23 December – 29 December
PAUL
Welcome to Idaho Skies for the fourth week of December. We’re your hosts,
Paul…
RACHEL
…and Rachel.
PAUL
Did you get a new
telescope for Christmas?
RACHEL
If you did, you have
an excellent opportunity to try it out. There’s a brilliant star above the
gibbous moon on Christmas night.
PAUL
So after looking at
the moon, point your new telescope towards the star.
RACHEL
Even at low power,
you will discover that it is round in shape and accompanied by four tiny stars.
PAUL
What you are
observing is the mighty planet Jupiter and three of its satellites, or moons.
RACHEL
The fourth star is
really a distant star and not a satellite of Jupiter.
PAUL
In most telescopes,
which invert images, you will observe from left to right, Io, Jupiter,
Ganymede, Callisto, and the star HIP 20785.
RACHEL
The star is brighter
than the satellites and gets its name from the Hipparcos star catalog.
PAUL
Astronomer and
physicist Galileo discovered Jupiter’s four large satellites 403 years ago.
Today we name the satellites in his honor.
RACHEL
The Galilean
Satellites are roughly the size of our moon, give or take. In a telescope
however, the satellites appear as stars.
PAUL
They are a diverse
group of moons ranging from Io, the most volcanic body in our solar system to
Europa, an ice-covered satellite which potentially houses a very deep ocean.
RACHEL
Watch them over
several nights as they orbit around Jupiter. Every night they take on a new
arrangement.
PAUL
The moon is full on
the morning of the 28th.
RACHEL
The full moon in
December is called the Cold Moon.
PAUL
Through binoculars,
or even your new telescope, shadows from changes in terrain are generally not
visible on the full moon.
RACHEL
What we notice the
most on the full moon is albedo features. Albedo refers to the reflectivity or
darkness of the moon.
PAUL
The features most
noticeable include dark lunar maria and bright crater aprons and rays.
RACHEL
Lunar maria are old
seas of lava. How did these seas form on the moon?
PAUL
Well, after the
moon’s formation, its core remained hot from gravitational collapse. Later it
remained hot because of the decay of radioactive elements.
RACHEL
This occurred around
3.8 billion years ago, when the moon and planets collided with the last of the
planetesimals, or building blocks of the solar system.
PAUL
The collision between
the moon and planetesimals created large impact basins on the moon’s surface.
RACHEL
Heat in the moon’s
core eventually led to the creation of pockets of magma, or molten rock deep
beneath the moon’s surface.
PAUL
The magma was able to
rise to the moon’s surface where the planetesimals had created the deep impact
basins.
RACHEL
Over millions of
years, the basins filled with sheet after sheet of thin lava.
PAUL
In some basins, there
is evidence for layers of lava over a mile thick.
RACHEL
That’s Idaho Skies for the fourth week of
December. The Quadrantid meteor shower reaches its peak next week.
PAUL
Follow us on Twitter at Idaho
Skies for this week’s event reminders and sky maps. For Idaho Skies this is
Paul…
RACHEL
and Rachel.
Idaho Skies is a production
of NearSys and Radio Boise 89.9 FM Caldwell/Boise and 93.5 FM downtown, K228EK
Garden City.
PAUL
Dark skies and bright stars.
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