In the months from late November through early March, in both the northern and southern hemispheres, the famous Pleiades star cluster grabs the attention of experienced and untutored stargazers alike. The little dipper-shaped cluster, which is about the width of your little finger held at arm’s length, presents a spectacular sight in binoculars or small telescope where it transforms from a tiny cluster of half a dozen members to an arresting array of couple of hundred of blue-white stars. The cluster itself is a snap to observe, but at its heart lies a far more challenging object, an ethereal reflection nebula created by starlight reflected by fine grains of stardust in an interstellar cloud that the cluster is passing through.
The Pleiades takes its name from the seven sisters who were daughters of the titan Atlas and the sea nymph Pleione, but nearly every world culture has a name and legend for this group. In Sanskrit, the cluster is called Kṛttikā, which refers to the six sisters of the god Murugan. The Japanese refer to this cluster as Subaru, from which the famous car company takes its name and logo. In the middle ages in Europe, the Pleiades was associated with Halloween because it reached its highest point near midnight on that date. Greek legend also tells of the Pleiades reaching high into the sky on a night in 1650 B.C. when the island of Santorini in Greece exploded in a volcanic eruption and destroyed the Minoan civilization on a nearby island.
Without the help of optics, most observers can pick out the six brightest stars in the Pleiades. In a good pair of binoculars or a wide-field telescope at lowest magnification, the cluster explodes into dozens of blue-white stars packed into a 2° field of view. But there’s more to see here than just stars. In 1859, an extensive blue-white nebula was discovered enveloping the stars of the Pleiades. It appears in early images as an oval blue-white gauziness with the cluster member Merope immersed in the brightest end of it. The nebula is easily seen in images from modern amateur astronomers, most particularly in the expert image at the top of this page from astrophotographers Terry Hancock and Robert Fields. The most conspicuous part of the nebula around the star Merope (“mare-OH-pee”) is sometimes called the Merope Nebula or, more formally, NGC 1435.
As longtime readers of this site and keen students of the annual Fundamentals of Stargazing course have come to understand, many star clusters are bathed in gauzy blue nebulosity generated by blue-white starlight reflected by fine and sooty dust particles left over from the formation of the cluster. But at 100 million years of age, the Pleiades is a little long in the tooth for that sort of light show. Modern studies suggest the dust enveloping the Merope and the other stars of the Pleiades is simply a relatively sooty section of the interstellar medium through which the cluster is passing. As the Pleiades moves through this part of space over the next many hundreds of thousands of years, it will leave this patch of interstellar dust behind and the nebula will disappear.
Getting the Merope Nebula to show up in images isn’t a huge challenge these days. But seeing it visually is not easy with anything other than binoculars of 70-80 mm or more in aperture and pristine dark sky. A larger scope with a 4″ or 6″ objective works better, but again, dark sky is essential to see the faint nebulosity. A magnification of 50x will do the job– you don’t need high power here. To reduce the overwhelming glow of Merope, place it just out of the field of view as you first look for the nebula. At first, you may see nebulosity everywhere among the glow of the bright stars of the Pleiades. This is illusory, or it may be caused by dew formation on your objective lens or your warm breathe condensing on your eyepiece. The Merope Nebula itself will be more localized near the star.