Step outside tonight to see the full moon rise in the East after
sunset. Sunset is at about 8:00 p.m. and moon rise is at about 8:30
p.m. so depending on your horizons it may take you a little while to
see the moon rise after 8:30 at your location. Often when you
observe the full moon rising, it "looks" bigger than it really is.
It's an optical illusion that is easy to test and interesting to see.
"The full Moon of June 18th is a "solstice moon", coming only two
days before the beginning of northern summer. This is significant
because the sun and full Moon are like kids on a see-saw; when one is
high, the other is low.
This week's high solstice sun gives us a low, horizon-hugging Moon
and a strong Moon Illusion.
Sky watchers have known for thousands of years that low-hanging moons
look unnaturally big. At first, astronomers thought the atmosphere
must be magnifying the Moon near the horizon, but cameras showed that
is not the case. Moons on film are the same size regardless of
elevation: example. Apparently, only human beings see giant moons.
A fun activity: Look at the Moon directly and then through a narrow
opening of some kind. For example, 'pinch' the moon between your
thumb and forefinger or view it through a cardboard tube, which hides
the foreground terrain. Can you make the optical illusion vanish?"
The above excerpted from the excellent Science@NASA's feature all
about the moon illusion:
Here is another good article about the moon illusion.
Both of these articles have some excellent graphics for you teachers
(and students) out there. And there is a full moon every month for
you to practice this activity with your friends and family.
Since you're out looking at the moon, swing your head around to the
West for a look at Mars and Saturn. You'll see they are appearing
closer and closer to each other. On July 10 they'll fit in the same
Jane Houston Jones
Senior Outreach Specialist, Cassini Program
JPL - 4800 Oak Grove Drive, MS 230-205
Pasadena, CA 91109 818-393-6435
Cassini SOC http://soc.jpl.nasa.gov/index.cfm
What's Up? http://education.jpl.nasa.gov/amateurastronomy/index.html