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Tuesday, November 21, 2017

The Moon and the planets orbiting our Sun are extraordinary sights viewed with magnification through simple binoculars or telescopes. Beyond these magnificent sights are some truly magical objects that could have been conjured up in dreams or by fantasy authors, yet actually, exist. These are Deep Sky Objects. They can sometimes be seen in binoculars but are generally better resolved (seen clearer) as the size of the observing telescope increases.

Generally speaking, a deep sky object is anything that appears in the sky, which isn´t a planet or the Sun within our Solar System. The Hubble Space Telescope (HST) and some of the lesser-known such as the Spitzer Infrared telescope have taken some wondrous images of deep space objects that might only appear as a smudge to the naked eye. Deep sky objects are classified into several categories.

Categories of Deep Sky Objects

  • Open Star Clusters are loose groups of numerous stars.
  • Globular Clusters are larger groupings of stars drawn together into more concentrated spherical shapes.
  • Diffuse Nebulae are clouds of glowing gas and dust.
  • Dark Nebulae are clouds of gas and dust that hide the stars behind them.
  • Planetary Nebulae have nothing to do with planets but are formed when a star reaches middle age, swells to many times their original size and puffs out layers of gas into space which glows around the hot star at the centre.
  • Supernova Remnants are caused when a star explodes as a supernova and leaves behind an expanding cloud of glowing gas. On average, supernovae occur about once every 50 years in a galaxy the size of the Milky Way.
  • Galaxies have different shapes and are composed of trillions of stars, clusters and nebulae of their own.
  • Galaxy Groups are clusters of galaxies.
  • Quasars are extremely bright centres of apparently otherwise normal galaxies.

Messier Objects

One classification of Deep Sky Objects is denoted by a prefix of ´M´ after the French astronomer Charles Messier who first catalogued them in the 18th century. These objects were accessible using Messier´s relatively small 4” aperture telescope, and appear spectacular using modern day technology.

Amateur astronomers compete to view all the objects from M1 (the Crab Nebula) through to M110 (a galaxy near Andromeda) in a single night from dusk to dawn. As Messier compiled his catalogue from a northern latitude, not all of the objects are visible in the southern hemisphere. The best conditions for completing a Messier marathon are at a latitude of 25º north, from mid-March to early April, at the time of a new Moon when interference from the Moon´s light is minimal. The objects should be viewed in a certain order, starting with those low in the western sky at sunset before they set out of sight below the horizon, then working eastwards across the sky. By sunrise the last few objects are seen before the sky becomes too bright.