Are cell mutations always bad? A mutation is a change in the genetic material of an organism. We are made from trillions of cells, each with a nucleus composed of DNA â a set of instructions that tells the cell what to do. Cells copy themselves with astonishing accuracy, but every now and then a piece of code is copied incorrectly.
Seven eclipses occur in a minimum of 12 lunar months (about 354.37 days). Given that the calendar year is only about eleven days longer than 12 lunar months, the first of the seven eclipses has to come in early January for the seventh eclipse to occur before the end of the year.
Solar Eclipse -- August 21, 2017. 1  Sun's corona at totality. 2  A solar eclipse occurs when the moon passes between Earth and the sun, blocking at least part of the sun as viewed from some areas of the earth. During a total solar eclipse, the moon completely obscures the sun so that only the sun's corona is visible for a moment in time.