AUSTRALIA – TO THE HORIZON AND BEYOND Part 1

Yr 7 Science

Topic 4

(Chapter 5)

Space & the Universe DP 1

Space is everything in the universe that lies outside the Earth’s atmosphere

Much of space is vast empty and void, hence the name – ‘Space’

No one knows how large the universe is, special telescopes are able to see clusters of stars (galaxies), up to 13 billion light years away.

Our solar system

Our solar system consists of the sun, nine planets (and their moons), an asteroid belt, and many comets and meteors. The sun is the centre of our solar system; the planets, their moons, the asteroids, comets, and other rocks and gas all orbit the sun.

What is in space besides planets and stars?

Most of the universe is empty space, called a vacuum, but it is an imperfect vacuum. There are clouds of interstellar dust and the tiny particles that make up the solar wind. There are many isolated particles and hydrogen atoms, which sometimes form clouds over a billion kilometres wide called "nebulae." Besides nebulae and interstellar dust, there are also bits of rubble as big as small moons to as small as grains of sand. These bits of rubble are called planetoids and asteroids. Radio, heat, and x-rays all echo through space, as do beams of light. There is radiation bursting forth in solar flares.

Space & the Universe cont: (DP 2)

Light travels faster than anything in the universe – nearly 300, 000 kms/sec.

A light year (I.e. how far light travels in a year) is equal to 9.5 trillion kms.

It takes light about 8 min to reach us from the Sun. How far away then is the Sun?

Space & the Universe cont: (DP 2)

An Astronomical Unit (AU) is another way (other than light years) of comparing the vast distances of space.

1 AU is equal to the distance of the Earth from the Sun I.e. approx 150 million kms.

Space & the Universe cont:

Since light takes so long to reach earth we see objects as they ‘were’, not as they ‘are’.

For example we see some bright stars as they were 1800 years ago, in the time of ancient Rome!

Major Features of the Universe (DP 1)

Stars (like our Sun) are huge fiery balls of incredibly hot gas. Primarily stars are made up of two gases – 3 quarters hydrogen and 1 quarter helium. They create energy through nuclear reactions (millions of times more powerful than a nuclear bomb). Reactions are caused by squeezing atoms of hydrogen gas deep inside the star.

A star will continue to glow, sending out light, heat, radio waves and other radiation until all the hydrogen is used up. Medium – sized stars like our Sun burn for about 10 billion years.

Hydrogen & the Hindenburg Disaster (Fact or fallacy?)

Major Features of the Universe cont- (DP 1)

Nebulae are gigantic clouds in space they are made up of dust and gas, often the remains of exploded stars. Nebulae gather due to the effect of gravity. Nebulaes are the beginning of stars. Nebulae some times glow red as they are warmed by radiation from nearby stars.

Galaxies are clusters of stars. Our Sun forms part of The Milky Way galaxy. The Milky Way can be seen easily at night by the naked eye.

Major Features of the Universe cont- (DP 1)

A solar system is a system of planets or other bodies orbiting another star (or sun), planets are held in place by the stars gravitational effect.

Our solar system consists of the Sun together with the nine planets and all other celestial bodies that orbit the Sun. Celestial bodies includes moons and asteroids.

The Sun is by far the most massive part of the solar system, containing almost 99.9% of the system's total mass.

Planets of our solar system (In order of distance from the Sun) DP 3

Planet AUs from Sun Characteristics

Mercury 0.4 Small rocky planet with atmosphere (0 moons)

Venus 0.7 Small rocky planet with atmosphere (0 moons)

Earth 1.0 Small rocky planet with atmosphere & with one moon. Presence of liquid water & optimum distance from sun to support life (one moon)

Mars 1.5 Small rocky planet with atmosphere (two moons)

Jupiter 5.2 Largest planet mostly gas (rock core & 18 moons+)

Saturn 9.5 Second Largest mostly gas planet (rock core & 18 moons)

Uranus 19.2 Large mostly gas & liquid methane planet (15 moons)

Neptune 30.1 Large mostly gas & liquid methane planet (2 moons)

Pluto 39.5 Smallest planet, rocky with (1 moon)

Planets in the nights sky

The word planet is derived from the Greek word planetes which means ‘wanderer’.

This is because if you observe planets such as Mars or Mercury they will appear to wander rather than just rotate their position. This is due to their differing orbits around the Sun.

Mnemonic for planets of solar system

"My Very Excellent Mother Just Sent Us Nine Pizzas"

Size of Planets.

The asteroid belt DP 4

A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. These objects all orbit the sun in roughly circular orbits that lie in the same plane, the ecliptic (Pluto is an exception; it has an elliptical orbit tilted over 17° from the ecliptic).

Ptolemy’s & Copernicus – Kepler Models of the Universe DP 6

Ptolemy (130AD) believed the Earth was the centre of the Universe

Nicolaus Copernicus (1512) relised that the Sun and not the Earth was the centre of the Universe. This model was confirmed in 1609 by Johannes Kepler

Planet Structure

The ‘solid planets’ (terrestrial)

The first four planets are made primarily of rock - Mercury, Venus, Earth and Mars. (Pluto is also made of rock)

The ‘gas planets’ (non-terrestrial)

The next four are the ‘gas giants’ – Jupiter, Saturn, Uranus and Neptune

Satelites

What is a satellite?An object in an orbit is called a satellite. A satellite can be natural, like the Moon, or human-made (or even perhaps extraterrestrial?). Satellites can travel around planets or around stars such as our Sun.                                                                         All the planets are satellites around the Sun. Almost every ship launched from Earth can be considered a satellite, as it is orbiting either the Earth or the Sun.

Temperatures on the Planets

Generally, the farther from the Sun, the cooler the planet. Differences occur when the greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere.

Planet Density

The outer, gaseous planets are much less dense than the inner, rocky planets. The Earth is the densest planet. Saturn is the least dense planet; it would float on water.

The Mass of the Planets

Jupiter is by far the most massive planet; Saturn trails it. Uranus, Neptune, Earth, Venus, Mars, and Pluto are orders of magnitude less massive

Gravitational Forces on the Planets

The planet with the strongest gravitational attraction at its surface is Jupiter. Although Saturn, Uranus, and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared.

Asteroids & Asteroid Belts DP 4

Asteroids are basically chunks of rock.

An Asteroid belt is as the name suggests a belt of asteroids. The asteroid belt we refer to (in our solar system) is the region of interplanetary space between Mars and Jupiter where most asteroids are found.

Rotation = Day and Night DP 5

The rotation of the Earth on its axis gives us day and night.

Costellations DP 8

Historically, constellations were groupings of stars that were thought to outline the shape of something, usually with mythological significance. There are 88 recognized constellations, with their names tracing as far back as Mesopotamia, 5000 years ago. Constellations are still used today by modern astronomers to assist in mapping out space and giving a reference point for locating planets.

Constellations and the Zodiac DP 8

The ancient astronomers associated dates with the constellations (in a narrow belt known as the zodiac) Twelve zodiacal signs were named by the Ptolemy (2nd-century) as follows: Aries (ram), Taurus (bull), Gemini (twins), Cancer (crab), Leo (lion), Virgo (virgin), Libra (balance), Scorpio (scorpion), Sagittarius (archer), Capricorn (goat), Aquarius (water-bearer), and Pisces (fishes).

Celestial Sphere DP 9

A celestial sphere is imaginery sphere surrounding the earth. At any one time we see no more than half of this sphere

WestEast

South Celestial Pole – DP 10

The SCP is the zenith for an observer standing directly at the south pole

The SCP can be located by using the Southern Cross (see page 165)

The stars can be observed to rotate around the CSP I.e. as the Earth rotates on its axis (23.5)

Plotting Star Positions. Prac 5.2 p.163

Azimuth and elevation are angles used to define the apparent position of an object in the sky, relative to a specific observation point.

The azimuth is the point of an object on the celestial sphere

The elevation is the height / angle of the object above the horizon

The zenith is the point straight overhead

Azimuth & Elevation DP 11

Azimuth is the lateral measurement and elevation (or altitude) is the perpendicular measurement (see text p. 164)

Note: the Zenith is directly above the observer.

Phases of the Moon DP 13

Waxing, Waning& Gibbous DP 13

Waning - Shrinking.

Waxing - Growing

Gibbous moon (swollen on one side) is between a full moon and a half moon, or between a half moon and a full moon.

Moon Facts

1. Moon travels around the Earth in a circle called an orbit. It takes the moon about 28 days to go one time.

2. The Moon is about 250,000 miles (384,400 kilometers) from Earth and has a diameter of 2,000 miles ( 3,476 kilometers).

3. The Sun always lights up (illuminates) half of the Moon at one time.

4. The Moon is not a light source, it has no light of its own. We can only see the moon because it reflects light from the sun.

5. The Moon appears to change shape but what we are actually seeing is the Moon lit up by the light from the Sun in different ways on different days.

6. We always see the same side of the moon. The Moon always keeps the same side pointing towards us so we can never see the 'back' of the Moon from the Earth.

Even more Moon facts

The Earth's Moon is the fifth largest in the whole solar system, and is bigger than the planet Pluto. The Moon has a nearly circular orbit (e=0.05) which is tilted about 5° to the plane of the Earth's orbit. Its average distance from the Earth is 384,400 km. The combination of the Moon's size and its distance from the Earth causes the Moon to appear the same size in the sky as the Sun, which is one reason we can have total solar eclipses. The Moon's orbital period is 27.322 days

If the speed of light is about 300, 000Kms per sec how long then does it take for reflected light from the the Moon to reach us? Just over 1 sec (1.3sec actually!)

Do stars move? Yes like us (our entire solar system) they are rotating around the centre of our galaxy. In relation to the size of the galaxy this movement is quite slow.

What formed the Moon?

The most popular theory is that the Moon was torn from the Earth in a huge planetary collision about 4.5 billion years ago. An object at least as large as Mars, it is proposed, crashed into Earth, throwing vast clouds of debris into orbit. This then cooled and coalesced under the influence of gravity to form the Moon.

So far, the hypothesis is supported by data: it fits with the evidence of lunar rocks and observations from spacecraft orbiting the Moon. As the material that formed the Moon would have come from the Earth’s crust and mantle, not its iron-rich core, the relative lack of iron on the Moon is potentially explained

Moon Positions

Solar Eclipse DP 15

A solar eclipse is when the moon obscures our view of the sun (I.e. the Moon comes between Earth and the Sun)

Eclipses

Eclipses occur more often than most people realise with a solar eclipse taking place roughly every 18 months. However, a total eclipse will only be seen from any specific location on Earth about once every 100 years. Last solar eclipse in Australia was on the 16th Feb 1999.

Lunar eclipse DP 15

Seasons DP 16 & 17

The Earth’s axis (23.45 degrees) is responsible for the seasons. It takes 365.26 days for the Earth to orbit the sun. The top diagram is of the northern hemisphere and the lower diagram is of the southern hemisphere. In the top diagram during winter where would Australia be located?

Seasons cont-

Summer night Spring day

Consider these diagrams!

Elevation of Sun DP 16 cont-

Due to its changing elevation and duration of exposure on the Earths surface the Sun radiant energy has differing seasonal effects on our environment.

Date definitions – Solstice DP 18

Summer solstice (22 Dec) On the day of Summer Solstice, the Earth’s south pole is tilted towards the Sun. The Sun rises south of east, sets south of west and reaches 751/2° above

the horizon at noon. This is, usually, the longest day of the year. Winter Solstice (22 June), Earth’s south pole is tilted away from the Sun. The Sun rises

north of east, sets north of west and reaches 281/2° above the horizon at noon. This is,

usually, the shortest day of the year. Which of the diagrams below represents the winter solstice?

Dates Defined – Equinoxes DP 18 cont-

There are two equinoxes each yearThere are two equinoxes each year – Spring (22 Sep) & Autumn (22 Mar). When simplified the – Spring (22 Sep) & Autumn (22 Mar). When simplified the term term simply simply referreferss to the two times of year when night and day are the same length to the two times of year when night and day are the same length..

On the day of the On the day of the Spring Spring and Autumn Equinoxesand Autumn Equinoxes, the Earth’s poles are the same distance from the Sun. , the Earth’s poles are the same distance from the Sun. The The Sun rises due east, sets due west and gets to 52° above the horizon at noon. On Sun rises due east, sets due west and gets to 52° above the horizon at noon. On bothboth day dayss there are there are roughly 12 hrs of day and 12 hrs of night.roughly 12 hrs of day and 12 hrs of night.

Does the diagram below represent both equinoxes?Does the diagram below represent both equinoxes?