THE SUN, at the center of our Solar System, is a G2V stellar class star orbiting in the Orion arm of the Milk Way. Once thought to be a below-average size star, we now know the Sun is larger than 85% of the stars in the Milky Way. Its surface temperature is about 10 thousand degrees Fahrenheit while its upper atmosphere can reach 36 million degrees. The Sun is about 4.57 billion Earth years old and has completed 20-25 galactic orbits. It will be a main sequence star for 5 billion more years and eventually become a red giant, then a white dwarf. Imprecisely called a “yellow dwarf,” our Sun is actually white. It appears yellow because of the Earth’s atmosphere. It is composed of 74.9% Hydrogen, 23.9% Helium, and other elements. The Sun has a dynamic magnetic field which flips polarity every 11 years. Magnetic field disturbances affect convection on the Sun’s surface and lead to cooler, darker areas (about 6400 degrees Fahrenheit) called sunspots. The Magnetic Field-Sunspot cycle may affect Earth’s weather and climate.
MERCURY is the smallest planet at 3,000 miles in diameter and also closest to the Sun at 34 million miles distant. Mercury orbits the Sun every 88 days and takes 58 days to rotate on its axis. This means that a day on Mercury can last 176 Earth days. There is no atmosphere – which creates a hellish environment. Temperatures in daytime climb to plus 790F degrees and drop to minus 274F degrees at night. Mercury can be difficult to observe as it is never far from the Sun. The best time for observing is when it is furthest from the Sun as seen from Earth. This is called maximum elongation and is still fairly close to the horizon. It appears as a bright, star-like object. Mercury’s surface is covered with millions of craters, but no surface features can be seen with a telescope.
VENUS is our nearest neighbor among the planets and is also the brightest planet in the night sky. If you know exactly where to look, you can see Venus in the daytime. Venus is the closest planet to Earth in size, just slightly smaller than we are. People once thought that Venus was a good candidate for finding life such as we have on the Earth. But now we know it to be very hot – several hundred degrees – and its atmospheric pressure is 92 times that of the Earth. When you see Venus in the sky it is never more than about 45 degrees above the horizon. It alternates between being an evening sky or a pre-dawn sky object. In the evening look for it in the west, and before dawn look for it in the east. It is easy to find, since when visible it is always the brightest object in the sky after the sun and moon. But if a bright object is high in the sky, it cannot be Venus. The next brightest object after Venus is Jupiter and occasionally Mars.
MARS is the last terrestrial planet and orbits just beyond Earth. Though small and dim, Mars is easily observed from Earth when the planets lie in close orbit. Mars has two tiny moons, Phobos and Deimos. Mars is Earth’s smaller twin in many ways. The Martian day is just over 24.5 hours long and it is tilted on its axis by 25.2o (Earth is tilted 23.5o). Unlike Earth, Mars was too small to retain enough of its internal heat and quickly cooled, losing most of its atmosphere. Mars wasn’t always dead. It once may have been much like Earth. Mars once had a much denser atmosphere, liquid seas, and monstrous volcanoes. Olympus Mons is not just the largest volcano on Mars but the largest in the solar system. Mars still has a limited atmosphere and carbon dioxide ice at its poles. This ice melts throughout the year, fueling weather changes across the surface. NASA is currently searching for evidence of microbial life on Mars.
JUPITER is the largest planet in the Solar System with a diameter about 11 times that of Earth. Jupiter is over five times farther from the Sun than the Earth is. It takes Jupiter about 12 years to go around the sun. Jupiter is so massive that it weighs two and a half times as much as all the other planets in the Solar System combined. Jupiter is a gas giant, composed mostly of hydrogen and helium. Jupiter has at least 63 moons. The largest ones were discovered by Galileo in the early 17th century. They are called the Galilean Moons and you can see them with a small telescope. Some people can even see them with a good set of binoculars. The moons go around Jupiter quite quickly – in as little as two days – so you can see them in different positions night after night. The planet is named after the Greek God, Jupiter. The names of the Galilean moons are Io, Callisto, Europa, and Ganymede. Ganymede has a diameter greater than the planet Mercury. The term Jovian is derived from Jupiter and describes the four gas giant planets in the solar system: Jupiter, Saturn, Uranus, and Neptune. They have very large masses and are farther from the Sun than the terrestrial planets.
SATURN is the second largest Jovian planet and orbits the Sun at a distance nearly twice the distance from Jupiter to the Sun. Like all gas giants, Saturn has a deep atmosphere and a small rocky core. The diameter of Saturn is 9.5 times greater than Earth and its core is about the size of Earth. Like Jupiter, Saturn’s atmosphere is primarily hydrogen. Saturn’s most notable features are the gorgeous dust rings that rotate about its equator. Once thought to be a unique feature of Saturn, we now know that all gas giants have ring systems. Saturn is notable for several truly bizarre and unique features. Wind speeds measured along Saturn’s equator can exceed 1,100 mph. Its density is lower than water, meaning it would float on Earth. Saturn has over 50 satellites, the largest of which is Titan. Titan is larger than Mercury and has a weak, nitrogen-rich atmosphere. Though it takes almost thirty (Earth) years for Saturn to complete one orbit, a day on Saturn is only about 10 hours long.
URANUS is 1,783 million miles from the Sun, so one orbit takes 84 Earth years. Its atmosphere is comprised of hydrogen gas and its surface is solid ice with a temperature of minus 350F degrees. The bluish color comes from a thin layer of methane gas that hovers above the planet’s 32,000-mile diameter surface. Uranus was discovered by the astronomer William Herschel in 1781. Through his telescope, he noticed what looked like a faint star that was not on current star charts. It was a new planet. The planet was named by Johann Bode in 1781 after the ancient Greek deity of the sky Uranus, the father of Kronos (Saturn) and grandfather of Zeus (Jupiter). Uranus has 27 known moons, most of which are named after characters that are mentioned in the works of William Shakespeare and Alexander Pope. The largest, Titania, is the eighth-largest moon in the Solar System, about one-twentieth the mass of Earth's Moon.
NEPTUNE is 31,400 miles in diameter and its distance from the Sun is 2,800 million miles. A trip around the Sun takes 165 Earth years. Its surface temperature is minus 364F degrees. Like Uranus, its atmosphere is bluish in color and made up of hydrogen gas with a surface of solid ice. Neptune is 17 times the mass of Earth, slightly more massive than its near twin Uranus. Neptune was not initially found with a telescope. In 1846 a French scientist, Urbain Le Verrier, noticed that the orbit of Uranus seemed to be affected by another unseen planet. A telescopic search found Neptune. Neptune was known to have 13 moons until NASA announced the discovery of Neptune's 14th moon in 2013. The image of the new moon, Neptune's tiniest, was captured by the Hubble Space Telescope.
BEYOND THE SOLAR SYSTEM by Ray Yeager
LIGHT-YEARS As we consider objects outside of our Solar System, we have to change the way we consider distance and add the term "light-year." Light travels 5,903,000,000,000 miles in a year, or one light-year. The nearest star is Proxima in the constellation Centauri and is 4.2 light-years away; but it is a dim, red star and cannot be seen with the naked eye. The brightest star in the night sky is Sirius, found in the Winter constellation Canis Major and is 8 light-years away
THE UNIVERSE is difficult to describe. It is believed that if you traveled across the universe, you would eventually arrive where you started, just as you would if you traveled it a straight line here on Earth. But this does not necessarily mean it is round. It began with what is called the big bang and instantly expanded or inflated in all directions. It is thought to be 90 billion light-years across and about 14 billion years old. It began almost instantly with tremendous heat with mostly hydrogen and small amounts of helium. As the universe cooled, clumps of hydrogen and helium atoms began to coalesce and the first stars were born, forming the first galaxies.
GALAXIES are the largest objects in the universe. Our galaxy, called the Milky Way, contains over 100,000 billion stars. Galaxies revolve and our solar system is found in one of the outside rotating arms. The closest galaxy is the Andromeda Galaxy (M31) that contains over 200 billion stars. It is thought that there may be over 150 billion galaxies in the universe. This galaxy is found in the constellation Andromeda. A medium size telescope (6 inch in diameter) will show a faint glow of stars.
STARS Looking up at the night sky at a dark location like SKY'S THE LIMIT, you will see an incredible number of stars. Some are brighter than others – which you may think indicates the star is closer to us. Most stars are brighter because they are younger. They appear bluish white. Stars that appear reddish usually are older. Stars that appear yellow like our Sun are considered middle aged. Temperature is another indication of brightness. A white star is the youngest and is about 36,000 degrees F. Yellow stars are about 5,400 degrees, Red 2,700. degrees.
OUR STAR: THE SUN Our Sun and stars were created from rotating clouds of hot gas in interstellar space. When these collapsing clouds of gas get hot enough, nuclear fusion begins to fuse hydrogen into helium, creating tremendous heat and light. Our Sun is 870,000 miles in diameter and is 93 million miles distant, Just the right distance for the Earth to develop an atmosphere and gravity that can harbor life as know it. It takes 8 seconds for the Sun’s rays to reach Earth. Our Sun is made up of 75% hydrogen and 25% helium. The surface temperature is about 10,500 degrees F of burning gas. Of course, never look at the Sun – even through a telescope – without protection. Special glasses are very inexpensive and can be found on the Internet. Special eyepieces are better to see occasional sunspots which are dark, cooler patches of gas that are controlled by the Sun’s strong magnetic fields and are larger than our Earth. Also, at times you may see tiny loops of gas and flares.
GLOBULAR CLUSTERS are tightly packed stars that are found in the outskirts of our galaxy and contain very old stars. M13, one of the brightest, is found in the Summer constellation Hercules. Clusters are easily seen with all types of scopes.
NEBULA (pl. nebulae) Nebulae, from the Greek word “cloud” mostly consist of gas and dust. Some are remnants of old stars that have exploded such as M1, the Crab nebula. Some are emission nebulae that are lit from behind by new stars and some are dark nebulae where light from stars is being absorbed by light and dust. Most nebulae are faint and difficult to see in much detail, but the Winter constellation Orion nebula, M42, and the Crab nebula can be seen with moderate size scopes.
ASTEROIDS AND METEORS are pieces of rock that were left over after the forming of the planets. Asteroids can be as large as a 10-story building and could destroy a city. Meteors are more basketball-size down to the size of a grain of sand. Hundreds enter our atmosphere every day and a few may hit the ground (meteorite), but most burn up as they strike our atmosphere and appear as beautiful, bright streaks of light. Several meteor showers appear regularly each year as the Earth passes through the tails of comets as they orbit our Sun.
COMETS are huge pieces of rock and frozen water. As they approach the Sun the rocky ice begins evaporating, creating a ball of glowing gas with a tail. It is a marvelous sight, and many can be seen form Earth. A comet that has been captured by the gravity of the Sun will return on a regular basis. Halley's comet returns every 75 years. It last appeared 1986 and should return about 2061. Other comets, depending on their orbit, may not return for thousands of years. One hypothesis is that the dinosaurs were killed off by a comet or a large asteroid that hit the Earth about 65 million years ago. Comets are named after their discoverer.
MESSIER OBJECTS Many deep sky objects are identified with the lettter "M" on star charts. Charles Messier was a comet hunter. Distant comets look like tiny fuzzballs. So, in 1774 he began to number these distant objects so as not to keep mistaking them for comets. His catalog has 110 objects. Later, when larger telescopes were invented, more distant objects began to be identified as NGC, or New General Catalog.
CONSTELLATIONS are groups of stars that early civilizations used in their story telling as far back as 4000 B.C. The Lion, Bull, Scorpion, and Hunter can be found in ancient writings. The first star atlas was published in 1603 and by 1928, 88 constellations were recognized. Learning which constellations are unique to each season is important in observing. Frequently, constellations are mentioned to help locate deep sky objects, but often the time of year is not noted. Knowing the constellations tells you when certain objects will be visible.
TIPS FOR OBSERVING THE PLANETS by Ray Yeager
Mercury can be difficult to observe as it is never very far from the Sun. During it's Western Elongation (furthest from the Sun as seen from Earth, in the evening or morning) it appears as a fairly bright star but very close to the Sun. Check the Internet for best observing dates.
Venus is the brightest object in the night sky other than the Moon and is easy to find during its elongation. Look low in the East or West.
Mars, being outside of the Earth's orbit, might be found anywhere in the night sky depending on the time of the year. It will appear reddish in color and fairly bright. To observe details will require an 8-inch scope or larger and a steady tripod.
Jupiter will appear bright, and details such as the cloud bands and the famous Red Spot can be seen with a medium size scope. Binoculars will easily observe Jupiter's 4 brightest moons.
Saturn will not be as bright as Jupiter, but the beautiful and famous rings can be seen with at least a 6-inch scope. A larger scope will be needed to better see the amazing rings. A few of Saturns moons can also be seen.
Neptune and Uranus will be faint naked eye objects. At least an 8-inch scope will be needed to see a bluish diameter.
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