The time between successive new moon phases is 29 and a half Earth days. The moons phases where briefly described in my last post in Astronomy called Our Astronomical Companion however as I found it so fascinating I wanted to go a little deeper into it and explain in detail the phases it goes through. One major misconception is that the phases of the moon are linked to the earth’s shadow, however the only time earth’s shadow comes into play is during eclipses of the moon which occur every six months. In fact it’s the moons own shadow which accounts for its phases.
New Moon: The moon rises and sets with the sun whose light is shining directly behind the moon and so the side that faces earth is covered in its own shadow and is not visible. A New Moon is a one day event and occurs at a very specific time which can be measured down to the second. The nights sky is considerably darker at this stage.
Waxing Crescent: The first Phase after the New Moon The moon has moved in its orbit and so a slim crescent is visible in the west after sunset which over the next seven days or so will become increasingly brighter or “Wax” in illumination.
First Quarter: Commonly called a “Half Moon” is when the moon is one quarter of the way around in its orbit of Earth and is a one day event which occurs roughly 7 days after the New moon. A Quarter Moon also named as we see 1/4 of the illuminated surface.
Waxing Gibbous: The moon appears high in the east at sunset and is more than half-lighted, but less than full. This phase lasts roughly seven days with the moon continuing to “Wax” until its peek at the next stage. The word “Gibbous” has it’s roots in the Latin word “gibbosus” meaning humpbacked.
Full Moon: We can see the entire illuminated portion of the moon. At this point the Moon and Sun are on a line, with Earth in between. This is the opposite in many ways of the New moon which is totally covered in its own shadow and its timing can be measured to the second. Each new full Moon has its own name which i will talk about in a later post.
Waning Gibbous: The first phase after a Full Moon occurs finds the moon in an ever decreasing state of illumination or “Waning” It lasts roughly 7 days and is visible over the eastern horizon in the hours between sunset and midnight. This phase is the one that looks most like the Death Star from Star Wars to me!
Third Quarter: Also referred to as “Last Quarter” is another “Half Moon”, but the illuminated part is opposite of the First Quarter. A Third Quarter moon is a one day event when the moon is three quarter of the way through it’s orbit around the earth. It rises around midnight, appears at its highest in the sky at dawn, and sets around noon.
Waning Crescent: Sometimes refereed to as an “Old Moon” is best viewed an hour or two before the sunrise in the east before dawn. This last phase begins after the Third Quarter and will last around seven days until the cycle begins again with a New Moon.
Todays or be it tonight’s moon phase is a Waxing Crescent with 32% Illumination. The skys will hopefully stay clear enough for you to see the Moon in the wester sky after sunset. The Moon holds so many more fascinating topics for discussion so I will be returning to it again soon! Below are a few links to the sites I gathered my information on but I would like to advise you to check out www.astronomycast.com www.universetoday.com and moongiant.com.