The solar system consists of planets and other bodies that orbit the Sun in predictable paths.

There are hundreds of billions of stars in our Milky Way galaxy. The Milky Way itself is only one of hundreds of billions of galaxies. Since our sun is an average-sized star, scientists have long hypothesized that many other stars have planets orbiting them. However, until recently we had no evidence about planets orbiting other stars.

There is a saying that states, “Absence of evidence is not evidence of absence.” The main reason we did not know about other planets was that our technology had not advanced far enough. Stars are much farther away from us than the furthest objects within the solar system. The nearest star is 268,000 times further away from us than the distance from Earth to the sun. So, any planet orbiting another star has to be at least that far from us.

Not only are they very far away, planets are much smaller than stars. For example, the sun has 99.86% of the mass in the solar system. The sun is 1,000 times larger than Jupiter, the largest of solar system planets. Not only are other planets very far away and small, they are dark. We see planets such as Mars and Jupiter at night because they are reflecting the light from the sun, not because they shine.

Using new technologies, astronomers have found evidence that planets do indeed orbit other stars. We are just beginning to learn about these planets in other solar systems. For now, the only solar system that we really know is our own. We don’t know if our solar system is typical or totally weird.

As in all the strands, these standards can be taught in many ways and in many sequences. The order in which they were written does not imply that they are supposed to be taught in that sequence. The concept map below provides one way to organize these standards. The wording of some of the standards has been slightly changed for space reasons and to emphasize a particular conceptual flow.