Learning Center
The information will help you with different topics in astronomy such as learning the constellations,
phases of the moon, and much more.
Lesson 1 - Learning the Constellations
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Learning the constellations in the sky is simple to do and can be done from your home. You do not have to be in a very dark sky. However, you do need to be able to see the main stars of the constellations. If you do not see the stars very clearly, you will need to find a darker location. You need to pick up a sky chart to help you recognize the constellation pattern. You can pick up a copy of Sky & Telescope magazine at your local book store for the current month. In the middle of the magazine, there is a sky chart for the month. You can also pick up a sky chart wheel instead of the magazine. This is a chart where you set the date and time and it shows you what constellations are visible in the sky at that time. It usually can be found in some bookstores, astronomy store, or planetarium.
Now that you have your sky chart from Sky & Telescope or the sky chart wheel, you are ready to begin. Pick 2 days in the week to go outside about one and a half hours after sunset. The days you pick does not have to be the same for each week since the weather can change. You will need to go outside every week for one year. When the year is complete, you should know most of the constellations.
The procedure to do each time you go outside to look at the sky is the following:
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If you live in the northern hemisphere, locate the north star Polaris. This is a good reference point because it is always in the same place. The reason it does not move is that the star is directly overhead at the north pole. As the earth spins, the stars move east to west. At the north pole, any stars directly over head will not move since the earth rotates on its polar axis. People in the Southern hemisphere do not have a bright star near the pole.If you live in the northern hemisphere, locate the north star Polaris. This is a good reference point because it is always in the same place. The reason it does not move is that the star is directly overhead at the north pole. As the earth spins, the stars move east to west. At the north pole, any stars directly over head will not move since the earth rotates on its polar axis. People in the Southern hemisphere do not have a bright star near the pole.
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Now that you have found where the north star is, turn and look toward it. South is now behind you, East is to your right, and West is to your left.Now that you have found where the north star is, turn and look toward it. South is now behind you, East is to your right, and West is to your left.
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Now, look to the west and find the constellations that are in the west on the sky chart. Saying the name of the constellation outloud when you see it will help you remember the name. Now, look to the west and find the constellations that are in the west on the sky chart. Saying the name of the constellation outloud when you see it will help you remember the name.
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Do the same thing for the South, East, North and overhead directions. Some constellations are faint and hard to see if you have a lot of light in the sky from the city. Ursa Minor (the little dipper) is not easy to see in the city. Most people find it by locating Polaris first, this star is at the end of the handle in the little dipper.Do the same thing for the South, East, North and overhead directions. Some constellations are faint and hard to see if you have a lot of light in the sky from the city. Ursa Minor (the little dipper) is not easy to see in the city. Most people find it by locating Polaris first, this star is at the end of the handle in the little dipper.
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If the sky chart you are using has the name of bright stars, look for them as well.If the sky chart you are using has the name of bright stars, look for them as well.
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Do the steps one through five each week, 2 nights a week, for one year and that will do it.
Once you have learned the constellations, you will never forget them. As you go outside each week, you will see the sky change from one season to another. Finally, when you get under a very dark sky away from the city lights, the constellations will seem to have disappeared in the many stars above. But you will begin to see them quickly again.
One final note, if you are using Sky & Telescope magazine, be sure to locate the planets Mercury, Venus, Mars, Jupiter, and Saturn when they are visible in the sky. Watch the movement of the moon. You will see that it moves from west to east over a period of time. The planets do this as well but move too slowly to see. However, Mercury, Venus, and Mars are close enough to see this movement. One final note, if you are using Sky & Telescope magazine, be sure to locate the planets Mercury, Venus, Mars, Jupiter, and Saturn when they are visible in the sky. Watch the movement of the moon. You will see that it moves from west to east over a period of time. The planets do this as well but move too slowly to see. However, Mercury, Venus, and Mars are close enough to see this movement.
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Lesson 2 - Phases of the Moon
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In this lesson, I am going to talk about the lunar phases that occur as the moon orbits the earth. I will cover general information about the phases, explain why we see the phase we do during the month, and how to tell time by looking at the phase of the moon. At the bottom of this page is a Java Applet that shows you how the moon moves around the earth and what the phases are when it does.
First let’s get into some general information about the moon’s orbit around the earth. The moon takes almost 28 days to orbit the earth, 27.32 to be exact, and 1 lunar day lasts 27.32 earth days. As the moon rotates around the earth, it also rotates around its own axis at the same rate. This is why we always see the same side of the moon.
The eccentricity of orbit is 0.055, which means there is a 5.5-degree tilt as the moon orbits the earth. If this tilt were not there, we would see an eclipse of the moon and sun every month. Since the moon can be below or above the earth’s orbital plane there is no eclipse. However, there are two points in the earth’s orbit around the sun where the full or new moon is in correct alignment to cause an eclipse. When this happens and the moon is full, we see a lunar eclipse. If the phase of the moon is new, we see a solar eclipse.
The moon orbits the earth in a counter clockwise direction. Since this is the case, the moon moves from west to east across the sky. If you watch the moon move during one night, it looks like the moon goes from east to west. This is because of the earth’s rotation. If you watch the moon over a few nights, you can see the movement from west to east by looking at the background stars. Because of the direction the moon moves, it rises about 50 minutes later each day. As the moon moves each day, the phase of the moon changes.
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During the crescent phase of the moon, you get great views of the craters.
The Moon during a Lunar Eclipse
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Earth Shine - A Few Days After New Moon
1st Quarter Moon (7 days old)
Gibbous Moon After 1st Quater But Before Full
Full Moon (Day 14 in obit around the earth)
Gibbous Moon After Full Moon but before 3rd Quater
3rd Quarter Moon (Day 21)
Moon 19 hours before New Moon
30 minutes before sunrise
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The phases of the moon work in a cycle. It starts with the new moon. This occurs when the moon is between the earth and the sun. Remember, because of a 5.5-degree tilt, a solar eclipse may or may not occur. During this phase the sun and moon are close together in the sky. This is the reason we never see the moon when the phase is new and why astronomers look at stars during this time. As the moon orbits the earth, we start seeing the sunlit part of the moon forming the crescent phase of the moon. During this phase, we can see the daytime and the nighttime part of the moon allowing us to see the entire moon.
The reason we can see the dark side of the moon is because of earthshine. Earthshine is the reflection of sunlight off the earth back to the moon. We see this part of the moon only during the crescent phase a few days after or before a new moon. As the moon begins to show more of a phase and gets brighter, the dark side of the moon becomes invisible.
On the seventh day of the moon’s orbit, the phase becomes first quarter. Half of the moon is in daylight and the other in darkness. Because the moon is so bright, we can’t see the nighttime side. So why is this phase called first quarter instead of half phase? Simply put, the moon has completed one quarter of its orbit around the earth. The moon is 90 degrees from the sun at this point. You can tell when the moon is first quarter because the sunlit side is to the west, on the right side. A third quarter moon also shows half of the moon, but the sunlit side of the moon is on the left, facing east.
After the first quarter moon, we start seeing more of the sunlit part of the moon. Around day 10 of the moon’s orbit, it becomes a gibbous phase and stays this way until we have a full moon.
The full moon occurs on day 14 of the orbit around the earth. Now we can see the entire daytime side of the moon. When the sun, earth, and moon are in perfect alignment, we get a lunar eclipse. Since the moon orbits at a tilt, we don’t always get an eclipse every full moon. A full moon is 180 degrees from the sun. So the moon rises when the sun sets. When the moon rises, it looks much larger than when it is directly overhead. This is because the light is deflected though the earth’s atmosphere. When the moon is low, the light from the moon passes though more of the earth’s atmosphere than directly overhead. The moon is always the same size in the sky. You can prove this with a small telescope. Look at the moon when it is first rising with an eyepiece that fills the entire moon in your telescope. Then look at it again when the moon is high in the sky with the same telescope and eyepiece. You will see that the moon is the same size at anytime.
As the moon goes into day 17 of its orbit, it becomes a gibbous phase again. This time however, the sunlit part of the moon is on the left side facing east. After full moon, the moon will rise later each night until it is a new phase again.
On day 21 of the moon’s orbit, it rises around midnight local standard time. This is the third quarter phase of the moon. It’s called third quarter because it has traveled three quarters of the way in its orbit around the earth. You know that the phase is third quarter when you see a half moon high in the sky at sunrise with the sunlit part of the moon to the left.
By day 25, the moon enters crescent phase again. The earthshine begins to show the nighttime side of the moon. Each day the crescent becomes thinner and thinner until the moon disappears on day 28 becoming a new moon once again.
The phases of the moon can also help you tell what time of day it is. In order for you to get a close guess on the time, you need to know roughly what time the sunrise or sunset is for that day. These are the facts you need to remember. The first quarter moon rises six hours after sunrise and sets six hours after sunset. The same is similar for the third quarter moon. It rises 6 hours before sunrise and sets 6 hours after sunrise. Finally the full moon rises when the sun sets and sets when the sun rises.
Did You Know:
The moon is not the only body in the solar system that can have phases.
The earth has a phase when seen from the moon.
The planets Mercury and Venus have the same phases as the moon when seen from earth.
Timetable Chart
This example is assuming that sunrise is at 6:00 am and sunset is 6:00pm at a location of forty degrees north latitude.
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First Quarter Moon
It is 12 noon when the moon rises in the east.
It is 3 p.m. when the moon is half way up the sky between the eastern horizon and the highest point the moon can get looking south.
It is 6 p.m. when the moon is at its highest point in the sky looking south.
It is 9 p.m. when the moon is half way up the sky between the western horizon and the highest point the moon can get looking south.
It is midnight when the moon sets.>
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Full Moon
It is 6 p.m. when the moon rises in the east.
It is 9 p.m. when the moon is half way up the sky between the eastern horizon and the highest point the moon can get looking south.
It is midnight when the moon is at its highest point in the sky looking south.
It is 3 a.m. when the moon is half way up the sky between the western horizon and the highest point the moon can get looking south.
It is 6 a.m. when the moon sets.
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Third Quarter Moon
It is midnight when the moon rises in the east.
It is 6 a.m. when the moon is at its highest point in the sky looking south.
It is 9 a.m. when the moon is half way up the sky between the western horizon and the highest point the moon can get looking south.
It is 12 noon when the moon sets.
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New Moon
The New Moon is near the position the sun is located.
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Lesson 3 - About the Planets
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In this lesson you will learn about the nine planets in the solar system and how they move through the nighttime sky. This lesson does not go into details about each planet because there is a section about the planets located in the Info Center of the Web site. What this lesson does cover is where the planets are in the sky and when is the best time to see them. The orders of the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
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Lets talk about some terms I will use first.
A conjunction is when any two objects in the sky are very close together. When a planet is in conjunction with the sun, you would not be able to see that planet at night.
An opposition is when a planet is opposite the sun. A full moon would be a good example of an opposition with the sun. A full moon occurs when the sun sets at the same time that the moon rises because it is opposite the sun.
Retrograde for a planet occurs when opposition is near. Everything in the sky moves east to west for a given day. But the moon, sun, and planets move west to east over a long period of time. You can see this with the moon because it is so close. Just watch the moon move against the background stars for 5 nights in a row. A planet begins to move backward in a westward direction instead of eastward, this is called retrograde. After opposition occurs, the planet changes direction back to normal.
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Now that we have some of the terms defined, let me cover the two inner planets - Mercury and Venus. These planets can never have an opposition because they orbit the sun closer than the earth does. They do have three types of conjunctions with the sun. A superior conjunction occurs when the sun is between the earth and the sun.
When you see Venus or Mercury in the evening sky, that means the planet is moving toward us to an inferior conjunction. When it is seen in the morning sky, the planet is moving away from us.
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planet. An inferior conjunction occurs when the planet is between the earth and the sun. A rare event occurs called a solar transit meaning that the planet is in inferior conjunction and crossing the sun's disk. This must be a perfect alignment of the earth, sun, and Mercury or Venus. (See Info Center for more information about solar transits.)
So when is the best time to see Mercury or Venus in the sky? Since Mercury is close to the sun, it is never very far away from it. The best time to see Mercury is just before sunrise or just after sunset. There are usually two times a year that conditions are good to see Mercury in total darkness. When Mercury or Venus is at greatest elongation, then the planet is as far away as it can get at that time. The diagram shows the positions which Mercury or Venus can be in.
Venus is farther away from the sun and can be seen higher in the sky at night. When Venus is at its greatest elongation, you can see Venus in the sky three hours before sunrise or after sunset. Both planets show phases in a telescope. When the planet is in superior conjunction, it is in a full phase and is very small in angular diameter. As Mercury or Venus moves around the sun, the phase becomes half phase and then crescent as it approaches inferior conjunction. The planet also grows in size as it gets close to earth.
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Now I will shift to the outer planets Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. These planets cannot have inferior conjunction because their orbits are farther than earth's. They do have superior conjunction with the sun, but since this is the only type of conjunction the planet can have, it is simply called a conjunction. The other planets also have oppositions once a year except Mars. Because Mars' orbit is closer to earth than the others, its opposition occurs every two years. These planets don't really have a phase seen from earth so you would never see Jupiter in a crescent phase. As these other planets approach opposition, they begin their retrograde motion backward in the sky. This is because the earth is catching up with the planet as it orbits the sun. When the earth is at opposition with the planet, it is half way done retrograding. After opposition, we get far enough away and the retrograde motion stops. All the outer planets do this but Mars is the easiest to see. Next time Mars approaches opposition, watch it every three nights and you can see this movement.
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You do not need a telescope to see Mercury, Venus, Mars, Jupiter, and Saturn but you do for Uranus, Neptune, and Pluto. All the planets, sun, and moon follow a path in the sky known as the ecliptic. The ecliptic consists of 13 constellations also known as the signs of the zodiac. Astrology was built using 12 of the constellations 2,000 years ago. Because the earth wobbles like a top in a 26,000-year period, there are now 13 constellations that the sun, moon, and planets move through. So if your sign is a Virgo, then you are really a Libra using today's stars. I suspect astrology will have to be revised or dropped in the next 2,000 years because it gets worst as time goes on. Anyway, the planets move along this path because that is where the solar system's orbital plane exits.
The planets are easy to find in the sky. Every month this Web site and others give you information where the planets are at and when you can see them. Remember that Mercury and Venus are always near the western horizon after sunset or in the east before sunrise. The other planets can be seen any where in the sky along the ecliptic. The best time to see Mercury or Venus is at greatest elongation and the other planets at opposition. You can also pick up a copy of Sky & Telescope or Astronomy Magazine for details about the planets in the solar system.
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Project:
You can build your own solar system for a school project. The materials are easy to get and it is fun to do. Go down to your local arts and crafts store and pick up some round Styrofoam balls. You will need to determine what sizes to get. Look up the information on each planet in Info Center of this Web site. There you will find information on the planets and see what your weight and age would be if you lived on that planet. Once you have the sizes you need, get some paint to add the correct color to them. Once they are dry, you can hang them up or mount them some other way. I did this in ninth grade and my science teacher was impressed with my efforts.
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Lesson 4 - Learning About The 4 Seasons
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In this lesson I will talk about what causes our four seasons, spring, summer, fall, and winter. I will cover this by telling some of the myths about what many think are the cause of our seasons and then some well known facts. There is a lab at the end of this lesson and it will help you understand why summer is so hot and winter is cold.
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The earth orbits around the sun in 365 1/4 days making up one year on earth. At the same time the earth is tilted 23.5 degrees from its axis of rotation and this is the only reason we have our four seasons. One myth that has been around for decades is that we are closer to the sun on one side of the orbit than the other which causes our seasons. The earth's obit works this way, but it has no effect on the seasons.
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The average distance the Earth is from the Sun is 93 million miles. The difference between aphelion (farthest away from the Sun) and perihelion (closest to the Sun) is 3 million miles, so that perihelion is about 91.4 million miles from the Sun. Earth goes through the perihelion point a few days after New Year's Day, just when the Northern Hemisphere has winter. Aphelion is passed during the first days of July. This means the summer occurs in the United States when we are as far away as possible from the sun. This by itself shows that the distance from the sun has no effect on our seasons.
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What is important is that when Earth passes through perihelion (closest to the sun), the northern end of Earth's axis happens to tilt away from the Sun, so that the areas beyond the Tropic of Cancer receive only slanting rays from a Sun low in the sky.
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There are 5 major zones on the earth.
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Northern Frigid Zone runs from the north pole to the Arctic Circle
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90.0º to 66.5º
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Northern Temperate Zone runs from the Arctic Circle to the Tropic of Cancer
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66.5º to 23.5º
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Torrid Zone runs from Tropic of Cancer to the Tropic of Capricorn
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23.5º to -23.5º
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Southern Temperate Zone runs from the Antarctic Circle to the Tropic of Capricorn
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-66.5º to -23.5º
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Southern Frigid Zone runs from the south pole to the Antarctic Circle
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-66.5º to -90.0º
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As light travels through the atmosphere, some of the energy is absorbed. This is why the sun feels less intense in the winter than in the summer. Notice how light ray #1 doesn't travel very far through the atmosphere. This corresponds to the sun being "directly overhead." Ray #2 travels slightly farther through the atmosphere, and ray #3 farther still. Finally, ray #4 has travel through a great deal of atmosphere. Thus, it has much less energy left when it reaches the ground. This is part of the reason why the polar regions are colder than other parts of the earth.
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Another factor that causes the climate to be colder for places farther from the equator is that a given amount of light (and heat) is spread over a larger area, so the energy is less concentrated. This is also why the highest temperatures on a given day are on or slightly after noon.
Notice how area #2 is slightly larger than area #1, and area #3 is much larger. The energy per square meter reaching the earth at a latitude of 60° is only half that of the energy reaching the earth at the equator.
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Below is a summary of the four seasons seen from the United States
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The Spring Equinox (around March 21st)
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The direct rays are at the equator
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Six months of daylight begins at the North Pole
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Six months of darkness begins at the South Pole
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Twelve hours of daylight and twelve hours of darkness all over the earth
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It is the longest day of the year on the equator
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The sun rises due east and sets due west
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Spring begins in the Northern Hemisphere
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Autumn begins in the Southern Hemisphere
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The Summer Solstice: (around June 21st)
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The direct rays are as far north as they go; the Tropic of Cancer
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The North Pole is in the middle of a six-month period of light
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The South Pole is in the middle of a six-month period of darkness
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It is the longest day of the year in the Northern Hemisphere
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It is the shortest day of the year in the Southern Hemisphere
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It is the shortest day of the year on the equator
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The sun rises north of east and sets north of west
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Summer begins in the Northern Hemisphere
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Winter begins in the Southern Hemisphere
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The Autumn Equinox (around September 23rd)
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The direct rays are at the equator
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Six months of darkness begins at the North Pole
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Six months of light begins at the South Pole
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Twelve hours of darkness and twelve hours of light all over the earth
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It is the longest day of the year on the equator, again
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The sun rises due east and sets due west
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Autumn begins in the Northern Hemisphere
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Spring begins in the Southern Hemisphere
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The Winter Solstice: (around December 21st)
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The direct rays are as far south as they go; the Tropic of Capricorn
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The North Pole is in the middle of a six month period of darkness
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The South Pole is in the middle of a six month period of light
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It is the shortest day in the Northern Hemisphere
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It is the longest day in the Southern Hemisphere
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It is the shortest day of the year on the equator, again
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The sun rises south of east and sets south of west
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Winter begins in the Northern Hemisphere
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Summer begins in the Southern Hemisphere
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So why is it so hot in July and August when the first day of summer is June 21st? Similarly, why is December 21st, the day of least sunshine, the beginning of winter when January and February are usually much colder? The answer is simple and there is only one thing to blame, the oceans.
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The oceans, which heat up and cool down only slowly are the main cause. By June 21 they are still cool from the winter time, and that delays the peak heat by about a month and a half. Similarly, in December the water still holds warmth from the summer, and the coldest days are still on the average a month and a half ahead.
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