Skywise Unlimited

Astronomy 101

This section contains a series of short essays that may answer questions you have about some of the fundamental concepts in astronomy. Although you will find more extensive treatment by using on-line encyclopedias or search engines, browsing these pages will give you a basic introduction to the topics.

Analemma
Ever notice on globes of the Earth there is a figure 8 printed in the middle of one of the oceans?
Asteroids
The majority are between the orbits of Mars and Jupiter. This region is known as the Asteroid Belt.
Aurora
Auroral activity strongly correlates with solar activity. Peak activity repeats on an 11-year cycle.
Big Bang
The explanation is widely accepted today. It was critics of the interpretation who coined the name.
Black Holes
A region of space where the force of gravity is so intense that not even light can escape.
Bode Titius
Bode and Titius, reported a numerical sequence into which the sizes of the planetary orbits fit.
Brightest Stars
A list of the 20 brightest stars in the sky, with names, magnitudes, distances, etc.
Comets
Big dirty snowballs made of ice, dust and bits of rock, and are about the size of cities and towns.
Constellations
The sky is divided into 88 parts. They are sometimes grouped into 8 distinct families or groups.
Coordinates
Two primary ways to describe a position in the sky. The Horizon System, and the Equatorial System.
Cosmology Glossary
Terms used in cosmology, which is the study of the beginning and the evolution of the Universe.
Cruithne
An asteroid with a bizarre orbit. It appears to make a series of bean shapes which form a horsehoe.
Dark Matter
Astronomers estimate that most matter is of some form that is impossible to detect directly.
Eclipses
Alignments of the Sun, Moon, and Earth, resulting in dramatic large scale shadow play.
Galaxies
Collections of stars, dust and gas, and other matter. Containing between millions and trillions of stars.
Historical Figures
The giants of astronomy over the last 2000 years have guided and shaped our view of the cosmos.
HR Diagram
The "Rosetta Stone" of stellar astronomy. It plots a star's luminosity against its surface temperature.
Hubble's Law
The motion of the galaxies in the Universe appears to be a smooth recession away from each other.
Intelligent Life
Is anybody out there? Why would they come all that way to make circles in our crops?
Kepler's Laws
Kepler is remembered for "cracking the code" that describes the orbits of the planets.
Leap Year Rules
Years perfectly divisible by four, except years which are both divisible by 100 and not divisible by 400.
Light Waves
Light radiates from a source in waves. Each wave has two parts; an electric part, and a magnetic part.
Lunar Libration
Over time we can see more than 50% of the Moon's surface from Earth due to a combination of effects.
Messier Objects
The french astronomer cataloged deepsky objects. Considered showpieces for deepsky enthusiasts.
Meteors
Sometimes called "shooting stars," most are bits of gravel the size of your fingernails or smaller.
Milky Way
Billions of stars too far away to pick out individually but together they add up to a haze across the sky.
Moon
A detailed Moon map, moon facts, lunar formation theories, and an audio clip of the first landing.
Moon Phases
As the Moon orbits we see varying combinations of the lighted and the dark parts of the surface.
Planets
Large bodies of mass that orbit around a star, like several that reside in our own solar system.
Precession
The position of the Sun on the vernal equinox is slowing shifting westward across the sky.
Rainbows
There are a variety of optical effects possible when light shines onto moisture in the atmosphere.
Redshift
A light source spectrum is seen as blueshifted as it approaches, and redshifted as it moves away.
Seasons
The tilt of Earth's axis relative to its orbit, not differences in the distance to the Sun.
Stardust
Dust is a relative newcomer to the Universe. It joined gases after some of the first stars exploded.
Stellar Evolution
Stars begin as offspring of a cloud up to 300 light-years across. Such a cloud is known as a nebula.
Sun & Fusion
The Sun has layers with different properties, about 75% hydrogen and 25% helium.
Telescopes
The size and quality of the objective element is the most important consideration. Bigger is better.
Tides
Why are there two high tides and low tides every day, the Moon passes overhead once per day?
Time of Day
Universal Time, time zones, daylight savings time, sidereal time, Julian Day numbers, and more.
Twilight
Three types; civil, nautical, and astronomical, are defined by the position of the Sun.
Zodiac
The circle of animals along the ecliptic, the path described by the Sun during the course of a year.