Astronomy: The Week Ahead – Sun 12 Jul to Sat 18 Jul



Sunday July 12

Antares is the red giant star marking the heart of Scorpius, the scorpion. Place it where our Sun is, and it would extend beyond the orbit of Mars. Yet, its density is so light, it would float in water. Antares is a double star, with the primary star shining reddish at magnitude 1.09. The companion is sometimes called the Green Pea, and requires steady seeing and high magnification to see in the glare of its partner. At magnitude 5.5, the Green Pea is 1/370th the brightness of Antares, and less than 2.5 arcseconds separation.


Monday July 13

Here’s a morning double star that is easy to locate. Enif is Epsilon Pegasi, an optical double with components shining at magnitudes 2.5 and 8.7. It has a wide separation of 144 arcseconds, and offers an unusual treat. Its nickname is the Pendulum Star. Center the pair in your eyepiece between 60 and 100 power. Tap the telescope, and watch the primary star gently wobble to and fro, while the secondary member moves wildly at a right angle to the primary. Astronomer John Herschel was among the first to note this oddity.


Tuesday July 14

Have you been watching Venus moving quickly eastward of Jupiter this week? Tonight they are over 5 degrees apart. Venus is also very close to Leo’s brightest star Regulus today, separated by 2-1/3 degrees of arc.

Also of note today, New Horizons FlyBy of Pluto is taking place. Expect some stunning detailed images of this icy world. And, today is also the 50th anniversary of the Mariner Mars flyby!


Wednesday July 15

Summer is flying by, and the Milky Way is spinning overhead. It’s a great time to go to a Star Party. Some are local and some regional, drawing hundreds of astro-enthusiasts over multiple nights.

With New Moon today, it’s a great opportunity to observe nebulae and galaxies at one of these fun events. On the West Coast the Golden State Star Party starts today and runs through Saturday in far northeast California, under very dark skies. It’s not too late to pack up the camping gear and see what’s up!


Thursday July 16

The constellation Perseus is rising above the northeast horizon before sunrise this morning. Its most notable stars are Mirfak, shining at magnitude 1.79, and the famous eclipsing variable star Algol which ranges from magnitude 2.3 to 3.5 over a period of 2.867 days. Its most famous deep sky object is the Double Cluster, NGC 884 and NGC 869, easily visible in binoculars. The Milky Way passes through Perseus, but is dimmed by intervening molecular clouds. Find Perseus above bright Capella in Auriga, and Aldebaran in Taurus.


Friday July 17

Find Perseus in the predawn skies and enjoy views of the famous Double Cluster. Look to the northeast, for the distinctive W shape of Cassiopeia and imagine a line from the center star through the next lower star, then twice that distance to a fuzzy patch in the sky. Binoculars or a telescope will show two open clusters, NGC 869 and NGC 884, shining at magnitudes 3.7 and 3.8. The clusters lie 7,000 light years from us and each one contains over 300 blue-white supergiant stars. The pair are 60 arcminutes in diameter, a full degree of sky, so binoculars work well, or a low power eyepiece will fit both in one view.


Saturday July 18

Look to Leo on the western horizon as skies darken this evening. Jupiter and Leo will show their increasing separation, with Venus now passing the bright star Regulus in its eastward motion. Joining these three objects will be a young Moon, just 2.9-days-old in its waxing crescent phase, 9 percent illuminated. The Moon and Venus will be 1.37 degrees apart, and fit easily in the view of any binoculars. Can you see earthshine illuminating the portion of Moon in lunar night? Let me know if you viewed this and what you think!

Happy viewing!