Tonight – October 26, 2017 – the moon is a fat waxing crescent in the evening sky, as seen from around the globe. From northerly latitudes at nightfall, in the coming evenings, you’ll see the moon riding low in the sky, beneath the famous Summer Triangle asterism. Meanwhile, south of the equator, the moon appears high in the sky and above the “upside-down” Summer Triangle.
For all of us, around the globe, first quarter moon will come on October 27 at 22:22 UTC (6:22 p.m. EDT, 5:22 p.m. CDT, 4:22 p.m. MDT or 3:22 p.m. PDT; translate UTC to your time zone). Diana from Potsdam, New York, noticed an interesting phenomenon that occurs with the first quarter moon every autumn. She asked:
Why are the evening crescent and the first quarter moon always so low in the autumn evening sky?
This moon phase is low in the evening sky in autumn because the ecliptic, or pathway of the moon and planets, appears lowest in the sky on autumn evenings. Of course, the moon and the ecliptic don’t get all that low in the sky as viewed from the tropics. But if you live at mid-temperate or higher latitudes (places farther from the equator and closer to the poles), then the lowness of the evening crescent and first quarter moon in autumn becomes quite apparent.
Be mindful that autumn comes at opposite times of year for the Northern and Southern Hemispheres. If you’re in the Southern Hemisphere now, then take everything we’ve just said and apply it to the months of March and April! And know that in October – instead of riding low in the sky – your springtime evening crescent and first quarter moon ride high in the sky at nightfall.
On spring evenings, the ecliptic swings way high in the sky. In springtime, from either the Northern or Southern Hemisphere, the evening crescent moon travels almost straight up from the sunset point from day to day, and the first quarter moon shines close to overhead at dusk and nightfall.
Tonight – on October 26, 2017 – the autumn evening crescent sits rather low in the sky at nightfall as seen from northerly latitudes.
Bottom line: This week’s crescent moon is waxing toward first quarter phase on October 27, 2017. This post talks about why the first quarter moon in October appears low in the autumn sky, and high in the spring sky.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.