Astronomy

The study of the composition, position and movement of all objects in space.

The Solar System includes:

a) Planets b) Sun c) moon, asteroids, comets, meteors

Planets

Terrestrial planets: - small - contain mostly rocky material - includes Mercury, Venus, Earth and Mars

Gaseous planets - large - composed of huge quantities of different gases - includes Jupiter, Saturn, Uranus and Neptune

Note: Pluto is classified as neither a

terrestrial or gaseous planet – it is now classified as a “minor planet”

Minor Bodies Types of Minor Bodies: a) asteroids b) meteors c) comets

Asteroids – “minor planets” Irregular shaped rocky bodies “left-overs” from planet formations. Asteroid belt – between Mars and Jupiter (most

asteroids exist there). Size: 16 km to 955 km in diameter.

Meteors – “stones from the sky” Small chunks of rock or metal that burn brightly as

they enter Earth’s atmosphere. Friction causes the meteor to burn, producing

streaks of light (“shooting stars”) Large meteors that pass through the Earth’s

atmosphere and land on the Earth’s surface are called meteorites.

Meteoroids (rocks drifting through space) are thought to be from the asteroid belt or fragments from collisions.

Meteors may also come from material left behind from comets.

Comets – “travellers” Rocky metallic particles coated with frozen water,

ammonia, methane and carbon dioxide; As comets move closer to the sun they reflect light. Some of the solid ice begins to change to gas as the

comet gets closer to the sun, forming a tail.

Earth’s Motion (Chapter 25) Rotation: turning motion of the Earth Axis of Rotation: imaginary straight line through Earth between the

north pole and south pole; slightly tipped (23.5o) angle of the axis does not change as Earth moves

on its path around the sun.

Evidence of Rotation: 1. Foucalt Pendulum Foucalt observed a pendulum over the course of a

day, and found the the swing shifted over time. Once it is set in motion, a pendulum can not

change its direction of swing Therefore, the Earth must have instead shifted

beneath the pendulum.

Evidence of Rotation: 2. Coriolis Effect Winds and ocean currents are deflected to the

right in the northern hemisphere and to the left in the southern hemisphere.

This would only occur if the earth is rotating counter-clockwise.

Effects of Rotation: Length of day (time for earth to turn once on its axis) Day/night (only half of Earth is facing sun at any time) Amount of sunlight (longer nights when northern

hemisphere is tilted away from the Sun) Direction of sunrise/sunset – Earth rotates

counterclockwise (turns from west to east), so the sun rises in the east and sets in the west.

Earth’s Revolution: Movement of Earth in its orbit around the Sun The Earth (and all planets) revolve

counterclockwise around the sun (when viewed from North Pole)

Earth’s Revolution: Earth travels in an elliptical orbit (distance

between Earth and Sun changes over the year). perihelion – Jan. 2 (closest point to the Sun) aphelion – July 4 (furthest point from the

Sun) 1 revolution = 365.24 days (1 year)

Evidence of Revolution: Parallax: nearby stars appear to shift position

when compared to distant stars (pencil demonstration)

Seasonal Changes in Constellations Different constellations are visible at

different times of the year

Effects of Earth’s Revolution Hemisphere that leans towards the sun has a longer

period of daylight and the density of incident light rays from the sun is greater. This results in warmer temperatures (summer)

Areas near the equator do not experience dramatic changes in daylight periods, or in the angle of sunlight and therefore do not have seasons.

Seasons Summer Solstice – longest daylight period: June

21st Winter Solstice – shortest daylight period:December 21st

Equinoxes – when sun is directly overhead of the Equator, and day time = night time

Vernal (Spring) Equinox: March 21st Autumnal Equinox: September 22nd

THE MOON Rotation: the moon turns on its axis

over the same time period it orbits around the Earth; therefore, the same side of the moon ALWAYS faces Earth.

Surface of the Moon: Composed of: Highlands – light areas

Craters – basins and plains (also called MARIA)

Dark side has a thicker crust (100 km vs. 60 km – due to Earth’s gravitational pull?)

History of the Moon: Likely formed from collision between the Earth and a

Mars-sized object approximately 4.6 billion years ago (when the earth was newly formed)

Mass of molten rock was knocked into space and cooled to form the moon.

History of the Moon: Initially, the surface was bombarded with particles,

forming large and small craters;

Later, lava poured out of gaps in the larger basins for nearly 1 billion years, forming the maria.

For the last 3 billion years, no volcanoes have erupted; the moon is geologically inactive.

Moon’s Orbit The Moon revolves around Earth from west to east

in an elliptical orbit (27 1/3 days)

Distance is about 386,000 km from Earth

Closest point in its orbit is called the perigee, furthest is the apogee.

Moon’s Phases Daily changes in the Moon’s appearance

The sun lights the half of the moon facing it

However, the half of the moon that faces Earth is usually not the half lit by the sun.

Moon’s Phases The face changes from all dark to all light over two

weeks – WAXING

The face changes from all light to all dark over the next two weeks – WANING

The Sun: An Average Star The sun’s energy is produced by nuclear fusion

As the closest star to Earth, it provides heat and light.

The energy from the sun comes from NUCLEAR FUSION, where HYDROGEN atoms fuse together to form HELIUM atoms, releasing heat, light, and other forms of energy.

Distances to the Stars When studying the solar system, distances

are often described using the astronomical unit (A.U.): 1 A.U. = distance from sun to earth

= 1.50 x 108 km

Distances to the Stars When studying the universe, we deal with

HUGE distances

For convenience, the light-year was developed.

Light-year: distance light rays travel in one year.

Distances to the Stars In one second, light travels 300 000 km.

In one year, light travels 9 460 000 000 000 km

= 9.5 x 1012 km

Distances to the Stars 1. To find # of light years (given km):

#L.Y. = distance in km 9.5 x 1012 km per L.Y. 2. To find # of kilometres (given L.Y.):

#km = (distance in L.Y.) x (9.5 x 1012 km per

L.Y).

Examples: 1. Alpha Centuri is 41 trillion km away, or 4.1 x 1013 km # L.Y. = distance in km 9.5 x 1012 km/L.Y. = 4.1 x 1013 km 9.5 x 1012 km/L.Y. = 4.3 light years.

2. Betelgeuse is 490 L.Y. away. # km = (distance in L.Y.) x (9.5 x 1012 km/L.Y.) = (490 L.Y.) x (9.5 x 1012 km/L.Y.) = 4.7 x 1015 km

Brightness of Stars Magnitude: the “brightness” of a star. Apparent Magnitude: Brightness of a

star as it appears to us on earth.

Luminosity: Actual amount of light energy given off by a star at a standard distance.

Absolute Magnitude: expresses the luminosity Equals to apparent magnitude if the star

was placed 32.6 L.Y. away from earth. Determined using apparent magnitude and

calculated distance to the star

Star Classification Spectroscopy Scientists use spectroscopes to split light

energy given off by the sun and other stars.

Each chemical element shows a unique spectrum when viewed through spectroscope.

Star Classification Spectroscopy

The spectrum of a star can then tell us:

○ The elements that make up a star; ○ Proportions of the different elements; ○ How fast the star is moving toward or

away from the Earth.

Spectral Types Colour of a hot object changes as

temperature increases: Dull Orange Yellow Bluish Red White Using spectroscopes, scientists have

grouped stars into 7 colour types called spectral types.

Table: Spectral Types of Stars

Hertzsprung-Russell (H-R) Diagram of Star Types Graph of surface temperature

vs. absolute magnitude

Shows that usually the brightness of stars increases as the surface temperature increases

Divides stars into four groups, based on where they lie on the diagram

Main sequence stars band running through middle of diagram, including our

Sun

Red Giants cool, but very large and bright stars (upper right of

diag.) Supergiants extremely large, bright stars (top of diagram) White Dwarfs hot, but very small and dim stars (lower left of

diag.)

Structure of the Universe Universe: consists of everything that

exists, all the matter and all the energy, as well as the space between the matter.

In the Past Ancient astronomers believed that the

Earth was standing still, while everything else moved around it –

This was known as an Earth-Centred Universe.

1600s

Galileo Galilei improved the telescope and determined that stars were much further away than the planets.

He suggested that planets and the Earth revolve around the sun (Sun-centred solar system)

Today’s Ideas Sun and other stars are also moving;

Stars are gathered in large groups surrounded by gas and dust (galaxies).

Types of Galaxies Edward Hubble developed a classification scheme for

galaxies, based on four types: Elliptical

No spiral structure Almost round to cigar-shaped

Types of Galaxies Spiral Outstretched, curved arms, like a

pinwheel

Types of Galaxies Barred Spiral Similar to spiral, but also has a prominent

bar through the nucleus

Types of Galaxies Irregular Lacks either spiral structure or nuclear

bulge, and doesn’t have the symmetry of an elliptical galaxy (random collection of stars)

Origins of the Universe Big Bang Theory Approximately 10 –20 billion years ago, the universe

was an infinitely dense, very small hot mass

This mass exploded and started expanding outward.

As the universe cooled and condensed, the galaxies and solar nebulas formed.

Next, planetisimals and meteors formed from individual solid particles combining with other particles.

Smaller planetisimals either collided with larger ones to form planets, or became asteroids and/or moons.

Oscillating Theory

Like the Big Bang Theory, it suggests that the universe is still currently expanding.

It will continue to expand to some maximum size, and then will begin to contract.

Contraction will continue until the universe becomes small and dense enough for another explosion and expansion to occur.

Evidence for Big Bang/Oscillating Theory Red Shift – galaxies observed through a

spectroscope have a longer wavelength than normal, suggesting these galaxies are moving away.

Background Radiation – unexpected

radiation has been observed coming from all directions in space, suggesting it may be a remnant of the radiation from the initial “Big Bang” explosion.