Nova Cas takes another brightness bump! Nova Cassiopeiae 2021 erupted to magnitude 7.7 last March. It has stayed mostly about that bright ever since — making it a "slow nova" — but with a brightness spike to 5.5 in early May and smaller bumps since then. For a while it seemed done for, but as of July 27th UT it had climbed back up to 6.0. Then by the 30th it had dropped to about 7.2. Charts and comparison stars.
FRIDAY, JULY 30
■ As summer progresses, Arcturus moves down the western side of the evening sky. Arcturus forms the bottom point of the Kite of Bootes. The Kite, rather narrow, extends upper right from Arcturus by 23°, about two fists at arm's length. The lower right side of the kite is dented inward, as if some celestial intruder once banged into it.
SATURDAY, JULY 31
■ On this Saturn-day, Saturn is one day before opposition. Do you notice that Saturn's rings are distinctly brighter, compared to Saturn's globe, than they usually are? This Seeliger effect is caused by the solid ring particles backscattering sunlight to us when the Sun is almost directly behind us. The dusty surfaces of the Moon and Mars do this too, but Saturn's clouds do not. In the case of Saturn the effect is named for Hugo von Seeliger, who studied it in detail and published his findings in 1887.
■ Last-quarter Moon (exact at 9:16 a.m. EDT). By the time the Moon rises late tonight, around midnight or 1 a.m. local daylight saving time, its terminator will be no longer exactly straight but very slightly concave. Look about 15° above the Moon for the brightest stars of Aries, 2nd and 3rd magnitude.
By the very first hint of dawn Sunday morning the Moon will be quite high. Spot the Pleiades to its left, Aldebaran a similar distance below the Pleiades, and the much looser Hyades just above and right of Aldebaran.
SUNDAY, AUGUST 1
■ Saturn is at opposition, opposite the Sun as seen from Earth. This year Saturn's rings are tilted 18° to our line of sight — a lot less than their maximum tilt of 26°, which they displayed from 2016 through 2018, but nowhere near the edge-on aspect they will present in 2025. But their current middling tilt seems (to me anyway) to make Saturn look the most characteristically Saturnlike. (See the pic near the bottom of this page.)
■ Today is Lammas Day or Lughnasadh, one of the four traditional "cross-quarter" days midway between the solstices and the equinoxes. Sort of. In the many centuries after this tradition took hold in Europe the calendar drifted with respect to the seasons, until our current Gregorian calendar was instituted a few centuries ago to stop such problems. So in 2021, the midpoint between the June solstice and the September equinox actually falls on August 6th, at 5:02 p.m. Eastern Daylight Time (21:02 UT).
That minute is the exact center-balance of astronomical summer: the very top of the circle of the year (as defined by the astronomical seasons, for the Northern Hemisphere.)
MONDAY, AUGUST 2
■ With the advance of summer the Sagittarius Teapot, in the south after dark now, is tilting and pouring from its spout to the right. The Teapot will tilt farther and farther for the rest of the summer — or for much of the night if you stay out late.
■ Tonight, telescope users can watch Jupiter's moon Europa slowly disappear into eclipse by Jupiter's shadow around 12:29 a.m. EDT. Following behind is Io, which will likewise disappear into Jupiter's shadow around 2:19 a.m. EDT. (Subtract 1 hour from these to get CDT, and so on.)
Earlier in the night, Jupiter's Great Red Spot should cross Jupiter's central meridian around 10:24 p.m. EDT. The spot should be visible almost as easily for about an hour before and after, in a good 4-inch telescope if the atmospheric seeing is sharp and steady. A light blue or green filter helps a bit.
The Red Spot transits about every 9 hours 56 minutes. But not quite like clockwork! It drifts east or west in Jupiter's atmosphere somewhat irregularly. A change often becomes detectable to visual transit timers over a span of some months. Our transit-time predictions are based on fairly recent observations, but don't be surprised if the Red Spot has taken it into its head to move a few minutes off schedule.
TUESDAY, AUGUST 3
■ Hunting Hebe. The asteroid 6 Hebe is a little past opposition, a pinpoint of about magnitude 8.4 north of the Sagittarius Teaspoon. A pair of 10x50 or larger binoculars, used with care and precision under a dark sky, may be enough for you to pick it out using the finder chart in the July Sky & Telescope, page 50. (The chart there shows Hebe's position for 0:00 UT on the dates indicated, which falls on the evening of the previous date for North America.)
WEDNESDAY, AUGUST 4
■ If you use a telescope much you're probably familiar with Lyra overhead, harboring Vega, the Double-Double, and the Ring Nebula among other sights. And nearby is Albireo, the beak of Cygnus and one of the sky's finest gold-and-blue double stars.
But between Albireo and Lyra, what about the much-overlooked globular cluster M56? At magnitude 8.3 you might even be able to detect it with large binoculars in a dark sky. To pinpoint the spot, hone in with Matt Wedel's "Lost in Space," his Binocular Highlight column and chart for this lesser-known find in the August Sky & Telescope, page 43.
■ It may be the height of summer, but wintry Gemini is arisen in the east by the time dawn begins. The waning crescent Moon crosses it on Thursday and Friday mornings, August 5th and 6th, as shown below.
THURSDAY, AUGUST 5
■ The Big Dipper hangs diagonally in the northwest after dark. From its midpoint, look to the right to find Polaris (not very bright) glimmering due north as always.
Polaris is the end of the Little Dipper's handle. The only other Little Dipper stars that are even moderately bright are the two forming the outer end of its bowl: 2nd-magnitude Kochab and 3rd-magnitude Pherkad. On August evenings you'll find them to Polaris's upper left (by about a fist and a half). They're called the Guardians of the Pole, since they ceaselessly circle around Polaris through the night and through the year.
FRIDAY, AUGUST 6
■ Bright Vega passes closest to overhead around 10 or 11 p.m. now, depending on how far east or west you are in your time zone.
How closely it misses your zenith depends on how far north or south you are. It passes right through your zenith if you're at latitude 39° north (Washington DC, Cincinnati, Kansas City, Lake Tahoe). How closely can you judge this just by looking?
Deneb crosses closest to the zenith two hours after Vega. But to see Deneb exactly straight up you need to be farther north, at latitude 45°: Portland, Minneapolis, Montreal, southern France, northern Italy.
SATURDAY, AUGUST 7
■ Have you been seeing any Perseids meteors yet? For now you'll only see the very occasional Perseid during your observing sessions, but their numbers are gradually increasing. The shower is due to peak late next Wednesday night, August 11, but occasional forerunners begin showing up as much as two or three weeks beforehand. Already the sky is moonlessly dark. For more on this year's Perseids see the August Sky & Telescope, page 48.
It's almost certainly a Perseid around this time of year if, when you trace its path backward far enough across the you find that this line intersects the northern part of Perseus.
This Week's Planet Roundup
Mercury is hidden in conjunction with the Sun.
Venus (bright at magnitude –3.9) shines low due west during twilight. It sets around twilight's end.
Mars is hidden deep in the sunset.
Jupiter (magnitude –2.8, in Aquarius) and Saturn (magnitude +0.2, in Capricornus) shine in the east-southeast after dark. Jupiter starts the night lowest, but it's by far the brighter of the two. Saturn glows yellowly 19° (about two fists at arm's length) to Jupiter's upper right. The pair levels out around midnight, depending on your date and location. By then they're nearly at their highest in the south, at their telescopic best.
Saturn reaches opposition on August 1st, Jupiter on August 19th, so they're already essentially as close and big as they'll get this 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 49 of August.
Uranus (magnitude 5.7, in Aries) is high in the east-southeast before dawn begins.
Neptune (magnitude 7.8, at the Aquarius-Pisces border 23° east of Jupiter) crosses high in the 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