Celestial Lights
By Phyllis Pitluga, Sept 29, 2006

Can you name the worlds of our solar system?

Most of us grew up learning that Pluto was our ninth planet, and university students memorized the order of the planets from the first letters of the words in the phrase “Mary’s Violet Eyes Make John Stay Up Nights Panting” (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto). Now, John can stop panting, because Pluto has been officially removed from the planetary lineup. Pluto is now considered a dwarf planet. 

The dwarf planet nicknamed “Xena” I wrote about in last month’s Celestial Lights is now officially renamed Eris (pronounced ee´-ris) by the International Astronomical Union. In Greek lore, Eris is the goddess of discord and strife. Its moon has been named Dysnomia, the demon spirit of lawlessness. So, our dwarf planets are Ceres (between Mars and Jupiter), Pluto and Eris.



The Milky Way arches across the evening sky

Once the Moon moves out of our early evening sky by October 8, the full splendor of our galaxy can be enjoyed from a dark-sky site. Living within our Milky Way, we see it as a pathway across the sky. In our autumn evening view of the Milky Way Galaxy, half of it is above our sight line and the other half is hidden beneath. The faint white pathway of light is coming from the distant trillion stars that make up our galaxy; the Sun is just one of these stars. 

In the autumn, the Milky Way spans the sky from the southwest to overhead and then down in the northeast. The center of the Milky Way is to the southwest. Looking toward the center (current southwest) about 25,000 light years away, we are looking in the direction of the immense black hole imbedded in the center. Only with specialized research telescopes do we detect its dynamic effects on this central region.

Looking overhead at the Milky Way, dark divisions in the pathway of light are opaque gases and dust blocking the starlight beyond. The outer edge of our galaxy is viewed in the northeast. The individual stars to either side are stars a bit higher and lower in our neighborhood of our home galaxy. We can be glad that we are in the quiet suburbs of our galaxy and not in the central environment of the super black hole. 

Sky Calendar, October 2006

By following the Moon as the biggest and brightest “pointer” in the sky, during the month you can identify different planets and bright stars. On following nights you can relocate them but without the Moon—the Moon moves about 25 times its own diameter from one night to the next.

The Moon is much closer than the planets of our solar system, and the stars are even farther. So, when the Moon appears close to a celestial light, they are truly separated by millions, billions or trillions of miles.

Tuesday, October 3: The waxing gibbous (growing oval-shaped) Moon passes six moon-diameters beneath the telescopic planet Neptune.

Wednesday, October 4: The waxing gibbous Moon passes half a moon-diameter beneath the telescopic planet Uranus.

Friday, October 6: The full Moon rises at sunset; the October full Moon is the Hunter’s Moon, so called because its bright light allows hunters to continue to hunt into the night. This full Moon is notable this year because 15 hours earlier, the Moon is closest to Earth in its monthly journey around our planet. This means that the high tides will be extraordinarily high today; for the next two weeks the Moon rises about 50 minutes later each night. 

Tuesday, October 10: The waning gibbous (shrinking oval-shaped) Moon passes half a moon-diameter above the Pleiades Star Cluster.

Friday, October 13: The last quarter Moon rises after midnight.

Monday, October 16: The planet Mercury can be glimpsed low in the west-southwest dusk sky; over the next three weeks Mercury will be orbiting to a path between the Earth and the Sun, passing across the Sun as a mini-mini eclipse, called a transit (this is a relatively rare event and will be featured in November’s Celestial Lights); the waning gibbous Moon passes four moon-diameters above Saturn.

October 20–November 4: The Zodiacal Light will be visible in the dawn sky away from other bright lights; this cone of light is from myriad grains of meteoric material in the plane of our Solar System; each grain is like a teeny moonlet reflecting the Sun’s light. Together, they create the Zodiacal Light; this time of year the cone of light is angled up nearly perpendicular so it stands up from the glow of dawn.

Sunday, October 22: New Moon (the Moon is not visible because the dark side faces Earth). 

Tuesday, October 24: The waxing crescent Moon passes three moon-diameters below Mercury and 10 moon-diameters below Jupiter in the evening sky.

Wednesday, October 25: The crescent Moon passes less than one moon-diameter below the star Antares, the brightest star in the constellation of Scorpious. 

Sunday, October 29: First quarter Moon (halfway across the sky at sunset) and Daylight Saving Time ends.


Phyllis Burton Pitluga is Astronomer Emerita of the Adler Planetarium and Astronomy Museum, Chicago, and is now a San Miguel resident.