The questions everyone asks

Who has been to the Moon?

Twelve people have walked on the Moon — all NASA astronauts on Apollo missions between 1969 and 1972. In total twenty-fo…

How many people have walked on the Moon?

Twelve people have walked on the Moon — all of them NASA astronauts, on six Apollo landings between 1969 and 1972.…

How many people are in space right now?

This page counts the people currently off the planet from the live crew record — the number below is current as of the m…

How far is the Moon from Earth?

The Moon is about 384,400 km (238,900 miles) from Earth on average — but the distance changes constantly, from roughly 3…

How long does it take to get to the Moon?

About three days for a crewed mission on a direct trajectory — that's how long Apollo took, and how long Artemis is plan…

How many planets are there in the Solar System?

Eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was reclassified as a dwarf planet in 20…

What is the closest planet to Earth?

Venus comes closest to Earth in its orbit — but averaged over time, Mercury is the planet nearest to Earth. Surprisingly…

How hot is the Sun?

The Sun's visible surface is about 5,500°C (9,940°F). Its core is far hotter — around 15 million°C — where nuclear fusio…

How cold is space?

Empty space far from any star sits at about 2.7 kelvin — roughly −270°C (−455°F), just a few degrees above absolute zero…

How old is the universe?

About 13.8 billion years, measured from the Big Bang — the best current figure from the Planck satellite's mapping of th…

Is Pluto a planet?

No — since 2006, Pluto has been classified as a dwarf planet, not a planet. It orbits the Sun and is round, but it hasn'…

What is the biggest planet in the Solar System?

Jupiter — about 143,000 km across, more than eleven Earths wide, and more massive than all the other planets combined.…

What is the hottest planet in the Solar System?

Venus — not Mercury. Its surface averages about 465°C (870°F), hot enough to melt lead, because a thick carbon-dioxide a…

Is there sound in space?

No — space is very nearly a vacuum, and sound needs a material like air or water to travel through. In empty space there…

Why do astronauts float in space?

Not because there's no gravity — there's plenty. Astronauts float because they're in continuous free fall: their spacecr…

What is a light-year?

A light-year is a distance, not a time — it's how far light travels in one year: about 9.46 trillion kilometres (5.88 tr…

How fast does light travel?

Light travels at about 299,792 kilometres per second (186,282 miles per second) in a vacuum — the fastest speed anything…

Why is the sky blue?

Because air scatters the Sun's blue light more than its red light. Sunlight hits the molecules in our atmosphere, and th…

What is a black hole?

A black hole is a region of space where gravity is so strong that nothing — not even light — can escape once it falls in…

How many stars are in the Milky Way?

Somewhere between 100 and 400 billion — the exact number isn't known, because most of the galaxy's stars are faint and h…

How many galaxies are there in the universe?

Estimates range from about 100 billion to as many as two trillion galaxies in the observable universe — and each holds a…

Can you see the Great Wall of China from space?

No — not with the naked eye. Despite the popular myth, astronauts have confirmed you can't pick out the Great Wall from …

What is the North Star?

The North Star is Polaris — the star that sits almost directly above Earth's North Pole, so it stays nearly fixed in the…

How big is the Sun?

The Sun is about 1.39 million kilometres across — roughly 109 Earths side by side — and holds 99.86% of all the mass in …

What were the Apollo missions?

Apollo was NASA's program to land humans on the Moon, running from 1961 to 1972. Eleven crewed Apollo missions flew, six…

What is the Deep Space Network? (How does NASA talk to spacecraft?)

The Deep Space Network is NASA's set of giant radio antennas — its tracking facilities — that communicate with and navig…