Sit. Rep. #134: Moon: Sidereal vs Synodic, Draco the Dragon


1- The term “moon” is by definition:  A natural satellite about a heavenly body.  But Earth’s moon is also called The Moon or Luna.  Currently, there are over 200 known moons in our solar system.  Most orbit planets but some orbit asteroids.  Of the 4 moons that are bigger than our Moon, 3 orbit Jupiter.  Their names are Ganymede, Io, and Callisto. And they are called the Galilean moons.  Ever wonder why they are not called the Jupiter Moons?  They were discovered by Galileo Galilei between December 1609 and March 1610.  What he discovered were the first observed objects to orbit another planet other than Earth.   These 3 names come from Greek Mythology.  All are considered offspring from mythological Zeus.

The additional large moon in the solar system is Titan.  Titan orbits Saturn.  Titan is second only to Ganymede in size.  Titan was discovered by Christiaan Huygens in March of 1655.  He also discovered the rings around Saturn.  The name Titan also comes from Greek Mythology.

O: Why is the Moon almost always hungry?
P:  It is full only once a month.


2- There are 2 different (at least) ways to measure our Moon’s revolution about the Earth.  One is to measure against the revolution against the stars.  This is called the “sidereal month“.  And is (about) 27.32 days.  The second way is to measure against the Sun and that runs (about) 29.53 days.  That is called a “synodic month“.

Q: What is the astronauts’ favorite candy?
R: It is a toss-up between Mars Bars & Milky Ways.

Same Luna Face:

3-  We sometimes use the term “tidally locked”.  That references the moon that rotates at the same speed that it revolves.  The same face of the moon that we see every night is the same face that we will see every night.  This is also called “synchronous rotation.”  Note: Callisto is tidally locked to Jupiter.

The Dark Side of the Moon is not always dark.  To be more accurate call it the “Far Side of the Moon.”  The far side was not seen until 1959 when it was photographed by the Soviet Luna 3 space probe.  It was first seen directly by human eyes during the Apollo 8 mission in 1968.

S: What is the first day of the week onboard the International Space Station?
T: Moon day.


4- One more technical term.  Libration means that we see more than 50% of the moon’s surface because our position changes.  During the night of a full moon, our position to observe the moon changes between 21:00 hours and 03:00 hours but the moon has not moved a lot.    There is also libration when we observe the moon at different latitudes.  Hence over the period of a lunar month, we get to see about 58% of the moon’s surface.

U: What do astronauts subscribe to to listen to music?
V: Nep-Tunes.

Meeting Plans & Notes:

Find the North Star – Polaris
Find the constellations on the ecliptic
Find the circumpolar constellations, Ursa Major, Ursa Minor, Cassiopeia, Cepheus, and Draco
What phase is Luna
Try to locate Sirius, the dog star

Practice observing, looking up days and nights

Howling away,

Campfire Skits:   by Thomas Mercaldo

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