I. Introduction

The peculiar variable star, epsilon Aurigae, lives within a cosmic context. Since the beginning people have looked at the night sky with wonder. At first glance it appeared the nigh sky was fixed except for the Moon's movement. The points of light we know as stars were thought to be embedded in a celestial sphere. The Greeks were the first to devise a system for determining the brightness of the stars. While they used a system of just six magnitudes it was at least a start. A magnitude 1 star was considered the brightest they could see while magnitude 6 was the faintest, 100 times fainter in fact. We now know there are stars much brighter than magnitude 1 (our Sun is a star and is magnitude -26.8, Sirius, the brightest star in the night sky is magnitude -1.47 and Vega is magnitude 0.03) There are also billions of stars fainter than magnitude 6. One must remember that the lower the magnitude number and extending into negative numbers, the brighter the star. A magnitude -2 is many times brighter than a magnitude +2 star.

Studying the heavens became full time jobs for some people. Most of these people considered the stars fixed in position., but it wasn't long before it was discovered that some stars moved with respect to others. These were called wanderers which we now know are not stars at all, but planets.

To better talk about the stars and identify where they are, patterns of stars where grouped into constellations. The Greeks may have been the first to specify certain groups of stars and give them names. Most cultures also grouped stars into constellations, but used different star groupings and different names. While constellations are not real, they do help identify where in the sky a star or object is located.

Today there are 88 official constellations. Some of these can only be seen in the Northern Hemisphere while others only in the Southern Hemisphere.

Variable Stars

At first it was thought that stars were fixed in brightness and unchanging. Those who studied the stars night after night discovered some of the stars seemed to remain fixed in the sky, but varied in brightness. At the time observers had no idea what they were seeing. One star, known as Algol, dimmed down very noticeably for a few hours every few days and created much fear. It faded every few days. and this was called the "wink of the demon."

Variable stars are stars seen from Earth that vary in brightness over a period of time from minutes to decades. There are several mechanisms that can cause this variation. Some stars pulse. As the nuclear fuel is consumed the star expands a bit and gets brighter. It then falls back to a dimmer mode. Other star systems have more than one star in them. If the orbits of the stars are such that one star passes in front of another as seen from Earth, a decrease in brightness from that star system will be seen. This type of variable star is known as an eclipsing binary star system. Even the closest eclipsing binary systems are too far away to easily be resolved into the individual stars. However, much can be determined about the star system by noting the variation of brightness. This is known as photo-metry [light-metering] of stars. Photometers are used to measure these changes and are special very sensitive light meters.

Auriga, Capella and the Kids

The constellation Auriga is visible from the Northern Hemisphere and the northern part of the Southern Hemisphere. It is highest in the early evening sky during the northern hemisphere winter months. Auriga is the Latin name for the Charioteer. Mythology portrayed Auriga as a charioteer with three children on his arm. Aurigae was also known as Erechtheus, son of Hephaestus. The Romans called him Vulcan. Hephaestus, who was crippled as a child, was believed to have invented the chariot for his son so his son could move him about more easily.

The brightest star in the constellation Auriga is Capella or alpha Aurigae. To the Northeast of Capella is a triangle of stars with the closest star epsilon Aurigae (Almaaz or Al Anz-the he-goat) at the vertex and zeta (Haedi) and eta (Hoedus II) at the bottom of the triangle. This triangle is known as the Kids. The Kids are the three children on the arm of Auriga. These stars are all bright (around 3rd magnitude) and easily visible with the naked eye even in light polluted areas. Both epsilon and zeta Aurigae are long period eclipsing binary star systems and even eta varies a little, but not due to a companion.

Epsilon Aurigae

Epsilon Aurigae is one of the most mysterious star systems known. It has the longest period of all known eclipsing binary systems with a period of a little over 27 years. To add further to the mystery while one would think that such a long period would produce a fairly short eclipse, the surprise is that the eclipse lasts nearly 2 years. While those two facts are interesting by themselves things get even more interesting during the middle of the eclipse. What happens is the star system gets brighter at mid-eclipse. Some astronomers have likened the object causing the eclipse to a gigantic paving brick with a hole in the middle.

While professional astronomers are very interested in understanding the system, the long period between eclipses, the fact that it is a 3rd magnitude system and one that requires many continuous nights of observations all tend to preclude most professional observations. Indeed many astronomers are lucky to observe one eclipse during their career and usually two is about it. In part due to the high level of brightness, the object does not require large telescopes, so observations of it tend to be of lower priority for major observatories except during eclipse.

Backyard Astronomers

Photometry of variable stars is ideal for backyard astronomers. Even with modest telescopes and equipment much can be learned and Epsilon Aurigae presents an ideal project. Because of the star system's brightness it is easily observed and quality data can be taken even in a light polluted area. In addition, being able to pop out back each clear night and make observations with no need to petition a major observatory, makes continuous following of this system ideal for the backyard astronomer. This is an area where it is relatively easy for a backyard astronomer to do real science.

In addition to astronomical photometry, there are other techniques that are used to gather data about a star system. These include spectroscopy, polarimetry and interferometry. While advanced backyard astronomers can do spectroscopy these techniques have been beyond the capability of a backyard astronomer until recently

In this book, we will review the historical context surrounding epsilon Aurigae and some related systems, discuss observational methods associated with the science of eclipsing binaries and then discuss the eclipse of 1982-84, the work done since and the pre-status of the eclipse of 2009-11. Given that science often leads to more questions, conclusions from the 2009-11 eclipse will set the stage for studies of the next eclipse cycle, forecast to begin in the year 2036, whether or not Earth dodges impact by asteroids like Apophis.