Summer vacations have come to a close and fall weather is here. September brings change to the Pacific Northwest. Watchers of the night sky will see changes daily, and at the same time notice that, for a while at least, some things above us stay the same.

Autumnal equinoxSunset watchers will experience the most obvious change during September; sunset will occur earlier every evening.

As the sun moves toward the southern hemisphere, sunrise will occur later every morning, and our length of daylight will shrink. At 2:19 p.m. on Sept. 22 the sun will cross the equator, bringing fall to the northern hemisphere and spring to our friends “down under.” The length of day and night will be equal on Sept. 24. By the end of the month Northwesterners will have lost one full hour of sunlight.

A lingering summer sky

Earth’s axial tilt and yearly motion about the sun provide the reason for the seasons, and for the same reason the nightly view of summer constellations and milky way will gradually give way to the sights of winter. The constellations Taurus, Orion and Gemini may be found rising in the east in September after midnight. Although the stars of summer set earlier each night, the sky darkens earlier, preserving our view. The wonders of summer will seem to hang in the same place, high in the sky, well into October shortly after nightfall. Imbedded in the milky way, Cygnus the Swan, with broad wings and out-stretched neck, will linger as if waiting to fly south for the winter.

Bob Duke is a local amateur astronomer, astronomy educator and weekly contributor to The Daily Astorian

Change in motionIt is always a joy to watch the relative motions of the moon and planets against the fixed and steady stars. Brilliant Venus and the moon will put on a show to reward all who arise an hour before the sun, around 6 a.m. during mid-September. Find a clear view to the east and observe every morning from Sept. 15. On the morning of Sept. 20, the planet will meet with the bright star Regulus in a spectacular conjunction, when both objects share the same right ascension in the sky. Use binoculars to see the greatly contrasting colors of these objects.

Jupiter in the eveningAn evening planetary conjunction will mirror the morning conjunction of Venus and Regulus on Sept. 20. Look to the southeast for the solar system’s largest planet as it brushes close to a star in the constellation Capricorn. Due to the brilliance of Jupiter and the relative dimness of Iota Capriconi, the event will be less spectacular than the morning apparition. Use binoculars for the best effect.

Last month Jupiter made its closest approach to earth for the year. The giant planet will continue to shine brilliant to the eye and appear large in a small telescope all month.

Bob Duke is a local amateur astronomer, astronomy educator and weekly contributor to The Daily Astorian.