The Moon Covers Aldebaran while Morning Mercury Meets Mars, plus Lyra for September Stargazing!
September Stargazing Round-up — Lyra
With the Moon out of the evening sky for the next few weeks and darkness falling a bit earlier, it’s a good time to tour the night sky.
Once it’s dark, tilt your head back and look waaay up. Or set out a blanket, gravity chair, or chaise. Point your finger directly overhead. That’s the zenith — the point of the sky directly above you. During the night, various stars and constellations will pass through that patch of sky as the Earth’s rotation carries them from east to west. While objects occupy that position, they will always appear at their best. That’s because you are looking through the least amount of intervening air.
In early evening in mid-September every year, the constellations of Lyra (the Harp), Cygnus (the Swan), Hercules, and Draco (the Dragon) occupy that spot. I’ll post a sky chart here. Over the next few weeks, we’ll tour them, pointing out some objects you can look at with binoculars and small telescopes. Up first is Lyra. In Greek mythology, Lyra is the musical instrument created from a turtle shell by Hermes and later used by Orpheus in his ill-fated attempt to rescue his lost love Eurydice from the underworld. We Canadian astronomers call Lyra the “Tim Hortons Constellation” because it contains both a doughnut and a double-double (coffee)!
Facing south and looking just to the lower right of the zenith, you’ll easily spot the very bright star Vega, or Alpha Lyrae — the brightest star in the constellation. Vega, the fifth brightest star in the entire night sky, partly because it is only about 25 light years away, and partly because it is a very hot luminous star. The name Vega arises from the Arabic “Al Nasr al Waqi”, or the “swooping eagle”. Traditionally, the Lyre was pictured as being grasped in the talons of an eagle.
Vega is heading towards the Sun and will continually brighten over time, becoming the brightest star in the night sky a few hundred thousand years from now. Meanwhile, the wobble of the Earth’s axis will also cause Vega to become the North Pole Star around 14,500 AD, as it was around 12,000 BC. This star is a star!
Vega also is the brightest, highest, and most westerly of the three beautiful blue-white stars of the Summer Triangle. Moving clockwise, Altair is about three fist widths below and to the left of Vega. Deneb, slightly dimmer than the other two, completes the large triangle at the upper left. The separation between Deneb and Vega is shorter, only 24° or 2.5 fist widths.
Chinese culture celebrates a love story in which Cowherd Niú Láng (牛郎) is the star Altair. He and his two children, (β and γ Aquilae, the stars that flank Altair) are separated from their mother Zhī Nǚ (織女) the “Weaving Girl” (Vega) who is on the far side of the river, which is represented by the Milky Way. Each year, on the seventh day of the seventh month of the Chinese lunisolar calendar, magpies make a bridge so that the family can be together again for a single night.
Look for a medium-dim star about a finger’s width to the left of Vega. A similarly dim star sits about a finger’s width below it. The three stars form a neat little triangle with Vega at the right. Binoculars or a small telescope will reveal that the triangle’s star to the left of Vega, designated Epsilon Lyrae, is actually a close pair of stars. A really good telescope will reveal that each of the pair of stars is itself a very close together pair! This quadruple star system, or “double-double”, is about 162 light-years from Earth. Even more interesting, each little pair is circling one another, and the two pairs may also be orbiting — in a neat little square dance that takes thousands of years to complete!
The other corner of our little triangle is the star Zeta Lyrae, and it, too can be split into a double star with binoculars. Both are white and one is slightly brighter than its partner. These stars are about 152 light-years away, and they themselves have partners that are too close to split visually.
Zeta is also the top right star of a narrow upright parallelogram about two fingers wide and four fingers tall that forms the rest of the constellation. Moving clockwise, we find Sheliak, Sulafat, and Delta Lyrae. Sheliak, meaning “Harp”, is the brightest of a tight little grouping of stars visible in a telescope. Sheliak itself has a close-in dim partner that orbits the main star so that, every 13 days, the brighter star is blocked and the total brightness drops by a noticeable amount. This is called an Eclipsing Binary system.
Next, at the bottom of the parallelogram, sits Sulafat, meaning “Turtle”, and named for the shell forming the body of the Lyre. Sulafat is a hot blue giant star 620 light-years away. Similar in colour to Vega, Sulafat is much larger — an old star on its way to becoming an orange giant many years from now.
Finally, at the upper left of the parallelogram is Delta Lyrae. Sharp eyes and binoculars will easily reveal that this is yet another pair of stars — one blue (upper) and one red (lower). The two are not related — the blue star is several hundred light-years farther away than the red one. They just happen to appear close together along the same line of sight.
So, where’s the doughnut? Train your telescope midway between Sheliak and Sulafat, and look for the little, dim, grey smoke ring known as the Ring Nebula (also known as Messier 57). This little bubble of gas in space is the remnant of a dead star that was very much like our Sun. These common objects are called planetary nebulae because they show a little round disk, like a planet. Finally, using binoculars or a telescope, extend to the lower left the line that joins Sheliak to Sulafat. At about twice their separation (from Sulafat) is a Globular Star Cluster called Messier 56. It will appear as a dim fuzzy patch — a Timbit!
Let me know how your exploration of Lyra goes. There are lots of double stars in the constellation.
The Moon and Planets
The Moon reaches its Last Quarter phase in the wee hours of Wednesday morning. Last quarter moons rise about midnight and persist into the daytime morning sky, leaving the evenings darker for stargazing. The 90° angle made between the Sun, Earth, and Moon at last quarter cause the moon to be half illuminated, lit on the eastern (left-hand) side. The terms gibbous and crescent are used to describe objects that are more than half illuminated, or less than half. By the way, only bodies that venture between us and the Sun can ever appear as crescents when viewed from the surface of the Earth. Those are the Moon, Venus, and Mercury (and some asteroids).
The day before last quarter, from midnight to dawn on Tuesday, September 12, the waning gibbous moon will pass through the stars marking the triangular face of Taurus (the Bull). As dawn approaches, the moon moves towards Taurus’ brightest star Aldebaran. You can try using a backyard telescope to see the Moon pass in front of (or occult) the star. In the Great Lakes region, the Moon covers Aldebaran around 8:48 am EDT and moves off it about 10 am (times varies by location). Observers in western North America and Hawaii will see the event in a dark sky.
For the rest of the week, the Moon wanes and rises later, and passing though the legs of Gemini (the Twins) and then appearing as a thin crescent above Venus in the eastern pre-dawn sky on Sunday morning.
This week, Mercury is giving us its best appearance of the year for mid-northern skywatchers all over the world, and it’s easily seen with plain old eyeballs. Look for it very low in the eastern sky from the time it rises, about 5:30 am local time, until about 6:30 am. On Tuesday morning, the planet will reach its widest angle west of the sun, and peak visibility. If you want to try using a telescope, Mercury will exhibit a waxing half-illuminated phase. But be sure to point the telescope away from the eastern horizon well before the Sun comes up.
On Monday morning, Mercury will sit only a finger width below the bright star Regulus and about three finger widths to the upper right of much dimmer Mars. As the week progresses, Mercury will drop away from the star and approach Mars, passing so close that on Saturday and Sunday morning both planets should appear together in a telescope eyepiece (but Saturday is best). While Mercury will pass in a week or two, Mars will become easier and easier to see after it rises about 5:30 am local time.
And don’t forget to check out extremely bright Venus. Recently showing a gibbous phase, It’s much higher than Mercury because it rises in the eastern sky after 4 am local time. This week, the planet continues to descend slowly sunward towards Leo (the Lion).
Jupiter is the bright white object low in the southwestern evening sky after sunset. It sets before 9 pm local time this week. Saturn is the medium-bright, yellowish object partway up the southern sky as the evening darkens. It sets in the west just before midnight local time. Once it’s dark, you can see the fist-sized Teapot-shaped group of stars to the left of Saturn and the distinctive Scorpius (the Scorpion), with its tail curving eastwards low above the horizon, to the right of the ringed planet.
Blue-green Uranus, situated along the eastern (left-hand) string of stars that form Pisces (the Fishes), rises about 9 pm local time and is observable for the rest of the night in binoculars under a dark sky (but not this week!). There’s a medium-bright star about a finger’s width below Uranus.
Tiny blue Neptune is approximately opposite the Sun in the sky, putting it near its closest and brightest for this year. Also observable all night, it is located about two finger widths to the lower left of the medium-bright star Hydor in Aquarius (the Water-Bearer). It is too faint to be seen with the unaided eye.
Stargazing News for this week (from September 10th, 2017) by Chris Vaughan.