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Deep Space Objects

This article appeared in the March 18, 2011 edition of the Davis Enterprise.

By Vinita and Calvin Domier
Special to the Enterprise

Everyone is invited to the Sat. Mar. 26, 2011 meeting of the Davis Astronomy Club at Explorit's 5th Street location starting at 7:30pm. You do not have to pay any dues to be a member of the Davis Astronomy Club. If you are interested in astronomy, you are welcome to attend.

This month we will discuss deep sky objects. After the initial thrill of viewing the craters of the Moon, the rings of Saturn, the moons of Jupiter, etc., through their small telescopes, many backyard astronomers want to see deep space objects like the Orion Nebula, the Andromeda Galaxy, Crab Nebula, etc.

Deep sky objects (DSOs) is a term used in astronomy to denote objects in the night sky other than solar system objects, single stars, and multiple star systems. Most DSOs are not visible to the naked eye, but can be seen with a small telescope or good binoculars. There are three main types of DSOs:

(1) Star Clusters are groups of stars that are bound together by gravity.
• Globular clusters are compact spherical groups of 10,000 – millions of old stars 10 – 30 light years across.
• Open Clusters are loosely bound groups of few hundred young stars about 30 light years across.

(2) Nebulae are interstellar clouds of dust and gases.
• Bright or Diffuse nebulae are (a) emission nebulae with glowing ionized gas clouds, or (b) reflection nebulae lit by nearby stars’ lights.
• Dark nebulae can only be detected when they obscure other stars and nebulae.
• Planetary nebulae are the outer gaseous layers ejected from old dying stars.

(3) Galaxies contain 10 million –1 trillion stars, interstellar gas and dust, (and dark matter and dark energy), all orbiting a common center of gravity. The galaxies are categorized by their shapes: (a) elliptical, (b) spiral, and (c) irregular.

Charles Messier, an avid eighteenth century French comet hunter, put together a list of DSOs so astronomers would not confuse them with comets. His final 1791 list had 110 DSOs, ranging from M1 to M110. These DSOs are now known as Messier objects. As Messier did his observing in Paris, his list did not include DSOs visible beyond -35°S latitude.

The New General Catalogue of Nebulae and Clusters of Stars (NGC) is the most comprehensive catalog of 7840 DSOs known as NGC objects. It was initially compiled in 1880s by J.L.E. Dreyer using William Herschel’s observations and published in 1888. It was expanded with two Index Catalogues (IC I in 1896 and IC II in 1905) using John Herschel’s observations of DSOs in the Southern Hemisphere.

All the 110 Messier objects are known by their Messier number and also by their NGC number. Some DSOs also have names. For examples: Andromeda Galaxy is M31 and NGC 224, Orion Nebula is M42 and NGC 1976, Crab Nebula is M1 and NGC 1952, Beehive Cluster is M44 and NGC 2632, Hercules Cluster is M13 and NGC 6205.

It is possible to see all 110 Messier objects (the relatively bright DSOs) in one night. Messier night sky viewing marathons are possible close to 25°N latitude near the Spring Equinox (late March or early April). The DSOs have to be viewed in prescribed order, starting in the west at sunset and finishing in the east at sunrise to accomplish this astronomical feat.

Telescope viewing will be available after the presentation, weather permitting. As the moon will be in last quarter phase, it will rise after midnight. This makes it ideal viewing conditions for DSOs. As Saturn is close to opposition (on April 3), it will rise at sunset and set at sunrise. It too will be ideal for telescope viewing.

Also tomorrow: What’s a buckyball? or a carbon nanotube? Come find out at NanoDays 2011 at Explorit’s 3141 5th Street site. Visitors will be able to try hands-on activities about nanoscience and also explore the “Game On! The Science of Sports” exhibition.  Event runs from 1:00-4:00 and general admission will be $4 (or free for Explorit members).

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Explorit Science Center’s 3141 5th St. site is the location for field trips, programs for groups, and astronomy club meetings.  It is also the hub for Explorit’s traveling programs that reach an 18-county region.  The site is open to the public for special events and to groups by reservation. For more information call (530) 756-0191 or visit http://www.explorit.org.

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