A crescent Moon, the planet Venus and the star Spica have been photographed together above the Tatra Mountains in Poland, a pairing that shows how planetary motion shapes the night sky. The image also points to recent news about Spica itself, which astronomers reported earlier this year to be a triple star system rather than the double long assumed.
What the image shows
In the frame, the crescent Moon hangs above the Tatras. Bright Venus sits close by, slightly lower toward the horizon. Spica, the brightest star in the constellation Virgo, appears to the left of Venus.
Such groupings are known as conjunctions. They occur when planets, moving against the background of fixed stars, appear from Earth to pass near other celestial objects. The alignments are not coincidences. They follow the laws of celestial mechanics and can be predicted precisely.
The behavior is also the origin of the word “planet,” which derives from the Greek for “wandering star.” Ancient observers noticed that these bright points shifted night after night while the stars kept their places.
Spica: a binary that turned out to be more
Spica is one of the brightest stars in the sky and lies only about 250 light-years from Earth. In 1890, astronomers established that it is a binary system, made up of two massive blue stars that orbit each other every four days.
That picture has now been revised. Earlier this year, Spica was reported to be a triple system, which means the star keeping company with Venus in this scene has a third component beyond the known close pair.
The image is a reminder that familiar objects can still yield new findings. Venus will continue to shift against the stars, and the conjunction seen over Poland is a passing arrangement. Spica’s multiple-star structure is a property of the star itself and was recognized in stages: the binary in 1890, the third member only recently.
Source: science.nasa.gov
