Discover: Phases of the Moon

Our Moon

The moon has been studied for many years for its beauty and predictable changes in our night sky. Sometimes, we see the Moon as a sliver or a half-circle. Sometimes, the Moon is completely round, and sometimes we cannot see it at all. Depending on where the Moon and the Sun are, shadows on the Moon make it look different. Every month, the Moon passes through a cycle of changes called phases of the Moon.

Remember from previous activities in this unit that the Moon does not give light of its own, but it reflects light from the Sun. The part of the Moon that we see from Earth depends on how much light from the Sun is reflected on the Moon. As the position of the Moon changes, what we see on Earth changes. The Earth orbits around the Sun, but the Moon is our natural satellite. It revolves or orbits around the Earth. In fact, we always see the same side of the Moon because the Moon rotates (spins) at the same rate that it orbits the Earth. This causes one side of the Moon to always face towards Earth. This is called the Near Side. We cannot see the “back” of Far Side of the Moon from Earth.

The Moon takes about 29 days to complete one cycle around the Earth. Did you know the Moon orbits the Earth counter clockwise from west to east?

Some of the earliest calendars were based on this predictable pattern of moon phases as the basis for a “month”. Did you know the word "month" means "of the moon"?

Tides and the Moon 

Did you know that the Moon's gravitational pull is responsible for the ocean's tides?

The Moon's gravitational pull causes ocean water to 'bulge.' As the Moon orbits our planet and as the Earth rotates, the bulge also moves. This bulging is known as high tide. When the Moon is close to the Earth, its strong force leads to high tides. When it is further away from the Earth, the Moon’s gravitational force causes lower tides.

Different phases of the Moon are connected with different sizes of tides. When the Sun lines up with the Moon and the Earth, such as during a New Moon or Full Moon, the tides are larger. The water "springs" higher than normal so the tide is called "spring tide". On the other hand, if the Sun and the Moon are 90 degrees apart such as during the First Quarter Moon or Third Quarter Moon, then tides are smaller than normal. This is because the Sun's gravitational force cancels some of the effects of the Moon's pull. This is called a neap tide.

  Check Your Answers

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Eclipses 

Some cloudless nights, the moon is not visible at all! Such nights might be quite dark because only the stars are giving light. The Moon might not be visible because the Sun, the Earth and the Moon are aligned in a certain way called an eclipse. An eclipse is a special occasion that happens 4-7 times a year and can only be seen from certain places on Earth.




Never look directly at the sun during a solar eclipse. Although it seems dark, there is still light energy from the Sun’s corona that can damage eyes.  

  History Connection

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Have you heard someone say that something unusual happens “once in a blue moon”?

Normally, twelve full moons occur in a year, but occasionally a second full moon occurs in a calendar month. This second full moon has been called a “blue moon” since 1932 when the Maine Farmer’s Almanac called it that!

Visit the Moon Giant website to read more about blue moons. It answers questions such as why there is a second full moon in one month, how often they occur, when the next one is, and many more.