Astronomy and Astrology

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Author: Janice VanCleave

What You Need to Know

The Earth orbits the Sun and rotates. Rotation is the spinning of an object about its axis, which is an imaginary line through the center of the object. During these Earth movements, the Sun and the stars are relatively stationary as Earth orbits the Sun. But from Earth, it appears that the Sun and the stars rise above the eastern horizon (the line where the Earth and sky appear to meet), move across the sky, and set below the western horizon. If the stars could be seen during the day, it would appear that they move faster than the sun. The ecliptic, which is the apparent path of the Sun across the sky, traces an imaginary circle around Earth. The ecliptic runs through the zodiac, which is an 18° wide band of the sky, 9° above and 9° below the ecliptic.

The zodiac is divided into twelve parts called signs. Each sign is a patch of sky 30° wide and 18° high. A sun sign is the sign of the zodiac the Sun rises with at dawn. There are 12 signs, and each is associated with a constellation (a group of stars that appear to form a pattern in the sky) called a zodiac constellation. The name of each sign is the name of the zodiac constellation in it. The zodiac constellations are listed in the chart below.

How Do Sun Signs Work?

In the diagram, position 1 shows Earth, the Sun, and the constellation Pisces at dawn. The Sun is in the sign called Pisces, but the Sun's brightness prevents the stars making up the Pisces constellation from being seen at dawn. Nevertheless, for about 30 days some or all of the stars of Pisces are behind the Sun at dawn.

How Do Sun Signs Work?

What Does This Have to Do with the Sun Moving to Different Parts of the Sky?

Because Earth revolves around the Sun, from Earth it appears that the Sun moves counterclockwise from one zodiac sign to the next during the year. This means that the Sun appears to move from Pisces to Aries, then to Taurus, and so on. Actually, Earth is moving from position 1 to position 2, then to position 3, and so on.

Real-Life Science Challenge

What is the difference between astronomy and astrology? Astrology is the notion that the positions and motions of the stars and planets determine people's personalities and influence the course of their daily lives. Astronomy is the scientific study of celestial bodies. Because astrology does not use scientific methods to reach its conclusions, it is considered a pseudoscience.


Now, start experimenting to demonstrate how the Sun is seen in different parts of the sky during the year.


  • Use a curved piece of cardboard to represent the zodiac band and Styrofoam balls to represent the Sun and Earth.
  • Design a way to represent Earth orbiting the Sun.
  • Design a way to point out the Sun sign for each position of Earth during its orbit.
  • Since the stars cannot be seen during the day, design a way to determine the nighttime constellations during different sun signs.

Fun Fact

Horoscopes are predictions or advice for the future of a person based on the position of planets and signs at a specific time. Your horoscope would be for your birth sign, which is the sign the Sun was in when you were born. Birth signs are determined by dates, which were established thousands of years ago. For example, the birth sign for birthdays from February 19 through March 20 is Pisces. But since birth sign dates were established, Earth's axis has changed position. Babies born on February 25 would have a birth sign of Pisces according to astrologers (people who predict the future using the position of celestial bodies), but their true sun sign would be Aquarius.

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