Astronomy

• 1.1.1 explain how the formation of the solar system created the sequence of bodies and the relative motion that defines our solar system

• explain the hierarchy of the solar system compared to the universe• 1.1.2 explain how the relative motions of the earth, sun and moon

cause ocean tides• explain the reason that Earth has four seasons based on the tilt of

Earth’s axis of rotation and Earth’s motion relative to the sun• relate Earth’s initial formation to its present day spherical shape• 1.1.3 explain how the sun produces energy which is transferred to

the Earth by radiation• 1.1.4 explain how incoming solar energy makes life possible on Earth

1.1.1 be able to describe the motions of precession and nutation & their effect on Earth’s orbit around the sun be able to describe Earth’s primary motions relative to those of the solar system and galaxy be able to demonstrate how bodies in space both create and are affected by the gravitational attraction of adjacent bodies resulting in elliptical orbits be able to explain barycenter1.1.2 be able to demonstrate the relative positions of Earth to the sun during different seasons 1.1.3 identify combustion and burning objects describe, compare and contrast nuclear fusion and fission be able to explain the equilibrium between gravity and particle motion in the core of a star navigate the electromagnetic spectrum and identify features of associated wave energy1.1.4 explain how the seasons are a result of the Earth’s tilted axis and the amount of solar energy that Earth receives

The Sun-Earth-moon system

Tools of Astronomy

• Light – electromagnetic radiation– Visible light (what humans can see)– Infrared– Ultraviolet– Radio waves– Microwaves– X rays– Gamma rays

• Electromagnetic radiation is arranged by wavelength and frequency– Can be classified by either wavelength or

frequency• Frequency and wavelength are related

c = λf– c = speed of light = 3.0 x 108 m/s– f = frequency λ = wavelength

Telescopes

• 3 benefits:– Can attach different detectors to observe all

wavelengths– Brings much more light into focus than the human

eye– Allow use of specialized equipment

• 2 types:– Refracting: use lenses to focus light– Reflecting: use mirrors to focus light

Instruments in Space

• Earth’s atmosphere blocks infrared (IR) radiation, ultraviolet (UV) radiation, X rays and gamma rays

• Images from wavelengths that do pass through Earth’s atmosphere are blurred

• Can allow for close-up observations and collection of samples

THE MOON• Solid, rocky body• Radius is about 27% of Earth’s• Mass is about 1% of Earth’s • Age of the moon is about 3.1 to 3.8 billion yrs

Formation of the Moon

• 3 Theories– Capture Theory: during the formation of the solar

system a large body got too close to the forming Earth and got trapped by gravitational pull

– Simultaneous Formation: moon and Earth formed at the same time in the same area

– Impact Theory: a Mars-sized object hit Earth about 4.5 billion yrs ago during the formation of the solar system

Lunar Surface Features

• Highlands• Maria• Impact craters• Ejecta and rays• Rilles• Regolith

Sun-Moon-Earth Interactions

• Daily Motion– Rotation of the Earth– 15o every hour

• Annual Motion– Earth’s orbit along the ecliptic around the Sun

• Earth’s tilt• Solstices• Equinoxes• Moon phases• Eclipses

Earth’s Tilt

• Earth’s axis is tilted about 23.5o relative to the ecliptic– This along with Earth’s orbit gives us seasons– Causes the Sun’s altitude to change throughout

the year– Solstices– Equinoxes

Solstices Summer Solstice – around June 21

Sun is directly overhead at Tropic of Cancer

Winter Solstice – around December 21Sun is directly overhead at Tropic of Capricorn

Equinoxes

• Autumnal Equinox – around September 21– Sun is directly overhead at the equator

• Vernal Equinox – around March 21– Sun is directly overhead at the equator

• Length of day and night are the same

Phases of the Moon

Tides• Effect of the Moon’s gravity on Earth• Occur every 12 hours

Spring tides higher than normal because the Moon and Sun are aligned

Neap tides lower than normal because the Moon and sun are at right angles to each other

Eclipses• Solar– Moon passes between the Earth and Sun

• Lunar– Moon passes through the Earth’s shadow

The Solar system

Early Theories• Geocentric Model – theory that the Earth is the

center of the solar system• Retrograde motion – when a planet appears to

move in the opposite direction (east to west)• Heliocentric Model – developed by Nicolaus

Copernicus in 1543 theory that the Sun is the center of the solar system

• Tycho Brahe – late 1500s made many accurate observations of planetary positions used by other early astronomers

Johannes Kepler• Developed three laws• Kepler’s 1st Law – planets orbit the Sun in an

ellipse (oval shape)• Kepler’s 2nd Law – an imaginary line between a

planet and the Sun covers the same amount of area in the same amount of time

• Kepler’s 3rd Law – the size of a planet’s ellipse is related to its orbital period

P2 = a3

P = orbital period a = semimajor axis

• Galileo Galilei – 1st person to use a telescope– Discovered 4 moons around Jupiter

• Isaac Newton – developed the law of universal gravitation

F = G F = force (in Newtons) m1 & m2 = mass of the bodies (in kg)

G = 6.6726 X 10-11 m3/kg/s2

r = distance between the bodies (in m)

• Center of mass – balance point between two orbiting bodies– Between the Earth and the Sun this point is nearly on the

Sun’s surface

m1m2

r2

PrecessionNutationRotation

Barycenter = center of mass

How the Solar System Formed• Collapsing interstellar cloud

Terrestrial Planets• MERCURY

Location: closest to the SunMoons: no moonsAtmosphere: very thin, mostly oxygen and sodiumSurface: much like Earth’s moonInterior: solid nickel-iron coreDay Length: 58.5 Earth days

• VENUSLocation: 2nd planet from the SunMoons: no moonsAtmosphere: thick, mostly carbon dioxideSurface: relatively smooth due to lava flowsInterior: liquid metal core Day Length: 243 Earth days

• EARTHLocation: 3rd planet from the SunMoons: one moonAtmosphere: thick, mostly oxygen and nitrogenSurface: life sustainingInterior: solid nickel-iron coreDay Length: 24 hours

• MARSLocation: 4th planet from the SunMoons: 2 moons – Phobos, DeimosAtmosphere: thin & windy, mostly carbon dioxideSurface: craters in the south, plains in the north, ice caps at both polesInterior: solid nickel-iron core Day Length: almost 25 Earth hours

Gas Giants• JUPITER

Location: 5th planet from the Sun; has a ringMoons: 4 major – Io, Europa, Ganymede, CallistoAtmosphere: very thick, mostly hydrogenSurface: no true surface; gas & liquid gasInterior: may have an Earth sized solid core Day Length: 10 Earth hours

• SATURNLocation: 6th planet from the Sun; has many ringsMoons: 1 major - TitanAtmosphere: thick, mostly hydrogenSurface: no true surface, gas & liquid gasInterior: may have a small, solid coreDay Length: nearly 11 Earth hours

• URANUSLocation: 7th planet from the Sun; has 10 ringsMoons: 2 major - Titania, OberonAtmosphere: thick, mostly hydrogenSurface: no true surface, gas & liquid gasInterior: may have a small, solid core Day Length: 17 Earth hours

• NEPTUNELocation: 8th planet from the Sun; has 6 ringsMoons: 1 major - Triton Atmosphere: thick, mostly hydrogenSurface: no true surface, gas & liquid gas Interior: may have a small, solid coreDay Length: 16 Earth hours

• PLUTO – a planetoidLocation: 9th from the SunMoons: 1 moon - CharonAtmosphere: thin atmosphere of methane and nitrogenSurface: mix of ice and rock Interior: unknown Day Length: about 6 Earth days

Galaxies and the Universe

• Our solar system is in the Milky Way Galaxy

• Most scientists believe that there is a massive black hole at the center of our galaxy• It is called Sagittarius A*• It is thought to be about 93 million miles

across• It is thought to weigh about the same as 4

billion Suns

Formation of the Universe• Age is about 13.5 billion years

• Big Bang Theory (not the TV show)– Expansion of space and matter

• Steady-state theory– Universe looks the same on large scales – New matter is created and added to the universe

as it expands

Death of the Universe• Big Crunch – universe stops expanding and

then collapses back in on itself• Big Freeze – universe never stops expanding,

becomes progressively too cold to support life• Flat Universe – universe stops eventually stops

expanding and also becomes too cold for lifeBig Rip – rate of expansion is increasing due to

dark matter which will eventually tear the universe apart

stars

OUR SUN