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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