Supermoon!

Scientists think our moon formed about 4.5 billion years ago when a massive object roughly the size of Mars smashed into a young Earth. The collision flung fiery bits of rock into space. This debris clumped together into a giant ball of magma, or molten rock. Over millions of years, the magma cooled into a solid body, forming the moon we know today. It’s about 3,476 kilometers (2,160 miles) across—one-quarter the diameter of Earth.

Scientists think our moon formed about 4.5 billion years ago. A massive object smashed into a young Earth. The object was about the size of Mars. The crash threw fiery bits of rock into space. They clumped together into a giant ball of magma, or molten rock. Over millions of years, the magma cooled into a solid body. It formed the moon we know today. It’s about 3,476 kilometers (2,160 miles) across. That’s one-quarter the diameter of Earth.

“Supermoon” is not an official scientific term. But it does have a scientific explanation. The path that the moon follows as it orbits around Earth is not a perfect circle. It’s a slightly off-center oval. Because of this, the moon’s distance from Earth changes as it moves. The moon’s closest point, called its perigee, is about 360,000 km (224,000 mi) from Earth. “If we look at the moon near this closest point, it appears larger than it normally does,” says Kim Cone, a lunar scientist at the University of Rochester. Several times a year, perigee coincides with a full moon. That’s when you get a supermoon! It looks 17 percent bigger and 30 percent brighter than a full moon that occurs at apogee—the farthest point from Earth.

“Supermoon” is not an official scientific term. But it does have a scientific explanation. The moon orbits around Earth, but its path is not a perfect circle. It’s a slightly off-center oval. So the moon’s distance from Earth changes as it moves. The moon’s closest point is called its perigee. It’s about 360,000 kilometers (224,000 miles) from Earth. “If we look at the moon near this closest point, it appears larger than it normally does,” says Kim Cone. She’s a lunar scientist at the University of Rochester. Several times a year, a full moon occurs at perigee. The result is a supermoon! It looks 17 percent bigger and 30 percent brighter than a full moon at apogee. That’s the farthest point from Earth.

Every night, the moon looks a little different. Sometimes it’s a thin sliver. Other times, it’s round and full. Or it disappears completely! The moon isn’t shape-shifting—all that’s changing is our perspective.

Light from the sun is constantly shining on half of the moon. As the moon circles Earth, we see different portions of the side that’s illuminated. This creates the moon’s phases. It takes 29.5 days for the moon to orbit Earth. Each cycle starts with the new moon. During the first half of the cycle, the moon is waxing—appearing to grow wider. During the second half, the moon is waning—appearing to grow thinner.

Every night, the moon looks a little different. Sometimes it’s a thin sliver. It’s round and full at other times. Or it disappears completely! The moon isn’t shape-shifting. All that changes is our point of view.

Light from the sun always shines on half of the moon. As the moon circles Earth, we see different parts of its bright side. This creates the moon’s phases. The moon takes 29.5 days to orbit Earth. Each cycle starts with the new moon. During the first half of the cycle, the moon is waxing. It appears to grow wider. During the second half, the moon is waning. It appears to grow thinner.

In a typical year, there are 12 full moons—one per month. Each month’s full moon has a unique nickname. Many originate from early Native American tribes, who relied on the moon to track the passage of time. June’s Strawberry Moon marks the best time to gather strawberries in the Northeastern U.S. The Beaver Moon in November occurs when beavers finish preparing their homes for winter. “These labels have a lot of cultural significance,” says Cone. “They show the important role the moon has played in human history.”

The moon has other nicknames too. A Blood Moon describes the rusty hue of the full moon during a lunar eclipse—when Earth passes between the moon and the sun, blocking much of the sun’s light. Or in some years, there’s a 13th full moon. That’s called a Blue Moon!

Most years have 12 full moons, one per month. Each month’s full moon has its own nickname. Many come from early Native American tribes. They used the moon to track the passage of time. The Strawberry Moon is in June. It marks the best time to gather strawberries in the Northeastern U.S. The Beaver Moon occurs in November. That’s when beavers finish preparing their homes for winter. “These labels have a lot of cultural significance,” says Cone. “They show the important role the moon has played in human history.”

The moon has other nicknames too. A Blood Moon describes the full moon’s rusty color during a lunar eclipse. That happens when Earth passes between the moon and the sun. Earth blocks much of the sun’s light. And some years have a 13th full moon. That’s called a Blue Moon!

The moon’s dusty surface is pockmarked with thousands of craters from impacts with space rocks. The moon has no liquid water and almost no atmosphere. Without this protective layer of gases, temperatures swing from -184°C (-300°F) at night to 110°C (230°F) during the day. Twelve astronauts have visited the moon so far—and they needed protective spacesuits to survive these harsh conditions.

Thousands of craters cover the moon’s dusty surface. They came from impacts with space rocks. The moon has no liquid water and almost no atmosphere. Without this protective layer of gases, temperatures swing to extremes. They go from -184°C (-300°F) at night to 110°C (230°F) during the day. Twelve astronauts have visited the moon so far. They needed protective spacesuits to survive these harsh conditions.