The constellations represent the story of our universe, and they contain a representative sample of much of what we can see in space. This high-interest video from The History Channel provides a nice overview of a wide range of topics in astronomy. (Note: The video must be obtained separately, it is available as a DVD or on YouTube
The study guide is multiple choice in format, and students can use it to follow the progress of the video. PDF and MS Word files are included in the download.
History Channel's The Universe: Constellations Overview
The video introduces a wide range of topics related to constellations and stars.
The entire sky itself is organized into a construct known as the celestial sphere, the illusory sphere of stars that appears to surround the earth. Though fiction, this idea is useful in that the sphere can be subdivided into the coordinates of right ascension and declination. The two-dimensional appearance of stars in the night sky is compared to a city skyline in that the distances to individual skyscrapers are not readily distinguishable. The path of the sun is termed the ecliptic, it resembles a line that crosses the celestial sphere. The constellations of the ecliptic are termed the zodiac, the famous “birth-sign” constellations (it is noted that the constellation Ophiuchus also crosses the ecliptic and can be considered the “13th sign” of the zodiac). The Greek astronomer Ptolemy observed that about 1500-2000 stars are visible in the entire sky. Another region of the sky, the Milky Way, appears as a cloudy path of light that crosses the celestial sphere. Here we see the thickest part of our galaxy appearing to surround our location. The celestial sphere is not constant; stars appear to slowly shift over time due to their intrinsic motions through space. Barnard’s Star is the fastest star in apparent (proper) motion, and the sky will look much different thousands of years from now due to the proper motions of the stars. Other changes in the celestial sphere are due to earth’s own motion. Precession, the slow wobble of the earth’s axis in 26,000 years, causes the entire sky to shift, and it causes different North Stars to be visible in the past and future (Currently Polaris is the North Star, Thuban was in the past). The constellations are also unique to earth. From a different star such as Vega, entirely different star patterns would be visible.
The video highlights the following constellations: Cepheus (the King of Aethiopia), Orion (the Hunter), Draco (the Dragon), Taurus (the Bull), Ophiuchus (the Serpent Bearer), Crux (the Southern Cross), Ursa Major (the Great Bear), Cygnus (the Swan), and Centaurus (the Centaur).
Types of constellations are described: Circumpolar (never rising or setting); zodiacal (described above); “dark cloud” constellations, visible along the Milky Way, of the Incas; and the 88 “official” constellations established in the early 20th century by the International Astronomical Union (IAU). Also described are the “unofficial” star patterns termed asterisms. Examples are the Big Dipper and the Belt of Orion.
Many well-known stars are highlighted: Delta Cephei, Aldebaran, Betelgeuse, Gamma Velorum, Barnard’s Star, Thuban, Mizar, Deneb, Alpha Centauri, and the bright star cluster Omega Centauri.
Classes of stars are described: Variable (stars that change in brightness); double (stars that have unseen companions visible in a telescope, about 60% of stars are double).
The stellar evolution, or life cycles of stars, are demonstrated with the following examples: Newly formed stars in the Orion Nebula; T-Tauri stars, active and young like rebellious teenagers; senior stars such as red giants; massive, explosive senior stars such as red supergiants, and Wolf-Rayet stars; and star death represented by Cygnus X-1, a potential black hole formed by the death and collapse of a massive star.
The measurement of star distance is described. Parallax, the apparent shift in the position of stars due to earth’s revolution, is used to measure the distances to stars closest to earth. Far off distances are measured using “standard candles”, which are stars of known brightness that can be used to calculate actual distances. Examples of standard candles are Cepheid variable stars and supernova explosions. Cepheid variable stars pulsate in a way related to actual luminosity.
The star knowledge of our ancient ancestors is highlighted for the Egyptians, Greeks, Arabs, and the Incas. The controversial idea that the Giza Pyramids were meant to form a star map of the Belt of Orion is described. The Greeks were the first known people to catalog the visible stars, and they invented about half of our modern constellations. The Greeks also determined that the earth was round. The star knowledge of the Greeks was passed along to the medieval Arabs who preserved and augmented it, later passing it back to Europe. The dark cloud constellations of the Incas are also described.