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84 lessons · 8th Grade
Earth rotates on its axis once every 24 hours, causing day and night. The side facing the sun experiences day, while the opposite side experiences night.
Earth revolves around the sun once every 365.25 days, creating a year. The tilt of Earth's axis (23.5 degrees) causes the seasons as different hemispheres receive more direct sunlight.
The solar system has eight planets orbiting the sun. The four inner planets (Mercury, Venus, Earth, Mars) are rocky, and the four outer planets (Jupiter, Saturn, Uranus, Neptune) are gaseous.
The moon orbits Earth about once every 27 days. We see different moon phases (new, crescent, quarter, gibbous, full) because the sun illuminates different portions as it orbits.
Stars are massive balls of hot gas that produce light and heat through nuclear fusion. Our sun is a medium-sized star that provides the energy needed for life on Earth.
A solar eclipse occurs when the moon passes between Earth and the sun, blocking sunlight. A lunar eclipse occurs when Earth's shadow falls on the moon.
Constellations are patterns of stars that ancient cultures used for navigation and storytelling. The Big Dipper, Orion, and the Southern Cross are well-known constellations.
Galaxies are enormous collections of stars, gas, and dust held together by gravity. Our Milky Way galaxy contains hundreds of billions of stars and is a spiral galaxy.
Asteroids are rocky objects orbiting the sun, mostly found in the asteroid belt between Mars and Jupiter. Comets are icy objects that develop tails when they approach the sun.
Light from the sun takes about 8 minutes to reach Earth. A light-year is the distance light travels in one year—about 9.5 trillion kilometers.
Nebulae are clouds of gas and dust in space where new stars are born. When gravity causes a nebula to collapse, it heats up and nuclear fusion begins, forming a star.
The International Space Station orbits Earth about 400 kilometers above the surface. Astronauts conduct scientific experiments in microgravity conditions there.
Gravity keeps planets in orbit around the sun and moons in orbit around planets. The strength of gravity depends on mass and distance between objects.
Mars is called the Red Planet because iron oxide (rust) covers its surface. Scientists send rovers to Mars to search for evidence of past water and possible microbial life.
The sun goes through an 11-year cycle of activity. During solar maximum, more sunspots and solar flares occur, which can affect satellites and power grids on Earth.
