Monthly Meeting Report


October 10, 2004

by James Kevin Ty

Images by James Kevin Ty


The ALP held its October meeting at Alice Villa-Real's 041010-c.jpg (44992 bytes)residence.  ALPers that were present on that meeting were Alice Villa-Real, James Kevin Ty, Allen Yu, Edmund Rosales, Dr. Jett Aguilar, Dr. Jesus Rodrigo Torres, Angie Tan, Melisa Bata, Joel Munoz, Leah Visaya, Dante Cruz, Jon Alcartado, Rich Pijuan, Oscar Lei, and Hans Gideon Cerdenia.

The meeting started at around 3pm with ALP vice president Edmund Rosales tackling on the topic "How To Tell Time Using The Moon." He started by tackling on the motions of the Moon across the sky. The Moon has 2 movements in space which were : a) it spin on its axis and b) it revolves around the   the Earth.  It takes around 27-1/3 days to spin once on its axis and the same period (sidereal month) to revolve once around the Earth relative to the stars.   Because the two periods are the same, the Moon always presents the same face to us.  

041010-b.jpg (48599 bytes)As the Moon travels in its orbit around the Earth, it goes through different parts of illumination because of its changing position relative to the Sun. This presents the different phases of the Moon. The Moon goes through its phases in about 29.5 days and this is known as Synodic month.  It is the Moon's period of revolution around the Earth relative to the Sun.  It is longer than the sidereal month, because the Earth itself is moving around the Sun and it takes the Moon an extra 2 days to return to the same position relative to the Sun. Edmund then asked Allen to be his assistant to demonstrate it work in real time :)

When the Moon lies in the direction of the Sun, it presents a dark face towards us which we called NEW MOON. Gradually, a slim crescent appears and which grows to a half moon in about a week which we called the FIRST QUARTER.   A week later, the whole face is lit up which we called the FULL MOON. Then the lit portion will gradually recedes to a half moon again which we called the LAST QUARTER. This cycle will repeat itself all over again.

He then explain on how to use the position of the Sun against the Moon to give you an estimated knowledge of the time of the day. Since the Moon moves about 12 deg per hour, one can estimate the time using its position across the sky.   During Full Moon, the difference between the Sun and the Moon across the sky is about 180 deg while during the First Quarter, the distance between the two in the sky is about 90 degrees.

After  the very educational lecture of our Vice-President 041010-e.jpg (34072 bytes)Edmund Rosales, it was ALP PRO Alice Villa-Real's turn tp share to fellow ALPers her astro experiences during   her just concluded US trip.  She made a powerpoint presentation of her trip to Mount Palomar as well as some other major observatories within the vicinity of Mount Palomar Observatory.  Sharing her experiences was like the ALPers were there too as her lecture was both interesting as well as educational.

Finally, ALP president James Kevin Ty gives an initial impression on the different types of sky maps that are available for astronomers to use.   He concentrated on the planisphere as he distributed planisphere sets for the members to construct for themselves.  He gives some pointers on how it can be constructed in a very layman's way and the ALPers were excited to have a hands on experience to build one. After careful thought, it was decided that there will be a hands on program on building the planisphere with fellow ALPers altogether in  next month monthly meeting which will be held again at Alice's place on November 7.  The meeting ended at around 5:15pm.



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2003 , 2004 Astronomical League of the Philippines Inc.