by John P. Pratt
©1998 by John P. Pratt. All rights Reserved.
The text book for our astronomy class gives all kinds of data about the planets Mercury and Venus that was gathered from fly-bys and probes, but it doesn't tell you how to go out and look that the planets in the sky! So let's learn the basics of the Evening and the Morning stars.
Both Mercury and Venus are both evening and morning stars. That is because they are nearer to the sun than the earth is, so they can never appear very far from the sun in the sky. In other words, when the sun sets in the evening they might be in the west, near the sun as an evening star. Or they could be in the morning sky before sunrise, again, near the sun. But neither Mercury nor Venus can be opposite the sun in the sky, such as rising at sunset. Hence, they are called the evening and morning stars. Actually, "evening star" or "morning star" nearly always refers to Venus, which is by far the brightest celestial object in the sky after the sun and moon. Mercury is much dimmer and only visible for a few weeks of the year.
Sidereal Period. The sidereal period of a planet is what is normally called simply the "orbital period." It means the period of the planet orbiting the sun as seen relative to the stars, and it is the period listed in most tables of planetary data as orbital period. The sidereal period of Venus is about 225 days, or seven and a half months. The sidereal period of Mercury is about 88 days.
Synodic Period. The synodic period of a planet is the period relative to the sun as seen from the moving earth, and is by far more important than the sidereal period for the evening and morning stars because they are always near the sun. That is, the whole idea of evening and morning has to do with the sun, so the length of time of the evening/morning star cycle is the synodic period, or the period between successive crossings between the earth and the sun.
In the case of Venus, Venus orbits the sun 13 times in 8 years, that is, during the period in which the earth orbits the sun 8 times. For this reason, Native Americans said the number of Venus was 13, while the number of the earth was 8. Thus, if Venus orbits the sun 13 times while the earth does 8 times, then Venus must pass us 5 times during those 8 years. Thus, Venus passes between the earth and the sun 5 times in 8 years, meaning that it completes 5 synodic periods in 8 years, or 5 complete evening/morning star cycles. The Mayans had carefully tracked the cycles of Venus, and had noticed that 5 Venus cycles of 584 days just equalled 8 years of 365 days (5 x 584 = 8 x 365). Notice the great difference between the sidereal and synodic periods of Venus: its sidereal period is less than 8 months, but its synodic period is 1 3/5 years.
For Mercury the difference is not so great between the sidereal and synodic periods. The sidereal period being 88 days means that while it orbits the sun once, the earth has only gone through about one quarter of a year. Thus, it takes about another month for Mercury to come around and again align with the sun. It turns out the synodic period is 115.88 days, which means that Mercury goes through 3 entire evening/morning star cycles each year. Remember pi from math (the ratio of the circumference of a circle to its diameter?)? Remember that one approximation of pi is 22/7? Well it turns out that there are not just 3 Mercury cycles per year, but about pi per year, and 22/7 is even more exact because in 7 years Mercury goes through 22 cycles. To see how the evening and morning star cycles work, consider the following illustration of the orbit of Venus.
Evening and Morning Star. The earth is shown at the bottom of the illustration, and for our
purposes, consider it to be at rest. So let's look at Venus at different places in the orbit. It is
orbiting around the sun counterclockwise in this illustration, and the earth is rotating on its axis in
that same direction, causing night and day. When Venus is on the left side of the illustration
between positions 3 and 5, it appears as an evening star, when it is on the right side between
positions 6 and 2, it is a morning star. In the other positions on the near and far side of the orbits,
it is too near the sun to be seen. The periods as evening and morning star each average about 263
days, the disappearance on the near side of the sun is about 8 days, and on the far side is about 50
days, for a total of 584 days for the entire cycle.
The Feathered Serpent. Native Americans of Central America had a legend about Venus which is still useful to help remember where Venus is in its orbit. The equated Venus, which they called the Dawn Star, with their god Quetzalcoatl, the "Feathered Serpent." They believe he came to earth and lived as a man and that the evening star represented his life. Thus, point 3 in the orbit when Venus first rises in the west as an evening star would represent the "birth" of Venus. It is then on the far side of its orbit, and so it is at about its faintest at birth. It then grows a little brighter every day as an evening star in the west, like a child growing up, until it gets to point 4 in the orbit. That point is called the greatest eastern elongation because it is as far east of the sun as it can get. By this time, Venus is in its "prime" of life, and is very bright. It then continues to get even brighter for about another month until it is so bright it can cast a shadow on a moonless night and is often the cause of flying saucer reports from someone who looked at the sky for the first time. Because it is at this time so near the earth, it seems to plunge surprisingly quickly into the earth and "die" at point 5 in the illustration.
It is about the death of Venus that the Native Americans have best preserved their legends for us. A good reference on this is Skywatchers of Ancient Mexico by Anthony Aveni (Austin, Texas: U. of Texas, 1980). He quotes (p. 187) the legend from the Anales de Quauhtitlán (Seler, 1904, pp. 364-365):
"at the time when the planet was visible in the sky (as evening star) Quetzalcoatl died. And when Quetzalcoatl was dead he was not seen for 4 days; they say that he dwelt in the underworld, and for 4 more days he was bone (that is, he was emaciated, he was weak); not until 8 days had passed did the great star appear; that is, as the morning star. They said that then Quetzalcoatl ascended the throne as god"
So what is the symbolism of points 1 and 2? The position of point 1 is the most mysterious because it does not correspond to an obvious orbital point. It is taken from the Venus Tables of the Dresden Codex, a Mayan document on astronomy, and corresponds to the day 90 days before the birth of Venus. The legends have not filled in those details as far as I know, but it is easy to do from the Sacred Round count symbolism.
The Cycle of Life. All of the Central American calendars had a 20-day count of days which symbolized the cycle of life. The first day represented the beginning of man's journey, being either conception or the creation of the spirit before birth. Mayan sources tell us that the second day represents the day when the spirit enters the fetus before birth, and the third day represents birth. That fits the orbit of Venus also, so I propose that is a good way to remember the Venus cycle. Point 1 is the beginning point of the orbit, representing the "creation" of Venus. Point 2, when it enters darkness, corresponds to the spirit entering the darkness of the womb, followed by point 3 which represents birth.