My friend tells me he might make it home for Christmas “if all the stars align.” But, assuming they all did align, wouldn’t their gravitational force have some sort of untoward effect on life on Earth?
Well, stars are pretty far away to have that sort of effect.
I think that saying is more a half-assed astrology thing.
From dictionary.com:
You’re using definition one; your friend is using definition two. So, no problemo.
So, to be more precise, what I am asking is whether the stars aligning in the first definition would make any difference.
That is, if you take the earth and draw a straight line through the Sun and beyond, through every star in the universe, would the gravitational forces on earth be affected in any discernable way?
Well I remember years ago I heard that if the moon is in the seventh House and Jupiter aligns with Mars then peace will guide the planets and love will steer the stars. But it could have just been a rumour.
Remember that gravity decreases with the square of distance. So any gravitational effect across a distance of millions of light years is going to be nonexistant for all practical purposes. Someone driving a truck down your street is going to have a bigger gravitational effect on you than all the stars in the universe.
In classical astrology the planets (Mars, Jupiter etc.) were thought of as wandering stars, so the phrase likely dates to this alignment of planets. Basically if fortune favours them they’ll show up. Even so the planets are not really all in a row as some tend to orbit the sun at differing angles from the equatorial plane of the solar system. In short no big deal.
Now if you’re taking it to mean every single star in the heavens is lined up well that’s simply never going to happen as the whole universe would have to be on one side of the earth.
Ok so I have some time here.
Say 100 Million stars per galaxy and there are 100 Million galaxies within a universe of 14 lyrs. So if we line up every star (10e16) over 28e9 light years that would be a star every 5 AU. (for reference the Sun is 1 AU away)
Now let’s assume 1 solar mass per star, the acceleration on the earth due to the stars would be
a=asun/25 * SUM (1/i^2) from 1 to 4.6e16
(asun is the current acceleration on earth from our sun)
(I think). So basically the acceleration due to these stars will start off at 1/25th of our sun’s current effect on Earth and drop by an inverse square from there. I think if you sum it up it tends to square root of e. ~ 1.644 leading to a grand total of 6% of the current acceleration due to our sun.
Basically after the 10th star the acceleration due to addition stars becomes progressively more negligible.
I now wait for Angua (and others) to correct me. 
Pigs will have wings, hell will freeze over and monkeys will fly out of your butt.
gravity is cumulative though. if every star in the universe lined up on one side of planet earth my guess is we would be sucked into the rapidly forming black hole that is busy eating the universe for being silly enough to form a big buffet line.
Grey, would that 6% be sufficient enough to yank Earth out of its stable orbit and plummet it into the Sun?
The sun is on the other side, of course, at 5 AU. Since that would be the only side with matter (or that matters at that point) we’re going to fall towards it. I wouldn’t wager a lot on a stable orbit existing within the setup I laid out (string of stars 5AU apart for 28 Billion light years)
Except I don’t think that quite answers the OP. When I envision the “stars aligning” (inasmuch as I ever envision such a thing) I think of them as remaining at the same distance from Earth, just swinging 'round to line up in a straight line. So, I think what the OP wants to ask is this:
If you took every star in the universe and positioned them in a straight line on one side of the Sun such that each maintained its present distance from the Earth, would the gravitational forces on earth be affected in any discernable way?
And even if he doesn’t want to ask it, it seems like a more interesting question to me. In part because it changes the parameters: the nearest star is 4.2 light years away (the 26 nearest stars and the 100 nearest stars), which tremendously decreases the first term of your sum; also, the total number of stars within a given distance increases cubically, as opposed to linearly, which ought to increase the influence of the terms down the line.
The Cubs would win the Pennant, Gigli would sweep the Oscars, my ex girlfriend would stop calling me, Angua would go out with me, cable would be free, cats and dogs living together…
In other words… all I have is smart ass responses. Enjoy!
shrug. You do the math then.
If we take 4 lyrs as an average distance than we wind up with stars about 10 Million time farther away from earth than the current “edge of the universe”.
I suppose you could simply assume the mass is smeared out over 14 billion light years, with the center of mass being at 7 billion light years out. That would give us an acceleration of 3e-16 m/s^2. Or we could dump all that mass at 4 lyrs with a resulting acceleration of about 900 m/s^2.
1/r^2 is really powerful when there’s such huge gaps between things.
Gravity would be the least of our worries. If you lined up all 70 sextillion stars (7X10[sup]21[/sup]) within the 30 billion light year (3X10[sup]10[/sup]) diameter of the visible universe, you’d end up with roughly 2,333,333,333,333 stars/LY. That’s one star every 4.29X10[sup]-13[/sup] LY, a star every 2.5 miles.
Most stars are thousands of miles in diameter, so the earth would be embedded in 30,000,000°C+ plasma very near the core of two catastrophically merging nuclear furnaces. We humans would stand less of a chance of surviving than the proverbial nitrocellulose cat in Hell.
I think the simple answer to the question is “no”. If you look at the Milky Way, we are on an outer arm. So, one can reasonably say that the stars are already “aligned” (in the sense that most of them are in approximately the same direction).
And, the other factor is that all the stars “near” us are rotating around some central point. All that gravity just keeps us rotating. If everything lined up, things wouldn’t be much different than they are now, because everything would still be moving. We’d simply keep rotating as always.
I’ll make it home if I get my ducks all in a row.
What is the gravitational value of a row of ducks?