During its orbit around the Earth, the visibility of the Moon's illuminated part constantly changes.
Moon, moon phase, orbit of the Moon, orbiting of the Moon, new moon, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, lunar month, moon crescent, Earth, Sun, astronomy, geography
Lunar phases seen from Earth (Northern Hemisphere)
Sea of Showers
Sea of Cold
Sea of Serenity
Sea of Tranquility
Sea of Fertility
Sea of Crisis
Sea of Nectar
Sea of Clouds
Sea of Moisture
Sea of Cleverness
Sea of William Henry Smyth
Ocean of Storms
Highland region on the Moon's other side
The Moon is the fifth largest satellite in the Solar System. It orbits the Earth at a distance of 384 thousand kilometres. Its diameter is a quarter of the Earth’s. Its mass is only one eighty-first of that of the Earth. Therefore its gravity is weaker. Its surface warms up to 130⁰C during the day, but due to the strong heat radiation, it cools down to -160⁰C at night.
Its surface is composed mainly of volcanic rocks, covered by a thick layer of debris. We can see darker, lower-lying basins, so-called seas, and lighter, higher plateaus on the Moon. The basins, with the mountains and craters ringing them, were created by gigantic meteorite impacts. However, the volcanic rock layer and craters created by geological processes prove that there also used to be active volcanoes on the moon.
So far the Moon is the only celestial body apart from the Earth where man has ever set foot. US president John F. Kennedy announced on 25 May 1961 that during the course of that decade man would travel to the Moon and return safely back to Earth.
The first manned mission, Apollo 11, lifted off in July 1969, and on the 21st of July the first people to set foot on the Moon were Neil Armstrong and Buzz Aldrin. "That's one small step for man, one giant leap for mankind." These were the first words Armstrong spoke as he emerged from the lunar module.
Position of the Sun, the Moon and the Earth
the orbit of the Earth
orbital period: 365.25 days
average distance from the Sun: 149,600,000 km
The Earth orbits the Sun. While the Earth orbits around the Sun once, it rotates around its axis about 365.25 times. This time period is one year. The orbital velocity of the Earth is 30 km/s.
The tilt of the Earth’s axis is 23.5°. As a result, within one year the angle of incidence of sunlight changes at the same location, and this is the reason why seasons change. Our planet rotates (relative to the Sun) once every 24 hours. Due to the centrifugal force caused by the rotation, the planet is somewhat flattened.
The Earth’s only natural satellite is the Moon, which formed about 4.53 billion years ago. The Moon’s gravity creates tides, which keep the axis of rotation of the Earth at an almost constant angle and slow down the planet’s rotation slightly (the length of one day increases by 0.002 seconds every 100 years).
The Moon is the fifth largest satellite in the Solar System and the only natural satellite of the Earth. It orbits the Earth at a distance of 384 thousand kilometres. Its diameter is a quarter of the Earth’s. Its mass is only one eighty-first of that of the Earth. Therefore its gravity is weaker.
The Earth orbits the Sun. While the Earth orbits around the Sun once, it rotates around its axis about 365.25 times. This time period is one year. The tilt of the Earth’s axis is 23.5°. Our planet rotates (relative to the Sun) once every 24 hours.
While orbiting the Sun, the Earth and the Moon orbit their common centre of mass (located below the surface of the Earth). The Moon is in synchronous rotation around the Earth: its axial rotation and orbital period are the same; therefore, we always see the same side. Its orbital period is 27.32 days, while the lunar phase period (from full moon until the next full moon) is 29.53 days. This difference results from the Earth's orbiting around the Sun, that is, its movement relative to the Moon. So it takes more than two days for the Moon to look the same.
The visible shape of the Moon is constantly changing; this change is repeated every 29 and a half days (a lunar month). These shapes are called lunar phases.
When the Moon is between the Sun and the Earth, the Sun illuminates the side facing away from the Earth; therefore, the part that faces us is hardly visible. This phase is called the New Moon.
Then the crescent Moon starts to 'grow', its shape increasingly resembling the capital letter D. In about one week, it reaches the First Quarter, when the Sun and Moon are seen at a right angle from the Earth, so we can see the eastern half of the illuminated part.
The Moon continues growing, and in another week we can see a bright disc. This phase is called the Full Moon. At this time the Moon is on the opposite side of the Earth from the Sun, so the Sun illuminates the entire side of the Moon that faces the Earth.
Then, as the Moon orbits the Earth, its visible part decreases and it starts to look like the letter C. In one week, it enters the Last Quarter phase. The Sun and the Moon are seen again at a right angle, now on the other side of the orbit compared to the first quarter. The western side of the Moon looks bright. Then it continues decreasing and it becomes invisible in the sky.
The lunar phases (the New Moon, First Quarter, Full Moon and Last Quarter) return cyclically.