Imagine that you are at home watching TV.
You’re watching your favorite show when your
little brother walks by and stands in front of the
TV. Now, you can’t see the TV anymore, but he
eventually keeps walking. A few minutes later,
he’s back in the same spot, blocking your view.
You notice that after he does this a few times
that he’s actually walking around the couch at a
certain speed. So you look at the clock, and you
notice that he walks in front of the TV once every
three minutes. You tell your friend that you
predict that there will be another “Brother-TV
eclipse” (meaning your brother will block the TV)
in three minutes. Your friend is astonished when
your prediction is correct! This is similar to how
astronomers predict solar and lunar eclipses,
except that their calculations are a little more
I’ll use a solar eclipse as an example. With
a solar eclipse, the moon blocks the sun. This can
only occur because the sun is about 400 times
bigger than the moon but about 400 times farther
away! Astronomers can predict when this will
happen because after many years of observation,
they were able to determine how fast the moon is
moving and orbit and how fast the sun is moving in
orbit. (You can see how this calculation might be
a little harder than your brother calculation
since your brother was the only thing that was
moving in that case.) To make it a little more
difficult, you have to be in the right spot with
the right angle to see the solar eclipse.
There a lot of other things to consider when
trying to calculate eclipses. For example, the
earth and moon and sun are all feeling the pull of
gravity from each other and from other planets,
which can slightly change their orbit and motion.
Astronomers also have to remember that these
rotating bodies are not all perfect spheres; the
earth, for example, is sort of stretched out. Now,
after considering all of these different things,
astronomers punch the numbers into a computer
program and can use their math to predict the next
If you want to do it yourself, some astronomers
came up with this equation, which can work all the
way until the year 2050:
ΔT= 62.92 + 0.32217 ∗ t + 0.005589 ∗ t2
ΔT is just the year in which the next solar
eclipse would occur.
The “t” is based on the year and month
you are in. First, you have to figure out
y = year + (month−0.5)/12
Then, you can find “t”, which uses the number
that got for “y”, and then you can plug that in.
t = y−2000
If you solve and get a value for ΔT (which
relates to the earth's rotation), you still aren't
done yet! You would have to use this value and
plug it into some special software that includes
the position, speed, acceleration, and shape of
the earth, moon, and sun. Then, you'd have a good
guess of the next solar eclipse.
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