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This is the Griffith Observatory Sky Report through September 26th, 2018. Here’s what’s happening in the skies of southern California.
The equinox occurs at 6:54 p.m., PDT on September 22nd, and starts autumn in the northern hemisphere and spring in the southern hemisphere. This is the moment when the position of the sun on its annual path, the ecliptic, crosses from the northern hemisphere to the southern hemisphere, across the celestial equator. The resulting illumination of the globe leads to days and nights on that date of nearly equal length. Griffith Observatory staff will demonstrate the workings of the equinox shortly before the sun crosses the meridian at local noon, and again shortly before sunset. Autumn will end with the Solstice on December 21st.
Shortly after sunset, the bright planets Venus, Jupiter, Saturn, and Mars, are visible, in that order, along an arc that reaches from the southwest to the east-southeast. It is best to observe Venus, Jupiter, and Saturn as early as possible because they set at 8:00, 9:00, and 11:50 p.m., respectively.
Each of the planets shows distinctive features through telescopes. Venus, now bright enough to see by unaided eye before sunset, in the southwest sky, easily shows a crescent phase by using a magnification of 10 power or more. Jupiter, above and to the left of Venus in the constellation Libra the Scales, shows its brightest four moons with only 10 power, while 25 power or more will start to reveal the banded structure of its clouds. Saturn, in the constellation Sagittarius the Archer and just west of the southern meridian, shows its ring system, also by using a magnification of 25 power or more. Mars, gleaming orange to the east of Saturn in Capricornus the Sea Goat, requires at least 100 power to see its dark markings and bright southern polar cap, and it is the most challenging of the bright planets to observe.
The moon’s phase waxes from gibbous to full on the 24th. As this is the first full moon in autumn, it is known as the Harvest Moon. The Harvest Moon is the occasion of traditional celebrations around the world. The waning gibbous moon rises at 10:04 p.m. on the 26th.
The International Space Station will pass directly over Los Angeles on the evening of Thursday the 21st. A rival to Venus in brilliance, the ISS will first appear near Venus at 7:55 p.m. in the southwest. The space station will climb until it appears directly overhead at 7:59 p.m., and then it will descend to the northeast. It will vanish into Earth’s shadow while it is still 21 degrees high at 8:01 p.m. Use binoculars of 10 power or more to see the square appearance created by the arrangement of the giant solar panels of the ISS.
Free views of the Sun during the day and of the moon, planets, and other celestial objects at night are available to the public in clear weather through Griffith Observatory’s telescopes from Tuesday through Sunday, before 9:30 p.m. Check our website for the schedule. The next free public star party on the grounds of Griffith Observatory, hosted by the Los Angeles Astronomical Society, the Sidewalk Astronomers, and the Planetary Society, will take place on Saturday, September 22nd.
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From Griffith Observatory, I’m Anthony Cook, and I can be reached at griffithobserver@gmail.com.