A week past the autumn equinox, darkness has gained 20 minutes over daylight, and darkness gains an additional 20 minutes every week during the rest of October. Evening stargazing begins earlier, and awakening in the morning for a rendezvous with morning planets and stars is within range of normal waking time.
In the evening sky, the stars of the Summer Triangle, like the leaves on the trees, are still with us. High overhead in the southeast to south at nightfall, the brightest stars in the sky mark the triangle’s three corners. Deneb, 1.25 magnitude, at the tail of Cygnus the Swan, is the dimmest of the three. Vega, 0.00 m, the brightest, is the highest point and Altair, .75 m, yellowish-white, the lowest.
The Great Square of Pegasus floats above the eastern horizon at nightfall. Planet Saturn is in the southeast, below and to the right of the Great Square. Saturn, 0.56 m, often appears reddish to my eyes. Below the ringed planet, winter star Fomalhaut, 1.15 m, rises close to the southeast horizon. Note that the smaller the number the brighter the celestial object.
Study the diagram and caption at the top of the page for the location of the gibbous moon, -12.79 m, rising above the east-northeast skyline at about 8 p.m. on September 30. The moon is followed by planet Jupiter, -2.79 m, visible at about 9 p.m. and brighter every evening. The two travel the sky all night. Not to be missed, on October 1, the moon rises at 7:47 p.m., with Jupiter very close behind, so the pair appear almost touching at about 9 p.m. in hilly locations.
Astronomically, twilight is defined as the time when the sun is 6 degrees below the horizon and up to the time it has risen, or the time between when it has set to when it is 6 degrees below the horizon. In the morning, this period is known as dawn; in the evening, it is called dusk.
at 6:51 a.m. Relative magnitudes are not reflected in this schema. Credit: Judy Isacoff/StarryNight7
The most luminous celestial object after the Sun and moon, planet Venus, now the Morning Star, rises in the east before daybreak and is a piercing point of light in the pale blue sky of morning twilight. (See timetable, above). In this schema, Venus, -4.51 m on the September 30, appears to the left of Sirius the Dog Star, -1.47 m. Sirius is the brightest star visible in northern skies. To the right and above Sirius, spot the moon and Jupiter in the southwest. The foursome form an outstanding arc that delights the viewer after the constellations have faded as the sky brightens. Mercury, much dimmer, appears on the eastern horizon at 5:35 a.m. on October 1 and 6 a.m. on October 6. Mercury, brightening, will be visible from horizon views, under ideal conditions, through early October, soon to be lost in the sun’s glare.
In closing, to learn about and participate in the protection of Earth’s night skies that are increasingly threatened by light pollution, I urge you to register for Under One Sky Global Conference 2023, a 24-hour Virtual, Worldwide Event, November 3–4, 2023. Sponsored by DarkSky International, Early Bird registration is $15 through October 1, then $25.
Sources and Resources
- DarkSky International
- For a remarkably illustrated guide to current astronomical events, go to EarthSky.org’s Visible planets and night sky for September and October.
- Noctalgia — Grief at loss of dark skies, light pollution.