SCI ♡ Astronomical Events

Known to Men Before the Advent of Telescopes

Ancient Astronomy and Calendars

before telescopes, humans relied on their senses to understand the universe

Babylonians, Assyrians, & Egyptians

• knew the length of the year

• Egyptians adopted a calendar based on 365 days

• tracked the yearly cycle of the star Sirius, linked to the Nile's flooding

Chinese Civilizations

observed comets, meteors, and Sun's dark spots

Mayan Civilization

developed a calendar based on the movements of Venus

Polynesians

utilized the stars for navigation

Diurnal Motion

• daily motion of stars and other celestial bodies across the sky due to Earth’s rotation

• observed as the sun rising in the east and setting in the west

Fixed Stars

Greek astronomers have described these as moving in the sky at the same arrangement and speed as most of the stars are

Wandering Stars

• stars whose movements deviate from what seems to be fixed stars

• Planetes in Greek

• seven wandering stars

  • Sun, moon, Mercury, Venus, Mars, Jupiter, & Saturn

Eclipse

occurs when the Earth or Moon casts a shadow on the other

Lunar Eclipse

• earth is directly aligned between the sun and moon

• the earth casting a shadow on the moon

• only occurs during the full moon phase

Solar Eclipse

• happens when the moon passes between the earth and sun

• moon casting a shadow on the Earth’s surface

• only occurs during the new moon phase

Ptolemaic System

• Claudius Ptolemy

• center: EARTH

• all other celestial bodies revolve around the earth

• stars are located and fixed in the outermost celestial sphere

Copernican System

• Nicholas Copernicus

• center: SUN

• all planets including earth revolves around the sun

• only the moon revolves around the earth

• stars are located and fixed in the outermost celestial sphere

Tychonic System

• Tycho Brahe

• center: EARTH

• moon and sun revolve around earth

• all other planets revolve around the sun

• stars are located and fixed in the outermost celestial sphere

• retrogade: same as Copernican System

Johannes Kepler’s 3 Laws of Planetary Motion

1. Law of Ellipse

2. Law of Equal Areas

3. Law of Harmony

Law of Ellipse

• orbits of all the planets are elliptical with the sun at one focus of the ellipse

• an ellipse is a somewhat flattened circle

• a closed curve in which the sum of the distances from any point on the ellipse to foci (two points inside) is constant

Law of Equal Areas

• line joining a planet and the sun sweeps out equal areas in space in equal intervals of time

• thus, a planet moves fastest when it is nearest to the sun

Law of Harmony

• the square of a planet’s orbital period (years) is proportional to the cube of the semimajor axis of its orbit (in astronomical units or au)

• thus, the larger the orbit’s size, the longer it takes to orbit the sun