It can be almost impossible to grasp the true size of the Solar System. We can use a planetarium program and zoom out and zoom out and go, "Oh, Earth is just a dot now," or we can throw around millions and billions of kilometres but it really doesn't mean anything to our brains that are wired to judge the distance to the nearest tree, as the sabre toothed tiger comes leaping towards us. Just rarely, however, we might catch a tantalising glimpse of how immense the Solar System actually is.
Some time ago I was was outside and I happened to look up at the moon. It was in the west and slightly older than a waning quarter. The sun was in the east at approximately the same angle of elevation above the horizon. What captured my attention was that the illumination of the moon didn't look right. From my position and the apparent positions of the moon and sun, drawing an imaginary line from the sun to the moon, I should have been able to see a gibbous moon. But the moon was a quarter moon at best.
Now it has long been commented that owing to a freak of nature, the moon and sun look to be almost identical in size, from Earth. When I look at the moon and sun in the sky, the illusion is that they also seem to be the same distance away, making an isosceles triangle with the observer as the third corner. That's all very comforting but quite wrong, of course.
When I projected another imaginary line from the moon, normal to the lunar hemisphere being illuminated, it seemed to point off up and away, somewhere in space, as if the sun was actually in a different position. The sun (apparently) could not possibly be shining on the far side of the moon which was to the west of my observing position, since the sun was in the east.
That's when I had my 'Total Perspective Vortex' moment. The position of the sun and the illumination of the moon could only be reconciled if the sun was some unimaginably hideous distance away and unimaginably, hideously larger. Solving the puzzle of the moon's phase gave me a sudden insight into the true scale of the Solar System. Like the cold, implacable forces of the subatomic universe this insight was just a little bit frightening. And then I went inside.
Next time there's a quarter moon or crescent in the sky with the sun on the opposite side of the meridian, why not see if you can catch a bit of total perspective.
I was feeling quite pleased with myself until I read an article in the latest AS&T. Apparently Aristarchus noticed the same thing and used his observations when calculating the size of the sun and so on.
I was feeling quite pleased with myself until I read an article in the latest AS&T. Apparently Aristarchus noticed the same thing and used his observations when calculating the size of the sun and so on.
So I was only 2300 years too late.
Yeah but Aristarchus didn't come in here and explain it to us with a great diagram
For the millions, billions of stars that form a galaxy, when two galaxies collide, very, very few, if any, stars from the colliding galaxies will actually collide themselves in the mayhem. Not only is space big, really big, it is also very, very empty.
Good, simple logic Tim. You realise though that you are still a heratic, . Next you'll be saying that the universe is not Terra Centric, but Solar Centric. Let's see you explain that one!!!
For the millions, billions of stars that form a galaxy, when two galaxies collide, very, very few, if any, stars from the colliding galaxies will actually collide themselves in the mayhem. Not only is space big, really big, it is also very, very empty.
The sun has a radius of about 695500 km and so a volume of about 1.4*10^18 km^3.
It is 4.2 LY to Alpha Cen, so we can say the Sun is the centre of a sphere 2.1 Ly in radius disjoint from those of other stars. Give or take a bit, that's a volume of 3.3*10^40 km^3
So the Sun's volume occupies 4.3*10^-23 of its bit of space. You could fit 2.3*10^22 Suns in that volume.
Even given 200*10^9 stars in each of two colliding gallaxies it makes the odds of two stars colliding make the odds of winning Lotto look good.
On the other hand, the interstellar gas and dust collisions would cause a lot of star formation.
For the millions, billions of stars that form a galaxy, when two galaxies collide, very, very few, if any, stars from the colliding galaxies will actually collide themselves in the mayhem. Not only is space big, really big, it is also very, very empty.
Good, simple logic Tim. You realise though that you are still a heratic, . Next you'll be saying that the universe is not Terra Centric, but Solar Centric. Let's see you explain that one!!!
Isn't it full of dark matter though which makes up over 95% of the universe? This is a measurable phenomenon that is observed by how it's gravity affects other matter. This is what I've read somewhere anyway. Nothing is always something
Can someone please answer this philosophical/theoretical question? If fuel was never a problem and we discount the likelihood of eventually burning up by moving too close to stars, getting sucked into a black hole or captured by another race of beings in a distant galaxy is it possible to just keep going through space?
If a space ship took off from the equator of Earth at right angles to the Earth and headed out into space what would happen to it? Would it just hypothetically keep flying as the universe changes through the trillions of years it takes to get through the universe? Is there an end to space or is there a metamorphic infinity? I honestly don't know
. Next you'll be saying that the universe is not Terra Centric, but Solar Centric. Let's see you explain that one!!!
