Astronomy Chapter 5: Planetary Motion and Orbits

Solar System Characteristics

• The Sun is the central star of the Solar System
• Eight planets orbit the Sun in elliptical orbits
• Over 67 natural satellites (moons) orbit the planets
• Asteroids and meteoroids are small, rocky objects found throughout the system
• Comets are icy bodies that orbit the Sun

Structure of the Solar System

• The Sun is at the center of the Solar System
• Planets revolve around the Sun in elliptical orbits
• Gravity and planetary motion keep planets in orbit
• Planets rotate about their axes, creating an oblate spheroid shape
• All planets lie on the ecliptic plane

Star or Planet?

• Planets appear to move relative to stars when viewed from Earth
• Planets' features are distinguishable with a telescope, unlike stars

The Inner Planets

• Also called terrestrial planets
• Characteristics include rocky crusts, dense mantles, and dense cores
• They are different in composition and structure

Planet Mercury

• Slow rotation causes temperature extremes (400°C to -170°C)
• Many impact craters
• Thin, almost non-existent atmosphere
• Smallest planet

Planet Venus

• Dense atmosphere (about 90 times the pressure of Earth's atmosphere)
• Atmosphere is mostly carbon dioxide
• High surface temperatures due to the greenhouse effect
• Slow rotation

Planet Earth

• Density atmosphere (about Earth's atmosphere),
• Mainly nitrogen and oxygen

Planet Mars

• Thin atmosphere, mostly carbon dioxide
• Evidence of past volcanism
• Frequent dust storms
• Rocky surface with evidence of water erosion
• Polar ice caps made of solid CO2 (dry ice)

The Outer Planets

• Also known as Jovian planets
• All gas giants with many moons
• Some have rings made of gas
• Unique features among Jovian planets include multiple moons and rings

Jupiter

• Largest planet
• Mostly hydrogen and helium
• Strong magnetic field due to electric currents
• Surface has alternating bands of swirling gases
• The Great Red Spot is a sustained hurricane-like storm
• Has at least 16 moons and 4 visible rings

Saturn

• Has at least 22 moons
• Has the most complex ring system in the Solar System
• Lowest density in the Solar System

Uranus

• Axis of rotation is almost horizontal relative to the plane of its orbit
• Axis is tilted on its side
• Has at least 17 moons and 11 small rings
• Primarily made of methane gas

Neptune

• Similar to Uranus in size, mass, and composition
• Has at least 8 moons and 4 small rings

What is a Planet?

• Must orbit the sun
• Must have enough gravity to make it round
• Must "clear its neighbourhood" of smaller objects

What is a Dwarf Planet?

• An object that orbits the sun, has enough mass to assume a round shape, has not cleared its orbital area of other objects, and is not a moon.

What is an Exoplanet?

• A planet that orbits a star outside the solar system

What about Pluto?

• Now classified as a dwarf planet
• Elongated orbit
• Has at least 3 moons
• Classified as a member of the Kuiper Belt

Kuiper Belt

• A belt of objects outside of Neptune's orbit
• Extends to 3 billion kilometers beyond Neptune's orbit
• Contains over 70,000 objects

Oort Cloud

• Contains the most distant objects orbiting the sun
• Most comets originate here

Other Bodies in the Solar System

• Dwarf planets are round
• Satellites are objects in orbit around planets
• Asteroids are located between the orbits of Mars and Jupiter
• Comets are icy bodies that have a nucleus, coma and tail

Comets

• Primarily made of rock, frozen water, ammonia, methane, and carbon dioxide
• Some describe comets as dirty snowballs
• When comets get closer to the sun, ice evaporates forming a coma and tail
• Comets originate in the Oort Cloud

Parts of a Comet

• Nucleus
• Coma
• Dust Tail
• Ion Tail

Meteoroids

• Small bits of rock and metal in the solar system that are less than 1 mm in diameter
• When meteoroids enter an atmosphere, they're called meteors if they burn up
• If they reach the earth's surface, they're called meteorites

Kepler's Laws and Planetary Satellites

• Each planet orbited the sun in an elliptical orbit, not a perfect circle
• Planets sweep out equal areas in equal amounts of time as they orbit

The Moon's Orbit

• The Moon orbits the Earth in an elliptical orbit
• The Earth is located at one focus of the ellipse
• Period of one rotation = period of revolution around Earth

Phases of the Moon

• The moon appears to cycle through phases

Lunar Eclipse

• Moon moves into Earth's shadow

Solar Eclipse

• Moon passes between the sun and earth, blocking all or part of the sun's light

Hybrid Solar Eclipse

• Combination of a total and annular solar eclipse

Tides

• Moon's gravity causes "bulges" in Earth's oceans
• Spring tides occur when the sun, moon, and Earth are aligned
• Neap tides occur when the sun, moon, and Earth form a right angle

Structure of the Sun

• Diameter is 1,380,000 km (110 times Earth's diameter)
• Surface temperature is 5,500°C
• Interior temperature is 15,000,000°C
• Primarily composed of hydrogen (70%) and helium (28%) with trace heavier elements

Sunspots

• Darker areas on the photosphere
• Allows us to observe sun's movement
• Magnetic field is 1000 times stronger than surrounding photosphere

Solar Flares

• Outbursts of energy from sunspot areas
• Large energy flares
• Part of the sun's magnetic field activity

Solar Prominences

• Large, flame-like arches of material suspended above the sun's surface by magnetic fields

Solar Wind

• Constant streams of charged particles (mostly protons and electrons) from the corona

Sun's Energy

• Nuclear fusion of small atoms into larger ones

Constellations

• Groups of stars, which appear to form shapes
• Based on stories from mythology
• Represent humans, animals, or fictional creatures

Stellar Distances

• Measured relative to the speed of light (300,000 km/s)
• One light-year is the distance light travels in one year

Star's Composition

• Primarily hydrogen (98-99%) and helium (1-2%) with heavier elements

Star's Colour

• Depends on surface temperature
• Red stars are lower temperature, blue stars are higher temperature

Magnitude/Brightness

• Apparent Magnitude: Brightness as viewed from Earth
• Absolute Magnitude: Actual brightness

Stability of Stars

• Stable if explosive energy balances gravity

Hertzsprung-Russell Diagram

• Shows luminosity and temperature of stars

The Life Cycle of Stars

• Stellar nebula
• Protostar
• Main sequence star
• Giant or supergiant
• White dwarf

Planetary Nebulae

• Halo of glowing gases surrounding a white dwarf
• Results of a medium-sized star's death

White Dwarfs

• Hot carbon-oxygen core of a previous star

Black Dwarfs

• Theoretical remnant of a cooled white dwarf

Supernova

• Star collapses and produces a shock wave. Outer layers blast into space
• There are two possibilities depending on the star's mass.

Galaxies

• Large systems of stars bound together by gravity
• Typical diameter of 100,000 light-years
• Typically 100 billion stars

Types of Galaxies

• Spiral galaxies have nuclei and arms of stars
• Elliptical galaxies are shaped like ellipses
• Irregular galaxies have no particular shape

Measurement and the Big Bang

• Determining distance to stars using parallax

Measurement of Distance: Magnitudes

Cepheid Variables (Stars)

• Vary in brightness over a regular period of time
• Useful for measuring distances
• Distance is calculated by comparing apparent magnitude to known absolute magnitude

Measurement of Speed-Using Doppler Effect

• Light coming from objects moving toward us or away from us gets shifted to different wavelengths

Expanding Universe

• Distant galaxies appear more red than expected
• Suggests the universe is expanding
• All other observed galaxies are moving away from us
• This suggests the universe is expanding

The Big Bang Theory

• All matter and energy started at one point
• A huge explosion propelled matter and energy outwards in all directions

Test your knowledge on planetary orbits, the characteristics of Galilean satellites, and the laws of planetary motion in this quiz. Explore topics such as the solar wind, fusion processes in the sun, and the moon's tidal effects. Perfect for students of astronomy or anyone interested in celestial mechanics.