Astronomy Facts
107 flashcards by MentisLibrary
The solar system, planets and moons, stars and their remnants, galaxies, cosmology and practical observing, with the figure behind each answer and the misconception it corrects.
- What is the Sun?
- A main sequence star of spectral type G2V at the center of the solar system, holding about 99.8 percent of the system's mass.
- What is a black hole?
- A region where gravity is so strong that nothing, not even light, can escape from inside its boundary.
- What is a nebula?
- A cloud of gas and dust in space, which may be a nursery for new stars or the debris of a dying one.
- What is a supernova?
- The explosion of a star, either a massive star whose core collapses or a white dwarf pushed past its mass limit.
- What is a constellation?
- An officially defined region of the sky, each containing a traditional pattern of stars.
- What is an asteroid?
- A rocky or metallic body left over from planet formation, most of them orbiting between Mars and Jupiter.
- What is a comet?
- A body of ice, dust and rock that grows a glowing coma and a tail when solar heating turns its ice straight into gas.
- What is a solar eclipse?
- The Moon passing between the Sun and Earth and casting its shadow on the surface.
- What is a lunar eclipse?
- Earth passing between the Sun and the Moon, so the Moon moves into Earth's shadow.
- What is dark matter?
- Matter that emits no light but reveals itself by gravity, holding galaxies together and bending light that passes them.
- What is a dwarf planet?
- A body that orbits the Sun and is round under its own gravity but has not cleared other objects out of its orbital path.
- What powers the Sun?
- Nuclear fusion in the core, where hydrogen nuclei fuse into helium and a small fraction of the mass is released as energy.
- How old is the solar system?
- About 4.6 billion years, dated from the oldest solid grains found in meteorites.
- What is an astronomical unit?
- The average distance from Earth to the Sun, the standard yardstick for distances inside the solar system.
- What is the solar wind?
- A continuous stream of charged particles, mostly protons and electrons, flowing outward from the Sun's corona.
- What is a sunspot?
- A cooler, darker patch on the Sun's surface where intense magnetic fields suppress the flow of heat from below.
- What is the Sun's corona?
- The Sun's outer atmosphere, a faint halo of plasma visible to the eye only during a total solar eclipse.
- What is the solar cycle?
- The roughly eleven year rise and fall in the Sun's magnetic activity, tracked by counting sunspots.
- What is the ecliptic?
- The plane of Earth's orbit around the Sun, and therefore the line the Sun traces through the constellations over a year.
- What is the heliosphere?
- The bubble of space carved out by the solar wind, inside which the Sun's particles and magnetic field dominate over interstellar space.
- Name the eight planets in order from the Sun.
- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- Why is Venus hotter than Mercury?
- A runaway greenhouse effect. Venus has a thick carbon dioxide atmosphere that traps heat, while Mercury has almost no atmosphere at all.
- What is the Great Red Spot?
- A giant high pressure storm in Jupiter's southern hemisphere, watched continuously since about 1830 and probably far older.
- Which planet has the largest volcano?
- Mars, with Olympus Mons, the tallest volcano known anywhere in the solar system.
- Why is Mars red?
- Its surface dust is rich in iron oxide, the same compound as rust.
- What are Saturn's rings made of?
- Countless particles of nearly pure water ice, from dust grains to boulders, orbiting in a disc that is extraordinarily thin.
- Which planet rotates on its side?
- Uranus, whose axis is tilted about 98 degrees from its orbital plane, most likely after a giant collision.
- Which planet has the fastest winds?
- Neptune, where wind speeds around 2000 km per hour have been measured.
- Why is Pluto no longer counted as a planet?
- In 2006 the IAU required a planet to have cleared its orbital neighborhood, and Pluto shares its region with many other Kuiper Belt objects.
- Which planet has the shortest day?
- Jupiter, which turns once in just under ten hours despite being the largest planet.