Shower Thoughts - A Still More Glorious Dawn
I've had the chorus to this song in my head for DAYS now.
"A still more glorious dawn awaits - not a sunrise, but a galaxyrise. A morning filled with four hundred billion suns with the rising of the Milky Way"
It's a vivid image, and if you search Google for "galaxy rise" you can find a lot of people have put their minds to working out what that might look like. It would probably look like this, only better:
Anyway, if got me thinking - would a planet that were not tethered to a star, but rather just kind of slowly orbiting a galaxy, be able to receive enough heat and light to sustain life? I mean, even if it's really far out, four hundred billion stars must pump out a lot of heat, right?
Well, yes and no. They do pump out a lot of heat, but unfortunately (or rather fortunately, as we will see) their heat doesn't travel far. In order to have a true galaxyrise, our imaginary planet would have to be thousands of light years away from the galaxy, if not hundreds of thousands. If the heat from all those billions of stars was enough to warm that planet, giving it liquid water and a chance at supporting life, then the galaxy itself would effectively have to be one giant star. Heat and light wouldn't just travel outwards from the galaxy - it would travel through and down and around as well, each star sending out an ever-expanding sphere of heat and light that would eventually meet up with that of the next star. Any planets in orbit around those stars would be effectively cooked.
Lucky for us, the heat from a star can't travel all that far from it. Light, like so much else in the universe, obeys the inverse square law, meaning that the power light has diminishes radically as we travel away from the light source. So, an observer two AU away, twice as far from the sun as the earth is, would receive one-quarter the light. Move three AU away and get one-ninth the light, and so on. Move out to Pluto, about five and a half light-hours away, and the heat and light you get from the Sun is pretty negligible - about 1/1500th of what we get, if I've done my math right. Move one light year from the sun and you probably wouldn't be able to tell it from any other nearby star.
All of this means that no matter how many stars you have in your galaxy, it would never be able to support life around a lonely extra-galactic planet. If we want a galaxyrise, we'd need our imaginary planet to orbit an extragalactic star. Even then, galaxyrise would be an evening phenomenon, rather than a morning one, and would probably only be visible for half the year.
Still, it's a beautiful image and I'd love to see it if I could....
By the way - "If you wish to make an apple pie from scratch, you must first invent the universe." That sounds like a cannabis-inspired idea if ever I've heard of one....
Click to view"A still more glorious dawn awaits - not a sunrise, but a galaxyrise. A morning filled with four hundred billion suns with the rising of the Milky Way"
It's a vivid image, and if you search Google for "galaxy rise" you can find a lot of people have put their minds to working out what that might look like. It would probably look like this, only better:
Anyway, if got me thinking - would a planet that were not tethered to a star, but rather just kind of slowly orbiting a galaxy, be able to receive enough heat and light to sustain life? I mean, even if it's really far out, four hundred billion stars must pump out a lot of heat, right?
Well, yes and no. They do pump out a lot of heat, but unfortunately (or rather fortunately, as we will see) their heat doesn't travel far. In order to have a true galaxyrise, our imaginary planet would have to be thousands of light years away from the galaxy, if not hundreds of thousands. If the heat from all those billions of stars was enough to warm that planet, giving it liquid water and a chance at supporting life, then the galaxy itself would effectively have to be one giant star. Heat and light wouldn't just travel outwards from the galaxy - it would travel through and down and around as well, each star sending out an ever-expanding sphere of heat and light that would eventually meet up with that of the next star. Any planets in orbit around those stars would be effectively cooked.
Lucky for us, the heat from a star can't travel all that far from it. Light, like so much else in the universe, obeys the inverse square law, meaning that the power light has diminishes radically as we travel away from the light source. So, an observer two AU away, twice as far from the sun as the earth is, would receive one-quarter the light. Move three AU away and get one-ninth the light, and so on. Move out to Pluto, about five and a half light-hours away, and the heat and light you get from the Sun is pretty negligible - about 1/1500th of what we get, if I've done my math right. Move one light year from the sun and you probably wouldn't be able to tell it from any other nearby star.
All of this means that no matter how many stars you have in your galaxy, it would never be able to support life around a lonely extra-galactic planet. If we want a galaxyrise, we'd need our imaginary planet to orbit an extragalactic star. Even then, galaxyrise would be an evening phenomenon, rather than a morning one, and would probably only be visible for half the year.
Still, it's a beautiful image and I'd love to see it if I could....
By the way - "If you wish to make an apple pie from scratch, you must first invent the universe." That sounds like a cannabis-inspired idea if ever I've heard of one....