When I look at the evening sky this time of year, I think about the long-running successful dramatic family television shows from the mid 1970s through early 1980s, "Little House on the Prairie."
Faithful viewers will remember two mainstays of that show, Harriet and Nels Oleson. Harriet was portrayed as the snobby, rather mean and ridiculously haughty town gossip, while Nels, proprietor of the town's general store, (Olesen's Mercantile) was in contrast, a meek, good-natured soul and a friend to all. Yet, throughout the show's nine-year run, Harriet always remained true to her nasty, gossipy, scheming, troublemaking self, much to Nels' chagrin.
What's any of this got to do with the night sky?
If you look high toward the northern part of the sky around 8 or 9 o'clock in the evening, local time, you'll be able to see what could certainly pass as the celestial version of Harriet and Nels.
Boldly standing out, is a zigzag row of 5 bright stars, which at this time of the year resembles the letter M. Those stars represent Cassiopeia, the Queen of Ethiopia, who like Harriet was apparently pretty much a gossip and a troublemaker in her own right.
In fact, legend tells us that Cassiopeia went so far as to offend none other than the sea god Neptune by boasting that her beauty rivaled that of the Nereides (sea nymphs). Neptune promptly answered Cassiopeia's boasts by flooding the seacoast and sending a vicious sea monster named Cetus, to ravage the land.
In contrast to Queen Cassiopeia, her husband, Cepheus, the King quietly sits nearby and is chiefly composed of relatively dim stars. And much like Nels was with Harriet; poor long-suffering Cepheus is nowhere near as prominent as Cassiopeia.
Nonetheless, on clear November evenings, you should be able to trace out the inverted house-shaped figure of the Ethiopian King, for at this time of year, rather than a King, Cepheus seems to resemble an upside-down church with a steeple. Better yet, maybe we could call it an Alpine ski lodge with a classic steep, snow-shedding roof. Were we to speak of the "Harriet and Nels connection," perhaps we could even refer to it as the building that housed Oleson's Mercantile!
This spire-like figure of stars points toward the general vicinity of Polaris, the North Star, and its dim stellar outline is best seen on moonless transparent nights as it now wheels high above the celestial pole.
At the southernmost point of the spire is Delta Cephei, the most celebrated of the class of variable stars known as the Cepheids. Sky catalogues contain literally hundreds of such pulsating stars that appear to regularly brighten and fade as they expand and contract. Their steady and rhythmical cycles are known with great precision, running from about two to 50 days while their brightness change (in most cases) amounts to about one magnitude.
For example, Delta Cephei has a period of 5 days, 8 hours, 47 minutes and 32 seconds, and at maximum, it sends us about twice as much light as at minimum, varying in magnitude between 3.6 and 4.3.
But more importantly, these Cepheid stars are powerful tools in gauging distances to other galaxies. Harvard Observatory astronomer Henrietta S. Leavitt (1868-1921) discovered in 1912, that there's a close relationship between the period and intrinsic brightness of a Cepheid - the longer the period, the greater the star's luminosity. An astronomer need only determine a Cepheid's period and apparent magnitude. The former value then gives us the star's absolute magnitude; by comparing its apparent and absolute magnitudes it is then easy to calculate the star's distance, which in turn gives the distance of the galaxy in which it is located.
Thus, the relationship between a Cepheid variable star's pulsation rate and the change in its observed luminosity has allowed astronomers to use these stars as "celestial yardsticks" to measure stellar distances. Without the Cepheids, we would have great difficulty in determining distances of tremendously far-away objects like distant galaxies.
Cepheus also hosts some outstanding attractions for binocular viewing.
One is Mu Cephei, better known as William Herschel's Garnet Star. With careful scrutiny, its ruddy cast is apparent even to the unaided eye on a dark night and it is stunning in good binoculars. Another binocular attraction is the Milky Way. You'll enjoy sweeping the Cepheus region on dark nights. An amazing profusion of celestial treasure passes in review before you - star trains and clusters, highly tinted single, double and multiple stars, and even hints of faintly glowing nebulosity and dark obscuring clouds of gas and dust. This rich treasure trove seems fitting for the dim, misty countenance of King Cepheus. Might we then imagine the Milky Way's as his flowing royal gown woven out of stardust?
I bet it would have made even Harriet Oleson envious!
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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.
| DEFINITIONS |
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1 AU, or astronomical unit, is the distance from the Sun to Earth, or about 93 million miles.
Magnitude is the standard by which astronomers measure the apparent brightness of objects that appear in the sky. The lower the number, the brighter the object. The brightest stars in the sky are categorized as zero or first magnitude. Negative magnitudes are reserved for the most brilliant objects: the brightest star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest stars visible under dark skies are around +6.
Degrees measure apparent sizes of objects or distances in the sky, as seen from our vantage point. The Moon is one-half degree in width. The width of your fist held at arm's length is about 10 degrees. The distance from the horizon to the overhead point (called the zenith) is equal to 90 degrees.
Declination is the angular distance measured in degrees, of a celestial body north or south of the celestial equator. If, for an example, a certain star is said to have a declination of +20 degrees, it is located 20 degrees north of the celestial equator. Declination is to a celestial globe as latitude is to a terrestrial globe.
Arc seconds are sometimes used to define the measurement of a sky object's angular diameter. One degree is equal to 60 arc minutes. One arc minute is equal to 60 arc seconds. The Moon appears (on average), one half-degree across, or 30 arc minutes, or 1800 arc seconds. If the disk of Mars is 20 arc seconds across, we can also say that it is 1/90 the apparent width of the Moon (since 1800 divided by 20 equals 90). |
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