FRIDAY, AUGUST 5
■ First-quarter Moon (exact at 7:07 a.m. on this date EDT). The Moon shines in central Libra after dark. To its left are Delta Scorpii and then brighter Antares. Spica is farther to the Moon's lower right. Arcturus shines brighter even farther to the Moon's upper right.
SATURDAY, AUGUST 6
■ Now the evening Moon shines in the head of Scorpius. Look for orange Antares just to its left and Delta Scorpii just to its right (for the longitudes of North America).
■ Tonight is the midpoint of summer: halfway from the June solstice to the September equinox. The exact moment is 1:09 a.m. Sunday morning August 7th EDT (5:09 August 7th UT). This is the very top of the circle of the year as defined by the astronomical seasons.
For the Northern Hemisphere, that is. It's the exact bottom of winter for the Southern Hemisphere.
But is this really the best definition of summer's center? Misha17 writes, "Keep in mind that the solstice occurred near aphelion, and the Earth's motion (and solar counter-motion through the ecliptic) is now picking up speed. So the Sun is moving a little faster along the ecliptic -- and covering more degrees -- in the latter half of the season.
"An alternative midpoint would be when solar Right Ascension [in the natural, equinox-of-date system] is 9:00:00 -- midway between 6:00:00 at the June solstice and 12:00:00 at the September equinox." And that works out to be rather different, by 2.3 days.
But me, I'd say summer's midpoint is halfway in time, rather than halfway in the Sun's position.
SUNDAY, AUGUST 7
■ Bright Vega passes closest to overhead around 10 or 11 p.m., depending on how far east or west you are in your time zone.
How closely Vega 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 by looking?
Deneb crosses closest to the zenith almost exactly two hours after Vega. To see Deneb perfectly straight up you need to be farther north, at latitude 45°: both Portlands (Oregon and Maine), Minneapolis, Montreal, southern France, northern Italy.
MONDAY, AUGUST 8
■ Three doubles at the top of Scorpius. To the right of Antares is the head (or forehead) of Scorpius, a near-vertical row of three stars. The brightest of them is Delta Scorpii, the one in the middle.
The top one is Beta Scorpii: a fine double star for telescopes, separation 13 arcseconds, magnitudes 2.8 and 5.0.
Just 1° lower left of Beta is the very wide naked-eye pair Omega1 and Omega2 Scorpii. They point roughly back to Beta. The two Omegas are 4th magnitude and ¼° apart. Binoculars show their slight color difference; they're spectral types B9 and G2.
Upper left of Beta by 1.6° is Nu Scorpii, separation 41 arcseconds, magnitudes 3.8 and 6.5. In fact it's a telescopic triple. High power in good seeing reveals Nu's brighter component itself to be a close binary, separation 2 arcseconds, magnitudes 4.0 and 5.3, aligned almost north-south.
TUESDAY, AUGUST 9
■ The two brightest stars of summer are Vega, overhead soon after dark, and Arcturus, shining in the west. Vega is a white-hot type A star 25 light-years away. Arcturus is a yellow-orange-hot, type K giant 37 light-years distant. Their color difference is plain to the unaided eye and more obvious in binoculars.
To me, the tints of bright stars stand out a little better in the deep blue of late twilight. How about you? Could this be a color-contrast effect of seeing yellow, orange, or orange-red stars on a deep blue background?
WEDNESDAY, AUGUST 10
■ Whenever Vega crosses nearest your zenith, as it does not long 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.
THURSDAY, AUGUST 11
■ Full Moon (exact at 9:36 p.m. EDT). The Moon rises around sunset and shines all night close to Saturn — since both are close to their oppositions.
FRIDAY, AUGUST 12
■ The Perseid meteor shower should be at its peak late tonight, but the light of the Moon, just a day past full, will compromise the view this year. Only the brightest of the meteors will shine through. The shower is most active from 11 or midnight until dawn local time, when your side of Earth faces most directly into the oncoming meteors (i.e., the shower's radiant is highest).
Layer up warmly even if the day was hot; remember abuut radiational cooling under a clear, open sky. A sleeping bag makes good mosquito armor, and use DEET on the parts of you that remain exposed. Lie back in a reclining lawn chair facing away from the Moon. Be patient.
The shower's radiant, in northern Perseus under Cassiopeia, would be the meteors' perspective point of origin if you could see them coming from far away in space. But the meteors only become visible in their last moments when they hit the upper atmosphere, and this can happen anywhere in your sky.
SATURDAY, AUGUST 13
■ Saturn is at opposition tonight, directly opposite the Sun in our sky. So it's highest around the middle of the night.
In a telescope, do you notice that Saturn's rings seem a little brighter than usual compared to Saturn's globe? This Seeliger effect is caused by the solid ring particles backscattering sunlight to us when the Sun is almost directly behind us (i.e. Saturn at opposition). The dusty surfaces of the Moon and Mars also display this "opposition surge," 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.
This Week's Planet Roundup
Mercury is very low in the sunset glow. About 20 or 30 minutes after sunset, try scanning for it with binoculars just above the horizon almost due west. Good luck. At least Mercury is fairly bright: roughly magnitude –0.2 all week.
Venus, magnitude –3.9 in Gemini, continues to rise as dawn begins. As dawn brightens, look for it low in the east-northeast. It's far below Capella.
Mars rises around midnight or 1 a.m. and stands high in the east-southeast as dawn begins, shining at an impressive magnitude +0.1 between Aries and Taurus. It's twice as bright as similarly colored Aldebaran a fist or so to its east.
Mars is still pretty small in a telescope, 9 arcseconds in apparent diameter, but it's growing — by about half an arcsecond per week now. It'll reach opposition December 8th, 17 arcseconds wide.
Jupiter rises due east soon after the end of twilight, shining at a bright magnitude –2.7 at the Pisces-Cetus border. It's highest in the south (transiting) just before dawn begins. In a telescope Jupiter is now a good 46 arcseconds wide, nearly its maximum. Jupiter comes to opposition September 26th.
Saturn, magnitude +0.4 in western Capricornus, reaches opposition on the night of August 13-14. Spot it very low in the east-southeast in late twilight, higher in the southeast in late evening, and at its highest and best in the south around 1 a.m. Saturn's rings appear roughly as wide, end to end, as Jupiter's disk. See "Saturn at Opposition" in the August Sky & Telescope, page 48.
Uranus, magnitude 5.7 in Aries, is in the background of Mars this week.
Neptune, magnitude 7.8 at the Aquarius-Pisces border, is high in the south before the first light of dawn, west of Jupiter.
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 and graphics 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 called UT, UTC, GMT or Z time.)
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 a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.
You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner.
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