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SCIENCE NOTES
ASTROPHYSICS

Science Notes

History
Ancient
Times

Johannes
Kepler

Ptolemy

Isaac
Newton

Galileo
Galilei

Ancient Times
Astronomy used for:
 planting crops
 religious purposes
 navigation
Ptolemy (Greek Scientist)
Ptolemaic System:
 Earth is a sphere
 Earth at the centre of the universe
 Sun, Moon, planets and stars orbit
the earth in circular orbits

Nicholas Copernicus (Polish Scientist)
Copernican System:
 circular orbits
 Sun-centered universe
 planets, stars, Moon orbiting the
Sun

Science Notes

Johannes Kepler
Eliptical Planetary Orbits:
 orbit of every planet is an ellpispe;
sun at one of the two foci
 line joining planet and sun sweeps
equal areas during equal time
periods
 (orbital period of planet)2 directly
propotional to (semi-major axis of
its orbit)3
Galileo Galilei
Sightings with a Telescope:
 mountains on the Moon (craters)
 Venus having moon-like phases (proving sun-centered
orbit)
Isaac Newton
Law of Universal Gravitation:
 planets orbit Sun
 gravitational attraction between planets and Sun
 Sun pulls on moving planets and keeps them from moving
off in a straight line
 every other object excerts gravitational force according to
its mass
 earth’s gravity is what makes objects fall on the ground
 moon is earth’s satellite; earth is sun’s satellite
 moon is a satellite to the oceans of the earth, causing tides
 calculate masses of planets and shape of the Earth

Universe created 15 billion years ago
...

Temperature of space is -270 0C
...
9% of the mass of the solar system
Sun’s energy comes from hydrogen atoms fusing to form helium
atoms in the core (hottest part of Sun)
only corona of Sun is visible during an eclipse
gives of gamma rays, UV rays, visible light, microwaves, radiowaves,
infra-red and x-ray energy
sunspots: dark spots with a lot of magnetic energy
solar flares: explosions from the surface of the Sun

The Earth
 third planet from the sun
 formed 4
...
25 days) to complete one revolution
around the Sun
 Earth spins on its axis while revolving
 axis is tilted, not straight
 hemisphere square on to the sun receiving rays has summer
 other hemisphere receiving rays at more of an angle has winter
 longest day: summer solstice; shortest day: winter solstice
 equinox: night equinox in autumn and spring (day and night same
time)
 seasons change as Earth orbits sun
 Sun rays are more intense in summer because they go through less
atmosphere
 equatorial countries have wet and dry seasons
 seasons in NZ: (summer (dec-feb) autumn (mar-may) winter (junaug) spring (sep-nov)

Science Notes

The Moon
 formed same time as the Earth (4
...
5 hours between tides
spring tides are high and occur twice monthly
neap tides are low and occur twice monthly

Science Notes

The Moon
Phases
 produces no light of its own, moonlight is reflected sunlight
 appearance of the moon changes in a 29-day cycle
 moon revolving around the Earth causes these phases

Science Notes

The Moon
Eclipses
Lunar:
 moon sometimes passes into Earth’s shadow, so for a few
hours it disappears from view, called a Lunar Eclipse
 when entire moon enters Earth’s umbra (darkest part of
shadow), it is called a total eclipse
 when only part of moon enters Earth’s umbra, it is called a
partial eclipse

Solar:
 much less often
 moon passes exactly between Earth and Sun and casts its
shadow onto part of the Earth
 Sun appears to be blotted out from the shadowed part of Earth
 Sun’s corona becomes visible
 The moon can fully eclipse the Sun because it is both 400 times
smaller and closer to the sun during a total solar eclipse

Science Notes

The Solar System
The solar system consists of the Sun, eight planets and their moons, and
aestroids and comets
...

Planet Types
Terrestrial planets: (Mercury, Venus, Earth and Mars) small in size, made
of rock
...

Terrestrial planets’s orbits are closer to the Sun than giant planets, in
between the two groups is the asteroid belt, made of thousands of rocks
orbiting the Sun
...

Formation
Solar system was created 5 billion years ago when a cloud of dust and gas
spun; hydrogen in the center gathered into a huge ball, which developed
into the Sun, further out, small balls of dust/gas condensed, forming
planets, moons, asteroids
...

Constellation: a group of stars
...

Meteors: Piece of rock that enters the Earth’s atmosphere
...

 a discovery in 2003 found Eris which was bigger than Pluto
 Pluto is regarded as a ‘dwarf planet’ or a Trans Neptunian Object



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