Touring the Triangle, Aquarius Emits Meteors, and Jupiter and Saturn Shine in Evening!
Watch out for Meteors
Overnight on Saturday, into Sunday morning, the Southern Delta Aquariid Meteor Shower peaks. Typically, we get 15–20 meteors per hour at the peak time — some having beautiful persisting trails. While they are visible anywhere in the sky, they will appear to originate, or radiate, from a point low in the eastern predawn sky — the star designated Delta in the constellation of Aquarius (the Water Bearer). The material for the shower is believed to be a wide train of debris deposited in space by repeated returns of Comet 96P Machholz. It takes more than a month for the Earth to traverse the debris field. Meanwhile, the particles become captured in our gravity and burn up as they streak towards the ground. The early setting first quarter Moon will deliver a relatively dark sky for meteor watchers.
Touring the Triangle
When you are out on the next clear night, be sure to look for the three bright and beautiful blue-white stars of the Summer Triangle which shine high in the eastern sky every July. Once you have it identified, you can find some treasures within it, and follow its progress across the night sky until late fall.
Find an open area and face east. Almost straight overhead is the bright star, Vega. It’s the fifth brightest star in the entire night sky and one of the first stars to appear after dusk. Now look for the other two corners. Altair is not as bright as Vega and sits about 3.5 outstretched fist diameters (34°) to the lower right of it. The third star, Deneb, is about 2.5 fist diameters (24°) to the lower left of Vega and and higher up than Altair. It’s a very big triangle!
Can you see the four fainter stars forming a small parallelogram just below Vega? It’s about a thumb’s width wide and a few finger widths long. This shape is the body of the musical harp that makes up the constellation of Lyra (the Lyre). Vega marks the top of the instrument’s neck. Vega’s visual magnitude, or brightness, is the zero reference point for the scale of star brightness values. Objects brighter than Vega have values lower than zero, and vice versa. Spica, the star near Jupiter this summer, has a value of about 1, making it 2.5 times dimmer than Vega. (It’s a logarithmic scale.)
Vega also makes a little triangle with two other dim stars, each about a finger’s width apart. The star to Vega’s upper left is Epsilon Lyrae, also known as the Double Double. Can you tell it’s actually two stars tight together? Try using binoculars. In a telescope, each star splits again!
The bright star Deneb marks the tail of great Cygnus (the Swan). A faint star about two fist diameters (22°) to its right, in the middle of the Summer Triangle is Albireo, a colourful double star that marks the swan’s head. A widely spaced string of modest stars running up-down traces out the swan’s wings. (Look closer to Deneb than Albireo for them — swans have long necks!) The brighter star in the middle of the wing span is Sadr, marking the swan’s belly. If you are in a dark location, you should also be able to see that the Milky Way runs right through Cygnus, as if she is about to land for a swim on that celestial river!
The most southerly of the triangle’s corners is marked by Altair — the head of the great eagle Aquila. In fact, its name translates from “the flying eagle”. At only 16.8 light-years distance, Altair is one of the nearest bright stars — so close that its surface has been imaged! The star also seems to be spinning 100 times faster than our sun, probably generating an equatorial bulge. Like Cygnus, the Aquila the eagle is oriented with its wingtips up-down. The tail bends to the lower right. Two little stars named Terazed (above) and Alshain (below) sit on either side of Altair, like a balance. As a matter of fact, these two little stars’ names derive from an old-fashioned scale balance.
Grab your binoculars and look about midway between Vega and Altair for a little grouping of stars called The Coathangar. (Hint: For North American observers, it’s oriented with the hook downwards to the west.) Finally, have a look for two little constellations in the area. Sagitta (the Arrow) comprises five faint stars running left-right, above Altair. The three on the right (west) end form the feathers. Below Sagitta, and about 13° to the left of Altair is cute little Delphinus (the Dolphin). Four stars form a diamond-shaped body and another star to the lower right marks the tail flukes! The star names for Delphinus include a very interesting story. Look it up!
There’s one more small constellation inside the Summer Triangle, but its dim stars make it difficult to make out. It’s called Vulpecula (the Fox), and it sits about a palm’s width above and parallel to Sagitta. Two birds, a dolphin, and a fox! (And — there’s the lizard Lacerta just to the east and a little foal Equuleus below Delphinus!) Enjoy your tour of the triangle and visit to this celestial zoo!
Sun, Moon, and Planets
New Moon occurred this morning (Sunday), leaving the night skies dark this weekend. This new moon occurred less than two days after perigee, the moon’s minimum distance from Earth. The combination of the closer moon, and both the Sun and moon gravitationally tugging on the earth from the same direction, will generate higher tides globally. On Monday night you can start to look for the slim silver crescent of the young moon low in the western sky, right after sunset. It’ll be easier on Tuesday and subsequent evenings when it’s farther from the Sun and a little thicker.
In the southwestern sky on Friday evening, July 28, and visible until about midnight local time, the waxing crescent moon will sit two finger widths above Jupiter. Virgo’s brightest star Spica will be positioned a palm’s width to their east (left).
Finally, next Sunday, the moon reaches its First Quarter phase, when it’s half illuminated (on the western side). First quarter moons grace the western evening sky and set about midnight — perfect for observing in binoculars and telescopes. Feast your eyes on the dramatically shadowed terrain all along the terminator, the boundary separating the dark and lit sides. It’s worth looking at every night several days before and after first quarter because the terminator highlights new regions as the moon waxes fuller.
Mercury reaches its widest angle east of the Sun next Sunday evening. Then next week it starts to drop lower and shift westward again. In the meantime, look for the elusive planet low in the west between 9:30 and 9:50 pm local time. On Monday and Tuesday, the bright star Regulus will sit only a finger width to the upper right of the planet. After sunset on Tuesday only, the young crescent moon will sit 8 degrees (less than a fist diameter) to the upper left of Mercury, but you’ll need to look by 9:30 pm local time.
Viewed in a telescope this week, Mercury will exhibit a half-illuminated phase. Due to the way the Ecliptic (the plane of our Solar System) angle varies with latitude, mid-latitude Southern hemisphere observers get a much better view of the planet.
Extremely bright Venus rises in the eastern sky about 3 am local time and can be seen easily until dawn. This week, the planet continues to descend slowly sunwards. Viewed in a telescope, the planet presents a more than half illuminated phase.
Saturn is the bright yellowish object partway up the southern sky after the evening sky darkens. It reaches its highest elevation of about 10:30 pm local time, and then sets in the west well before dawn. Use your backyard telescope to look for some of the half-dozen moons visible near the ringed planet. Due to the tilt of Saturn’s axis of rotation, the rings are spilled open towards us and the moons can appear above, below, or to either side of the planet.
Jupiter is the extremely bright object in the southwestern evening sky this week. It sets about 11:45 pm local time. The planet’s four large Galilean moons are easily visible in a small telescope. A larger telescope will also show the round black shadows they cast when they cross (or transit) the planet — and the Great Red Spot. The Great Red Spot is visible on Jupiter for about three hours centred on Monday, July 24 at 10:22 pm and Saturday, July 29 at 9:33 pm (in dark twilight).
The icy giant planets Uranus and Neptune are well-placed for viewing after midnight. Uranus, in Pisces (the Fishes) rises about midnight local time and is visible with binoculars under a dark sky. Neptune, which rises about 10:30 pm local time this week, is in the southeastern sky about two finger widths to the lower left of the medium-bright star Hydor in Aquarius (the Water-Bearer).
Stargazing News for this week (from July 23rd) by Chris Vaughan.
