Ch.1, Sec.1 – Astronomy - some of the earliest civilizations used astronomy to create calendars, necessary for planting crops effectively (Mayans) astronomy: the study of the Universe Our Modern Calendar year: the time required for the Earth to orbit (one revolution) once around the Sun (365.25 days) month: a division of the year that is based on the orbit (one revolution) of the Moon around the Earth (29.53 days) day: the time required for Earth to rotate once on its axis (23 hours, 56 minutes)

Ch.1, Sec.1 – Astronomy - The Mayans knowledge of astronomy allowed them to create structures, like Chichen Itza, where the Sun’s movement on the equinoxes (March 20 & September 22) casts a perfect shadow of one of their gods – Kukulkan!

Ch.1, Sec.1 – Astronomy Who’s Who of Early Astronomy 1. Ptolemy – the first astronomer to create a solar system model, but he was incorrect by having Earth at the center of the Universe (A.D. 140)

Ch.1, Sec.1 – Astronomy 2. Nicolaus Copernicus – the first astronomer to create an accurate solar system model and had the Sun at the center of the Universe (A.D. 1543)

Ch.1, Sec.1 – Astronomy 3. Tycho Brahe – favored the Ptolemaic theory of an Earth centered Universe, but did make significant observations regarding the planets and stars (A.D. 1500s)

Ch.1, Sec.1 – Astronomy 4. Johannes Kepler – favored Copernicus’ Sun-centered Universe and created three laws of planetary motion (elliptical orbits)

Ch.1, Sec.1 – Astronomy 5. Galileo Galilei – became the first astronomer to use a telescope and observed distinct features from the moon and the planets

Ch.1, Sec.1 – Astronomy 6. Isaac Newton – showed how gravitational force attracts everything in the Universe including planets orbiting the Sun (smaller objects are attracted to larger objects)

Ch.1, Sec.1 – Astronomy Modern Astronomy - In 1924, Edwin Hubble was able to view other galaxies other than the Milky Way, thus proving the Universe is much bigger than expected