Science 9 - AP
Science 9
Unit E: Space Exploration
1.0 Human Understanding of Space
1.1 Early Views About the Cosmos
A. Tracking the Cosmos
• ancient people looked to the skies to predict the coming of summer and winter
• summer solstice marks the longest day of the year…June 21 in the Northern Hemisphere
• winter solstice marks the shortest day of the year…Dec 21 in the Northern Hemisphere
• many ancient structures were built to predict the timing of the solstices
eg) Stonehenge
• equinoxes are two times in the year when daylight and nighttime are equal in length (March 21 and September 21)
B. Planetary Motion
• objects in the sky are constantly moving
• ancient peoples wished to make sense of it all
• models of planetary movement and star movement emerged
• constellations are patterns assigned to groups of stars in the night sky
C. Geocentric Model
• 2000 years ago Aristotle proposed an Earth-centered (geocentric) model of the universe
• sun, moon, Mercury, Venus, Mars, Saturn and Jupiter orbit Earth
• early astronomers used this model to calculate moon phases but couldn’t explain other celestial events
D. Heliocentric Model
• in 1530, Copernicus suggested a sun-centered (heliocentric) model of the universe
• Earth and the other planets orbit the sun
• in the 1600’s, Galileo was the first scientist to use a telescope
• Brahe studied and recorded the movement of the planets
• later, Kepler added elliptical (oval-shaped) orbits to the model
1.2 Discovery Through Technology
A. Astronomical Tools
• merkhets and quadrants were used by Egyptians to chart the stars
• Arabians used astrolabes and cross-staffs
• scientists like Galileo used telescopes, which contained combinations of different lenses
• telescopes are still used to observe objects in space
B. Astronomical Units
• units like meters and centimeters are too small for measuring distance in space
• astronomical unit (AU) is the distance from the center of the Earth to the center of the Sun
• 1 AU = 149,599,000 km
• AU’s are used to describe positions of objects in our solar system
C. Light Years
• in one second, light travels 300,000 km
• sunlight takes 8.5 minutes to reach Earth
• a light-year is the distance traveled by light in one year: 9,500,000,000,000 km = 9.5 trillion km
• light-years are used to measure great distances between stars and galaxies
1.3 The Distribution of Matter in Space
A. Stars
• a star is a hot, glowing ball of gas (mainly hydrogen but also helium)
• stars vary in colour, size and density
• hot stars are blue, cool stars are red
• a Hertzsprung-Russell Diagram shows that stars fall into distinct groupings
B. Star Birth
• a nebula is an accumulation of gas and dust
• steps in birth:
1. swirling dust and gas collapse under gravity
2. core mass and temperature increase
3. core of material glows, forming a protostar
4. when the core temperature reaches 10 million degrees C, fusion begins and a star is born
C. Life & Death of a Star
• the mass of a star determines the type of star
• most stars start out in the main sequence
• the life cycle depends on the mass of the star
D. Galaxies
• a galaxy is a grouping of millions or billions of stars, gas and dust held together by gravity
• can be spiral shaped (Milky Way), elliptical, or irregular
1.4 Our Solar Neighbourhood
A. Protoplanet Hypothesis
• model for explaining the birth of solar systems:
1. cloud of gas and dust begins swirling
2. ................
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