Strange Astronomical Perceptions
Our faithful star and moon seem a lot larger
as they rise or set, and we have a lingering perception embedded in our
memories that both are always big and bright, fostered by all the stunning telephoto
shots of them looming over landmarks around our planet and by depictions of them
in art and graphics.
But the perception of them being larger
near the horizon is only a mental illusion. They remain their visual sizes
throughout their entire apparent motions across the sky. Apparent because of
course it’s the earth that provides that 24-hour motion deception by rotating
on its axis. The sun appears to move its own diameter every two minutes as the earth is rotating to the east. Depending on how close you happen to be to
the equator, you’re moving at up to 1,100 miles per hour just because of that
rotation. We don’t sense it because we only feel acceleration or deceleration,
not constant velocity. (Think about sitting in a car on a smooth road doing a
constant seventy; you don’t feel it, and you only know you’re moving by the
scenery rushing by. Close your eyes and you could be sitting still.)
We also have the idea that the sun appears
much larger than the moon. In truth, they appear the same size. The sun is
indeed 400 times larger than the moon, but it’s also 400 times father away from
us. That’s the reason the moon can sometimes completely eclipse the sun
briefly.
Believe it or not, the moon (or the sun) is
only the same perceived size as a quarter as viewed from nine feet away. Yet if
you have 20/20 vision you can pick out amazing detail on the moon including
some cratering and the darker maria (so named because they resembled seas to
early observers). The moon seems so bright, yet it really is the color of
asphalt. It only appears to be bright against the utter blackness of space.
To me the most mind-bending astronomical perception
of all is the apparent static state of our Milky Way stars and the many other
galaxies strewn across the universe. In truth, nothing is static out there.
Everything is in motion, rotating or orbiting or rushing through space, as our
entire solar system is doing collectively. As our entire Milky Way galaxy is
doing as well.
We’re speeding sixty-seven thousand miles
an hour right now just in our annual journey around our own star yet, again, we
feel it not at all because that velocity is constant.
The dazzling collection of starlight that
enters our eyes tonight is not the universe we perceive it to be. It can only ever
be an ancient rendition. It is starlight that’s just now arriving from tens and
dozens and hundreds and thousands and millions of our years in the past.
At 186,000 miles per second, it takes four
and a half years for just the light from the nearest star other than our
sun to make that incredible journey of twenty-six thousand billion miles.
Phil
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