Explore the Universe - Lunar Phases

We have all watched the Moon as it has changed its phase.  By the time we are thirty years old the Moon has gone through nearly 375 cycles.  The Moon is a beautiful sight in the night sky, a bastion of the sky for more than 4 billion years.  What causes the Moon to go through different phases?

The below diagram shows the Sun, Earth and the Moon.  The Moon phases pictured below occur when they are at that angle between the Sun and Earth.  When the Moon is between the Sun and Earth it will be a 'New Moon' and will not seem to appear in the sky.  The Sun is illuminating the far side of the Moon.  As the Moon orbits the Earth it slowly appears as a 'Waxing Crescent'.  Waxing is a term synonymous for 'growing'.  When the Moon is at a 90° angle it becomes a 'First Quarter' Moon.  Some people are confused why it is called a quarter when it seems as though half the Moon is illuminated.  It is referred to as a quarter because it is a quarter of the way through the lunar cycle.

The Moon continues to orbit and becomes a 'Waxing Gibbous' Moon, growing larger towards the next phase of a 'Full Moon'.  The Sun shines directly onto the near side of the Moon and observers on Earth see it as fully illuminated.  The Moon then starts orbiting back towards the Sun to become a 'Waning Gibbous'.  When it reaches 270° it is half illuminated again and called 'Third Quarter' or 'Last Quarter'.  It then continues its trek back to the beginning of the cycle going through its 'Waning Crescent' phase.  Around 29 days since it began the cycle it becomes a 'New Moon' again and restarts the process.

Phases of the Moon

The images above (including the Sun but excluding the Earth) were taken from the backyard.  The below diagram displays the dates and times.  To qualify for the Explore the Universe certificate the 'Last Quarter', 'First Quarter' and 'Full Moon' must be recorded within 18 hours of the actual time the exact phase occurs.  This is recorded below.

Lunar Phases Observation Record

I have a love/hate relationship with Moon phases.  A 'Full Moon' produces a lot of light making it more difficult to fall asleep.  It also brightens the sky with awful light pollution rendering deep-sky observing less fruitful.

The 'First Quarter' phase is one of my favourites.  The Moon is visible in dark skies early in the evening so it is perfect for kids to see before they go to bed.  The terminator goes through some intriguing craters that can be easily viewed from Earth.  Also, by the time adult bedtime arrives, the Moon has set allowing an easier sleep.

Viewing the waning phases in a dark sky is also difficult because it occurs early in the morning accessible by staying up very late or waking up very early.

Keep an eye on the sky and try to figure out what phase the Moon is at.  The weekly posts on my blog will highlight the 0°, 90°, 180°, 270° phases.