Also know as the Seven Sisters, the Pleiades is named for the seven stars that can be seen with excellent eyesight. It is a relatively nearby open cluster located about 440 light years away and estimated to be 115 million years old. The cluster also happens to be passing through some gas and dust in space that can be seen in long-exposure photographs as blue nebulosity. This gas and dust, called reflection nebulosity, is illuminated by the reflected light of nearby stars. In this image just a very subtle hint of some of this blue nebulosity is visible. This image was shot when the Pleiades was setting into the light pollution of Philadelphia. It is also only 1 minute of total exposure. These two factors contribute to the how little blue reflection nebulosity was captured in the photo. To capture the faint blue reflection nebulosity, you really need a lot of exposure from a dark-sky site. The Pleiades is often mistaken for the Little Dipper because it is small and looks somewhat like the Big Dipper. The Pleiades contains nine stars with magnitudes brighter than 6th magnitude. At a dark sky site, an observer with good eyesight should be able to see more than a dozen stars. Image Data
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