The Summer Triangle

Go out tonight as dusk settles and look halfway up into the eastern sky. As twilight fades, you should be able to see three bright stars arranged in a large triangle. This venerable star pattern, known to amateur astronomers as the Summer Triangle, has long been the starting place for people wanting to learn the constellations.

Highest in the sky around 9 o'clock is Vega, a blue-white star whose name means 'swooping eagle.' Vega is not only the brightest luminary in the Triangle, it is also the fifth-brightest star in the sky (not counting the Sun). Vega is the brightest member of the constellation Lyra the Lyre -the harp of Orpheus. You can probably just see the other five stars of the group that make a triangle at one corner of a parallelogram.

Northeast of Vega is Deneb, which is Arabic for 'tail.' Since its name means tail, it must represent the tail of something - in this case, Cygnus the Swan. According to Roman mythology, this great white bird was sacred to Venus. Cygnus is one of the more distinctive summer constellations. Many prefer to call it the Northern Cross, a seventeenth century Christianized version of the star pattern. In this form, it represents the cross upon which Jesus was crucified, and that was later recovered by Saint Helena (mother of Constantine). Christians see a divine sign in the Northern Cross, for around 9 o'clock on Christmas Eve, the cross stands erect above the northwestern horizon just before setting.

The Sign The Northern Cross

As the cross, Deneb forms the head. But as a long-necked Swan, Deneb brings up the rear. The Swan is flying south directly through the Milky Way (which you can clearly see if you don't live near a large light-polluted city). The Swan's head is marked by the second-brightest star in Cygnus, Alberio. This star is worth viewing in a small telescope. Alberio itself has a decided orange hue, but very near it lies a smaller blue star that is a companion sun. The two strike a beautiful contrast.

Lying further south and forming the apex of the Summer Triangle is bright white Altair, the leading light of Aquila the Eagle. This celestial bird, however, is winging its way in a more northerly direction, opposite that of Cygnus. In nearly all ages, Aquila has been known as a bird of prey. The Arabic name for this constellation, al-Nasr al-Tair, the Flying Vulture, is where we get the name of its brightest star.

The Summer Triangle can be used as a guide to locate other constellations. A line extended from Deneb to Vega points to Hercules, while a line from Altair through Vega points at the squarish head of Draco the Dragon, a constellation that arches around the pole star. A line from Altair through Deneb leads to Cepheus the King, a faint pattern in the shape of a crude drawing of a house. And a line from Vega through Deneb shows the way to Andromeda and the Great Square of Pegasus, both of which rise late on midsummer evenings.

The Summer Triangle remains visible in the evening skies until late November, when it stands over the west-northwest horizon at sunset -with Deneb marking the apex and Altair and Vega forming the base.

Also this week:

• The Delta Aquarid meteor shower is active between July 29 and August 6. More meteors will be seen after 3 a.m. coming from the south. Typical numbers per hour range between 10 and 20.

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