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Understanding Moon Phases

 moon phases

The moon goes through a cycle of phases each month which changes our view of the moon based on its position in relation to Earth and the sun. The moon phase shows the illuminated portion of the moon that is being lit by the Sun.

There are a total of eight moon phases: 

  1. New moon
  2. Waxing Crescent
  3. First quarter
  4. Waxing Gibbous
  5. Full moon
  6. Waning Gibbous
  7. Last (third) quarter moon
  8. Waning Crescent

Eight Moon Phases

A total of eight moon phases | Time and date

To find out what the current moon phase is from your location, you can use Today’s Moon Phase from Moon Giant. This will tell you the current moon cycle for today’s (tonight’s) date.

The Moon’s Orbit 

It may help to know a little about the moon’s orbit to understand what is happening during each of the moon phases.

It takes the moon the same amount of time to orbit the Earth as it does to complete a full rotation on its axis (i.e. approximately 27 Earth days). This orbit has been affected by the Earth’s gravitational pull which has helped to slow the moon’s orbit causing the moon and Earth to be synchronized. 

Due to this synchronization, we only ever see the ‘near side’ of the moon from Earth, which is only half of the lunar total surface. The amount of near side that is seen, depends on the amount of available sunlight.

full moon

The near side of the Moon as seen from Earth.

What causes the Moon Phases?

As mentioned above, the moon goes through a cycle of phases each month as it orbits Earth and each phase is dependent on the moon’s position in relation to the Sun.

The moon phase we see from Earth is the portion of the moon that is lit up by the Sun, which can range from zero-percent illuminated (new moon) to 100 percent illuminated (full moon).

Sunlight changes our view of the moon

Changes in moon phases as the Moon orbits Earth based on sunlight | McAuliffe-Shepard Discovery Centre

This means our view of the illuminated portion of the moon changes as the moon orbits around Earth, working its way through the different moon phases. 

For example, at the new moon phase, the moon is a complete shadow. As the moon continues to orbit Earth, the visible area grows (i.e. waxes) to a fully illuminated moon. The phases will then reverse where the visible area decreases (i.e. wanes). 

 

Moon Phases in Order 

As mentioned above, the moon cycles through eight phases.

New moon:

The moon is between Earth and the Sun, the moon shadow faces Earth.

  • Moon phase type: Primary
  • Percentage of Illumination: Zero percent
  • Description: We cannot see the moon

Waxing Crescent

  • Moon phase type: Intermediate
  • Percentage of Illumination: Zero to 50 percent
  • Description: a thin crescent of light on the right 

crescent moon

A waxing crescent moon with Earthshine visible. 

First-quarter:

Moon is at a right angle with respect to the Sun from Earth.

  • Moon phase type: Primary
  • Percentage of Illumination: 50 percent
  • Description: the right side is illuminated

Waxing Gibbous

  • Moon phase type: Intermediate
  • Percentage of Illumination: 50 to 100 percent
  • Description: halfway between a half-moon and a full moon (right side is illuminated)

Full moon:

The moon is on the opposite side of Earth from the Sun, the illuminated side faces Earth.

  • Moon phase type: Primary
  • Percentage of Illumination: 100 percent
  • Description: the entire moon is illuminated

Waning Gibbous

  • Moon phase type: Intermediate
  • Percentage of Illumination: 100 to 50 percent
  • Description: halfway between a half-moon and a full moon (left side is illuminated)

Last quarter moon:

The moon is at a right angle with respect to the Sun from Earth.

  • Moon phase type: Primary
  • Percentage of Illumination: 50 percent
  • Description: the left side is illuminated 

Waning Crescent

  • Moon phase type: Intermediate
  • Percentage of Illumination: 50 to zero percent
  • Description: a thin crescent of light on the left 

The above information is per the Northern Hemisphere. In the Southern Hemisphere, the opposite sides appear to wax or wane. 

The dates and times of these phases change each month given the amount of time it takes the Moon to orbit Earth (27 days) and the approximate time it takes to complete one cycle of phases (29.5 days), known as a synodic month. 

The intermediate phases last, on average, a quarter (i.e. 7.4 days) of the synodic month while the long duration between full moon to new moon (or vice versa) lasts approximately 15 days. 

New Moon and Astrophotography

If you are an astrophotographer, then always knowing the current moon phase is not new to you. A full moon can make astrophotography difficult as the moon reflects bright sunlight into the sky, washing out faint deep-sky objects.

It can also create less contrast and detail in the images you capture during a full moon. For these reasons, your best opportunity for astrophotography is on a clear night during the new moon. 

Backyard astrophotography setup

Moonlight lighting up my backyard during a full moon.

Astrophotography during a full moon is possible but you will need to makes some changes to your gear and the targets you shoot.

For example, selecting only bright objects away from the moon, choosing star clusters over nebulae, shooting narrowband Ha, and using light pollution filters. 

moonlight

A full moon shines brightly through a thin layer of clouds. 

Planets are much brighter than deep-sky objects like galaxies and nebulae. Large, bright planets (from our perspective on Earth) like Venus, Mars, Jupiter, and Saturn are relatively easy to photograph using modest equipment. 

The nights surrounding the full moon are a great time to photograph our solar system neighbors at high magnification. Here is a picture of the planet Jupiter captured with a bright (80% illuminated) moon nearby.

Jupiter astrophotography

Planetary astrophotography is unaffected by a bright moon.

You can use moonlight to help illuminate a nighttime landscape, creating an image that reveals stars and constellations, and a moonlit foreground below. A rising full moon presents a fantastic opportunity to capture the moon with interesting foreground details in front of it. 

The hauntingly beautiful colors of a full moon through Earth’s atmosphere make for a dramatic scene. The image below was captured from a farmer’s field as a “supermoon” rose in the fall. 

Supermoon

The full moon rises over a farmer’s field.

Related Post: How to Take Great Pictures of the Moon (with examples)

Moon Phase Calendar

There are many websites and mobile stargazing apps available today that will provide a moon phase calendar. So if you are interested in skipping the complicated mathematical formulae to determine the cycle, you may want to look at a few of these resources. There are a few listed below for reference. 

The Moon: Calendar Moon Phases (Apple/Android)

Features: moonrise, moonset, moon phases, lunar days, illumination, distance, and position. Includes bonus features.

The Moon App

My Moon Phase – Lunar Calendar (Apple/Android)

Features: view the moon cycle for any date, see how cloudy the sky is expected to be, the moon’s distance from Earth, receive notifications when the moon reaches a particular phase etc.

My Moon Phase App

Time and Date (Website) 

Features: graphic depiction of moon phase for your location, including dates for the next full moon and first-quarter phases. It also breaks down the moon phases for the year into the new moon, first quarter, full moon, and third quarter for your location and provides a separate graphic showing this information. 

Helpful Resources: