get to our closest approach to Vega, it will have moved significantly away from us laterally.
As for q2 in the OP, I will let someone else calculate that (so I’m lazy). For q3, the answer is almost certainly not. For q4, the answer is we don’t know. Our sun has orbited the galaxy at least 18 times so far in its lifetime and we don’t know the movements of all the other stars in the galaxy. It’s true that the other nearby stars are orbiting at about the same speed and we will stay near them for a while. But none of them are in our exact orbit, so we will not hang out with them for more than a few million years.
Q5, it depends on how close another star gets. Within half a lightyear or so, a star will stir up comets in the Oort cloud, causing many to come into the inner solar system. So there’s a greater chance the Earth will get hit by one of them. But to significantly change the orbit of the Earth, it would have to get really close (within about 5 AU). Fortunately, stars very rarely get anywhere near that close to each other unless they are in a dense star cluster.
Notice that he called it a “very close encounter” but the nearest approach will be 50,000 times the distance of the Earth to the Sun. Shows you how astronomers think.
Now, if you’re talking about fear and loathing of a Vega, i.e. the notorious Chevy compact of the 1970’s, then you do have something to fear and loathe, if ever one comes your way.
Hmmm…wouldn’t an encounter that close likely cause a cometary shower though? Thus greatly increasing Earth’s likelihood of being beaned. Not that I’m too worried; if we (or our distant descendants) can’t deal with a few stray comets in a million years, then to heck with us. And if we (or our distant descendants) aren’t around in a million years, I confess I find it hard to get too worked up over the fate of the Intelligent Rat People or the Giant Mutant Sapient Cockroaches or whoever/whatever it is that’s inhabiting the place at that time.
So, asteroid/cometary showers aside, how would that affect us? at 50,000 A.U., how big and bright would the star be in our sky? Would we still have a true night? Would plants photosynthesize when the sun (our sun) isn’t out?
Magnitude 0.6 is fairly bright, but not nearly bright enought to turn night to day. There are now ten stars in the sky as bright or brighter than 0.6, including Vega.
Depends on the absolute luminosity of Gliese 710, which I don’t know. Given that it is an M1 main sequence star, however, I would guess that that is not very high.
For comparison, our Sun has an absolute luminosity of +4.85. Since the absolute luminosity is, essentially, the luminosity that the star would appear to have at 10 parsecs, the apparent luminosity at 0.2 parsec would of course be (10/0.2)[sup]2[/sup], or 2,500 times as bright. Magnitudes are logarithmic; a difference of one magnitude means that one object is 100[sup]0.2[/sup] = 2.51 times as bright as the other. Being 2,500 times brighter is a difference of 2500[sup]0.2[/sup] = 4.78 magnitudes. This is less luminous than Sirius appears, and Sirius certainly doesn’t cause plants to photosynthesis. Given that an M1 main sequence star will certainly be less luminous than the Sun (it’s been a while since I looked at an H-R diagram, but I’d expect it to have an absolute luminosity of about +9 or so), Gliese 710 will be an unimpressive star that you wouldn’t notice unless it were pointed out as the Proxima Centauri of the future.
Depends what you mean by “burns out”. When it completes its main sequence and becomes a red giant in a few billion years from now? When it completes its red giant phase and becomes a white dwarf? Or when the white dwarf finally cools off to background temp? But, as this website (http://www.astro.uiuc.edu/~kaler/sow/star_intro.html#classes) says…
"The cooling time is so long, however, that all white dwarfs ever created are still visible, though the oldest are becoming cool, dim, and reddish. "
So, the sun will be around for a long time…but it won’t support life on Earth forever. (Actually, it may not even support life on Earth a half billion years from now because the sun will keep growing brighter/hotter as it gets older.)
But, since Phobos is in the house, I will like to throw out an Asimov reference pertaining the etymology of his name. Phobos comes from the Greek word for fear. His partner in space Deimos is Greek for terror. In Greek mythology they were Ares’ sons, which truly makes sense of their names, they being the offspring of the God of War.
So, either Phobos is a truly mean fellow or he really loves his astronomy. I tend to favor the second hypothesis.
Now, an anecdote, also extracted from an Asimov book. Asaph Hall was ready to give up his search for a hypothetical Martian satellite(s) but, urged by his wife’s insistence, decided to give it another shot. What do you know? That particular night he caught two fuzzy objects on his telescope lens. Thus, Phobos and Deimos were discovered. Coincidence? Destiny?
I’m glad you favor the second hypothesis!
Yes, I love astronomy. When choosing a username (one I have been using for a few years now), I wanted to use a cool-sounding moon name. It didn’t strike me until later what the name meant. Oops!
You should fear and loathe Vegas. Nasty little rustbuckets, overheating all the time, ridiculous aluminum engines that burnt oil right off the dealer’s lot, paper-thin paint that went to hell in
