You may omit the comma following a short introductory phrase: On Thursday the committee decided the dispute. In 1954 the Supreme Court desegregated the public schools. But if you omit this comma once, you should do the same throughout the paper for all short introductory phrases.
But, over time the differences seen among the ever growing number of these visitors has led to many more categories than three. At the present there are approximately fifty types of meteorites recognized. They still fall mainly into the three original families; the irons, the stony-irons and the stones.
A meteoroid is a solid body in interplanetary space before it reaches the Earth's atmosphere. A meteor denotes the fiery streak or shooting star which appears when a tiny meteoroid strikes the Earth's atmosphere and burns up.Most meteors result from meteoroids no more than a few centimeters in diameter.A larger meteoroid which survives the fiery passage through the Earth's atmosphere as a meteor and strikes the Earth's surface is called a meteorite. Meteoric material less than a tenth of a millimeter in diameter is called cosmic dust.ost meteors are composed of debris left behind by comets as they orbit the Sun. A meteor shower occurs when the Earth intersects a comet's path and moves through the stream of debris and dust emitted by the comet. The meteors in a shower appear to originate from one area of the sky called the radiant.