Let's grant that the stars are scattered through space, hither and yon. But how hither, and how yon? To the unaided eye the brightest stars are more than a hundred times brighter than the dimmest. So the dim ones are obviously a hundred times farther away from Earth, aren't they?
Nope.
That simple argument boldly assumes that all stars are intrinsically equally luminous, automatically making the near ones brighter than the far ones. Stars, however, come in a staggering range of luminosities, spanning ten orders of magnitude ten powers of ten. So the brightest stars are not necessarily the ones closest to Earth. In fact, most of the stars you see in the night sky are of the highly luminous variety, and they lie extraordinarily far away.
If most of the stars we see are highly luminous, then surely those stars are common throughout the galaxy.
Nope again.
High-luminosity stars are the rarest. In any given volume of space, they're outnumbered by the low-luminosity stars a thousand to one. It's the prodigious energy output of high-luminosity stars that enables you to see them across such large volumes of space.
Stichwörter: physics astronomy
At the very moment that humans discovered the scale of the universe and found that their most unconstrained fancies were in fact dwarfed by the true dimensions of even the Milky Way Galaxy, they took steps that ensured that their descendants would be unable to see the stars at all. For a million years humans had grown up with a personal daily knowledge of the vault of heaven. In the last few thousand years they began building and emigrating to the cities. In the last few decades, a major fraction of the human population has abandoned a rustic way of life. As technology developed and the cities were polluted, the nights became starless. New generations grew to maturity wholly ignorant of the sky that had transfixed their ancestors and that had stimulated the modern age of science and technology. Without even noticing, just as astronomy entered a golden age most people cut themselves off from the sky, a cosmic isolationism that ended only with the dawn of space exploration.
Carl SaganStichwörter: science space astronomy human-development
My dear Kepler, what would you say of the learned here, who, replete with the pertinacity of the asp, have steadfastly refused to cast a glance through the telescope? What shall we make of this? Shall we laugh, or shall we cry?
Galileo GalileiStichwörter: science astronomy telescope johannes-kepler kepler
Though we might like to think so, humankind is not at any special, unique or privileged location in the gargantuan, perhaps infinite, Universe.
Eric ChaissonStichwörter: universe earth astronomy humankind
At every level in our inventory, nothing seems special about our Earth, our Sun, our Galaxy, our Local Group. Evidently, mediocrity reigns throughout. Such is our niche in the Universe.
Eric ChaissonStichwörter: sun universe earth astronomy galaxy
... the blast signatures of a detonated supernova and that of a nuclear bomb are identical.
Eric ChaissonStichwörter: astronomy supernova nuclear-bomb
Some people think the Milky Way is a long line of stars, but it isn't. Our galaxy is a huge disk of stars millions of light-years across, and the solar system is somewhere near the outside edge of the disk.
Mark HaddonStichwörter: astronomy
At night the sky is pure astronomy.
Nicole KraussStichwörter: night sky astronomy
Discover the force of the skies O Men: once recognised it can be put to use.
Johannes KeplerStichwörter: science inspirational universe space astronomy
There is nothing particularly special about that location of the centre of mass. If you were to find yourself at the precise spot that is the centre of mass of the earth-moon system, the only thing unusual that you would notice is that there would be one thousand miles of rock on top of your head.
Pluto is only about twice the size of Charon, so if you put Pluto and Charon on the cosmic seesaw you would find that the balance point is a little bit outside Pluto, rather than inside it. Again, there is nothing particularly special going on there. If you were to find yourself at that precise spot, you would only notice that you were very, very cold and could no longer breathe.
Stichwörter: earth outer-space astronomy planets pluto centre-of-mass
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