The Constellations:
When we bring the ScienceSouth Starlab to area schools, the first question we ask the students is “Does anyone know what a constellation is?” Usually everyone raises their hand. Although many know that a constellation is a group of stars, only a few people can name more than two or three constellations.
A constellation is a group of stars that has a recognizable pattern, which appears to be constant over a period of thousands of years. The shape of a constellation is only as it appears from our viewpoint on Earth. The different stars in a constellation are usually not associated with each other in space, it is only as we perceive them in two dimensions; example, see Orion below.
When ancient people looked at the night sky, there were many more visible stars than we see today because the ancient people did not have any light pollution, or industrial fossil fuel pollution as we do today. It appears to be a natural human characteristic to find some type of order in disorder or randomness. So the ancient people chose some of the brighter stars and looked for some types of patterns. This organization of the stars into recognizable patterns was not done just for fun. The ancient people were well aware that the stars appeared to move through the sky, rising and setting throughout the night, and slowly changing from season to season. Therefore, having identifiable groups of stars allowed the ancients to measure time of night and changing seasons and the location of the viewer as they traveled about the Earth. This information was very useful for planting, harvesting, and navigation. Example: When the ancient Egyptians saw the star Sirius, in the constellation of Canis Major (The Big Dog) rise in the sky just before the sunrise, they knew that the Nile River would soon flood. This information allowed the Egyptians to plant their crops accordingly.
When the ancients identified these star groups, they gave them shapes that seemed to fit the world around them. Many constellations were seen as animals; bears, birds, sea creatures, farm animals, etc. Other constellations were seen as human-like forms usually identified with mythological beings; kings, queens, warriors, hunters, etc. Of course these constellations were all given names, which everyone would know and easily remember. The ancient Assyrians had a star based religion we know of today as astrology. As the Sun passed each month into another constellation, they felt that these stars affected their lives. Today these twelve constellations are known as the Signs of the Zodiac.
Although I have generalized the use of the words “ancient people,” the constellations were actually named over a long period of time. The oldest constellations that we still recognize today are Leo the lion and Scorpius the scorpion. These two constellations were noted on a carved stone shown below dated at about 4000 BC!
The Greek’s strong adherence to mythology added many constellation names over the period from 500 BC to 200 AD, at which time 48 constellation names were in use. The powerful Roman Empire then inherited the Greek myths, and changed the names of the constellations to the Latin names we still use today. From 700 AD to 1600 AD, the Arabs contributed many of the constellation star names we use today. Note: in Arabic the word Al means “the.” Example: the stars; Aldebaran, Algol, Alkaid, etc.
From 1600 AD onward several other constellation names were assigned, many in the Southern hemisphere. Some of these newer constellation names are not too familiar to us such as Telescopium the telescope, Pyxis the compass, and Fornax the furnace, etc. Finally, in 1930, the International Astronomical Union (IAU) finalized the constellation count at 88. In addition, the IAU placed boundaries around each constellation, so that there would be no free space between constellations. This resulted in the sky looking like puzzle pieces; see the region of Orion shown below.
These strictly defined constellation borders help astronomers describe the locations of various objects, such as distant galaxies. Note an “outside” view of our constellation boundaries shown below.
Lastly, we should realize that the constellation shapes and names we use today were all derived from the regions of Europe and the Mediterranean. The ancient peoples inhabiting North and South America, Asia, Australia and part of Africa had many other names and shapes they saw for groups of stars in the sky that applied to their cultures and religions.
Naked Eye Sights: See how many constellations you can find/identify this month.
The International Space Station will make a nice pass over Florence early in the evening of February 20th. The table below gives the times (24 hr. clock) and altitudes; maximum altitude at about 6:40 PM, right over the top of Orion. Also below is a star chart showing its passage through the stars, and a Google Earth type perspective.
| Event | Time | Distance (km) | ||
| Rises above horizon | 18:37:39 | -0° | 220° (SW ) | 2,142 |
| Reaches 10° altitude | 18:39:39 | 10° | 217° (SW ) | 1,307 |
| Maximum altitude | 18:42:28 | 63° | 146° (SE ) | 393 |
| Enters shadow | 18:45:32 | 9° | 53° (NE ) | 1,352 |
| Drops below 10° altitude | 18:45:27 | 10° | 53° (NE ) | 1,316 |
Telescope Sights (60-100mm): Take your last look at Jupiter in the southwest until it returns to the sky next fall.
See you next month!
