Content Benchmark E.8.B.4
Students know Earth is part of a solar system located within the Milky Way Galaxy. E/S
Earth in the Solar System
For 2000 years many believed that the Earth-centered Universe proposed by Aristotle and
Ptolemy was an accurate model of the solar system. In the 16th century a new idea was developed by the Polish astronomer Nicolai Copernicus (1473-1543). In his book called On the
Revolutions of the Heavenly Bodies, C opernicus proposed that the Sun, not the Earth, was the center of the Solar System. We know this model as a heliocentric or sun-centered system. Not only was the Sun placed at the center of the solar system, Copernicus’ model correctly arranged the planets in order. In addition to the Earth, there are seven other planets in the solar system.
Pluto, formerly classified as a planet, is now thought to possibly be a Neptunian moon and not truly a planet at all, it has been reclassified as a Plutiod or dwarf planet and is one of 3 or 4 such objects know in the solar system. In addition to the planets, comets, meteors, and an asteroid belt all orbit around the Sun.
Figure 1. Sun and Planets
(From http://www.aerospaceweb.org/question/astronomy/solar-system/solar-system.jpg
)

The Earth, like most planetary objects in the solar system rotates and revolves toward the east, when viewed from above the celestial North Pole. Earth, as seen from space, is a beautiful blue and white planet, mostly covered with water and is surrounded by a thin atmosphere. Our location in the solar system (third from the Sun) seems to be the perfect location for using the
Sun’s energy to provide an environment for living organisms. The Earth, the only planet known to support life, is found between the orbits of Venus and Mars.
The Earth has only one natural satellite, the Moon. The Moon orbits Earth, approximately once every 29 days. Together the Earth and Moon orbit the sun approximately once every 365 days, or one calendar year. The Earth and Moon are very close neighbors; the average distance between them is 384,403 km. This is about thirty times the diameter of the Earth. By comparison, the solar system is vast. The distances between planets can be hundreds of millions of kilometers.
Stating these distances in kilometers can quickly become unmanageable. For example, the
Earth’s maximum distance from the sun of 152 million km and its minimum distance of 146 million km. Based on this, it is easy to understand why astronomers use AU or Astronomical
Units as the unit of measurement to indicate distances within the solar system. An AU is approximately the mean distance between the Earth and the Sun, or about 149, 598, 000 km (93 million miles). Using AU’s as the unit of measure, Venus is about 0.7 AU from the sun, and
Mars is about 1.5 AU from the sun, while Neptune is approximately 30 AU from the sun.
For more information about the solar system this site is very useful http://www.solarviews.com
For distances of our solar system visit http://www.windows.ucar.edu/tour/link=/kids_space/distance.html
Figure 2 . Earthrise The photo of Earthrise from the moon was taken from Apollo 8 whose crew of Frank Borman,
Jim Lovell, and Bill Anders were the first humans to travel to the moon. Actually, the Earth never rises on the moon since the same side of the moon always faces the Earth. The orbiting capsule created the appearance of an Earthrise.
Credit: NASA, Bill Anders .

(From http://www.abc.net.au/science/moon/earthrise.htm
)
Figure 3 . Reflections on a Mote of Dust Carl Sagan (1934-1996). “We succeeded in taking that picture [from deep space], and, if you look at it, you see a dot. That's here. That's home. That's us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The earth is a very small stage in a vast cosmic arena.”
Excerpted from a commencement address delivered May 11, 1996. Dr. Sagan's book Pale Blue Dot expands on these ideas. Image from Voyager 1, 1990.
(From http://obs.nineplanets.org/psc/pbd.html
)
Our Solar System is in the Milky Way Galaxy
The Sun, officially known as Sol, is the closest star to Earth. It is close enough that astronomers are able to study its surface. All other stars are so far away that they are viewed as small points of light in the night sky. The closest star to Earth (besides our sun) is about 24,000,000,000,000 miles (38,000,000,000,000 kilometers) away. Most other stars are thousands of more times further away. Because of these vast numbers, astronomers do not use miles, kilometers, or astronomical units (AU) to measure distances in interstellar space, instead they use light years. A light year is the distance light travels in the course of one year. Using this unit of measure, the closest star is “only” 4.2 light years away from the sun. By comparison, the Earth is only 8 light minutes from the sun.
The Milky Way Galaxy contains well over 100 billion stars and is approximately 100,000 light years across. Despite the fact that the Milky Way contains hundreds of billions of stars all but one, our Sun, tend not to be visible during daylight hours. Due to this fact the Sun is often not thought of as a star. Most of the stars in the Milky Way are not visible from Earth; however, almost everything we can view in the night sky, with the naked eye, is part of our Milky Way
Galaxy.
The Milky Way Galaxy is a barred spiral galaxy which means basically it is a flattened disk shape with a central bulge and arms the extend out form the bulge in a spiral shape. The Solar
System takes approximately 225 million years to orbit the Milky Way Galaxy. The Sun is

located about 26,000 light years from the center of our galaxy, and is located within the "Orion" spiral arm, called the Orion Spur.
For more information on the stuff between the stars visit http://science.nasa.gov/headlines/y2000/ast31jul_2m.htm
Figure 4 . Near-infrared Image of the Milky Way. This image of our galaxy, the Milky Way, was taken with
NASA's Cosmic Background Explorer's (COBE) Diffuse Infrared Background Experiment (DIRBE). This neverbefore-seen view shows the Milky Way from an edge-on perspective with the galactic North Pole at the top, the
South Pole at the bottom and the galactic center at the center. The picture combines images obtained at several nearinfrared wavelengths. Stars within our galaxy are the dominant source of light at these wavelengths. Even though our solar system is part of the Milky Way, the view looks distant because most of the light comes from the population of stars that are closer to the galactic center than our Sun (Courtesy NASA) .
(From http://www.solarviews.com/cap/ds/milkyway.htm
)
For interesting information about the Milky Way galaxy see http://curious.astro.cornell.edu/milkyway.php

Content Benchmark E.8.B.4
Students know Earth is part of a solar system located within the Milky Way Galaxy. E/S
Common misconceptions associated with this benchmark
1. Students incorrectly believe the Sun revolves around Earth.
Because the Sun seems to “rise” and “set” each day it looks as though the Sun is moving around the Earth. Earth’s rotation from west to east each 24 hours creates a visual distortion as observers from Earth cannot see or sense the movement of the Earth. To an Earth bound observer the Sun seems to disappear at night and Earth does not appear to rotate. The Earth seems visually, to be the center of our solar system with objects revolving around Earth and not the Sun. At night the stars are visible to us; however, the Sun is not seen as a star, as is not in view.
For more information about Earth/Sun relationships and great visuals go to http://homepages.ius.edu/pgalvin/climate/sunearth.html
2. Students incorrectly believe planets are close together and are larger than our Sun.
Many times the scale of the solar system is poorly represented in illustrations. These are confusing for students and create misconceptions about the scales of distances and size in our solar system and galaxy. Teachers can reinforce the misconception by having students conduct activities that may provide a moderately accurate representation of one scale but grossly exaggerating the other. E.g. Students use a 1m to 2m portion of register tape to represent the scale distances of the plants from the Sun, but they draw grossly exaggerated circles to represent each of the plants. In reality, in the example above the plants would be so small that the line used to indicate their orbital path would likely be larger then the actual planetary diameter. Naturally occurring phenomena, such as, viewing an eclipse further distorts our view creating the idea that the Sun is smaller than the Moon. The Sun only appears to look small because it is 93 million miles away where as the Moon is only 345,000 kilometers away. In reality the Earth is very tiny compared to the Sun and the Moon is even smaller. If you think of the Sun as a basketball, the
Earth would only be the size of the head of a pin… a speck.
For activities about scale and distance within our solar system visit http://www.lpi.usra.edu/education/explore/solar_system/s_system_map.shtml
3. Students have difficulty with and confuse light year and astronomical unit (AU) when evaluating distances in space.
Distances in space are vast and difficult to comprehend. The light year and astronomical unit are important tools for astronomers. These units are helpful for students to understand really great distances in and beyond our solar system. The light year is a distance measurement. The actual distance can be calculated based on the fact that light travels 186,000 miles per second (300,000 kilometers per second). This unit is used as a measurement of distances in interstellar space (the distances between stars) and not the measurement of time. An Astronomical Unit is the mean

distance between the Earth and the Sun. The Earth orbits at a distance of 1 AU from the Sun.
This unit is used to measure distances in the solar system.
For more information this site defines astronomy terms and has many useful links see http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ask_astronomer/faq/terminology.shtml

Content Benchmark E.8.B.4
Students know Earth is part of a solar system located within the Milky Way Galaxy. E/S
Sample Test Questions

Content Benchmark E.8.B.4
Students know Earth is part of a solar system located within the Milky Way Galaxy. E/S
Answers to Sample Test Questions

Content Benchmark E.8.B.4
Students know Earth is part of a solar system located within the Milky Way Galaxy. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.
1. Kepler’s Laws of Planetary Motion
For students to understand how Earth is orbiting the Sun a model is needed that will explain the events that are related to Kepler’s Laws of Planetary Motion. These two sites have visual effects for students to see the actual motions of the solar system and help them visualize better than can be shown in texts.
To access the site on Planetary Orbits visit, http://zebu.uoregon.edu/textbook/planets.html
To access the site on Enchanged Learning visit, http://www.enchantedlearning.com/subjects/astronomy/solarsystem/where.shtml
2. Planets and Solar System
These sites are very comprehensive for the study of the solar system. The pictures and information are good sources.
To access the site on Solar System Exploration visit, http://solarsystem.nasa.gov/planets/
The site below has “A thousand yard model” that helps students visualize both size and scale of the solar system. http://www.noao.edu/education/peppercorn/pcmain.html
Ask an Astrophysicist site has a question and answer section which addresses student generated questions about the solar system and universe. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970518a.html
3. Milky Way Galaxy Images
These sites have exciting images of the Milky Way Galaxy and good current information with multi-wavelength images and data sets of the Milky Way.
To access the Goddard Space Flight Center site visit, http://mwmw.gsfc.nasa.gov//

4. Types of Galaxies and the Local Group
These sites are teacher friendly and explain the solar concepts well. There is very good information and comprehensive galaxy images.
To access the site on Galaxies visit, http://seds.org/MESSIER/galaxy.html
The Nine Planets is a multimedia site that provides great information about the solar system. To access the Nine Planets site visit, http://www.nineplanets.org/