MISSION THE MOON The moon is Earth's closest celestial companion Yet it is the only moon without a specific name This is because ancient astronomers didn't know other moons existed THE ORIGINAL CALENDAR For thousands of years the moon has been an important timekeeper As it orbits Earth different parts of the moon are visible Its cycle is the basis for our modern calendar Time can be marked by the moon's changing appearance A CLOSER LOOK Italian astronomer Galileo Galilei made the first scientific observations of the moon He studied it through one of the earliest telescopes Galileo saw that the moon's light and dark areas were really mountains and craters
Earth's The moon seen here from the International Space Station is Earth's nearest neighbor But it is still about 238 855 miles 384 400 km away HOUSTON WE HAVE LIFTOFF Today we know much more about our moon Astronauts and probes have studied it from every side Observing our moon is one way we can learn more about our universe
CHAPTER 1 ONE OF A KIND The moon is Earth's only natural satellite It is also the brightest object in the sky after the sun But the moon doesn't produce its own light Instead it reflects the sun's light Though the moon appears white its surface is gray The moon rotates around its axis just as Earth does One rotation of the moon takes about 27 days In that time the moon also completes one orbit around Earth As the moon travels its same side always faces Earth This is known as being tidally locked Earth's gravitational pull drags the moon into Earth's orbit But the moon has gravitational pull too While orbiting Earth the moon pulls Earth's water slightly toward it This creates ocean tides High and low tides occur as Earth spins and faces the moon at different angles
Our moon orbits Earth at a speed of 2 288 miles per hour 3 683 kmh The US spacecraft Galileo took this photo from 3 9 million miles 6 2 million km away
