D  e  s  e  r  t     E  x  p  o  s  u  r  e     June 2005

Constellation of the Month: Virgo, the Maiden

Because most of the ancient civilizations whose records we have were in the northern hemisphere, the June appearance of Virgo, the Virgin (or Maiden), is associated with planting season. The Persians called Virgo Khosha (Ear of Wheat), while the Hebrews called her Bethulah (Abundance of Harvest). The Babylonians called her Ishtar and the Egyptians, Isis—both goddesses of fertility.

A little over halfway up in the southern sky, our constellation of the month, Virgo, and its bright star Spica, have a visitor—the planet Jupiter. This is the only planet not down near the western horizon this month. The Virgo Cluster of galaxies is centered in the area around M87, the giant elliptical galaxy, and extends north into Coma Berenices.

To the Greeks, Virgo represents Demeter, the Earth goddess, who brings spring and the growing season. Demeter had a beautiful daughter with Zeus named Persephone, whom Hades, god of the Underworld, fell in love with. He wanted to marry her, but Demeter disapproved. Finally, tired of waiting, Hades drove his black chariot to Earth and carried off Persephone to the Underworld to marry her.

Worried when her daughter did not return home, Demeter began to search; in her absence, crops failed and people began to starve. When Demeter asked Zeus for help, he'd been bribed by Hades not to intervene so he would only tell her that Persephone was in the Underworld with Hades; Zeus asked Demeter to give up and accept the situation.

When she refused and people continued to starve, Zeus sent his messenger Hermes with a demand that Hades allow Persephone to return with him to Earth. Since the gods of Olympus were stronger than he was, Hades relented. But in a tearful reunion, Persephone told her mother that she loved Hades and wanted to be with him.

Zeus settled the matter by declaring that Persephone would spend half the year in the Underworld with Hades and half on Olympus with Demeter. So when Virgo rises in our eastern sky, Persephone travels to Mount Olympus to be with her mother and spring begins. In fall, Persephone returns to Hades, and her sorrowful mother's inattention allows the plants to die so we have winter.

To the naked eye, Virgo's most prominent feature is the bright white star Spica. Virgo is often depicted carrying two sheaves of wheat, and Spica—Latin for ear of corn or wheat—marks one of these. Spica is 220 light-years away, but even so seems very bright, because this giant star is some 2,000 times brighter than our Sun.

Virgo also contains hundreds of relatively bright galaxies. Just as stars in our galaxy sometimes exist in clusters, the galaxies themselves are grouped together in gravitationally bound clusters. The Virgo Cluster consists of more than 2,000 galaxies spread over Virgo, Coma Berenices and the surrounding constellations. This concentration of galaxies was discovered by comet hunter Charles Messier, who noted this area contained a "cluster of nebulae." Today we know this cluster is gigantic, and about 60 million light-years away.

Many interesting galaxies in this area are visible in small telescopes, though larger telescopes will provide a better view. One of the most interesting is M87, discovered by Messier in 1871. M87 is about 20 percent bigger across than our own Milky Way galaxy, at 120,000 light-years in diameter. The big difference is that our Milky Way is a spiral galaxy, with all the stars and gas in a giant pancake. M87 is an elliptical galaxy, which means it is not only 120,000 light-years across, but almost as high, encompassing many additional millions of stars. This makes it over three times the mass of our galaxy. In addition, M87 has a massive system of over 10,000 globular clusters orbiting it.

Not only is M87 more massive that our galaxy, but also more active. Its center contains a huge black hole with a mass of over 3 billion Suns squeezed into the comparatively tiny area of 60 light-years. This black hole is the source of the X-rays M87 emits. Early observations of the sky using sensitive radio receivers revealed a noise source in Virgo called Virgo A. We now know this is coming from the black hole in M87. There is also a jet of super-heated gas shooting out of the nucleus of M87. Stretching over 7,000 light years, the jet is composed of material kicked out from one of the poles of this huge black hole.

The Planets for June 2005

The action will be in the evening sky late this month, when Mercury, Venus and Saturn perform a do-si-do. Saturn remains in Gemini until June 30, when it enters Cancer. It will also become too low to easily observe by month's end. Shining at magnitude -0.1, Saturn's ball is now only 16.7 seconds of arc across at mid-month. The rings are tilted at 22.9 degrees, with the southern face showing, and 37.8 seconds of arc across.

Venus marks its return to the evening sky this month, popping out of the twilight around mid-month. By month-end Venus will still be low in the west-northwest after sunset. The Sun will illuminate 90 percent of Venus, making it look like an almost-full Moon. The 11 seconds-of-arc planet will be shining at magnitude -3.9. Mercury is also in the vicinity of Venus, but it will not appear in the evening sky until the end of the month, at magnitude 0.1 and only 7 seconds-of-arc across.

As the month begins, Saturn is alone, low in the evening sky. As the month progresses, Venus will pop up below Saturn. As we reach the end of the month, Mercury will pop up below Venus. With Saturn moving down and Venus and Mercury moving up, their paths are bound to cross. On Saturday night, June 25, Venus will be only a degree north of Saturn. During the day on Sunday, Mercury will also pass Saturn, placing both Mercury and Venus above Saturn by Sunday night. On Monday around 10 a.m., Mercury will pass Venus when they will only be 4 minutes of arc apart. This is the closest they have been since 1990.

Jupiter is high in the south at sunset, and remains near the star Porrima in Virgo. The Earth is pulling away from Jupiter, which is at magnitude -2.1, making it appear to shrink. At mid-month, Jupiter is 38.5 seconds-of-arc across. The Moon will be near it on Thursday evening, June 16.

Mars moves from Aquarius into Pisces, across a corner of Cetus and back into Pisces during June. Rising at 1:45 a.m., Mars is well up in the morning sky by sunrise. Mars is slowly growing larger, 8.5 seconds-of-arc across and magnitude +0.5 at mid-month. Enjoy the "dance of the planets" this month and "keep watching the sky"!

An amateur astronomer for more than 35 years, Bert Stevens is co-director of Desert Moon Observatory in Las Cruces.

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