Space and Sky

The Sun contains roughly ninety-nine percent of all the mass in the solar system.

Light from the Sun takes about eight minutes to reach our planet.

Ocean tides are caused mainly by the Moon pulling on Earth's water.

The Moon always shows Earth the same face because its rotation matches its orbit.

Venus is hotter than Mercury because its thick atmosphere traps heat efficiently.

Mars appears red because iron oxide dust covers much of the rocky surface.

Jupiter is the largest planet in the solar system and outweighs all the others combined.

Saturn's rings are made mostly of countless chunks of ice and rock.

Venus spins so slowly that one day there lasts longer than its whole year.

Neptune was predicted by mathematics before anyone ever saw it through a telescope.

Comets grow visible tails only when they approach the Sun and begin to warm.

Meteoroids are small rocky bodies that become meteors when they enter an atmosphere.

The Milky Way is a barred spiral galaxy holding hundreds of billions of stars.

A light-year measures distance rather than time, despite the word year inside it.

Black holes bend light so strongly that nothing escapes past the event horizon.

Gravity is weaker on the Moon, where objects weigh about one sixth of their Earth weight.

Stars twinkle because Earth's turbulent atmosphere bends their light before it lands.

The North Star sits nearly above Earth's axis, making it a reliable navigation marker.

Constellations are human patterns, and their stars often lie wildly different distances away.

The Sun will eventually swell into a red giant and shed its outer layers.

Sunlight is produced when hydrogen nuclei fuse into helium deep in the solar core.

Mercury has almost no atmosphere, so its surface temperature swings between extremes.

Jupiter's Great Red Spot is a storm wider than Earth that has raged for centuries.

Pluto was reclassified as a dwarf planet after similar icy worlds were found beyond Neptune.

Earth orbits the Sun in a slightly elliptical path rather than a perfect circle.

Seasons happen because Earth's axis stays tilted as the planet travels around the Sun.

A total solar eclipse occurs when the Moon passes directly between Earth and the Sun.

The Moon's phases come from changing angles between the Moon, Earth, and the Sun.

Auroras appear when charged particles from the Sun strike gases high in our atmosphere.

Saturn is less dense than water, although no ocean could ever hold a planet.

Asteroids are rocky leftovers from the early solar system, mostly orbiting between Mars and Jupiter.

The Oort Cloud is a distant shell of icy bodies surrounding the whole solar system.

Space is silent because sound needs a material medium such as air to travel.

Astronauts in orbit float because they are continuously falling around the Earth.

Objects in low Earth orbit travel fast enough to circle the planet in about ninety minutes.

Spacecraft launched decades ago still return faint signals from far beyond the planets.

Rovers on Mars drive across the surface under instructions delayed by many minutes.

Telescopes in orbit avoid the blurring caused by Earth's atmosphere when observing galaxies.

The first artificial satellite reached orbit in 1957 and transmitted a simple radio signal.

Humans first walked on the Moon in 1969 during a brief burst of exploration.

The Sun rotates faster at its equator than at its poles because it is gaseous.

Neutron stars pack more mass than the Sun into a sphere the size of a city.

White dwarfs are slowly cooling remnants of stars that once resembled our Sun.

Galaxies are moving apart as the space between them continues to expand.

The Andromeda Galaxy is the nearest large spiral galaxy and is drifting toward the Milky Way.

Star colors reveal surface temperature, with bluish stars hotter than reddish ones.

The Sun's corona is far hotter than its visible surface, for reasons still debated.

Meteorites often come from asteroids, though a few originated on Mars or the Moon.

Starlight reaching Earth tonight left its star years or even centuries earlier.

Planets do not produce visible light of their own; they shine by reflecting sunlight.

Earth is the only planet known to hold liquid water across much of its surface.

The Moon has no atmosphere, so surface tracks there can remain for millions of years.