Astronomy & Space questions
94 fact-checked questions — tap any to predict the answer, then read why.
- Which gas escapes fastest from Earth's atmosphere as it slowly leaks to space?
- Why is Earth's day getting slightly longer every century?
- Why was Earth's day stuck at 19.5 hours for 1.5 billion years?
- Why might using several small reactors be better than one giant reactor on the Moon?
- Why is fission likelier than fusion for first Moon bases?
- Why put a lunar reactor away from the habitat?
- Why can a small reactor do jobs a radioisotope power source cannot?
- Why are Stirling or Brayton systems vital in Moon reactors?
- Why is removing waste heat such a big problem for Moon engineering?
- Why are reactors attractive near shadowed lunar craters?
- Why is solar-only power hard for a lunar base?
- Why does the Moon look huge near the horizon?
- Why can the Moon sometimes be seen in the daytime sky?
- Why won't April's 'Pink Moon' actually look pink?
- Why does Earth have a glowing sodium layer high above it?
- Why do some SpaceX launches have such narrow launch windows?
- After sunset on the ground, a rocket launch can create a giant glowing shape in the sky that looks like a jellyfish. What causes this phenomenon?
- Why does a spacecraft lose direct signal behind the Moon?
- Why do aurora forecasts improve closer to the event?
- Why might you still miss auroras after a good forecast?
- Why can the same Kp index, the 0-to-9 number that rates how disturbed Earth's magnetic field is, mean a good chance of seeing an aurora in one place and almost none in another?
- In aurora forecasts, what does a higher number on the Kp index—a 0–9 scale of geomagnetic disturbance—tell you?
- Why does magnetic-field direction matter in aurora forecasts?
- Why do aurora forecasters track solar-wind speed and density?
- Why can auroras peak a while after a solar eruption?
- Why doesn't every solar eruption bring bright auroras to Earth?
- Which solar events most often boost auroras?
- Why do aurora forecasters watch the Sun first?
- Why does Artemis II practice building a radiation shelter onboard?
- During Artemis II, NASA's crewed flight around the Moon, why do the astronauts narrate what they see out loud in real time?
- Why does Artemis II review lunar targets right before the flyby?
- Why does Artemis II test water, toilet, and CO2 systems so early?
- Why does Artemis II use a free-return path around the Moon?
- Why does Artemis II fly near its separated upper stage?
- Why does Artemis II stay in Earth orbit for about a day before heading to the Moon?
- Why can we see galaxies whose light has traveled for billions of years?
- Why do stars die?
- Why are there asteroid belts?
- Why does gravity bend light?
- Why do some stars have planets?
- Why is the solar system flat?
- Why are exoplanets hard to see?
- Why does the ISS orbit Earth?
- Why is the universe expanding?
- Why can't stars fuse iron?
- Why is Pluto's orbit so stretched and tilted compared with the planets' orbits?
- Why can a Sun-like star leave behind a white dwarf after shedding its outer layers?
- Why are some stars red and others blue?
- Why is a light-year a unit of distance rather than a unit of time?
- Why does the collapse of a massive star’s iron core produce a supernova explosion?
- Why does the sun have sunspots?
- Why do nebulae appear in different colors?
- Why do stars become red giants?
- Why are quasars so bright?
- Why is Neptune blue?
- Why are there time zones on Earth?
- How do spiral arms form in galaxies?
- Why is space cold if the sun is hot?
- Why do pulsars pulse?
- Why did Earth end up with one large moon instead of a swarm of small ones?
- How can a massive star form a stellar-mass black hole at the end of its life?
- Why can we see the Milky Way?
- Why is Venus hotter than Mercury?
- Why do planets stay in orbit?
- Why does the sun appear yellow?
- Why do meteor showers occur?
- Why does Jupiter have the Great Red Spot?
- Why don't satellites fall to Earth?
- Why do we always see the same moon face?
- Why are most stars invisible to the naked eye in a clear daytime sky?
- Why do planets appear to wander?
- Why can't we hear sounds in space?
- Why do astronauts float in space?
- Why does Saturn have rings?
- Why do black holes trap light?
- Why is Jupiter so big?
- Why do asteroids and meteors differ?
- Why is space dark even though there are so many bright stars?
- Why is Mars called the Red Planet?
- Why can we often see the Moon during the day?
- Why do we have seasons?
- Why do planets orbit the Sun?
- How do eclipses occur?
- Why does the Moon affect ocean tides?
- Why does a year have 365 days?
- Why do stars twinkle but planets don't?
- Why is the sunset colorful?
- Why does the Moon seem to change shape in the sky?
- Why do comets grow long tails as they approach the Sun?
- Why is Venus the hottest planet?
- Why can't we see stars during the day?
- Why don't we feel the Earth spinning?
- Why are there craters on the Moon?
- Why can we only see one side of the Moon?