School in a Book: Astronomy

Everyone loves space. Why? I don’t know. It just sort of blows our minds, I guess. The following will give you many of the main astronomical terms and ideas, but do also read The Fabric of the Cosmos by Brian Greene and Steven Hawking’s A Brief History of Time. There’s also a great memoir by Scott Kelly of living on the ISS for a year called Endurance, as well as many excellent space documentaries.

Basic Astronomy

Space: All of the area outside the earth’s atmosphere. Space has no air. Its temperatures vary from far below freezing (such as areas blocked by planets to the rays of stars) to far above boiling water (such as areas not blocked from the rays of stars).

Universe: All of the billions of galaxies in existence. The Universe is held together by gravity and, at the same time, slowly expanding. It is mostly empty space, with matter like stars and planets at distances from each other that are comparable to the distances of particles in atoms. This is why collisions are infrequent, despite the many and varied paths taken by celestial bodies.

Gravity: The force everywhere in the Universe that pulls every object towards every other object simultaneously. The greater the mass an object has, the greater gravitational force it exerts. Gravity is sometimes called the “weak force,” as opposed to stronger forces that hold particles together.

Star: A ball of very hot gas in space. Stars can be white, red, yellow or blue.

Sun: The only star in Earth’s solar system. It is medium-sized: one million times the size of Earth and ten times the size of Jupiter. On its surface, the sun is 5,500 degrees.

Planet: A spinning ball of rock or gas that travels around a star (or a black hole) in an orbit. We can only see a few planets outside our solar system.

Moon: A mini planet that revolves around a regular planet instead of revolving around a star. The earth’s moon is dry and dusty with many craters. It takes 27 days for the moon to spin once, and 27 days for it to orbit once around the earth, which is why it doesn’t seem to be spinning. It is always facing away from us, so we’ve never seen the other side. People have gone to the moon several times. It takes about three days to reach the moon and each crew spent about three days there.

Phases of the moon: The views of the earth’s moon from the earth, which change in a 29.5-day cycle. The nine phases are: new moon (no light); waxing crescent moon (getting more visible and in a crescent shape); first quarter moon (half moon); waxing gibbous (getting more visible and in a lopsided circle shape); full moon; waning gibbous (getting less visible); last quarter moon (half moon); waning crescent; new moon.

Solar system: A group of planets revolving around a single star or a group of stars, or a small group of stars revolving around each other.

Sol: The name of our solar system. It orbits the center of our galaxy, the Milky Way.

Galaxy: A group of solar systems which orbit around each other. Many galaxies contain millions of stars. Sometimes galaxies cross paths and collide. It’s likely that most or all galaxies have a black hole at their center. Many galaxies orbit other galaxies, but not all. It is difficult to determine what galaxies orbit, if anything, due to the slowness of their movement and limitations of technology.

Milky Way: The name of the galaxy our solar system is in. It is about 100,000 light years across. It contains one star, eight planets, many moons, and an asteroid belt. The Milky Way doesn’t orbit anything, but other galaxies orbit it and Andromeda, the closest neighboring galaxy.

Andromeda: The nearest large galaxy to the Milky Way

Star cluster: Groups of stars that form together

Galaxy cluster: A group of galaxies

The Local Cluster: The galaxy cluster our galaxy is in

Supercluster: A group of galaxy clusters

Virgo Supercluster: The supercluster our galaxy is in

Orbit: The circular path taken by a planet, moon, star or other celestial body. Orbits can be maintained indefinitely because the gravity that pulls the orbiting object toward another object is balanced by the orbiting object’s momentum, which seeks to keep the orbiting object moving in a straight line. In empty space, friction, drag and other forces do not exist, so the object’s momentum is never lost.

One day: The unit of time marking one spin of the earth on its axis, which takes approximately 24 Earth hours. The part of the earth facing the sun has light, and the other doesn’t. It takes 365 days for the earth to orbit around the sun one time.

The Big Bang: The (theoretical) explosion that created the universe. This explosion may have happened approximately 15 billion years ago. It occurred when all energy and all matter in existence somehow gathered into a tiny speck with virtually no empty space between particles, then, under this enormous pressure, suddenly exploded and became randomly distributed in space. As the matter cooled, gravity caused larger bits to attract smaller bits and form large stars and planets.

Comet: A ball of dirty ice floating around space. When close enough to the sun, the ice melts partway and the solar wind blows a trail of gas and dust behind it, making a tail.

Asteroid: A big lump of rock or metal in space

Meteoroid: Dust or small space rocks (house-sized to coffee-ground sized) in orbit around the sun

Meteor/shooting star: A meteoroid that burns up in a planet’s atmosphere

Meteorite: A meteoroid that hits the surface of a planet

Rocket: An engine that burns fuel to achieve thrust and lift a spacecraft

Astronaut: Someone who goes to space to work. (Russian astronauts are called cosmonauts.) Astronauts learn to fly and land the space shuttle, fix parts of the space station or satellites, do scientific experiments and more. Some of their training is done underwater to simulate space conditions.

Space shuttle: A rocket-powered spacecraft that brings astronauts and supplies to the ISS and other satellites, then returns to Earth as an airplane. Booster rockets and fuel tanks fall off after they’re used. The crew compartment, located at the top of the shuttle, holds the flight deck and other areas for working and sleeping.

Hubble Space Telescope: A big telescope with a camera that orbits the earth and takes clear photos of deep space from outside our atmosphere. It is powered by solar panels.

Flight simulator: A replica of the inside of a spacecraft or airplane that allows astronauts to practice flying the aircraft

Space walk: A trip taken by an astronaut outside the space station or space shuttle, into empty space, to check or repair equipment. A strong spacesuit regulates the astronaut’s temperature and carries air.

International Space Station (ISS): The series of connected rooms, compartments and solar panels in space where astronauts live and work. It is located 230 miles above Earth. On the station, all water (including pee) is recycled. Many scientific experiments are conducted there.

Satellite: Any object in space that orbits a planet or the sun other than planets and moons. These include asteroids as well as man-made satellites that investigate space and carry radio signals around Earth.

Space probe: A robot that explores other planets and moons. Some space probes even leave our solar system and carry information about Earth, looking for other life forms.

Space tourism: Trips to space taken by non-astronauts for personal (not scientific) purposes. Space hotels, space bases on Mars and a space elevator have been proposed.

Our eight planets, in order from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Gas giants: Jupiter, Saturn, Uranus, Neptune. Rest are rock. Jupiter is largest, Mercury is smallest. Juiter has the Great Red Spot, a permanent gas storm. Saturn is very light, light enough to float in water.

Light year: The distance light travels in one year. It is used as a measurement of distances in space.

Solar mass: The mass of our sun. It is used as a standard unit of measurement of space bodies.

Nebula: Big cloud of gas and dust that stars are formed in

Supernova: A very large star that has reached the end of its life (and its supply of gas) and is exploding

Red Giant: A smaller or medium-sized star that is near the end of its life and has swelled up and turned red

White dwarf: A star that results from the Red Giant’s exterior gas burning off. After a time, it cools and fades away.

Black hole: An invisible, very dense ball of matter and energy with gravity so strong even light can’t escape it. Some are the remains of very large stars that, instead of dying, collapsed. Some black holes are only a few miles across, while others are several million miles across. Black holes continuously draw in more matter and expand due to their huge gravitational force.

Event horizon: The boundary of the region of a black hole from which no escape is possible

Pulsar: A collapsing star that instead of becoming a black hole keeps spinning faster and faster and getting denser as it collapses. It gives off waves (pulses) of electrons.

Solar wind: The stream of charged particles in the form of plasma that make the air glow at Earth’s magnetic poles, creating the aurora borealis (the Northern Lights).

Solar eclipse: A celestial event during which the sun is entirely obscured from view for a short time due to the path of the moon, which brings it between Earth and the sun

Lunar eclipse: A celestial event during which the moon is entirely obscured from view for a short time due to the path of the Earth, which brings it between the moon and the sun. At that time, the moon sits in the Earth’s shadow and no light from the sun illuminates it.


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