Jonti Horner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment. When we look out at the Solar System, we see objects of all sizes — from tiny grains of dust, to giant planets and the Sun.
A common theme among those objects is the big ones are more or less round, while the small ones are irregular. But why? The answer to why the bigger objects are round boils down to the influence of gravity. The bigger something is, the more massive it is, and the larger its gravitational pull.
For solid objects, that force is opposed by the strength of the object itself. As Everest gets taller, its weight increases to the point at which it begins to sink. Our next closest galaxy is the Andromeda Galaxy, which is about 2. The best estimate of the size of the observable universe given that it has been expanding for How fast are we traveling through space?? How fast does light travel? How far is it to space, the Moon, the Sun, the stars, etc?
How many stars are there? Nine crewed missions have flown to the Moon and back. The former Soviet Union logged the first successes with its Luna program, starting with Luna 1 in NASA followed with a series of robotic Ranger and Surveyor spacecraft that performed increasingly complex tasks that made it possible for the first human beings to walk on the Moon in Twenty-four humans have traveled from the Earth to the Moon.
Twelve walked on its surface. The last human visited the lunar surface in The Artemis program will send the first woman and the next man to the Moon and develop a sustainable human presence on the Moon and set the stage for further human exploration at Mars.
The program takes its name from the twin sister of Apollo and the goddess of the Moon in Greek mythology. Artemis 1 , formerly Exploration Mission-1, is the first in a series of increasingly complex missions that will enable human exploration of the Moon and Mars. During a lunar eclipse, Earth comes between the Sun and the Moon, blocking the sunlight from falling on the Moon.
There are two kinds of lunar eclipses:. During some stages of a lunar eclipse, the Moon can appear reddish. This is because the only remaining sunlight reaching the Moon at that point is from around the edges of the Earth, as seen from the Moon's surface. From there, an observer during an eclipse would see all Earth's sunrises and sunsets at once.
Our lunar neighbor has inspired stories since the first humans looked up at the sky and saw its gray, cratered surface. Some observers saw among the craters the shape of a person's face, so stories refer to a mysterious "man in the Moon.
And a year before astronauts walked on the Moon, " A Space Odyssey" told the story of astronauts on an outpost on the Moon. Decades later, it is still widely regarded as one of the best science fiction movies ever made. American astronauts have planted six American flags on the Moon. But that doesn't mean the United States has claimed it; in fact, an international law written in prevents any single nation from owning planets, stars, or any other natural objects in space.
Most of the planets in our solar system — and some asteroids — have moons. Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas.
Q: Why do pictures of Earth taken from the Moon show a black sky with no stars? Can the stars only be seen with an atmosphere? Amy Shira Teitel. Apollo Bouncing back from disaster. Michael Collins, Apollo 11 command module pilot, dies at What does Earth really look like?
Alan Shepard smacked golf balls on the Moon — and now we know where they landed. Cosmos: Origin and Fate of the Universe.
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