Astronomy & Space
Astronomy is the study of everything beyond Earth — planets, stars, galaxies, and the universe itself.
The Solar System
8 planets orbit the Sun: Mercury, Venus, Earth, Mars (inner rocky planets) | Jupiter, Saturn, Uranus, Neptune (outer gas/ice giants). The asteroid belt lies between Mars and Jupiter.
Stars & the Sun
The Sun is a medium-sized star — a giant ball of plasma powered by nuclear fusion (hydrogen → helium + energy). Star life cycle: nebula → main sequence → red giant → white dwarf (or supernova → neutron star/black hole for massive stars).
Galaxies
A galaxy is a massive system of stars, gas, and dust held by gravity. Our galaxy is the Milky Way — a spiral galaxy containing ~200–400 billion stars. Nearest large galaxy: Andromeda (~2.5 million light-years away).
Black Holes
A black hole forms when a massive star collapses. Its gravity is so strong that not even light can escape. The boundary is called the event horizon. At the center: the singularity.
Scale of the Universe
A light-year is the distance light travels in one year (~9.46 × 10¹⁵ m). The observable universe is ~93 billion light-years in diameter — a number too large to truly imagine.
FAQ
Is Pluto a planet? No — reclassified as a "dwarf planet" in 2006. It doesn't clear its orbital neighborhood.
Quick Quiz
Test what you just learned. Choose the best answer for each question.