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This is the Griffith Observatory Sky Report through September 27, 2017. Here’s what’s happening in the skies of southern California.
Northern Hemisphere summer ends and autumn begins at 1:02 p.m., PDT on the 22nd. This is the autumnal equinox, and it marks the moment when the sun crosses the celestial equator, moving south. On that day, day and night are approximately 12 hours long over most of the Earth. The sun rises due east and sets due west at the equinox. Autumn will end with the winter solstice on December 21st.
The moon returns to the evening sky on Thursday the 21st. It will then be a slender crescent. Look for it 30 minutes after sunset when it is located low in the twilit western sky, a few degrees to the right of the bright planet Jupiter. The moon’s phase waxes to first quarter on the 27th. Between the 21st and the 27th, the time of moonset advances from 8:05 p.m. to 11:59 p.m.
The ringed planet Saturn, in the constellation Ophiuchus the Snake Bearer is visible in the south-southwest as the sky darkens. It sets at about 11:00 p.m. To the eye it appears bright, star like, and golden. The moon appears above Saturn on Tuesday the 26th. The aid of a telescope is needed to see Saturn’s beautiful system of rings. Both our moon and Saturn are currently featured through the public telescopes at Griffith Observatory.
Between the 21st and the 25th, look at the eastern horizon at 6:10 a.m. to see a line up of bright objects. The brightest is the planet Venus, and above Venus is the bright star Regulus in the constellation Leo the Lion. Below Venus are the dimmer planet Mars and the innermost planet, Mercury. Swiftly moving Mercury will drop out of sight and is too close to the sun to see after the 25th.
The International Space Station will make one morning pass and three evening passes high over Los Angeles in coming days. On Thursday morning, 21 September, the ISS will appear between 5:16 and 5:20 a.m. The ISS will outshine Venus when it suddenly emerges from Earth’s shadow at an angular elevation of 53 degrees above the northwest horizon. Two minutes later it is overhead, then it descends to the southeast horizon. On the night of the 23rd, the ISS appears in the south-southwest at 8:05 p.m. It reaches its highest point, 49 degrees above the southeast horizon, at 8:09 p.m., and there it vanishes into Earth’s shadow. On Monday the 25th, the ISS moves from the west-southwest the north-northeast between 7:57 and 8:02 p.m. It appears at its highest, 53 degrees above the northwest horizon, at 8:00 p.m. On the following evening, Tuesday the 26th, the ISS is visible between 7:05 and 7:11 p.m. as it crosses sky from the southeast to the northeast, and it will appear at its highest when it is 66 degrees above the southeast horizon.
On Thursday the 21st, residents of southern California may be able to see the launch of a government reconnaissance satellite from Vandenberg Air Force Base at 10:38 p.m.
Look for the orange exhaust of the rocket as it ascends in the western sky as seen from Los Angeles. The United Launch Alliance Atlas 5 rocket is carrying the classified NROL-42 payload. The launch will be webcast live on the United Launch Alliance website.
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 30th.
Follow the Sky Report on Twitter for updates of astronomy and space-related events.
From Griffith Observatory, I’m Anthony Cook, and I can be reached at griffithobserver@gmail.com.