What’s Up this Week: July 31 – August 6, 2006

by Fraser Cain on July 31, 2006

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Greetings, fellow SkyWatchers! Are you chasing Comet 177/P 2006 M3 (Barnard 2)? If so, I’d like to hear your comments on this fast and diffuse traveler before the Moon takes it out for awhile. In the meantime, journey along to rest of the night skies, because….

Here’s what’s up!

Monday, July 31- Be sure to check IOTA information for this Universal date…the Moon occults Spica!

Tonight the three rings of Theophilus, Cyrillus and Catherina will be well highlighted as will a previous study – the Altai Scarp. Also to the far south along the terminator you will see Mutus, a small crater with black interior and bright, thin west wall crest. Angling further southwest from Mutus, look for a “bite” taken out of the terminator. This is crater Manzinus.

Once the Moon sets revisit the “King of the Rings” in Lyra! Nicely situated between Gamma and Beta Lyrae, those with larger scopes should look for visible brightening in the interior of the annularity. Power up. It might be your night to catch the central star. Observers with small scopes should to pay attention to an asterism of a half dozen stars that have been christened “The Chalice of the Ring” preceding it across the sky.

Tuesday, August 1 – Today is the birth date of Maria Mitchell. Born in 1818, Mitchell became the first woman to be elected as an astronomer to the American Academy of Arts and Sciences. She later gained worldwide fame when she discovered a bright comet in 1847.

Tonight on the lunar surface Mare Tranquillitatis (to the south) and Mare Serenitatis (north) are almost fully disclosed. Look where they meet for the curving arm of Archerusia Promontorium. On the Promontorium’s southern tip you’ll see the bright ring of crater Pliny. To Pliny’s southwest lay the scattered remains of Ranger 6, where it crashed blindly on February 2, 1964. Further southwest and toward the shore of Tranquillitatis is the final resting place of the successful Ranger 8 mission, which took 7137 pictures in its last 23 minutes of flight. Also in the area is the soft-landing site of Surveyor 5 – the first lunar probe to use an alpha particle spectrograph on the soil. So what’s the soil made of? Very similar to our own Earth’s basalt – a mixture of oxygen, silicon, aluminum and magnesium, with a bit of iron, nickel, calcium, carbon and sodium as well.

Now let’s move upward to go “star counting.” Turn your attention to Lyra. Can you see all four stars in the Lyre’s parallelogram? The sky overhead – despite the waxing Moon – allows you to see stars as faint as magnitude 4.5. Take a look inside the Hercules “Keystone” and see if you can make out any stars. If so, you’d be seeing stars as faint as magnitude 5.4 – but that would be quite an accomplishment under the circumstances. Now locate Corona Borealis between Hercules’ “Keystone” and Arcturus. How many stars can you see that are definitely a part of the circlet? You can see 2.3 magnitude Alphecca (Alpha), but how about 3.7 magnitude Nusakan (Beta) or 3.9 magnitude Gamma? Great! Try 4.2 magnitude Theta and Epsilon, but it’s getting harder. That’s five stars down to magnitude 4.2. Can you see six without aversion? Try holding them all in your direct vision. If you can, you will be seeing stars down to magnitude 4.7. But, if you can see seven stars in the circlet, that would include magnitude 4.9 Iota and be a very decent night with such a Moon. You have now learned how to assess limiting magnitudes!

Wednesday, August 2 – With the Moon now ending first quarter, this would be an excellent time to look for it in late afternoon skies. This evening, why not take the opportunity to explore the lunar surface with binoculars and look at four very cool features.

Central on the terminator tonight will be Sinus Medii – the adopted “center” of the lunar disc and the point from which latitude and longitude are measured. This smooth plain may look small, but it covers about as much area as the states of Massachusetts and Connecticut combined. On a curious note, in 1930 Sinus Medii was chosen by Edison Petitt and Seth Nicholson for a surface temperature measurement at full Moon. Experiments of this type were started by Lord Rosse as early as 1868, but on this occasion Petit and Nicholson found the surface to be slightly warmer than boiling water. Around a hundred years after Rosse’s attempt, Surveyor 6 successfully landed in Sinus Medii on November 9, 1967, and became the very first probe to “lift off” from the lunar surface.

Keep those binoculars handy as we look toward the Northern Cross – otherwise known as Cygnus the Swan. Start at the Swan’s beak – Albireo- and hold the binoculars very steady. Can you make out two stars where you thought there was one? If so, then you are seeing 3.2 magnitude Alberio’s distant companion, but don’t stop with binoculars. Bring out the scope and have another look. The brighter star is a warm golden yellow and the fainter is a pristine aqua blue. Many astronomers agree this is the premier pair of colors in the heavens!

Thursday, August 3 – Tonight let’s explore the lunar surface in hopes of catching an unusual event. On the southern edge of Mare Nubium is the old walled plain Pitatus. Power up. On the western edge you will see smaller and equally old Hesiodus. Almost central along their shared wall there is a break to watch for when the terminator is close. For a brief moment, sunrise on the Moon will pass through this break creating a beam of light across the crater floor known as the Hesiodus Sunrise Ray. If the terminator has moved beyond it at your observing time, look to the south for small Hesiodus A. This is an example of an extremely rare double concentric crater. This formation is caused by one impact followed by another, slightly smaller impact, at exactly the same location.

Now that we’ve seen a double crater, let’s have a look at a double star. Center on Delta Cygni – the westernmost star of the “Northern Cross.” This particular double is the ultimate resolution challenge for scopes of all sizes. This close, disparate pair pushes the limits. Be sure to power up and hope for a very steady sky.

Friday, August 4 – For Skywatchers, be sure to check out Antares and the Moon. A close event for some…an occultation for others! IOTA has the facts for your area.

Tonight let’s return to Pitatus and note how the view has changed in just 24 hours. Now barely visible, you can see where this once grand crater’s walls vary greatly in height. To Pitatus’ south are two twin mountain-walled plains. Let’s start by looking at Wurzelbauer to the west. Only when it’s near the terminator can you truly see where time has distorted and warped this once grand crater. Its slightly younger neighbor – Gauricus, to the east – will show many marks in its walls from smaller meteor strikes at high power.

Keep that power as we take a look at double star Pi Aquilae. Need help finding it? Start at Altair (Alpha Aquilae) and shift a little more than a finger-width north to Tarazed (Gamma). From Tarazed head a little less than finger-width northeast to find Pi. “Starsplitters” will find two tiny 6th magnitude specks whose centers are separated by a mere 1.4 arc seconds!

Saturday, August 5 – Today we celebrate the 76th birthday of Neil Armstrong, the first human to walk on the moon. Congratulations! Also on this date in 1864, Giovanni Donati made the very first spectroscopic observations of comet Tempel (1864 II). The three absorption lines he noticed led to what we now know as the Swan bands, arising from a form of molecular carbon (C2).

Tonight let’s head toward the lunar south as we take a close look at the dark, heart-shaped region Palus Epidemiarum. Caught on its southern edge is the largely eroded Campanus with well defined Cichus to the east and Ramsden to the west. Power up and look carefully at its smooth floors. If conditions are favorable, you will catch Rima Hesiodus cutting across its northern boundary and the crisscross pattern of Rima Ramsden in the western lobe. Can you make out a small, deep puncture mark to the northeast? It might be small, but it has a name – Marth.

Alpha Lyrae is now directly overhead at skydark. Brilliant blue Vega is the fifth brightest star in the night sky. Celebrated in Hollywood’s depiction of the Carl Sagan book Contact, most folks know that Vega lies some 26 light-years away. Due to its proximity to Earth, Vega isn’t as brilliant as it appears. Its absolute magnitude (0.5) is slightly fainter than its apparent magnitude (0.03). But, Vega is significantly brighter than our own Sun. If Sol were as distant, it would appear as a star of the 4th magnitude – some 58 times fainter. As a marker star, Vega has two other very significant roles – it is within a few degrees of the apex of the Sun’s Way as we move through the Milky Way galaxy and in 12,000 years it will be found within a few degrees of the celestial North Pole! For those with telescopes, look for a faint 10th magnitude companion within 1 arc minute south of Vega.

Sunday, August 6 – Although the great Gassendi will appear to be the most fascinating crater on the Moon tonight, let’s head north for something you ordinarily wouldn’t explore. Using Sinus Iridum as a marker, follow the bright moonscape westward to where its reaches into Sinus Roris to the north, Oceanus Procellarum to the west and Mare Imbrium to the south. Our guide feature in this bright, pockmarked area is prominent Mairan. On the very southern tip of this peninsula-like feature, look for two very unusual “domes.” Mons Gruithuisen Gamma stands on the eastern edge and a small stretch of grey sand separates it from Mons Gruithuisen Delta to its east.

Tonight let’s have a look at the second brightest star of the Summer Triangle – Altair. 16 light-year distant Alpha Aquilae, like Vega, is a Sirius-type star which is several times the size and mass of our Sun. Such stars burn hotter at the surface (approaching 10,000 degrees Kelvin) and appear much whiter to the eye as a result. An unusual feature of Altair is its exceedingly high speed of rotation – requiring just six hours to complete an “Altairian day” at the equator. Because of this, its girth is significantly greater than its height as gases on the equator move along at the surprising rate of 150 kilometers per second! As you observe Altair telescopically, look for a 10th magnitude companion roughly three arc minutes to the northwest.

May all your journeys be at light speed… ~Tammy Plotner with Jeff Barbour.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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