Southern Colorado Skies / OCTOBER 2017


Mercury – Unfortunately, Mercury will be lost in the glare of the Sun and therefore not in a good position for observing this month. Mercury is at superior conjunction (exactly opposite from Earth on the far side of the Sun) on October 8, as it passes from a morning to evening object – but don’t expect to see it again until the middle of November.

Venus – Look for bright Venus low on the eastern horizon as it rises about two hours before the Sun at the beginning of October. Venus passes close to Mars (with about 1/4 degree!) at dawn on Thursday, October 5 (Mars will be very dim, however – see below). By the end of October Venus will be deep into dawn’s glare, rising only about an hour and a half before the Sun.

Mars – At the beginning of October Mars will be only 3 degrees below Venus, but it’s so dim that you will probably need binoculars or a telescope to see it (watch out for the rising Sun!); the best time to see Venus and Mars together in the sky will be about one hour before sunrise. Mars and Venus will be within about 1/4 degree of each other at dawn on Thursday, October 5.

Jupiter – Jupiter is fading fast from the sky. At the beginning of October it’s still visible as a dim speck on the western horizon at dusk and undergoes conjunction (in direct line with the Sun) on October 26th; it reappears as a morning object in early November.

Saturn – Look for Saturn low in southwest during early evening all through October. The ringed planet sets almost 4 hours after the Sun on October 1st, but only about 2-1/2 hours after the Sun by Halloween. Saturn’s rings are at their maximum tilt (27 degrees) this month, making for a spectacular view even if you have a small telescope.


Halloween (October 31), along with All-Saints Day (November 1) and All-Souls Day (November 2), marks the approximate midpoint between the Autumnal Equinox (first day of autumn) and the Winter Solstice (first day of winter). October 31st was celebrated by the Celts as ‘Samhain’ (pronounced ‘sah-win’or ‘sow-win’), one of four “cross-quarter days” of the Celtic calendar (two other cross-quarter days are known in modern times as Groundhog Day and May Day; the fourth cross-quarter day is August 1st) .

Samhain means “Summer’s End” and was celebrated as a time of harvest. But cross-quarter days represented a time of transition, and Samhain meant that light (summer) was ending and darkness (winter) was beginning. At this time, “agents of chaos” could emerge from a rift in the fabric of the universe, and people wore disguises so they wouldn’t be identified and built scary jack-0-lanterns out of large pieces of vegetables to scare the agents away – later, we adopted such measures into the traditional Halloween activities of dressing in costumes and lighting pumpkins on our porches.


Like last month’s featured constellation (Andromeda), Cassiopeia was one of the principal characters in the movie Clash of the Titans (she was the mother of Andromeda in Greek mythology and the husband Cepheus – he has a constellation of his own). In this classic tale the hero Perseus saved Andromeda from a sea monster using his winged horse Pegasus (Perseus and Pegasus are two more constellations).

The above figure is a diagram showing the brighter stars in Cassiopeia as they appear in the northeast about 9 p.m. on October 15th. In astronomy, a constellation’s brighter stars are designated by Greek letters, with the brightest star given the letter alpha (a), the next brightest beta (b), and so forth. The diagram shows the five brightest stars in Cassiopeia – alpha, beta, gamma (g), delta (d) and epsilon (e). The designation ‘M’ refers to Messier objects, in this case the star clusters M103 and M76; for more information on Messier objects, see my article at or search the internet.


The Pleiades (pronounced plee-ah-dees) star cluster is almost directly overhead in the early morning hours of October – and directly overhead at midnight on Halloween! The Pleiades (or ‘Subaru’ in Japanese – that’s where the car company’s logo comes from) is easily visible with naked eyes, but really shows its glory when viewed though binoculars.

The entire cluster is about 14 light years wide and is located about 444 light years from Earth. From our vantage point this translates to about 2 degrees in width (about as wide as four full moons).

In Greek mythology, the seven Pleiades were the daughters of Atlas and Pleione. They were chased by the great hunter Orion until their pleas for deliverance were answered by Zeus, who changed them into birds and placed them in the sky. After Orion was killed, he was placed in the sky near the Pleiades to commemorate the chase. Atlas and Pleione were not forgotten and are also represented by stars in the cluster (the whole family is there!).




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