The solar system began as a cloud of dust and gas. The cloud began to spin and contract. It contracted into a disc with the sun at the center. Planets formed from the disk. Gravity caused rocky, terrestrial planets to form near the sun. Gas giants floated further out. Celestial bodies are round because they are molded by the effects of spinning. Every star in the galaxy may have planets.
The sun is a star. It is average in size. It is 93 million miles away. Its surface is 11,000 degrees. Sunspots are dark because they are cooler. The sun is a hydrogen bomb, shining by nuclear fusion. Hydrogen turning into helium emits energy in the form of light and heat. This energy is stored in fossil fuels: coal, oil and gas.
The sun is a middle-age star and will burn another 5 billion years. It will become a red giant. The planets will be consumed. Earth's oceans will boil away. The atmosphere will go. The sky will turn black.
There are two kinds of objects, those which shine by their own light like stars and those which reflect light like planets and moons.
The planet Mercury is so close to the sun that many astronomers have never seen it. Mercury's surface is cratered like the moon's. Like the moon, Mercury has no atmosphere.
NASA launched the Messenger spacecraft to Mercury. Scientists want to know why it is so dense.
Like Mercury, Venus is between Earth and the sun. For that reason, Venus never strays far from the sun in the morning or evening skies. It is seen in the western sky after sunset. Venus goes through phases which are visible through a small telescope. Venus is brightest in its crescent phase because it is closer to Earth. It gets as bright as -4.5 magnitude.
Venus is about the size of Earth. We might expect similarities. In fact, the surface of Venus is 900 degrees because of the greenhouse effect. Its atmoshere consists of carbon dioxide. It is hell. Still, Venus accompanied by a crescent moon is one of the beautiful sights in nature.
Earth
From space, Earth is a blue planet spotted with white cloud tops. Earth is 25,000 miles in circumference and 8,000 miles in diameter. It revolves around the sun every 365 days, the period defined as a year.
Earth's orbit varies over million of years. It stretches and shrinks. This accounts for 7 ice ages.
Earth tilts on its axis 23 1/2 degrees. This tilt causes seasons. The northern and southern hemispheres alternately lean into and away from the sun. When it is summer in the United States, it is winter in Australia.
Earth's moderate distance from the sun is a factor in the evolution of life. It is neither too hot nor too cold. Liquid water can exist. Where there is water, there is life. It rained millions of years to create oceans. Mountains were created by stresses in the earth. Earth's atmosphere came from volcanos. The atmosphere provides pressure and protection from harmful rays. Oxygen is produced by the photosynthesis of plants. Earth's atmosphere extends 300 miles.
Life began in the sea (or so we have read). Four billion years ago, chemicals began showing characteristics of life. Viruses are on the line between the living and nonliving. One-celled organisms developed, microbes. Plants colonized the land. Invertebrates evolved. Vertebrates followed. Fish evolved into amphibians which evolved into reptiles. Dinosaurs lived in the Mesozoic Era between 65 million and 220 million years ago. Tyrannosaurus, brontosaurus, triceratops, stegosaurus, ankylosaurus and duckbills ruled. I did a paper titled "The Other Sciences," which was dinosaur-based. A species is a group of animals whose members interbreed. There are over one million species of animals.
Continents formed one land mass. As continental drift occurred, reptiles evolved into birds and mammals. Some paleontologists believe birds are dinosaurs. There was a golden age of giant mammals in the Cenozoic Era. Mammoths and mastadons became extinct only at the end of the recent Ice Age. Man has existed in some form for 5 million years. He evolved from primates in southeast Africa and spread through Europe and Asia. From Asia, he populated the South Sea islands and walked across the land bridge at the Bering Strait into the Americas. That was 50,000 years ago. Races as we know them came into existence at the end of the Ice Age 20,000 years ago. Civilization was born in Egypt and Mesopotamia. Recorded history spans 5,000 years. Colonization of the Americas by Europeans from the Renaissance forward is the most important human migration in history. World population is currently 6 billion. 300 million are in the United States.
Natural history is understood in terms of the Geological Time Scale. Paleontologists study the fossil record. Fossils are found in sedimentary rocks, those laid down by water. Radio carbon dating determines the age of rocks. To know the age of rocks is to know the age of their fossils.
The Outer Planets (Mars)
The outer planets exhibit retrograde motion. They appear to travel backwards against the stars as the faster Earth overtakes and passes them. Mars is a dramatic example.
Percival Lowell studied Mars from his observatory in Flagstaff, Arizona. He saw what he mistook for canals built by Martians.
Mars gets its red color from dust storms. Its surface contains rust (iron oxide). Its polar caps are made of dry ice (frozen carbon dioxide). Mars has a huge volcano known as Olympus Mons and a canyon called Valles Marineris.
Mars' atmosphere is too thin for water. There is evidence that water flowed in the past. If so, life may have evolved. The way to know is to go there and bring back rocks to see if they contain fossils. A journey to Mars will take a year, 6 months to get there and 6 months to return.
The Viking spacecraft landed on Mars in 1976. It found chemicals said to mimic life. 3 essentials for life are water, nutrients and energy. Scientists study the Atacama desert in Chile, the driest place on earth, to learn about Mars.
The Mars Science Laboratory will be launched in 2009 and land in 2010. It will try to determine whether microbes evolved on Mars. There may have been a zone of life in the early solar system extending from Venus to the asteroids.
The Martian moons are Phobos and Deimos. In Homer's Iliad, they were Fear and Panic and attended the god of war.
The asteroid belt is between Mars and Jupiter. Jupiter's influence kept this collection of rocks from coalescing into a planet. Ceres and Vesta are asteroids.
Difference in size means a difference in gravity. Large planets like Venus and Earth hold atmospheres. Small worlds like Mercury and the moon do not. Medium-size Mars holds a thin atmosphere. Worlds with atmospheres do not have many craters because atmospheres vaporize meteors and erode craters. Earth has a few craters. Venus and Mars have more. Mercury and the moon are heavily cratered.
Gas Giants
Voyager 1 flew by Jupiter and Saturn and was deflected. Voyager 2 went on to Uranus and Neptune. Voyager 2 spent 12 years (1977-89) on its Grand Tour. All the gas giants were found to have rings.
Jupiter is a failed star. If it were larger, nuclear reactions would have begun and it would shine by its own light. It is made of hydrogen and helium, the most common elements.
Jupiter has bands because it rotates so fast that its clouds are stretched into patterns. The Great Red Spot is a huge storm. There is now a Red Spot Jr. The Galileo probe reached Jupiter in 1995.
Jupiter has 60 moons. Io, Europa, Ganymede and Callisto are the largest, named for Jupiter's lovers. They were first seen by Galileo, who invented the telescope in 1610. Io is interesting because it has the only volcanos in in the solar system beyond Earth.
Saturn is a butterscotch ball of gas light enough to float in water. Saturn's rings are its glory. There are 7 main rings. They are made of rock and ice. As Saturn orbits the sun every 29 years, we see its rings open at the top, edge-on, open at the bottom and edge-on again.
Saturn has 31 moons. Titan is larger than the planet Mercury and is the only moon in the solar system with an atmosphere. Its atmosphere is orange and dense.
The major gap in Saturn's rings was discovered by Cassini. Titan was discovered by Huygens.
The Cassini-Huygens spacecraft is the first to orbit Saturn. The probe descended into Titan's atmosphere and sent back data. The reason for studying its atmosphere is that it is thought to be similar to that of early Earth. Scientists want to know how life developed. $3.3 billion was spent on Cassini. It is mind-boggling, the money spent on these projects.
Uranus was knocked on its side. Modern astronomy is explained in terms of collisions. Consider that dinosaurs were killed off by an asteroid. If the ancients thought the heavens benign, today's universe is a violent place. Uranus is a green, featureless pool ball. It was discovered by William Herschel in 1781.
Voyager 2 photographed Neptune's Great Dark Spot in the blue methane.
Small, rocky Pluto at the edge of the solar system breaks the rules. Its orbit is erratic, bringing it inside Neptune. Pluto may have been a moon dislodged from somewhere else. It has a companion, Charon. Clyde Tombaugh discovered Pluto in 1930. NASA launched the New Horizons spacecraft in January, 2006. It will take nearly 10 years to reach Pluto at a distance of 3 billion miles. Pictures will arrive in 2015. I plan on being here.
The Voyagers have left the solar system and are on their way to the stars. They contain records of earth sounds, languages and music.
--------------------
Jim Colyer wrote Save The Planet.
Jim Colyer wrote Save The Planet.
