Avid skywatchers know spring is well advanced when the star Spica appears almost due south at dusk. Indeed, with summer set to officially arrive in the Northern Hemisphere on June 20 at 8:57 p.m. EDT, Spica is located within the large dim region of the constellation of Virgo.
Virgo is a dull star pattern that owes its importance mainly to its location within the zodiac, but Spica is its gem. The star is visible even from amid the glare of city lights.
Virgo is supposed to represent Astraea, daughter of Zeus and Themis, the personification of the goddess of Justice who was the last of the deities to abandon the Earth at the end of the fabled Golden Age.
Spica is the only conspicuously bright star in Virgo. A bluish-white star of great luminosity, Spica is so far away that its light requires 262 years to travel across the vast gulf of space that separates it from the Earth.
Since light travels at 186,282 miles per second (299,791 kilometers per second) it is obvious that Spica must be far brighter than our Sun but tremendously farther away. Indeed, its a brilliant "helium" type star, about 2,300 times more luminous than our Sun.
Spica ranks as the 16th brightest star in the night sky and can be regarded as a nearly perfect example of a star of the first magnitude. On the magnitude scale, brighter stars are noted with lower numbers, with negative ratings reserved for the very brightest objects, including the Moon and some of the planets. Stars dimmer than about magnitude 6 or 6.5 can't be seen without binoculars or telescopes.
As listed in the 2004 Observers Handbook of the Royal Astronomical Society of Canada, Spica's magnitude is given as 0.98, though the star actually varies slightly at irregular intervals from 0.97 to 1.04. It has a tiny companion -- invisible even to powerful telescopes -- that was discovered while analyzing its light with a spectroscope back in the year 1890.
The name Spica comes from the Latin Spicum, and is said to signify a spike or ear of wheat. It is derived from the ancient allegorical drawings of the goddess whose figure was somehow traced around the scattered stars by the imaginations of primitive stargazers. In many parts of the classical world she is the "Wheat-Bearing Maiden" or the "Daughter of the Harvest."
The goddess was shown holding several spears of wheat in each hand and Spica is in one of the ears of grain hanging from her left hand, evidently representing the harvest time which occurred when the Sun was passing this bright star. Interestingly, in another legend, Virgo supposedly represented Persephone, daughter of the goddess of the harvest, Ceres, and as such is associated with agricultural matters.
Henry M. Neely, who passed away in 1963, was known as "The Dean of New York Stargazers" and lectured until he was well into his 80s at New Yorks Hayden Planetarium. When point out various objects during a typical planetarium lecture, Spica was among his favorites. Back in the 1950s, Neely would often train his electric arrow-pointer on Spica and remark:
"Spica could have been totally destroyed at the time of the signing of our Declaration of Independence, yet men would still be seeing it shining serene and undisturbed in its accustomed place until the babies who are now in their mothers arms are aged men, cursing their rheumatism and the younger generation in the same breath."
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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.
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| 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. 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. |
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