Tuesday, September 14
Neptune reaches opposition at 5 A.M. EDT this morning. If you happen to be up early, you can catch the solar system’s most distant planet as it slowly sets in the west amid the stars of Aquarius. The easiest way to locate Neptune is to first find 4th-magnitude Phi (Ï•) Aquarii, then skim 4° northeast of the star. Magnitude 7.7 Neptune sits near a triangle of 6th-magnitude field stars, closest to the triangle’s southwestern point. The planet’s bluish disk spans a mere 2″, but it’s visible in binoculars as a flat-looking star. If you’ve got a telescope and good seeing, you’ll likely discern some color.
Because it’s at opposition, Neptune will again rise as the Sun sets and remain visible all night, so don’t worry about missing it if you prefer to observe in the evening. Wait an hour or two after sunset for the region to climb away from the horizon, where turbulent air often muddies the view.
Sunrise: 6:40 A.M.
Sunset: 7:10 P.M.
Moonrise: 3:24 P.M.
Moonset: —
Moon Phase: Waxing gibbous (60%)
Wednesday, September 15
Look north tonight after dark and you’ll see the Little Dipper just starting to swing downward, its cup upside-down and handle curving down toward Polaris, the North Star. Over the next several hours, the Dipper’s cup will continue to rotate toward the horizon, while Polaris stays fixed above Earth’s North Celestial Pole.
The cup is formed by four stars: Beta, Gamma, Eta (η), and Zeta (ζ) Ursae Minoris. Of those, Beta (also called Kochab) is the brightest, shining at magnitude 2. Polaris, the constellation’s alpha star, is just a bit brighter. In addition to its place of honor as our current North Star, Polaris is also a Cepheid variable star, whose period — the time it takes to dim and brighten again — is linked to its intrinsic brightness. Thanks to this relationship, Cepheid variables serve as valuable standard candles that allow astronomers to measure precise distances.
Sunrise: 6:41 A.M.
Sunset: 7:08 P.M.
Moonrise: 4:22 P.M.
Moonset: 12:31 A.M.
Moon Phase: Waxing gibbous (70%)
Thursday, September 16
The Moon passes 4° south of Saturn at 11 P.M. EDT. You can enjoy the view much earlier, though — Saturn is already nearly 20° high at sunset, and another 5° higher an hour later. At that time, the Moon is just less than 5° south-southwest of the planet and will continue to inch closer in the coming hours. Both are located in southwestern Capricornus, west of where you found Jupiter the other night.
Saturn itself glows at magnitude 0.3. That’s visible to the naked eye, but you’ll want some optical aid to see its stunning ring system, which stretches out on either side of the planet’s 18″-wide disk. Those rings are tilted 19° to our line of sight, which puts their northern face on view. See if you can differentiate the duskier outer ring, called A, from the brighter Ring B. The dark gap between them is the Cassini division.
Tonight, Saturn is wreathed in several of its small moons, although our own Moon’s light may make them more challenging to see. To the planet’s southeast are Dione and Tethys, while Mimas and Rhea stand to its northwest. Enceladus sits just off Saturn’s northeastern limb, while big, bright Titan — the easiest to see at magnitude 8.5 — is nearly 3′ west of the planet.
Sunrise: 6:42 A.M.
Sunset: 7:07 P.M.
Moonrise: 5:17 P.M.
Moonset: 1:36 A.M.
Moon Phase: Waxing gibbous (80%)
Friday, September 17
Bright Vega in Lyra is the sky’s fifth-brightest star, blazing high in the eastern sky after dark tonight. Part of its secret is that it’s so close — Vega is a mere 25 light-years from Earth. But it’s also a hot class A star, which also lends it some added oomph.
But don’t let this single star outshine the constellation in which it resides. Lyra the Lyre contains several other stars, including the four — Zeta, Beta, Gamma, and Delta (δ) Lyrae — that make up its parallelogram shape. Beta Lyrae, also called Sheliak, is an eclipsing binary system with a period of 13 days. Over the course of about two weeks, Sheliak dims from magnitude 3.8 to 4.3, then brightens again. You can see this for yourself by comparing it nightly with steadier Gamma, also called Sulafat, which matches Sheliak in brightness when the latter is at its peak and shines brighter when Sheliak is dimmest.
If deep-sky observing is on your to-do list, Lyra is also home to M56, a globular cluster in the constellation’s southern region. At magnitude 8.3, binoculars or a small scope will reveal this ball of stars, which stretches about 9′ across. At its distance of more than 32,000 light-years, that corresponds to a physical diameter of about 85 light-years in space. You’ll find it 4.5° southeast of Sulafat, or 3.7° northwest of Albireo (Beta Cygni).
Sunrise: 6:43 A.M.
Sunset: 7:05 P.M.
Moonrise: 5:52 P.M.
Moonset: 2:45 A.M.
Moon Phase: Waxing gibbous (88%)
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