Tag Archives: syzygy

Making Friends with the Night Sky: The Full Moon

Lunar eclipses can occur during the full moon period

Lunar eclipses can occur during the full moon period

Maui astronomer Harriet Witt describes our full moon, and how the alignment of the Sun, Earth and Moon – syzygy – can affect the planet.

Listen here [3:08m]:

Download here [2.9 Mb]: ftp://space.mit.edu/pub/ajb/radiopio/astrofacts_090801_mfns-fullmoon.mp3

What’s the facts:

Halfway through our lunar cycle, the Moon and the Sun are now on opposite sides of the Earth, so we see a fully sun-lit full Moon.  At this time, the Moon rises as the Sun sets, and the Sun rises as the Moon sets.  This alignment of Sun, Earth and Moon is called syzygy (pronounced “SI-zi-gee“) and occurs during both new and full moon.  This alignment magnifies the ocean tides on Earth (both the Sun and the Moon cause tides through gravitational force), and the full moon is a time when lunar eclipses can occur, about once or twice a year.   Imagine standing on the Moon at this moment; you would see a “new Earth”, or the dark side of the Earth, up in the sky.  Similarly, you would see a “full Earth” during the period of new moon.   In many ways, full moon is a period of opposition.  It is also a period of celebration, with many holidays occurring during full moon in tradiational cultures, such as the Chinese Lantern Festival, the Hebrew Passover, and the Muslim Shab-e-Bara’at.  The bright night also inspires full moon parties.   Have fun celebrating our closest celestial neighbor!

This Astrofact is dedicated to Mahina, our four-legged full moon.

Original air date 1 August 2009.

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Making Friends with the Night Sky: The New Moon

A glimpse of the moon through the trees, as it phases from new moon to cresent.

A glimpse of the moon through the trees, as it phases from new moon to cresent.

Maui astronomer Harriet Witt describes the new moon, the start of the lunar cycle.

Listen here [3:26m]:

Download here [8.1 Mb]: ftp://space.mit.edu/pub/ajb/radiopio/astrofacts_090722_mfns-moonnew.mp3

What’s the facts:

“A month is a Moonth, a Moonth is a moon.”  For many traditional calendars – Hawaiian, Chinese, Hebrew, Islamic – this is still true, although our western calendar has been tweaked to fit the months into one year.  The new moon is the start of the lunar month, and the time when the moon lies between the Sun and the Earth (this is called syzygy, a great Scrabble word).  Imagine yourself floating out in space well above the Sun, Moon and Earth, and you will see these three bodies in a row, with the Sun-lit side of the Moon facing away from the Earth.  So where is the new Moon in the sky?  Directly in front the Sun!

Why doesn’t the Moon block, or eclipse, the Sun every time the new moon phase happens?  It’s because the plane of the Moon’s orbit is actually inclined by about 5° relative to the plane of the Earth’s orbit (the ecliptic plane).  So most of the time, the Sun, Moon and Earth are out of alignment during new moon.  However, the Moon’s orbit actually rotates, or precesses, every 27.2 days.  So perfect alignment at new moon occurs about once every 18 years, a period the Babylonians called a Saros cycle (a complete explanation can be found here).  In fact, there are several Saros eclipse cycles because the Sun-Moon-Earth alignment doesn’t have to be perfect, so we get about two eclipses at new moon every year.

New moon is a great time for star-gazing as the Sun and the Moon will have both set in the evening.  So be sure to enjoy the dark skies that accompany the new Moon!

Original air date 22 July 2009.