Space and astronomy

60 to explore · page 2 of 2

• Watch What If? Lab What if we could travel at the speed of light? Light travels about 300,000 kilometers every second. At that speed you could reach the Moon in 1.3 seconds, but the nearest star after the Sun would still take more than four years. And physics says nothing with mass can ever quite reach light speed. Explore why.
• Watch What If? Lab What if we found life on another world? So far, the only life we know of is here on Earth. Scientists search for signs of life with rovers on Mars, spacecraft heading to icy moons and powerful telescopes. Find out how they look, why they test every clue so carefully, and imagine what a first discovery might be like.
• Watch What If? Lab What if we sent a message to the stars? Radio messages travel at the speed of light, about 300,000 kilometers every second. Even so, a hello to the nearest star beyond the Sun would take more than four years to arrive. Explore the real messages people have sent, from Voyager's golden records to the 1974 Arecibo message, and decide what you would say.
• Watch What If? Lab What if you could ride a comet? A comet's center is a dusty ball of ice a few kilometers across, racing around the Sun. In 2014, the European Space Agency's Philae lander touched down on comet 67P, and because the comet's gravity is so weak, it bounced! Imagine riding a comet, then see what a real spacecraft found.
• Watch What If? Lab What if you could see Earth from the Moon? From the Moon, Earth hangs in a pitch-black sky, glowing with blue oceans and white clouds. Like the Moon, it goes through phases: when we see a crescent Moon, Earth looks nearly full from the Moon. Discover Apollo 8's famous Earthrise, Earth's phases and the photos astronauts took of our blue planet.
• Watch What If? Lab What if you could see stars in the daytime? The stars don't go anywhere during the day. Sunlight scattered by our air makes the whole sky bright blue, and that glow hides the much fainter stars. Explore three ways the stars can show up in daytime: on the Moon, during a total solar eclipse, and in what happens to our sky.
• Watch Try it What If? Lab What if you could stand on Saturn? You could not really stand on Saturn: it is a ball of gas and liquid with no solid surface. But imagine floating at its cloud tops. Saturn has 95 times Earth's mass, yet in our model you would weigh only about 14 percent more than at home, because Saturn is so wide that its cloud tops are very far from its center.
• Watch What If? Lab What if you could walk on Jupiter’s cloud tops? Jupiter is so big that about 1,000 Earths could fit inside it, but it has no solid ground at all. Imagine standing on a platform at its cloud tops: you would feel more than twice as heavy, and you could watch a storm twice as wide as Earth.
• Watch Try it What If? Lab What if you jumped on the Moon? The Moon's gravity is only about one sixth as strong as Earth's. In our model, a jump that lifts a child about 29 centimeters on Earth carries them about 1.8 meters on the Moon, and they stay in the air for about 3 seconds instead of half a second.
• Watch Try it What If? Lab What if you tried to swing in space? A swing is a pendulum: gravity pulls the seat back down to the middle every time it rises. In our model, a swing with 2-meter ropes takes about 2.9 seconds to go there and back on Earth. Switch gravity off and the seat simply stays where you let it go.
• Watch Try it What If? Lab What if you used a parachute on Mars? A parachute works by pushing against air. Mars pulls more gently than Earth, but its air is extremely thin. In our model, a 10-kilogram box under a parachute lands at about 8 meters per second on Earth but about 18 on Mars, barely slower than with no parachute at all.
• Watch What If? Lab What if you visited an icy moon? Jupiter's moon Europa and Saturn's moon Enceladus are covered in ice, but scientists think salty oceans lie underneath. The squeezing pull of their giant planets keeps the insides warm. Imagine walking on the ice, peeking at the ocean below and joining the search for places where life could exist.