Planets, stars, and key concepts in astronomy
25 cards · science
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| Front | Back |
|---|---|
| Sun | G-type main-sequence star at the center of the solar system Contains ~99.8% of the solar system's mass; powered by hydrogen fusion. |
| Mercury | Smallest planet; closest to the Sun Airless world with extreme temperature swings; heavily cratered. |
| Venus | Hottest planet; dense CO2 atmosphere Runaway greenhouse effect raises surface to ~465°C; clouds of sulfuric acid. |
| Earth | Only known planet with life Liquid water oceans and a protective atmosphere enable habitability. |
| Moon | Earth's only natural satellite Tidally locked to Earth; the same side always faces us. |
| Mars | Terrestrial planet with a thin CO2 atmosphere Iron oxide gives it a red hue; hosts Olympus Mons, the largest volcano. |
| Jupiter | Largest planet; a gas giant Mass exceeds that of all other planets combined; Great Red Spot is a storm. |
| Saturn | Gas giant with prominent rings Rings are mostly ice; many moons orbit it. |
| Uranus | Ice giant with extreme axial tilt Axis tilted ~98°; likely knocked over by a past giant impact. |
| Neptune | Farthest planet; an ice giant Known for supersonic winds and transient dark spots. |
| Dwarf planet | Nearly round body orbiting the Sun that has not cleared its orbit IAU 2006 definition: in hydrostatic equilibrium but lacks orbital dominance. |
| Pluto | Dwarf planet in the Kuiper belt Reclassified in 2006; has a large moon, Charon, forming a binary-like pair. |
| Spiral galaxy | Disk galaxy with spiral arms and a central bulge Arms trace star formation; part of Hubble's tuning fork classification. |
| Barred spiral galaxy | Spiral galaxy with a central bar-shaped structure Bars can funnel gas inward; the Milky Way is barred. |
| Elliptical galaxy | Smooth, ellipsoidal galaxy with little gas or dust Dominated by older stars; shapes range from nearly round to elongated. |
| Irregular galaxy | Galaxy lacking a defined shape Often rich in gas and dust; forms and shapes influenced by interactions. |
| Nebula | Interstellar cloud of gas and dust; star-forming regions Includes emission, reflection, and dark nebulae. |
| Protostar | Young star before hydrogen fusion begins Forms by gravitational collapse within a molecular cloud core. |
| Main sequence | Stable hydrogen-fusing phase of a star's life Stars spend most of their lifetimes here; mass sets temperature and luminosity. |
| Red giant | Expanded, cool star after core hydrogen is exhausted Envelope swells while the core contracts and heats; helium fusion can follow. |
| White dwarf | Hot, dense remnant of a low-mass star Supported by electron degeneracy; radiates and cools over billions of years. |
| Supernova | Catastrophic explosion of a massive star or white dwarf Type II from core collapse; Type Ia from runaway fusion in a binary. |
| Light-year | Distance light travels in one year (~9.46 trillion km) A unit of distance, not time; about 63,240 astronomical units. |
| Astronomical unit | Average Earth–Sun distance (~149.6 million km) IAU-defined unit for solar system scales; exactly 149,597,870,700 m. |
| Redshift | Increase in wavelength as objects move away or space expands Key to measuring cosmic expansion via the Hubble–Lemaître law. |