1. Light Pollution: A Journey Through the Solar System
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Images courtesy of NASA/PL-Caltech

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3. Intro to the Solar System
Sol is the Latin root for “the Sun.” This is the root word for all of the things pertaining to the Sun, such as solar system, solar flare, and solar wind.
The solar system is estimated to be about 4.6 billion years old.
The solar system includes the sun, planets, comets, meteoroids, asteroids, and dwarf planets, which are all in proximity to the sun.
Only five planets can be observed with the naked eye from Earth, including Mercury, Venus, mars, Jupiter, and Saturn. Uranus, Neptune, and Pluto can only be seen with a telescope.
Even with all these objects, the solar system still consists of mostly empty space.
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Images courtesy of NASA/PL-Caltech

4. The Sun The Sun is the most prominent feature in our solar system.
The sun is the closest star to Earth at a distance of 93 million miles.
It provides most of the natural energy needed to live on Earth.
The sun is responsible for seasons, ocean currents and tides, weather, and climate on Earth.
It consumes almost 98% of solar systems combined mass.
It would take 109 Earth's fit across the Sun's disk, and its interior could hold over 1.3 million Earth's.
The sun is not red because it’s actually on fire. The color comes from the nuclear reactions inside its core rapidly turning the gas hydrogen into the gas helium.
The outer visible layer of the sun is called the photosphere and it can reach almost 11,000° F.
Like all the planets that orbit it, the sun also rotates. Because the sun is made of gas, the equator rotates faster than the north and south poles. It takes about 27 days for the equator to rotate once, and it takes about 36 days for the poles to rotate once.
The Sun is the most prominent feature in our solar system.
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Images courtesy of NASA/PL-Caltech

5. Mercury Temperature 430°C to - 185°C (800°F to -300°F)
Distance from the sun
58 million km
(36 millions miles)
Diameter
4,900 km (3,000 miles)
Length of Day
59 Earth Days
Length of Year
88 Earth Days
Mercury orbits the sun faster than any other planet at a speed of about 50 km/hour (31 miles/hour).
Mercury's orbit is very elliptical. At some points Mercury is as close as 47 million km (29 million miles) from the sun, and at other times it is 70 million km (43.5 million miles) from the sun.
Mercury's diameter is slightly less than 3,000 miles across, about the same size as the United States.
Mercury mostly has no atmosphere. That means there is no wind, rain, air, clouds, or water to erode the land. Mercury looks as it has for billions of years.
Mercury looks cratered like the moon because without wind or rain there is nothing to erode them.
Scientists believe that Mercury’s core is Iron, much like Earth’s.
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Images courtesy of NASA/PL-Caltech

6. 108 million km (67 million miles)
Venus
Temperature
460°C (860°F)
Distance from the sun
108 million km (67 million miles)
Diameter
12,100 km (7,520 miles)
Length of Day
243 Earth Days
Length of Year
225 Earth Days
Venus is the third brightest object in the Earth’s sky, besides the sun and the moon.
Venus is the hottest planet in the solar system because its dense clouds hold in tremendous amounts of heat.
The clouds on Venus rain sulphuric acid.
Venus is similar to Earth in size and surface activity (volcanoes, mountains, trenches, ect.)
Probes that have landed on Venus melted within a few hours because of the intense heat.
Venus rotates in retrograde, meaning that it rotates in the opposite direction of the other planets.
Venus' day is longer than its year, because it takes longer for the planet to rotate on its axis than it does for it to complete an orbit around the sun. This means the sun would rise in the west and set in the east.
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Images courtesy of NASA/PL-Caltech

7. 150 million km (93 million miles)
Earth
Temperature
60°C to -90°C
(140°F to -130°F)
Distance from Sun
150 million km (93 million miles)
Diameter
12,800 km (7,900 miles)
Length of day
24 hours
Length of year
365 days
Earth is the only planet in the solar system known to have life.
Earth is the only planet that humans can naturally live on.
Earth is the only planet in the solar system known to have liquid water.
Water covers over 70% of Earth's surface.
Earth's atmosphere protects its inhabitants from solar radiation and meteors.
Earth has plate tectonics, which is the theory that the land on Earth moves over the surface at a speed that is equivalent to the rate of fingernail growth. Plate tectonics cause land to collide into other pieces of land, resulting in volcanoes, trenches, mountains, and other land features.
The Earth has one moon and humans have visited it 6 different times.
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Images courtesy of NASA/PL-Caltech

8. How Light Pollution Affects Astronomy
Light pollution was first noticed by astronomers as an interference in their ability to view the night sky due to the “glow” of lights coming from nearby cities and towns.
Many astronomers today study the planets and universe with very large telescopes, but the first astronomers studied the universe with only their eyes and early simple telescopes.
In those days, the skies were bright with stars, but today in areas that contain human communities, that is no longer true.
Many individuals feel that astronomy is only important to astronomers, but astronomy affects everyone's daily life. The physics used to build satellites, cell phone towers, televisions, cars, x-rays, and many other modern inventions, were developed by astrophysicists.
Astronomy was an important part of many different cultures of the past, Egyptians being one of the most famous. Many other cultures built observatories, homes, and places of religious worship around the alignment of the stars. By erasing the stars from our night sky now, humans are blotting out the rich history of Earth's early cultures.
Astronomy offers insight into the origins of the universe. This includes how stars and planets develop, how space objects are related to each other, and how its possible for a planet to sustain life such as on Earth. Astronomy provides scientific evidence toward answering these important questions.
Many astronomers today study the planets and universe with very large telescopes, but the first astronomers studied the universe with only their eyes and early simple telescopes. In those days, the skies were bright with stars, but today in most cities and towns that is no longer true.
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9. Hubble Space Telescope
It has become more necessary as light pollution has increased and affected Earth-based telescopes.
Hubble has needed repairs several times, but still has the ability to produce amazing images of outer space.
HST was launched in 1990.
HST has helped to reveal the age of the universe, as well as making discoveries about dark energy, evolution of stars, evolution of galaxies, development of planets, and many other space objects.
HST is an in-space observatory, meaning that any astronomer in the world can request time on HST to do research, just like a ground based telescope.
HST has taken hundreds of thousands of pictures and beamed them back to Earth. More than 6,000 scientific articles have been written on HST's data.
Earth's atmosphere block many types of light, such as ultra-violet rays, gamma rays, and x-rays. Also, Earth is polluted with excessive light. HST is above the atmosphere and is not affected by our atmosphere which allows it to take many more pictures than ground based telescopes.
Hubble orbits the Earth every 97 minutes, which is a speed of about 5 miles per second. It crosses the United States in 10 minutes.
HST is repaired and upgraded by astronauts who arrive by space shuttle.
The desire to further study our galaxies inspired astronomers to launch a very large telescope into space.
The Hubble Space Telescope was the first optical observatory launched into space. It is one of many telescopes that are peicing together our universe.
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Images courtesy of NASA/PL-Caltech

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Before and After
The first half of this image was taken in front of a house in Toronto, Canada. The second image was taken during the great blackout in Toronto Canada. Citizens were amazed how well they could see the night sky in the city during the blackout.
In this comparison, it is easy to see how one home affects the visibility of the stars. Multiply this by the millions of other home lights, street lights, parking lot lights, bulletin board signs, and other lighting, and it becomes easy to imagine the amount of light that is being wasted. This wasted light is a tremendous waste of money and energy.
More than $10 billion is spent on energy waste each year due to inefficient, intrusive lighting.
Wasted energy results in over 38 million tons of carbon dioxide being unnecessarily released into our atmosphere.
All of this carbon dioxide contributes to global warming (climate change) and air pollution.
Turning off outdoor lights when they are not in use is a great way to reduce energy waste.
These pictures show the impact artificial night lighting has on the environment and night skies
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Why Did This Happen?
Light pollution is caused by:
Unshielded house, business, and street lights that cause glare and sky glow
Tall buildings in cities that keep their lights on throughout the night
Coastal development of hotels and tourist attractions that use bright lights to attract people
Fishing boats and fishing activity, cruise ships, and offshore oil platforms.
People who are unaware of the adverse affects, or who do nothing to improve the situation.
Often cities believe they will save money by using inexpensive street lighting, but in the long run it costs more because of the energy needs of the fixture.
It is more cost effective to spend more on the initial street lighting fixture, because the energy efficiency will save more money, usually within a year or less.
Many homeowners believe that more lighting equals better safety, when in reality safety is achieved by proper lighting levels, which more easily accommodate the human eye.
Often businesses believe bright lighting is a good way to attract customers. Other businesses, such as casinos near the Palomar Observatory in San Diego, CA, have found other ways to attract customers. Some of these ways include more advertising, and many signs. These casinos have not seen a decrease in business.
These pictures show some examples of lighting that cause light pollution. These can include cities, street lights, security lighting, and more!
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12. Other Effects of Light Pollution
Animals:
It has been shown through scientific studies that wildlife, including insects, amphibians, birds, fish, and mammals, need both daylight and darkness for normal functioning.
All the artificial light during night hours can result in confusion and a change in natural instincts.
These changes can include a decrease in eating, mating, and/or sleeping. It can also cause the animal to become more vulnerable to predators and wander into other dangerous situations.
Some examples of wildlife that have been affected by light pollution include the following:
Sea turtles in Florida are attracted to bright lights of hotels along the coast. Once their babies hatch, these turtles do not return to the ocean. Instead, they follow the bright city lights and wander into the local streets and freeways. This usually results in death for both the mother and baby turtles. As a result, these turtles have become an endangered species.
Fatal Light Awareness Propgram (F.L.A.P) studies how migrating birds often get misguided by bright city lights, landing in the cities instead of their proper locations. This causes an over-population of birds, which causes an under population of food. Many of these birds die. If starvation does not kill them, often times the city chemicals and cars do. Finally, it is well known that birds fly into bright lights at night, causing them to collide with buildings and fall to their death. It is estimated that millions of birds die this way each year.
Energy Consumption:
Over 10 billion dollars is wasted annually lighting the night sky in the U.S. alone.
A 2001 study conducted by P. Cinzano and F. Falchi, and C.D. Elvidge showed that two thirds of the world population lives in light polluted areas, never being able to view a fully dark sky.
Because light pollution uses energy, it also uses coal, natural gas, and petroleum to stay lit, wasting precious natural resources and turning them into air pollution.
Human health:
The circadian rhythm can be greatly affected by the amount of quality sleep a person receives each night. Artificial light allows people to be more active during night hours, which can cause disruptions.
The circadian rhythm, when thrown off by the effects of light during nights hours, can cause health risks, restless sleep, problems with reproduction and even cancer.
Scientists suggest using proper efficient lighting and/or blocking out artificial light during sleep. They also say that using red lights on electronic devices like alarm clocks may prove to be helpful.
Many people have experienced bright lights shining through their bedroom window at night. To combat this, many people must put up heavy curtains in order to sleep.
Research done by Dr. David Blask has shown that light at night reduces melatonin production in the human body. Melatonin is responsible for blocking the reproduction of cancer cells in the female body. Without it, women are at much higher risk for breast cancer.
The International Agency for Research on Cancer, a branch of the World Health Organization, considers night shift work a probable carcinogen. This is because people who work the night shift are subjected to artificial night lighting.
Light pollution affects plants and animals in their nighttime habitats, consumes wasteful amounts of energy, and negatively impacts human health.

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What can you do?
There are many cost effective ways that each of us can help with light pollution.
Turning out the lights in rooms you are not using saves energy.
Using motion sensors on your home security lights increases security, reduces energy use, and reduces light pollution.
Encouraging your neighborhood association to install only fully-shielded light fixtures in your neighborhood, with low pressure sodium bulbs, increases security, promotes energy efficiency, and promotes a healthy night time environment.
Work with neighbors to install energy efficient lighting on the outside of their home, as well as yours.
This is a picture of what the world looks like at night from a satellite. All those lights from cities and towns that do not use quality efficient lighting can be seen from space!
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14. Mars Temperature -5°C to -70°C (25°F to -130°F) Distance from Sun
228 million km
(141.6 million miles)
Diameter
6,790 km (4,200 miles)
Length of day
24.6 Earth hours
Length of year
687 Earth days
Mars has volcanoes, but none of them are currently active. The largest is Olympus Mons which is about 16 miles high. This is four times higher than Earth's highest mountain, Mt. Everest.
The southern hemisphere of Mars is vastly cratered and resembles the surface of Earth’s moon. The northern hemisphere, however, is much different with fewer craters that are far less eroded. This indicates they are younger than the southern ones.
Scientists believe that about 3.5 million years ago Mars suffered one of the largest floods in the solar system history. They do not know where the water came from or where it went.
On some parts of Mars there is water ice a few meters under the surface.
There is also water ice on each of Mars north and south poles, however, this water combined with the water found beneath the surface is not enough to account for the great river beds and water channels carved into Mars.
It is possible that scientists could find pre-historic life on Mars. It is likely that if they do, it will be very small organisms such as bacteria.
In addition to the largest volcano in the solar system, Mars also sports the largest canyon with a distance of about 3,000 miles, the distance from Los Angeles to New York.
Mars only has two moons, Phobos and Deimos.
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Images courtesy of NASA/PL-Caltech

15. Asteroids
Scientists believe that asteroids are rocky fragments left over from the formation of the solar system.
There are more than 90,000 numbered asteroids and several thousand more are discovered each year.
The extinction of the dinosaurs 65 million years ago has been linked to an asteroid collision near the Yucatan Peninsula.
Some asteroids have tiny fragments orbiting them, like mini-moons.
Unlike in movies, asteroids are very far apart, and the chance that more than one asteroid would collide with the same body in the solar system more than once every 10 million years is near impossible.
Most of our solar system’s asteroids lie between the orbits of Mars and Jupiter, but some have elliptical orbits that bring them very close to Earth.
They range in size from about 1 kilometer to 1,000 kilometers. They number in the tens of thousands.
There are only 26 known asteroids that are larger than 200km in diameter.
Ceres is the largest known asteroid and it contains 25% of the moss of all the known asteroids in our solar system.
Most asteroids are of the small irregular variety. None of them are large enough to have high enough gravity to pull into a spherical shape.
The total mass of all the known asteroids combined is less than that of the moon.
The danger of a collision with Earth is minimal. Astronomers are more interested in the origin of these objects.
Asteroids are metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. They are also known as "minor planets."
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Images courtesy of NASA/PL-Caltech

16. Jupiter Temperature -75°C at cloud tops (-100°F) Distance from Sun
778.4 million km
(483.7 million miles)
Diameter
142,800 km (88,700 miles)
Length of Day
9.9 Earth hours
Length of Year
11.86 Earth years
Jupiter is the largest planet in the solar system and is 11 times the size of Earth.
Jupiter has over 60 discovered moons that orbit around it.
Jupiter's moon Io is the most volcanically active body in the solar system.
Jupiter is made of all gas. This means it has no actual surface to stand on.
If you were able to stand on the surface, a person weighing 70 lbs on Earth would weigh a 180 lbs on Jupiter.
Most of Jupiter's visible clouds are made of ammonia. These clouds look striped from Earth, caused by the east-winds and west-winds in Jupiter's upper atmosphere.
These clouds are full of storms. The most famous is referred to as “the great red spot” which has existed as long as humans have invented telescopes strong enough to see it (300 years), and is so large that at least 2 Earth's can fit inside.
Jupiter is a large gas planet, mostly composed of hydrogen and helium. The weight of all this gas puts immense pressure on the center of the planet, possibly causing it to become solid.
Jupiter's magnetic field is 20,000 times as powerful as Earth's and extends all the way out past Saturn's orbit.
Jupiter has rings like Saturn, but they are much smaller and fainter.
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Images courtesy of NASA/PL-Caltech

17. Saturn Temperature -170°C at cloud tops (-270°f) Distance from Sun
1.4 billion km
(885.9 million miles)
Diameter
120,540 km (74,900 miles)
Length of Day
10.7 Earth hours
Length of Year
29.4 Earth years
Saturn is the furthest planet that can be seen with the naked eye.
Saturn was first discovered by Galileo in Because of its rings, scientists were not certain Saturn was a planet until 1659 when better telescopes allowed them to see it more clearly.
Saturn is most famous for its large, wide, and easily visible rings. They are so visible because they are thick rings of rock covered in ice.
Saturn is mostly made of hydrogen and helium.
Saturn is light enough that it would float in a gigantic bathtub.
Saturn has 48 known moons.
Saturn experiences aurorae similar to Earths (northern and southern lights).
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Images courtesy of NASA/PL-Caltech

18. 2.9 billion km (1.8 billion miles)
Uranus
Temperature
-200°C at cloud tops (-330°F)
Distance from Sun
2.9 billion km (1.8 billion miles)
Diameter
51,300 km (31,900 miles)
Length of Day
17.2 Earth hours
Length of Year
84 Earth years
Uranus was discovered in 1781 by William Herschel with the use of a telescope.
Uranus has rings like Saturn, but they are much smaller and fainter.
Uranus is the next planet after Saturn, but it is over twice Saturn’s distance from the sun.
Uranus is made of mostly hydrogen and helium gases. This gives it a blue appearance.
Uranus is referred to as the 'lazy planet' because it orbits on its side.
Winds on Uranus blow between 60 and 400 miles per hour.
Uranus experiences seasons that last over 20 years at a time.
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Images courtesy of NASA/PL-Caltech

19. 4.5 billion km (2.8 billion miles)
Neptune
Temperature
-200°C at cloud tops (-330°F)
Distance from Sun
4.5 billion km (2.8 billion miles)
Diameter
49,500 km (30,800 miles)
Length of Day
16.1 Earth hours
Length of Year
Earth years
Neptune was the first planet found by mathematical calculations rather than by observation.
Neptune's winds are over 9 times stronger than Earth. One storm was recorded at 750 miles per hour.
Neptune’s blue color is a result of methane in the atmosphere.
Neptune has storms that can be up to 4 times more destructive than any hurricane on Earth.
Neptune has rings, but they are smaller and much fainter than Saturn's rings.
Neptune has 13 known moons.
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Images courtesy of NASA/PL-Caltech

20. Pluto A Dwarf Planet Temperature -230°C (-380°F) Distance from Sun
5.9 billion km
(3.66 billion miles)
Diameter
2,300 km (1,400 miles)
Length of Day
6.4 Earth hours
Length of Year
248 Earth years
Pluto
Pluto is no longer a planet, but rather a dwarf planet. This is because Pluto orbits with other objects in the Kuiper belt, rather than objects in the disk of the solar system.
Pluto's orbit is very oval, which brings it closer to the sun than Neptune for 20 years out of its 248 year orbit.
Pluto was discovered in 1930 by Clyde Tombaugh.
Pluto is the only planet that has not been visited by unmanned space craft. However, the space craft New Horizons is scheduled to be at Pluto in and will give us more insight into Pluto's mysterious nature.
Pluto is only about 2/3 the diameter of Earth's moon. In even the best and biggest Earth-based telescopes, Pluto appears to be no more than a dot.
Pluto has one moon, Charon.
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Images courtesy of NASA/PL-Caltech

21. Kuiper Belt
The Kuiper belt is right outside the edge of the solar system, and is full of small icy bodies.
The Kuiper belt is the inner part of a larger region of space referred to as to Oort cloud. The Oort cloud occupies space that is between about 5,000 AU and 100,000 AU from the sun. One AU is the distance from the sun to Earth, or about 93 million miles.
Some bodies from the Kuiper belt come streaking into the solar system and we see them as comets.
Most of them are moving so fast that it takes less than 200 years to orbit the sun.
Pluto and other “planets” discovered beyond Pluto, orbit with Kuiper belt and Oort cloud objects.
Since Pluto was discovered in 1930, there have been other round planetoid objects discovered orbiting the sun in the Kuiper belt.
The Kuiper belt is located outside the orbit of Neptune. It consists of many small icy bodies and is a source of asteroids, comets, and meteors found in our solar system.
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Images courtesy of NASA/PL-Caltech

22. Comets
Hale Bopp
Unlike the other small bodies in the solar system, Comets are noticed sooner because of their greater visibility.
They are sometimes referred to as dirty snowballs.
As comets get closer to the sun, the ice they are made of begins to melt. This is why sometimes it appears that they have a tail.
Since comets are thought to be icy leftovers from the formation of the solar system, they may yield very important clues to how planets and other solar bodies form.
Short-period comets take less than 200 years to orbit the sun.
Most comets come from outside the orbit of Neptune.
Some comets that have been discovered can take as long as 30 million years to orbit the sun.
Around a dozen “new” comets are discovered per year.
The tail of a comet can be tens of thousands of miles long.
Some scientists believe that comets were responsible for bringing water and organic molecules to Earth when the solar systems was still developing.
Comets are a mixture of ices (both water and frozen gases) mixed with dust that were not incorporated into planets when the solar system was formed.
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Images courtesy of NASA/PL-Caltech

23. Meteoroids
Meteors can be the brightest object in the sky, yet it can also be the smallest objects observed by the human eye.
Meteors falling through the atmosphere are often referred to as shooting stars.
Meteoroids, much like asteroids, are rocks floating in outer space. Meteoroids, however, are much smaller and do not necessarily have orbits.
1,000 – 10,000 metric tons of meteorites fall to Earth each day. Meteorites are meteoriods that have struck the surface of Earth. Most of this material is so small when it hits the atmosphere that it falls gently to the surface of the Earth, like dust.
Evidence suggests that meteoroids can be made from similar material as comets, asteroids, and moons.
While these meteoroids fall to the ground daily, humans are rarely ever touched by them. The first documented case of a human being injured by a meteorite was in 1954.
Meteoroids become meteors when they enter the Earth's atmosphere. At this time, they are heated by friction, and streak across the sky with a glowing tail commonly called a shooting star.
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Images courtesy of NASA/PL-Caltech

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Thanks for learning about light pollution and how it affects the world around us!
For more information about light pollution and related topics, visit: The International Dark-Sky Association National Optical Astronomy Observatory The GLOBE at Night Project Starry Night Lights Astronomy picture of the day antwrp.gsfc.nasa.gov/apod/astropix.html NASA science.nasa.gov
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