RS Ophiuchi fades more slowly. On August 8th the recurrent nova RS Ophiuchi lept from its normal magnitude 11.2 to 4.8, dim naked-eye magnitude, after 15 years of simmering quietly near minimum. It fading rapidly at first, then more slowly. As of August 26th it had held at magnitude 8.0 for four days. See Bob King's Recurrent Nova RS Ophiuchi Just Blew its Top! with finder charts and comparison stars. Ophiuchus is ideally placed high in the early evening sky.
Nova Cassiopeiae 2021, meanwhile, has bounced around in brightness ever since it erupted from 15th magnitude to 7.7 in March. Its biggest bumps were to magnitude 5.5 in early May and 6.0 around July 27th. As of August 26th it too had been holding at 8.0 for several days, after dipping to 8.6 earlier in the month. Cas is also excellently placed in the evening sky. Charts and comparison stars.
FRIDAY, AUGUST 20
■ The Moon shines under Saturn this evening, and Jupiter shines to their left, as shown below.
■ The two brightest stars of summer are Vega, now overhead shortly after nightfall, and Arcturus, shining in the west. Draw a line down from Vega to Arcturus. A third of the way down, the line crosses the dim Keystone of Hercules. Two thirds of the way down it crosses the dim semicircle of Corona Borealis with its one modestly bright star, Alphecca or Gemma.
Also: Vega and the Keystone star closest to it form an equilateral triangle with Eltanin to their north, the nose of Draco the Dragon. Eltanin is the brightest star of Draco's quadrilateral head; he's eyeing Vega.
SATURDAY, AUGUST 21
■ Now the Moon shines under Jupiter, with Saturn to their right. The Moon is full tonight and tomorrow night; exact full phase occurs at 9:02 a.m. tomorrow morning, splitting the date difference (for evening skywatchers in the Americas).
■ As summer progresses and Arcturus moves down the western sky, the kite figure of Bootes sprouting up from Arcturus tilts to the right (depending on your latitude). The kite is narrow, slightly bent with its top leaning right, and 23° long: about two fists at arm's length. Arcturus is its bottom point where the stubby tail is tied on.
The Big Dipper now slants at about the same height in the northwest, to the Kite's right.
SUNDAY, AUGUST 22
■ The Moon again forms a big curving arc with Jupiter and Saturn, but now they're to the Moon's right. The arc spans three fists at arm's length.
MONDAY, AUGUST 23
■ By 10 or 11 p.m. the waning Moon is well up in the east-southeast. Spot bright Jupiter off to its upper right. They form a nearly equilateral triangle with Fomalhaut, the Autumn Star, rising below Jupiter. How early and low can you first see it? Is this your first sighting of Fomalhaut for this year's apparition?
TUESDAY, AUGUST 24
■ Another sign of the advancing season: Cassiopeia is high in the northeast, its W pattern tilting up. And below it, starry Perseus is reaching up.
The highest part of Perseus includes the wintry Double Cluster. To find it, look below the lowest two stars of the Cassiopeia W (they're the faintest two), by somewhat more that the distance between them. You're looking for what seems like a small spot of enhanced Milky Way glow. Binoculars or a finderscope will help you detect the Double Cluster even through a fair amount of light pollution. The pair are a glory in a telescope.
WEDNESDAY, AUGUST 25
■ As August proceeds and nights begin to turn chilly, the Great Square of Pegasus looms up in the east, balancing on one corner. Its stars are only 2nd and 3rd magnitude, and your fist at arm's length fits inside it.
From the Square's left corner extends the main line of the constellation Andromeda: three stars (including the corner) about as bright as those forming the Square.
This whole giant pattern was named "the Andromegasus Dipper" by the late Sky & Telescope columnist George Lovi. It's shaped sort of like a giant Little Dipper with an extra-big bowl, and it's currently lifting its contents upward.
THURSDAY, AUGUST 26
■ Low in the northwest or north at the end of summer twilights, would you recognize noctilucent clouds if you saw them? They're the most astronomical of all cloud types, with their extreme altitude and formation on meteoric dust particles. And they're fairly rare — though becoming more common in recent years as the atmosphere changes. See Bob King's article.
FRIDAY, AUGUST 27
■ Whenever bright Vega crosses nearest your zenith, as it does right after dark now, you know that the Sagittarius Teapot is at its highest due south.
Two hours later when Deneb crosses closest to the zenith, it's the turn of little Delphinus and boat-shaped Capricornus down below it to stand at their highest due south.
SATURDAY, AUGUST 28
■ Now that the Moon is out of the evening sky, it's prime Milky Way time. After dark, the Milky Way runs from Sagittarius in the south, up and a bit left left across Aquila and through the big Summer Triangle high overhead, and on down through Cassiopeia to Perseus low in the north-northeast.
This Week's Planet Roundup
Mercury is very deep in the sunset and fading further, from magnitude –0.4 to –0.1 this week. You might have a chance at it with binoculars or a wide-field scope. About 15 or 20 minutes after sunset, scan for it just above your west horizon about 18° (nearly two fists at arm's length) lower right of Venus. Good luck.
Venus, brilliant at magnitude –3.9, shines pure white in the west-southwest during twilight. It still sets around twilight's end.
Jupiter and Saturn shine in the southeast in late twilight and after dark. They're magnitudes –2.9 and +0.2, respectively, in Capricornus.
Jupiter starts the night lowest. Saturn glows 18° (about two fists) to Jupiter's upper right. The pair levels out around 11 p.m. daylight-saving time. By then they're about at their highest in the south, at their telescopic best.
Saturn reached opposition on August 1st, and Jupiter did so on August 19th. So this month they're at their closest, biggest, and brightest of the year. See "Saturnian Challenges" starting on page 52 of the July Sky & Telescope, also "Action at Jupiter" in the August issue, page 50, and "Dog Days with the Gas Giants" on page 40 of August.
Uranus (magnitude 5.7, in Aries) and Neptune (magnitude 7.8, at the Aquarius-Pisces border) are high in the southeast to south in the early-morning hours.
All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.
Eastern Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is also known as UT, UTC, GMT, or Z time. To become more expert about time systems than 99% of the people you'll ever meet, see our compact article Time and the Amateur Astronomer.
Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.
Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read how to use sky charts with a telescope.
Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically, meaning heavy and expensive. And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."
Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the heavens above. It's free.
"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
— Carl Sagan, 1996
"Facts are stubborn things."
— John Adams, 1770