Earth & space science · ages 10–16
Bluekite is a free place to explore the planets, the Moon and the big ideas that explain them — seasons, gravity, light-years and more. Short, clear and checked for accuracy, so you can learn something real in ten minutes.
Explore the solar system
Starting closest to the Sun and moving outwards. Tap More facts on any planet to see its size, the length of its year and how long sunlight takes to reach it.
Planet 1
Rocky planet
With almost no atmosphere to hold heat, Mercury swings from about 430 °C in the day to about −180 °C at night.
One Mercury day (sunrise to sunrise) lasts exactly two of its 88-day years.
Planet 2
Rocky planet
The hottest planet. Thick carbon dioxide clouds trap heat, so its surface is about 465 °C — hotter than Mercury.
Venus spins backwards compared with most planets, so the Sun rises in the west. One full spin takes 243 Earth days — longer than its year.
Planet 3
Rocky planet
The only world we know of with liquid water oceans on its surface — and the only one known to have life.
Earth's axis is tilted by about 23.5°. That tilt, not our distance from the Sun, is what gives us seasons.
Planet 4
Rocky planet
Home to Olympus Mons, the largest volcano in the solar system — roughly 2.5 times the height of Mount Everest.
Mars looks red because its dust contains iron oxide — rust. Its two small moons are called Phobos and Deimos.
Planet 5
Gas giant
Its Great Red Spot is a storm wider than the whole Earth, and astronomers have watched it for more than 150 years.
Jupiter has more than twice the mass of all the other planets put together.
Planet 6
Gas giant
Saturn is so light for its size that, on average, it is less dense than water.
Its rings are made mostly of chunks of ice, from tiny grains to boulders bigger than a house.
Planet 7
Ice giant
Uranus is tipped over by about 98°, so it seems to roll around the Sun on its side.
Because of that tilt, each pole gets around 42 years of sunlight followed by around 42 years of darkness.
Planet 8
Ice giant
Neptune has the fastest winds in the solar system — up to about 2,000 km/h.
Neptune was the first planet found using maths: astronomers predicted where it should be, then spotted it in 1846.
Distances are averages. “Length of day” means sunrise to sunrise. Moon counts are as of 2025 — astronomers keep discovering small moons around the giant planets. Planets are not drawn to scale.
Moon phases explained
The Sun always lights the half of the Moon facing it. As the Moon travels around Earth, we see more or less of that sunlit half. One full cycle, from new moon back to new moon, takes about 29.5 days.
Short lessons
Each lesson explains one idea in plain words, with a quick experiment you can try at home or in class.
Earth's axis is tilted by about 23.5°. As Earth travels around the Sun, first one hemisphere and then the other leans towards the Sun, getting more direct sunlight and longer days — that's summer. It isn't about distance: Earth is actually closest to the Sun in early January, during northern winter.
Try it: shine a torch straight down on paper, then at a slant. Which patch of light is brighter?
Imagine throwing a ball so fast that, as it falls, the ground curves away beneath it just as quickly. That's an orbit: the Moon and planets are always falling, but their sideways speed means they never hit what they're orbiting. Isaac Newton explained this with a thought experiment about a cannon on a very tall mountain.
Try it: swing a soft ball on a string in a circle. The string plays the part of gravity.
A light-year is a distance, not a time: how far light travels in one year, about 9.46 trillion km. Light is the fastest thing there is, yet it still takes over four years to reach us from Proxima Centauri, the nearest star after the Sun. When you look at the stars, you are seeing light that left them long ago.
Try it: sunlight takes about 8 minutes to reach Earth. How far away is the Sun in “light-minutes”?
The Sun always lights half of the Moon. As the Moon orbits Earth, we see different amounts of that lit half — none at new moon, all of it at full moon. The whole cycle takes about 29.5 days, and it has nothing to do with Earth's shadow.
Try it: in a dark room, hold a ball at arm's length near a lamp and turn slowly on the spot.
Mars's surface is covered in dust and rocks rich in iron oxide — the same compound that makes rust. Fine dust blown high into its thin atmosphere gives the daytime sky a butterscotch colour. Strangely, sunsets on Mars look bluish.
Try it: leave a steel wool pad damp for a few days (with an adult's help) and watch it turn reddish-brown.
The Moon's gravity pulls on Earth's oceans, raising a bulge of water on the side facing the Moon and another on the opposite side. As Earth spins through these bulges, most coasts get two high tides roughly every 24 hours and 50 minutes. At new and full moon, the Sun's pull lines up with the Moon's, giving extra-large “spring tides”.
Try it: check a local tide table and see how high tide moves about 50 minutes later each day.
Quick quiz
Everything you need is on this page. Your answers are checked right here in your browser — nothing is saved or sent anywhere.
Glossary
Space science has its own vocabulary. Here are the terms used on this site, in plain language.
No matching words. Try a shorter search, or suggest a new term.
For teachers
Bluekite has no accounts, no adverts and no tracking, so you can share the link with a class without collecting anyone's data. Use it on a projector, on student devices or on paper.
Print a clean, ink-friendly version of a section — perfect for handouts, display boards or homework.
Opens your browser's print dialog. Choose “Save as PDF” to keep a digital copy.
Contact
We check every fact on Bluekite, but science keeps moving. If you spot something out of date, have a question, or want a topic covered, let us know.
If you're under 13, please ask a parent, carer or teacher before sending us your email address. You don't need to tell us your full name.
Or email us: hello@bluekite.space