Bad Astronomy: Misconceptions and Misuses Revealed, from ...

SHADOWS IN THE SKY 123
time that adds up. As it gets farther away, it appears smaller in the
sky. That means eventually it will be too small to completely cover
the Sun during a solar eclipse. Instead, we’ll get an annular eclipse,
a solar eclipse where the Moon’s size is somewhat smaller than the
Sun, and you can see a ring of Sun around the dark disk of the
Moon. We get these eclipses now because the Moon’s orbit is elliptical,
and if the eclipse occurs when the Moon is at the highest
point in its orbit, the eclipse is annular. But, eventually, these will
happen all the time. The corona will forever be hidden by the glare
of the Sun and solar eclipses will be interesting, but lack the
impact they have now. That’s why, in the beginning of this chapter,
I said that total solar eclipses are a coincidence of space and time.
Given enough time, they won’t happen anymore.
PPP
I can’t leave this chapter without busting up one more misconception.
It is an extremely common story that Galileo went blind
because he observed the Sun through his telescope. I have said this
myself, even once on my web site. Andy Young e-mailed me about
it and set me straight.
Galileo did indeed go blind. However, it was not due to observing
the Sun. Galileo realized rather quickly that looking
through his small telescope at the Sun was a quite painful experience.
Early on he only observed the Sun just before sunset, when it
is much dimmer and safer to see. However, he later used a projection
method to view the Sun and observe sunspots. He simply
aimed his telescope at the Sun and projected the image onto a
piece of paper or a wall, casting a much larger image of the Sun.
This method is far easier and produces a large image that is easier
to study as well.
Certainly, using a telescope to observe the Sun can indeed
cause damage to the eye, since a telescope gathers the sunlight and
concentrates it in your eye (much the same way that you can burn
a leaf with a magnifying glass). However, this sort of damage
occurs very rapidly after solar observation, and Galileo did not go
blind until he was in his 70s, decades after his solar observations.
There is copious documentation that during the intervening years