Chapter 3 – the solar system Lesson 1-observing the solar system

Earth at the Center Patterns of stars are called constellations.

Greek Observations The Greeks called these several lighted objects planets. The Romans later named these planets: Mercury, Venus, Mars, Jupiter, and Saturn. Most Greek astronomers believed the universe to be perfect, with Earth at the center. In a geocentric system, Earth is at the center of the revolving planets and stars.

Ptolemy’s Model About A.D. 400, the Greek astronomer Ptolemy further developed the geocentric model. Even though Ptolemy’s geometric model was incorrect, it explained the motions observed in the sky fairly accurate.

Copernican Revolution In a heliocentric system, Earth and the other planets revolve around the sun. Copernicus was able to work out the arrangement of the known planets and how they move around the sun. Evidence collected by the Italian scientists Galileo Galilei convinced others that the heliocentric was correct.

Galileo’s Evidence Galileo used the newly invented telescope to make discoveries that supported the heliocentric model.  

Tycho Brahe’s Observations Carefully observed and recorded the positions of the planets for more than 20 years without a telescope.

Kepler’s Calculations Found that Mar’s orbit was a slightly flattened circle, or ellipse. Kepler found that the orbit of each planet is an ellipse.

Modern Discoveries Today we know that the solar system consists of the sun, the planets, and their moons, and several kinds of smaller objects that revolve around the sun. Astronomers today still use telescopes located on Earth, but they also placed telescopes in space to gain a better view of the universe beyond Earth.  

Lesson 2 – The Sun

The Sun’s Interior The sun’s interior consists of the core, the radiation zone, and the convection zone. Like Earth, the sun has an interior and an atmosphere.  

The Core The sun produces an enormous amount of energy in its core. The sun’s energy comes from nuclear fusion. The temperature in the sun‘s core reaches about 15 million degrees Celsius, high enough for nuclear fusion to take place.

CORE

The Radiation Zone The energy produced in the sun’s core moves outward through the middle layer of the sun’s interior, the radiation zone. Because the radiation zone is so dense, energy ca take more than 100,000 years to move through it.

The Sun’s Atmosphere The sun’s atmosphere includes the photosphere, the chromospheres, and the corona. The inner layer; when you look at an image of the sun, you are looking at the photosphere. During a solar eclipse, the moon blocks light from the photosphere. At the start and end of a total eclipse, a reddish glow is visible just around the photosphere; this glow comes from the middle layer of the suns’ atmosphere – the chromospheres. The outside layer of the sun which becomes visible during a solar eclipse. Looks like a white halo around the sun

Features on the Sun Features on or just above the sun’s surface include sunspots, prominences, and solar flare. Sunspots seem to move across the sun’s surface, showing that the sun rotates on its axis just as Earth does. The number of sunspots on the sun varies over a period of about 11 years. Sunspots usually occur on groups. Huge reddish loops of gas are called sunspots Sometimes the loops in sunspot regions suddenly connect, releasing large amounts of magnetic energy, causing gas to erupt-called solar flares. Solar flares can greatly increase the solar wind from the corona, resulting in an increase in the number of particles reaching Earth’s upper atmosphere. The result is rippling sheets of light in the sky called auroras. Solar Wind particles can also affect Earth’s magnetic field, causing magnetic storms, which can disrupt radio, telephone, and television signals and may cause electrical problems.

Lesson 3 – The Inner Planets

Earth Earth has three main layers – a crust, mantle, and a core. Earth is unique in our solar system in having liquid water at its surface. Earth’s surface is covered in 70 % of water. Earth has enough gravity to hold on to most gases. These gases make up Earth’s atmosphere, which extends more than 100 kilometers above it surface. Earth is the only planet that is rich in oxygen. Water in a gaseous form is called water vapor.  

Mercury Mercury is the smallest terrestrial planet and the planet closest to the sun. Many of Mercury’s craters have been named for artists, writers, and musicians, such as composers Bach, and Mozart. Mercury has virtually no atmosphere. Because Mercury’s mass is small, its gravity is weak. Mercury is a planet of extremes, with a greater temperature range than any other planet in the solar system.

Venus Venus’s density and internal structure are similar to Earth’s. But, in other ways, Venus and Earth are very different. Sometimes you can see Venus in the west just after sunset. It rises before the sun in the morning, and is known as the morning star. Venus’s density and internal structure are similar to Earth’s. But in other ways, Venus and earth are very different. Venus takes about 7.5 Earth months to revolve around the sun. It takes 8 months for Venus to rotate once on its axis. Venus rotates east to west. Astronomers hypothesize that this unusual rotation was caused by a very large object that struck Venus billions of years ago, to change its direction of rotation. Atmosphere is so thick that it is always cloudy there, which are made mostly of sulfuric acid. The pressure of Venus’s atmosphere is 90 times greater than the pressure of Earth’s atmosphere. Because Venus is closer to the sun than Earth is, it receives more solar energy that Earth does. The Magellan probe in 1990 confirmed that that Venus is covered with rock and has many volcanoes and broad plains formed by lava flows.

Mars Mars is called the red planet, which is due to the breaking of iron – rich rocks, which creates a rusty dust that covers much of its surface. The atmosphere is more than 95% carbon dioxide. Scientists think a large amount of liquid water flowed on Mar’s surface in the distant past. At present time water does not exist for long on Mar’s surface. It’s atmosphere is so thin that any liquid water would quickly turn into gas. Scientists think that a large amount of water ay still be frozen underground. Because Mars has a tilted axis, it has seasons just as Earth does. As the seasons change on the dusty surface of Mars, wind storms arise and blow the dust around. Astronomers now realize that the dark colors are often the result of windstorms. Many space probes have visited Mars. They examined a variety of rock and soil samples, which the rovers found strong evidence that liquid water was once present. Some regions of Mars have giant volcanoes, but they are no longer active. Mars has two very small moons. (Phobos, the larger moon and Deimos the smaller moon) Phobos and Deimos are covered with craters. Astronomers predict that Phobos will smash into Mats in about 40 million years.

Lesson 4 – The Outer Planets

Gas Giants and Pluto The four – Jupiter, Saturn, Uranus, and Neptune – are much larger and massive than Earth, and they do not have solid surfaces. These planets are called the gas giants. Pluto is included, but considered a dwarf planet. Like the sun, the gas giants are composed mainly of hydrogen and helium. Gravity keeps these planets gas’s from escaping, so they have thick atmospheres. The outer layer of the gas giants are extremely cold because of their distance from the sun. All the gas giants have many moons and are surrounded by a set of rings.

Jupiter Jupiter is the largest and most massive planets. Jupiter has a think atmosphere made mainly of hydrogen and helium. Jupiter also has a Great Red Spot which is a storm that is larger than Earth. The pressure at Jupiter’s core is estimated to be about 30 million times greater than the pressure at earth’s surface. Jupiter has the four largest moons: Io, Europa, Ganymede, and Callisto. All four are large than Earth’s Moon. Since Galileo’s time, astronomers have discovered dozens of additional moons orbiting Jupiter.

Saturn The second largest planet is Saturn. Saturn’s atmosphere also contains clouds and storms, but less dramatic then those on Jupiter. It is the only planet whose average density is less than water. Saturn has the most spectacular ring of any planet. These rings are made of chunks of ice and rock, each traveling in its own orbit around Saturn. Saturn’s largest moon, Titan is larger than the planet Mercury and was discovered in 1665. Four other moons of Saturn are each over 1,000 kilometers in diameter.

Uranus Uranus is twice as far from the sun as Saturn, so it is much colder. Uranus looks blue-green because of the traces of methane in its atmosphere. Was discovered in 1782 by William Herschel. Uranus’s axis of rotation is tilted at an angle of about 90 degrees from the vertical. Viewed from Earth, Uranus is rotating from top to bottom instead of from side to side. Astronomers think that billions of years ago Uranus was hit by an object that knocked it on its side. Uranus’s five largest moons have icy, cratered surfaces. The craters show that rocks from space have hit the moons. Recently astronomers discovered several more moons, for a total of at least 27.  

Neptune Neptune is a cold, blue planet. Its atmosphere contains some visible clouds. Discovered at least 13 moons orbiting Neptune. The largest is Triton, which has a thin atmosphere. Triton’s south pole is covered by nitrogen ice.  

Pluto and Dwarf Planets Pluto has a solid surface and is much smaller and denser than the outer planets. Pluto has three known moons. The largest is Charon, which is more than half the size of Pluto. Revolves around the sun only once every 248 Earth years and is very elliptical. Pluto was considered to be the ninth planet, until recently. A dwarf planet has not cleared out the neighborhood around it orbit.  

Lesson 5 – Comets, Asteroids, and Meteorites

Comets Comets are loose collections of ice, dust, and small rocky particles whose orbits are usually very long, narrow ellipses. When a comet gets close enough to the sun, the energy in the sunlight turns the ice into gas, releasing gas and dust. The brightest part of a comet, the comet’s head, is made up of the nucleus and coma. A comet’s tail can be more than 100 million kilometers long and stretch across most of the sky. Most comets are found in one of two distant regions of the solar system: The Kuiper Belt, and the Oort Cloud.   http://www.youtube.com/watch?v=ck7mE1ZhIIs&feature=related

Asteroids Most asteroids revolve around the sun between the orbits of Mars and Jupiter. Astronomers discovered four small objects between the orbits of Mars and Jupiter. They named the objects Ceres, Pallas, Juno, and Vesta. Astronomers have found more than 100,000 asteroids and they are constantly finding more. Scientists now hypothesize that asteroids are leftover pieces of the early solar system that never came together to form a planet. Some asteroids have very elliptical orbits that bring them closer to the sun than Earth’s orbit. Scientists hypothesize that many species of organisms, including dinosaurs, became extinct as a result of an asteroid hitting Earth.   http://www.youtube.com/watch?v=XXAZp8vMAh8

Meteors On average, a meteor streaks overhead every 10 minutes. Meteoroids come from comets or asteroids. When a meteoroid enters Earth’s atmosphere, friction with the air creates heat and produces a streak of light in the sky known as a meteor. The craters on the moon were formed by meteoroids. http://www.youtube.com/watch?v=6XTBrYWrey0

Lesson 6 – Is there Life Beyond Earth?

Goldilocks Conditions Earth has liquid water and a suitable temperature range and atmosphere for living things to survive. This Goldilocks term refers to temperature being just right for life.

Extreme Conditions Giant tubeworms have been found under the extremely high pressures at the bottom of the ocean. Single celled organisms have been found in nearby boiling temperatures of hot springs. These discoveries show that the range of conditions in which life can exist is much greater than a scientist once thought.

Life in Mars? Since life we know it requires water, scientists hypothesize that Mars may have once held conditioned needed for life to exist.  

Life on Europa? If there is liquid water on Europa, there might also be life. Scientists hypothesize that there is a liquid ocean under Europa’s ice.