An instrument used during the Middle Ages to find direction, make calculations in spherical trigonometry and tell the time. It was first described by Ptolemy in 125 CE. The Arabs developed and popularized the astrolabe. Its mature form consisted of a star map in a brass filigree known as a rete, or network. The rete rotated above a zonal climate plate that was engraved with circles representing astronomical coordinate lines appropriate for a particular latitude. One could simulate the rotation of the stars by turning the rete. Abraham Zacuto 1452-1515 a Jew who was Court Astronomer to Kings John II and Manuel I of Portugal, developed the first copper astrolabe.

The study of the relationship between the movements of the Sun, Moon and planets and Earthly events and human traits. Astrology had appeared in Mesopotamia by 2000 BCE and then passed to China, Greece and India. Astrology became more ambitious as knowledge of celestial motions increased and became more accurate. Tetrabiblos, a major work which influenced Western astronomy, was written by Claudius Ptolemy, the greatest astronomer in the Greek tradition.

“Judicial” astrology used a horoscope, or star chart, relating to a person’s moment of birth to discover that person’s character and their chances in life. The success of an enterprise was supposed to be influenced by the relative positions, or aspects, of the heavenly bodies when the enterprise was undertaken. Many European scientists took judicial astronomy seriously until the triumph of Newtonian thought in the late seventeenth century. However, astrology was condemned by two fathers of the Christian church, St. Augustine 354-430 and St. Thomas Aquinas c. 1225-1274, as well as by the Jewish philosopher and physician, Maimonides 1135-1204.

The first step in enjoying astronomy is to learn your way around the sky using only a dark sky, your eyes, and a star chart. Look for the more prominent patterns in the constellations and make note of the brighter stars. A star chart will give you a positional layout of the constellations, similar to a road map. You can then progress to using a pair of ordinary binoculars, and then to a telescope. A local astronomy society might allow you to use their telescope to view the night sky.

The further you are from city lights, the more objects you will be able to see in the night sky. You will be able to see thousand of stars, including the Milky Way, in very dark areas. Your latitude will also affect your view of the night sky. If you live in the northern hemisphere, you will not be able to see stars lying near the South Celestial Pole. The further north you are, the fewer stars you will be able to see south of the celestial equator. The time of year will also affect what you see, because as the Earth orbits the Sun, the night side looks out at different parts of the Universe.

To get the best all-round view, choose a site as dark and as far away from trees and buildings as possible. Make sure you are warm, so you can stay out long enough for your eyes to adapt to the dark. It can take up to half an hour for your eyes to achieve maximum sensitivity in the dark. Use a red lightbulb, rather than an ordinary flashlight, to read your star chart to help retain your dark adaptation.

To help orient yourself on your star charts, try to get an idea of where north is. Pick a prominent constellation or asterism on a chart and see if you can find it in the sky. You might be surprised to find that stars are quite far apart from each other in the sky; patterns that are easy to see on a star chart may be very spread out in reality and not so obvious. Some of the stellar patterns may also be changed by the fact that some of the fainter stars might not be visible. In a very dark sky, you may see many extra stars that interfere with stellar patterns.

Once you find an obvious pattern, follow the chart and try to find another one. This is the first step in a technique called star-hopping. You can use the naked eye, binoculars or a telescope to star-hop. As magnification increases, the distances you star-hop will become smaller, and your star charts will become more detailed.

Star charts do not show planets because planets are constantly moving. One way to distinguish a planet from a star is that planets hardly ever twinkle. They are not point sources of light, so the Earth’s atmosphere doesn’t affect their light as much as it affects starlight. A bright reddish “star” in the evening or morning twilight will be Mars. A brilliant “star” will be Jupiter. A fainter, yellower “star” will be Saturn.

The science that deals with the physical conditions in the Universe beyond the Earth. Astrophysicists study such matters as how stars are born and die, how they generate energy, how they move, how radiation is produced and absorbed, and where cosmic rays come from.

When Newton discovered that the force of gravity that causes apples to fall from the trees is the same force that guides the planets around the Sun, he created the first successful astrophysical theory. He showed that the whole Universe could be understood in terms of the same physical laws. In the mid-nineteenth century, the rise of spectroscopy led to an increase in astrophysical knowledge. Forming spectrums of light received from the stars enabled astrophysicists to determine their motion, temperature, composition and other properties.

The central part of an atom, which contains most of the mass of the atom. The atomic nucleus consists of positively charged protons and uncharged neutrons. Therefore, it has an overall positive charge.

A constellation, the Charioteer. Auriga contains Capella, the sixth brightest star in the sky. Two eclipsing binaries, Zeta Aurigae and Epsilon Aurigae, lie south of Capella. Zeta Aurigae is an orange giant. It is orbited by a blue star that causes eclipses every two years and eight months. Epsilon Aurigae is a luminous supergiant. It has a period of 27 years, the longest known period of any eclipsing binary. The nature of its orbiting companion is unknown. Auriga has a chain of three open clusters as well.

The solar wind is a stream of charged particles that flow away from the Sun. The particles that encounter Earth become trapped between two regions beyond the atmosphere that are known as the Van Allen radiation belts. At times the Sun releases an intense outburst of charged particles, causing the Van Allen belts to overflow. This causes particles to cascade down into Earth’s upper atmosphere, where they excite molecules of atmospheric gas, causing them to emit visible radiation. This radiation is known as an auroral display. Most of this activity occurs in the skies near the poles. The display is called the Aurora Borealis in the north and the Aurora Australis in the south.

The angular distance of an object in the sky measured parallel to the horizon, eastwards from north. Azimuth is measured in degrees, from 0 to 360. It is one of the coordinates in the horizontal system which identifies the positions of celestial objects. Altitude is the other coordinate in this system.