Northern Rockies Skies for February

January 29, 2013

A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis, Idaho Observatory; and Daryl Macomb, Boise State University.

Taurus the Bull; its general orientation: After Orion, the next most obvious winter constellation is Taurus the Bull. Located to the northwest of Orion, it is famous for its “V”-shaped outline of stars featuring an orangish star Aldebaran, the 13th brightest star in the sky, and a small bluish cluster of stars the Pleiades, or the seven Sisters. One of the original 12 constellations of the Zodiac, as cataloged by Ptolemy in the second century, it was well known and recorded as far back as the Bronze Age, some 15,000 years ago.

The Pleiades are located immediately to the northwest of Taurus, and you can draw an imaginary straight line from the Pleiades and Aldebaran to Orion and Betelgeuse.

Many cultures have noted Taurus and the Pleiades in their traditional stories and folklore. Most interesting today is the important astronomical significance of this constellation. In 1054 A.D., Arab and Chinese astronomers noticed a “new” star in Taurus that beamed brightly during the day and slowly burnt out of sight. Once astronomers looked in this location with their telescopes nearly 800 years after that event, the Crab Nebulae appears, looking like wisps of gas from a star ripped apart by a giant explosion.

In fact, the Crab Nebulae is just that, the remnant of a supernova explosion nearly 1,000 years ago. Furthermore, at the center of the Crab is the first discovered neutron star and pulsar which powers the nebula, just as theory predicted it.

Planet Alert: February is a great time to view Mercury right after sunset. You may even be able to see Mars close by. Jupiter is right next to Aldebaran this month and can be seen most of the night.


Famous Astronomers: William Herschel

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Sir Frederick Wilhelm Herschel (1738-1822) was born in Hanover, Germany. He grew up in a musical family and learned to play several instruments, including the oboe, cello, harpsichord and organ. Herschel's musical talents landed him in the military Hanoverian Guard, which suffered a defeat at the Battle of Hastenbeck, necessitating flight at the age of 19 to England, where he continued several musical careers. In the early 1770s, his interests broadened to include astronomy, especially after introduction to the Fifth Astronomer Royal of England, Nevil Maskelyne.

Herschel quickly became a most prolific astronomer -- both instrument builder and discoverer of many objects in the solar system and beyond. Some of his work was done in collaboration with his sister, Caroline.

During his career, Herschel built an astonishing number of telescopes (400), often grinding his own mirrors for the reflectors. While he is best known for his famous discovery (1781) of the seventh planet from the Sun, Uranus, his dedicated observing produced catalogs of lasting importance for stellar and nebular astronomy.

Over about 20 years, Herschel measured the changing position angles and separations of close "double stars," concluding that most of these systems are physical doubles -- pairs of stars orbiting each other due to their mutual gravitational attraction. With an array of telescopes, Herschel undertook a systematic survey of the sky, searching for non-stellar objects, ultimately discovering 2,400 "nebula" -- diffuse, non-point-like objects. His nebular studies were the first to categorize, by visual appearance, various kinds of nebula.

Later, the catalog was enlarged by his son, John, and other astronomers to produce the first "New General Catalogue." NGC numbering has been in use, up to the present, as the most common identifier for non-stellar astronomical objects.

Herschel discovered two moons of Saturn (Mimas and Enceladus) and two moons of Uranus (Titania and Oberon), the names later assigned by John Herschel. Sir Frederick Wilhelm Herschel measured the inclination of Mars' rotational axis to its orbital plane and discovered the Martian ice caps. His study of the apparent proper motion of stars led him to the conclusion that our solar system is in motion through space. Herschel is credited with the discovery of infrared radiation, due to his solar observations and laboratory work using a prism and thermometer to measure the heat of invisible radiation at wavelengths longer than the red portion of the spectrum.

Next time, we'll discuss Herschel's largest instrument, the "40-foot telescope."

To view this month’s sky chart, click here.

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