How quickly darkness falls at Equinox time – and how quick we must be to reach horizon-hugging planet Venus soon after sunset and Mercury before sunrise in the twilit sky. Find a horizon view to the west-southwest to watch for Venus to appear above the sunset glow within half an hour of sundown. In the hour before sunrise during the last week of September and the first week of October, look close above the eastern horizon for Mercury. During that period, an additional incentive to prompt our waking up to go outdoors in the early morning is the promise of witnessing the ethereal zodiacal light.
One recent evening a friend accompanied me on a half-mile walk to a high point from which to see Venus, also known as the Evening Star. We spotted the planet at about 7:20pm and gazed at Venus’ steady light until it set into the treetops. As we turned to walk home, my guest queried, “You come up here just to see Venus?” “Yes,” I replied, as we walked, observing the brightest stars emerge as twilight deepened. A fuller answer is that it’s like visiting family; I feel a part of what I see in the sky.
The celestial scene enjoyed a few days ago won’t change very much through the beginning of October, but it will unfold earlier. Arcturus twinkles to the right, west, of where Venus sets, and to the left, in the south-southwest, three points of a triangle attract our attention. Russet Mars, the left corner light, will drift further left. Saturn glows to the right of Mars, above true star Antares.
Sunset is at 6:59 today and close to half an hour earlier in two weeks! On the 2nd, begin to look for Venus at 6:15pm, with a wisp of a waxing crescent moon to the right of the Evening Star.
Shifting our focus to the morning sky during the final week of September, planet Mercury rises into view close above the eastern horizon about an hour before sunrise. Sunrise on the 26th is 6:48. The little planet closest to the sun brightens and climbs highest before dawn on the 28th, its best morning apparition of the year. With arm extended, find Mercury about one fist width above the horizon. On the 29th, delight in the sight of a delicate, waning crescent moon cupped below the little planet. New moon occurs on the 30th.
The autumnal equinox arrives on the 22nd at 10:21 a.m. The zodiacal light is a cone shaped glow visible in dark sky locations around the equinoxes: before dawn in autumn it is known as “false dawn” and after nightfall in late winter – early spring it is referred to as “false dusk.” The phenomenon is described as light reflected from asteroid bits and comet crumbs, or, according to another source, light reflected from fragments left over from the formation of the planets of our solar system 4.5 billion years ago.
The challenge is to be at a dark sky location (think country skies or seaside) with a view to the eastern horizon during the hour before astronomical twilight, which is 5:19am on the 29th. See you there as September’s crescent moons wane and during the early mornings of October, say, about 4:15 o’clock.