Spring Equinox, Finding Ceres
Observing >
Ready or not, spring arrives tonight. But just what determines when spring begins?
We all spend half the year tilted a little toward the sun, half of it
tilted a little away. When we are tilted away, the sun doesn’t get
as high in the sky, the daytime is shorter, and it is generally cooler.
The opposite happens when we are tilted toward the sun: the sun gets higher
in the sky, daytime is longer, it is warmer.
There must be some magic moment when we are not tilted toward or away
from the sun. Actually there are two magic moments each year - at the
end of March and at the end of September. They are the equinoxes.
On those days, the Earth has sunlight from pole to frozen pole; the sun
is “up” just as long as it is “down;” it rises due
east and sets due west. It’s like Solar Equality Day for everyone
in our Global Village. This March our planet proudly faces the sun without
a tilt at about 11:30 tonight at the spring equinox - the beginning of
spring.
The first days of spring this year happen to be a good
time to look for an asteroid, for one suspect in particular going by the
name of Ceres.
Back in the late 1700’s, when planet-discovering was all the rage,
astronomers were faced with a puzzle. The planets were all planted around
the sun in a nice pattern - almost. There was a great gap between Mars
and Jupiter where it was believed there should have been a planet. The
search was on!
In
1801, the Italian astronomer Guiseppe Piazzi discovered in The Gap what
appeared to be a moving star. It turned out it was actually a mini-planet
which he named Ceres. In the next hundred years, hundreds of these mini-planets,
all smaller than Ceres, were found between Mars and Jupiter in what is
now called the Asteroid Belt. All tens of thousands of them were probably
the building blocks for a planet that was never quite able to get its
act together.
Want a stab at finding Ceres? You’ll need at least a 7x50 binoculars
and plenty of patience. If you’re up to it, here we go...
Probably the best way to find it --- but, ironically, the worst time to look - happens tonight. The nearly full Moon makes a nice marker but bleaches the sky. Position your binoculars so that the Moon is just out of the field of view to the right as if it were trying to sneak into your binoculars at the 3 o’clock position, but can’t. Now, with a heightened awareness for detail, move your binoculars one entire field of view to the left. Ceres is in there.
Which of the several starry objects is it? You can do one of two things
to find out: 1) If you want to experience the Old Ways of astronomy, sketch
the part of sky you’re looking at. Sketching the same area the next
day will reveal that one of the “stars” has moved slightly.
That’s Ceres. (Parents, this makes a great and original science project
... or 2) You can cheat and go to http://firstlightastro.com/icolumn.html.
You’ll find there simple starcharts of that region in the sky and
a Quicktime movie to see how Ceres moves day by day. (There are also charts
and movies for earth’s tilt through the year.) By the way, if it’s
cloudy this week, don’t fret! Although the Moon will have gone elsewhere,
Ceres is in the same general area for the next month.
Until next time, happy hunting in the clearest springtime skies!
Mark Ritter is a freelance writer and high school astronomy teacher. Got
questions or need help? Write him at ritter@firstlightastro.com.
Posted by Administrator at 2000.03.19 09:45 AM | Comments (0)
The Alignment, Prelude
The Solar System >
Load your camera, brush off your binoculars, dust off your scope; there’s a beautiful sight a-coming your way this week as some planets and the Moon move together in the early evening. But first, as usual, some background!
The planets don’t buzz around the sun like moths
around a flame, in some haphazard, random way. Nearly all orbit the sun
on a plane - like runners on a circular track in a circular stadium. This
imaginary track on which they travel is called in the astronomy business
"the ecliptic."
Because the planets travel around the sun this way they can occasionally
appear very close to each other from our earthbound point-of-view. This
is what is happening now to Jupiter, Saturn, and Mars. Although they are
really hundreds of millions of miles from each other and from us, they
appear to be getting closer in the western early evening skies.
What’s really going on is this: Since we are closer than they to
the sun - the center of our solar stadium - we get to go around more quickly.
That’s the Law. We’re so far ahead of those poor slowpoke planets
that we are nearly on the whole other side of the solar system this month.
Soon the sun, that blinding light in the center, will make it impossible
to see them until later this year when we start to catch up with them
again.
These groupings usually mean an aesthetically pleasing sight in itself,
but this week the Moon joins in for the photo-op. This, my friends, is
inspiring.
The Moon, as it orbits around us, travels through the same part of the
sky as the planets do --- that very same ecliptic. This will be abundantly
obvious as you watch the slivery, silvery Moon go by Mars, then Jupiter,
then Saturn in the span of just a few evenings.
Here are some interesting things to watch for. (All refer to about 6:30
in the evening):
|
On Tuesday the 7th, look for bright Saturn, brighter Jupiter, and a dull, tiny red Mars right in a row in the western skies. They are all in a line (the ecliptic). Look just below Mars to see the slightest sliver of a young Moon. |
On Wednesday, the Moon has moved a little higher by now - just between Mars and brilliant Jupiter above it. Notice the sliver has gotten a little fatter. Moving to the side of the Earth as it's doing lights the Moon up a little more on one side. If you look a little closer you may notice not just the bright thin crescent but the whole sphere of the Moon dimly lit. But how? Because of us! The light of the sun reflected off the Earth lights up the nighttime side of the Moon. Moon people would be experiencing Earthshine |
On the 9th, the Moon loiters with Jupiter below it and Saturn above. The Moon and Jupiter are close enough to be in the same field of view for binoculars. If you hold your binoculars steady enough, you can see four bright satellites of Jupiter known as the Galilean satellites. (see below left) |
By the time we get to Friday, the Moon, Saturn, Jupiter, and Mars are all lined up in a nice row. The planets will continue to get closer to each other this month as the Moon leaves them for a brighter place. |
In two weeks we'll go asteroid hunting with a pair of binoculars. Until then, clear skies!
Posted by Administrator at 2000.03. 5 10:36 AM | Comments (0)