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Night Sky June 2005

Charlie Christmann

An Early Summer

    Sky Tour

Mark your calendars and set an alarm; the middle of June promises to amaze us with the planets gathering and the stars shining brightly. Start watching the west-northwestern sky about 9:00 p.m.

The spectacle begins on June 9, as Mercury just clears the horizon. Floating just above the horizon is the evening star, Venus. And above that is Saturn, sitting next to a three-day-old Moon. Jupiter watches over his kingdom from high overhead.

Now look to the left of Mercury and Venus and locate the bright star Capella. This is the alpha star in the constellation Aurigae. This star distinguishes itself by being the first-magnitude star closest to the pole and it is one of the three brightest stars in the Northern Hemisphere, at a magnitude of 0.08. Translated, Capella means “the she-goat.” At a distance of forty-two light-years, it is one of the sky's most famous double stars. Its two components are both yellow class G stars with roughly the same temperature as the Sun, but they are much larger and brighter. The first is fifty times more luminous than the Sun, the other eighty times brighter. Each is about ten times the diameter of the Sun. These stars are dying giants that have nearly depleted their hydrogen. The two stars are only about sixty million miles apart or about two-thirds the distance between Earth and Sun. They orbit each other in just 104 days.

On the other side of the Moon from Saturn is Procyon, in the constellation Canis Minor. Only slightly dimmer than Capella, it has a magnitude of 0.32 and is the eighth brightest star we see in the sky. The Greek name means "before the dog," since in the northern latitudes, the star rises before Sirius, the Dog Star. The star is an example of a "subgiant," one that is just beginning its death process, its internal core hydrogen about all burned away to helium. Procyon's chief claim to fame is a tiny companion, Procyon B, a white dwarf discovered in 1895. Recent Hubble Space Telescope observations show that Procyon B is only about the size of Earth.

Now look overhead. South and east of Jupiter shines the star Spica, in Virgo. Just a bit dimmer that the previous stars, at a magnitude of 1.04, Spica becomes prominent in the southeast in spring evenings. It can easily be found by following the curve of the Big Dipper's handle through Arcturus and then down. Sun passes Spica in the fall, making the star a harvest symbol that is reflected in its Latin name, meaning "ear of wheat." Spica is twenty-one hundred times brighter than the Sun, which explains its apparent brightness, even at 260 light-years away from Earth.

Now, look north and east of Jupiter to complete a triangle of bright “stars” and find Arcturus, the bright star of Bootes. Among the very brightest of stars, it shines with a soft orange glow. Arcturus, the Bear Watcher, seems to follow Ursa Major, the Great Bear, around the pole each day. Compared with most of the stars that reside in our galaxy, which orbit more or less circular orbits, Arcturus falls behind by about sixty-two miles per second (as do several others of the Arcturus Group). The lagging suggests that the star comes from an older population of stars that formed early in our galaxy's history.

Finally, look northeast for Vega, in the constellation Lyra. One of the most famed stars of the sky, Vega is the luminary of the dim constellation Lyra, which represents the harp of the great mythical musician Orpheus. Its name comes from an Arabic phrase that means "the swooping eagle." Lying just twenty-five light-years away, its proximity helps make it bright in our skies. It is also inherently luminous—fifty-four times brighter than our Sun—and has a magnitude of 0.03. Vega was one of the first stars to be discovered, with a large luminous infrared halo that suggests a ring of warm dust. Since Vega seems to be rotating with its pole directed toward the Earth, the dust cloud probably represents a face-on disk that may not be unlike the disk surrounding the Sun that may contain the planets.

Look low in the south-southeast. In the heart of Scorpius lies Antares. A brilliant jewel set within the Milky Way, Antares guides us to one of the great constellations of the sky. The name Antares, or Ant-Ares, means "like Mars," Ares being the Greek name for the god of war. Its great distance of six hundred light-years betrays its true brilliance; it is actually over ten thousand times brighter than the Sun.

Completing the tour is Altair, just rising over the eastern horizon in the constellation Aquila. Altair, the twelfth-brightest star in the sky, is the southern anchor of the famed Summer Triangle, which it makes with Vega and Deneb. The Arabic name Altair comes from a phrase meaning "the flying eagle." It is also a very rapid spinner. Its equatorial spin speed, while certainly not a record, is still an astonishing 130 miles per second (and may be greater, since astronomers are not sure of its tilt), as compared with the Sun's 1.25 miles per second. With a radius 1.8 times that of the Sun, the star has a rotation period of only ten hours at most, as opposed to nearly a month for our Sun.

    Planetary Gathering

Starting on June 9, watch Mercury, Venus, and Saturn each evening. Over the course of the next seventeen days, these three planets will come together and become almost a single point of light on June 25. Look early, as the group sets about 9:30 p.m. in the west. By June 28, Mercury and Venus will have pushed higher in the sky, leaving Saturn to itself. By the end of the month, you may just be able to see Mercury and Venus separating.

    The Planets and Moon

  • Mercury rises early evening with Saturn and Venus.
  • Look for Venus and the two-day-old Moon on the evening of June 8.
  • Mars slides into Pisces as a morning planet, rising about 2:00 a.m. The Moon and Mars are a tight pair on the morning of June 29.
  • Jupiter is up most of the night and shining brightly overhead. A gibbous Moon is near Jupiter on June 16.
  • Saturn is up at sundown and sets about 11:00 p.m. The Moon is next to Saturn on June 13.
  • The Moon is new on June 6 and full on June 21. June is the Full Strawberry Moon. Europeans call it the Rose Moon.
  • June 21 marks the summer solstice. Officially, summer begins at 12:46 a.m. MDT.






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