The moon.

The Moon's orbit is close to the plane of the ecliptic.

It is as if the Moon chases the Sun...
And then the Sun chases the Moon..
From new to full and back again.

The ecliptic is the path of the Sun on the celestial sphere as seen from the Earth.

The celestial sphere is how the sky appears to us on earth, as if it is a sphere- or bowl- of sky above us.

The lunar orbit plane is inclined to the ecliptic by 5.1°.
This means that the Moon can be higher, and lower and at the same celestial latitude as the ecliptic through out the year.

The Celestial Latitude is the angular distance of the Moon (or any star and planet) above or below the ecliptic.

Every so often the Moon crosses the ecliptic as it ascends or descends.

The place the Moon crosses the ecliptic is a node..

The Moon appears to move completely around the celestial sphere once in about 27.3 days as seen from the Earth. This is called a sidereal month.


While the moon is orbiting the Earth, the Earth is orbiting around the Sun. After completing a sidereal month the Moon must move a little further to reach the new position having the same angular distance from the Sun.

This longer period is called the synodic month.

As the Earth's orbit around the Sun is more egg shaped than circular, the time it takes for the Earth to travel around the Sun varies during the year. The average length of a synodic month is 29.530589 days (29 d 12 h 44 min 2.9 s).

The synodic month is used to calculate eclipse cycles.

Every sidereal month the moon moves eastwards from new moon to full, as it travels completely around the sky (360 degrees) in 27.3 days.

The moon moves eastward by 13.2 degrees each day.
The sun moves eastwards by about 1 degree per day).

The angle between the Earth, Sun and Moon (imagine Earth as the centre) changes over the month.

What this all means.

• The Moon rises and sets every day, like the Sun.
• The Sun always rises in the morning and sets in the evening.
• The Moon rises and sets at a different time each day.

There are a few days every month when the Moon is invisible because it is so close, on the celestial sphere, to the sun; either above it or below.

When the moon travels in front of the sun, we get a solar eclipse.

As the Moon travels Eastward away from the sun..it becomes visible.
3 days latter there is a thin crescent moon in the sky

The New moon rises in the morning, latter than the Sun, after the sun has risen. It follows the sun across the sky and sets after the sun has set.

A New Moon can only be seen in the evening.

As the days pass, the Moon  moves further left, and lags more and more behind the Sun. Soon the Moon is easy to see in the evenings, still above the western horizon after the Sun has set. It takes longer for it to disappear below the horizon.

Approximately a week after the moon was New it is now one-quarter of the way around its orbit (and half illuminated). The Moon is 90 degrees to the left of the Sun, and lags behind it as it rises, and sinks latter.

The Moon continues to grow and to lag further behind the sun, rising later each afternoon and setting later each night.

Eventually it becomes a Full Moon.

The Full Moon rises as the Sun is setting; it' is high in the south at midnight, and it sets  before Sun Set. 15 days after the invisible moon, the Full Moon is opposite to the Sun - 180 degrees away, and  something like twelve hours behind it.

Nineteen days after the invisible Moon, the Moon is shrinking. It now rises before the Sun and sets before it. The Moon rises late at night and sets in the afternoon.

Over the next few days, the Moon grows smaller and smaller until it is just a thin crescent that can only be seen at sunrise, coming over the horizon just before the Sun.

Then the Moon becomes too close to the Sun, and again, the Moon is invisible.