Showpieces of the Sky - M42 - Diffuse Nebula in Orion
The following is some information about those deep sky objects that we always show off at public star parties during different seasons of the year. You might want to check this list prior to our public events in order to dazzle visitors with your knowldege of things astronomical! Telling guests something about what they're seeing in the telescope makes a star party more interesting for them. Even in light-polluted skies, our instruments provide some inkling of the grandeur that these objects possess. Imagine the payoff to observers who linger with them in a dark sky! And the nice thing about these objects is that they're attainable in virtually any amateur-sized telescope. The list is roughly arranged beginning with winter objects and it ends with those especially well-placed in the autumn. However, many are accessible over a period of several months, so don't let this sequence be a hindrance when checking to see what's up.
M42 - Diffuse Nebula in OrionA mass of gas that is caused to glow by ultraviolet radiation from the stars embedded in it, like a fluorescent light bulb. Photographs show the color as distinctly red, due to the hydrogen, and green, due to oxygen. There is enough material in the nebula to form about 10,000 stars like our Sun. Stars are actually being formed within the nebula, which is referred-to as a "stellar nursery". The Trapezium in the heart of the gas cloud is a good example of a cluster of new stars. There are four bright stars in the Trapezium, plus two fainter ones. The diameter of the nebula is roughly 30 light years, or more than 20,000 times the diameter of our solar system. It lies at a distance of between 1600 and 1900 light years away from us.
M35 - Open Cluster in GeminiLocated at a distance of about 2200 light years and 30 light years in diameter. Although most open (galactic) clusters contain young stars, M35 has several middle-aged members, including some orange-colored giants. About a half degree southwest of M35 is another open cluster - NGC 2158 - which appears as a fuzzy patch. It has no physical relationship with M35, since its distance is 16,000 light years, or six times as far away as M35. NGC 2158 is one of the most remote open clusters.
Perseus Double Cluster (NGC 869 & NGC 884)These are two open clusters that lie near each other as we see them in the sky, but NGC 844 is about 1000 light years farther away than 869, at a total distance of about 7500 light years. NGC 869 contains about 400 stars and NGC 884 contains 300 stars, but the stars in 869 are some of the youngest known, while 884's stars are older, and they include three red supergiant stars.
M44 - The Beehive Cluster in CancerThis is one of the nearest and brightest open clusters, at 525 light years from Earth. It spans about 40 light years. This was one of the first objects observed by Galileo in 1610; he was amazed to find that it's composed of a myriad of bright stars. The brightest member of this cluster has a luminosity 70 times that of our Sun.
M81 & M82 - Galaxies in Ursa MajorThese two galaxies are the brightest members of a small group of galaxies that is located at about 7 million light years - just beyond our own "Local Group". M81 is a spiral galaxy similar to M31 in Andromeda and is about 36,000 light years across. M82 is a spindle-shaped galaxy with dark lanes visible in most telescopes. Strong radio emissions and polarization of its light indicate that M82 is an extremely active galaxy and suggest that a violent outburst occurred in the central region of the galaxy about 1.5 million years ago. M82 has a diameter of 16,000 light years and contains only one-fifth the mass of its neighbor, M81.
The Stars Mizar and Alcor in Ursa MajorMizar and Alcor are double stars visible to the naked eye in the handle of the Big Dipper (Ursa Major). There is a fainter companion to Mizar ("Mizar B") that's visible only with optical aid. In addition, both Mizar A and Mizar B are themselves spectroscopic binaries - double stars detectable only with spectroscopes. More info about this pair:
- The ability to separate Mizar and Alcor with the naked eye was once considered a test of good eyesight, but since it's now quite easy to spot Alcor, the dimmer of the two, it's believed that this star has brightened over several hundred years.
- Mizar A is of magnitude 2.4 at a distance of 88 light years. Inherently, it is 70 times brighter than our Sun. Alcor is of magnitude 4.0 and lies about 1/4 light year from Mizar.
- Alcor also is itself a double star; however, its companion lies too close to spot even through a telescope - it's a spectroscopic binary.
- This "double-double-double" system is moving toward Earth at the rate of 5.5 miles per second.
- Mizar and Alcor have the distinction of being the first double star system to be discovered and the first to be photographed.