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With Explore the Planets, investigate the planets, their moons, and understand the processes that shape them. By G. Jeffrey Taylor, Ph.D. See our DVD collection.
This is a digital copy of an old drawing. It shows the Sun surrounded by four Earths. There are four Earths, one for each season. Original art by ndreas Cellarius (1596-1665).
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(c)1995 Visual Language, All Rights Reserved

As the World Turns

In our time, scientists (and most people!) know that the constellations seem to move across the sky because the earth rotates on its axis. What, you may ask, does the turning of the earth have to do with the constellations' motion across the sky? The answer is that the earth moves in a way that makes it look as if the constellations are moving. It is a case of apparent motion. In the case of the earth and the constellations the earth rotates, with us on it, from west to east. The constellations appear to move from east to west, moving "backwards" from the real rotation of the earth. Actually, instead of saying the constellations rise we should say that the earth has rotated so that we can see different constellations. Then, as the earth continues to rotate the constellations apparently move across the sky. We now know that it is us, on earth, that have moved. As the night progresses constellations that are near or below the ecliptic "set" in the west, we know that the part of the earth we are standing on has turned so that the Earth is blocking our view of the stars that have "set".

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The Fall 2009 issue of The Earth Scientist, which includes articles on student research into building design for earthquakes and a classroom lab on the composition of the Earth’s ancient atmosphere, is available in our online store.

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Ready, Set, SCIENCE!: Putting Research to Work in K-8 Science Classrooms

What types of instructional experiences help K-8 students learn science with understanding? What do science educators teachers, teacher leaders, science specialists, professional development staff, curriculum designers, school administrators need to know to create and support such experiences?...more

Andromeda

The fall constellation Andromeda is a Princess. She looks like a "V"! Andromeda is close to the north pole, so only a few people in the Southern Hemisphere can see it in the spring. Andromeda's parents...more

Aquarius

Aquarius is also known as the Waterbearer. There are several myths about this constellation. In Greek mythology, Aquarius was the young boy, Ganymede. Zeus sent Aquila to kidnap Ganymede. The boy became...more

Cancer

The constellation Cancer is a crab. Look for Cancer from December through June. It's hard to see Cancer because the stars are so dim. To find Cancer, first find Gemini and Leo. Cancer is right between...more

Canis Major

Canis Major is known as the Great Dog. In Greek myth, it is one of Orion's hunting dogs. Many cultures saw the shape of a dog in this constellation. Sirius is the brightest star in the sky. It is also...more

Capricornus

The constellation Capricornus is a goat. Many years ago, people thought this constellation was a gate to the Heavens. Souls would go through it after a person died. The Greeks thought it was a sea-goat....more

Cetus

The constellation Cetus is known as The Sea Monster! It is a very large constellation. The Greeks thought the figure was the monster that tried to eat Andromeda. Perseus saved Andromeda and married her....more

The Unchanging Sky

The unvarying aspect of the relationships of the stars' positions may have suggested to the ancients something that was analogous to their beliefs about the universe. It is not surprising that they chose...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF