A Field Guide to the Stars and Planets - Softcover

Roger Tory Peterson, one of the world's greatest naturalists, received every major award for ornithology, natural science, and conservation, as well as numerous honorary degrees, medals, and citations, including the Presidential Medal of Freedom. The Peterson Identification System has been called the greatest invention since binoculars, and the Peterson Field Guides® are credited with helping to set the stage for the environmental movement.

The moon is often the most prominent object in the nighttime sky. The moon is somewhat more than one-quarter the diameter of the earth. This makes it the largest substantial satellite (moon) in the solar system in comparison to its parent planet. (Three moons of Jupiter and one each of Neptune and Saturn are physically larger than our moon; Pluto’s small moon Charon is nearly half Pluto’s size.) The moon orbits the earth every 271?3 days with respect to the stars. But during that time, the earth and moon have moved as a system about 1?12 of the way in their yearly orbit around the sun. So if the moon at a certain point in its orbit is directly between the earth and the sun, 271?3 days later it has not quite returned to that point directly between the earth and the sun. The moon must orbit the earth a bit farther to get back to the same place with respect to the line between the earth and the sun. The moon reaches this point in a couple of days, making the synodic period of the moon equal to 291?2 days. (The synodic period is the interval between two successive conjunctions coming to the same celestial longitude of two celestial bodies, in this case conjunctions of the moon and sun as observed from the earth.) It is the synodic months that are taken into account in lunar calendars.