By Rod Kennedy
As winter winds down and spring approaches, the stars of winter begin to creep toward the western horizon. This means that March is the best time to get one last look at these bright constellations. A favorite of stargazers is Orion the Hunter, partly because it is bright and easy to recognize, partly because it is rich with interesting objects. The area of Orion’s Belt is particularly interesting.
The three stars of Orion’s Belt are Mintaka, Alnilam and Alnitak. All three of these stars are extremely hot, and brith. The westernmost star, Mintaka is a type O giant star. A telescope pointed at Mintaka reveals a small hot companion star. The easternmost star, Alnitak appears as a triple star surrounded by a bright nebula. Directly south of Mintaka is the famous Horsehead nebula. The Horsehead, is a stunning example of a dark nebula; a nebula that has a dark portion outlined by brighter material. While this nebula is famous, it is very difficult to see with the human eye peering through the telescope. Long exposure photographs are needed to capture its true beauty.
The greatest treasure of Orion lies not in the bright stars themselves, but in the magnificent area of his sword. The sword hangs below Orion’s belt and is home to M42, the famed Great Orion Nebula. Besides the vastness of the nebula itself, the Orion Nebula contains a group of stars cataloged as Theta Orionis or the Trapezium. This group of stars all formed at the same time and from the same cloud of material. Around the Trapezium are dozens of additional stars that are still in their infancy.
The Orion Nebula glows because its gasses are excited by radiation from the new stars within. These gasses are a mixture of Hydrogen, Helium, Carbon, Oxygen and Nitrogen with Hydrogen and Helium being the most abundant. This makes sense if we understand that nebulae are vast stellar nurseries where stars are born. Within the nebula areas of high density begin to collapse under the force of gravity. As the gasses are compressed they are heated to the point where Hydrogen can fuse into Helium. At this temperature the fusion process begins and the star ignites.
Observers wishing to view something a bit closer to home should turn their telescopes toward Jupiter, in the constellation Taurus. Like the Orion Nebula, Jupiter offers a wide range of observing possibilities. First is Jupiter’s large moons, Io, Europa, Ganymede and Callisto. Observations taken night after night revel, as they did for Galileo, the motions of these moons around the planet. Astronomy magazines or websites usually offer charts that help identify which moon is which. Larger telescopes show the intricate cloud bands in Jupiter’s atmosphere and observers with good timing may even catch a glimpse of Jupiter’s Great Red Spot. The most patient observers might even have a chance to see the shadow of one of Jupiter’s moons move slowly across the cloud tops.
Winter may be coming to an end, but the sky changes more slowly. Amateur astronomers have long known that the higher an object is in the sky, the better the view. Turbulence in Earth’s atmosphere makes objects near the horizon shimmer and haze can hide them completely. Early spring affords observers one last opportunity to see their favorite constellations and objects before they slip into that turbulent zone and are lost until next winter.