Celestial Objects

The sky is really a lot more than blue with clouds, the sun, and the moon. We see shifting clouds and visualize objects flying by in our imaginary world. We take a quick peek and the sun at midday, squinting our eyes carefully so we will not be blinded, yet during sunset, we can look directly at the sun and marvel at the changing colors. But once the sun has gone down for the night and dusk given way to a dark sky, tiny white dots glitter against the velvet black background and we stand in wonderment over all which we suddenly see. These stars are actually up there all the time, but we do not notice them because the light from the Sun is so bright, that the tiny white dots of starlight are completely overmatched.

A casual look at the night sky will cause most people to see that stars are not all the same brightness and that they appear to form interesting patterns. A closer examination will reveal that the white dots are actually different colors ... red, orange, yellow, white, and even bluish. Night after night, the stars appear in the sky, and they all seem to stay in the same groupings.






These groupings of stars are called Asterisms, and familiar ones which have been given formal names upon which we all agree are termed Constellations. Night after night, the constellations do not change. Orion always looks like Orion, and he is always chasing Taurus without ever shooting it successfully. The stars within a constellation do not change from night to night, season to season, year after year. That is with a few exceptions.




If you were to know what to look for, you would find seven brightly shining objects which do not stay in the same stellar neighborhood, but actually wander among different constellations. These seven naked eye objects are the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn. The sun and moon you already know about, but the other five objects are planets which revolve around the sun at different distances and different speeds than our planet, so they appear to wander. Some of the planets are made of rock, like our earth, while others are made of gas like the sun. There are other gas planets out there too, but they are too distant for our naked eyes to see, and one of them is made up of ices. A planet is defined as an object of large size that independently orbits the sun. Some planets have moons similar to our own. A "moon" is defined as an object which orbits a planet. Some moons are larger than planets, but since these large moons orbit even larger planets, and not the sun independently, they are relegated to the status of moon.



Sometime, you will see a fuzzy ball with a little tail. These comets are periodic visitors to our night sky, and appear as if they should be moving because of their streaming tails. Indeed they are moving, but because they are so far away, their movement is imperceptible to our eyes during any night. Comets are actually huge balls of dirty ice which come from a place much, much farther away from the sun than our planet. The tail of the comet is gas and dust which sublimates from the comet surface and is blown away from the sun by strong solar winds.

If you stay outside long enough in a given night you have see streaking stars overhead. These shooting stars are not stars at all, but typically tiny grains of rock which collide with the earth. Space, you see, is not empty. There is still a lot of debris floating around out there, and earth continual runs into this stuff. As the tiny grain strikes the earth's atmosphere, friction from the air causes the grain to heat up to luminescence. As the grain hurtles to the ground as speeds of 66,000 miles per hour, the grain gets very hot and very bright. We see the streaking object, make a wish, and hope nothing too big conks us on the head. Every so often, larger rocks do hit the earth and do serious damage, but that is another story for a later time in the course.




If you have ever witnessed a major burst of northern light activity, you will never forget it. These northern lights are called the Aurora Borealis, and people in Australia see southern lights called Aurora Australis. The sky is not putting on a magical light show, but simply demonstrating what happens when ions get a little overexcited by extra solar energy.




Finally, the stars, planets, and occasional visitors are not the only things you can see with your naked eye. In the summer, and if you are up north in a really dark spot, you will see a swath of whiteness moving in a diagonal path from southwest to northeast. This swath is called the Milky Way because it looks like someone spilled milk onto the sky background. Actually, the Milky Way is a collection of 200,000,000,000 stars, and what you are looking at is the edge-on view of a vast pinwheel-shaped group of stars, so far away and yet so numerous that it appears like spilled milk. The Milky Way is our galaxy home, and our sun is just one of many stars which reside there.





There is a little patch of "fuzz" near the great square of Pegasus. This little patch is a galaxy of stars similar to our own Milky Way, but very, very far away. The galaxy is called Andromeda and is the most distant object you can see with your naked eye.



This about wraps up what you might find when you look outside at the sky. One of the expectations of this course is that you will become familiar with the basic constellations of the northern night sky. To learn the names and patterns of these constellations, click on Constellations, or return to either the Introduction to the Starry Sky, the Syllabus, or to the Home page.

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