Moon in Motion - Phases of Moon

The Sun continuously illuminates half of the Moon, meanwhile, the other half remains dark. When we think about the way the Moon seems to vary over the course of a month, we expect phases. However, frequent Moon observers know that the Moon also appears to twist, nod, and roll slightly throughout its journey across the sky. Why does the Moon seem to change its shape every night? In this article, we will be discussing the phases and shape of the Moon, and how it occurs as the Moon revolves around the Earth.

Phases of Moon

Different Phases of Moon

When we observe from the Earth, we can notice the series of transformations within the shape of the Moon day by day. That's what we call the phases of the Moon. There are a total of 8 Moon phases, which include, in order, new Moon, waxing crescent, half-Moon, waxing gibbous, full Moon, waning gibbous, third quarter, and waning crescent. This cycle repeats once a month. Let’s go through the individual phases of the Moon one by one to understand its movement.

1. New Moon

In this phase, the Moon is invisible from the Earth. Since the illuminated half of the Moon faces the Sun and its darker side faces the Earth, during this phase, the Moon rises and sets with the Sun. This is because it is on the same part of the sky. During this phase, the Moon does not pass directly between the Sun and the Earth.

New Moon

2. Waxing Crescent

This phase happens when half of the illuminated part of the Moon faces virtually away from the Earth. Only a small part would be observed from the surface of the Earth. From here onwards, the view becomes additional clear as its orbit carries the visible half into the view.

Waxing Crescent

3. First Quarter

In this phase, the Moon is a quarter of the way through its journey. We can see half of its illuminated side. We often call this phase the half Moon. However, it is just a slice of the whole Moon, that is, half the visible part. It appears around noon and sets during midnight. It provides an amazing view in the evening.

First Quarter

4. Waxing Gibbous

In this phase, most of the Moon’s visible part is out there to view from the surface of the Earth. The Moon will be brighter in the sky.

Waxing Gibbous

5. Full Moon

This phase is the most stunning one. This can be observed when we come nearer to the Sun’s illumination of the day side of the Moon, completely. We call this a full phase of the Moon. However, technically, we are viewing the actual half of the Moon. On this day, we can observe the entire half of the day side of the Moon that rises during sunset and sets when the Sun rises. This phase can exist for a couple of days before it gets into its next phase.

Full Moon

6. Waning Gibbous

In this phase, the Moon starts its journey back to the Sun, which means the opposite side of the Moon reflects the light. The visible part begins to shrink. The orbit of the Moon moves away from the viewer, which implies that the Moon is away from our Earth. Because of this, the Moon rises later and later each night. That’s why sometimes we can’t see the Moon at the same time we used to observe.

Waning Gibbous

7. Last Quarter

Again, in this phase, only half of the Moon is illuminated; the part that is visible from the Earth. But in reality, as mentioned before, we get to observe only half of the half part of the Moon. Just a piece of a slice! This phase is the last quarter Moon, also known as a third-quarter Moon, which rises around midnight and sets around noon. Because of daylight, we can’t observe it much. But sometimes we might have noticed the presence of the Moon during the daytime.

Last Quarter

8. Waning Crescent

In this phase, the Moon is nearly back to the point in its orbit where the dayside is almost facing the Sun and what we can observe from the Earth is just the thin curve of the Moon.

Waning Crescent

Earth Shine: A View to the Darker Part

We might have seen this darker part of the Moon. When the Moon is in one of the crescent phases, we can see this dark part of the Moon, which shines dimly. This phenomenon is caused by the Sun’s light which reflects off the Earth’s surface onto the face of the Moon. At this point Earth’s orbit is almost full from the Moon's side, the light it reflects is what we called earthshine, which is capable of illuminating the darker side of the Moon. It is very beautiful to observe.

Earthshine

Daytime Moons

This should be experienced by most people. During the daytime, we might have seen this faint presence of the Moon. The best time to look at this Moon is during the primary and last quarter phases. When the Moon is high enough on top of the horizon, the light from the Sun is brightly reflected off the Moon. The Moon is observed in the daylight except during its full Moon phase because it is below the horizon during the day.

Lunar Eclipse

Anywhere between four to seven times a year, our Earth, Moon, and Sun line up just right to form the cosmic-scale shadow, known as an eclipse. The Moon’s orbit around the Earth is tilted. This tilt is the reason why we've occasional eclipses rather than monthly eclipses.

There are 2 types of eclipses: lunar and solar. Lunar eclipses occur during the full Moon phase. Once the Earth is positioned exactly between the Moon and Sun, Earth’s shadow falls upon the surface of the Moon, dimming it and typically turning the lunar surface a striking red over a few hours.

Summary

Since the Moon's orbit isn't perfectly circular, its distance from Earth and its speed in orbit both change slightly throughout the month. The primary phases are the new Moon, first quarter, full Moon, and last quarter. The secondary phases are waxing crescent, waxing gibbous, waning crescent, and waning gibbous. The term waxing refers to the growth of the Moon's image, whereas the term waning refers to a shrinking image. We hope you have learnt something new about the Moon today! Visit our website to learn more about such phenomena.