Friday, December 30, 2011

Weekly SkyWatcher's Forecast: January 1-7, 2012

Written by Tammy Plotner

Sunday, January 1 - Greetings, fellow SkyWatchers! We start our observing year together just before dawn with the brief appearance of Mercury on the eastern skyline. You’ll catch it to the lower left (northeast) of brilliant red Antares.

On this night in 1801, the skies were clear in Italy and astronomer Giuseppe Piazzi had just made a discovery - what would eventually become the first known asteroid. Unlike today's instant communications, Piazzi had to relate his observations to others via the mail - but by the time they received it, his discovery had moved too close to the Sun and was lost. What we now know as minor planet Ceres was not relocated until it returned in September of that same year. With some help from Gauss and his method of calculating orbits, Ceres was identified again on the last day of 1801 and reconfirmed again on this date in 1802. If you’d like to view this bright asteroid for yourself, you can find it on the eastern border of Aquarius and viewable just after the sky gets dark. Check with resources guide for a planetarium program or on-line service to give you an exact location for your observing position and time.

We start our observing evening with the beautiful Moon. For unaided eye observers, you can spot bright Jupiter a couple of handspans away to the east – and beautiful red Aldebaran about the same distance further east. Now, get out your binoculars or telescope and let’s start the year off practicing some selenography. Tonight we will begin our lunar explorations as we look to the far north and identify the “Sea of Cold”—Mare Frigoris. This long, vast lava plain extends 1126 kilometers across the surface from east to west, yet never ranges more than 72 kilometers from north to south. Look for the unmistakable dark ellipse of landmark crater Plato caught on Frigoris' southern central shore.

Named after the famous philosopher, this mountain-walled plain with a dark floor is a Class V crater. Its slightly oval shape spans approximately 101 kilometers in diameter but is a shallow 1 kilometer deep - appearing far more elliptical due to its northern latitude. Plato's floor is its most curious feature. Consisting of 2,700 square miles of unique lava, and only broken by a couple of very minor and supremely challenging craters, Plato is one of the very few areas on the lunar surface that seems to have changed in recent history. The bright rim of Plato's enclosure is very ragged and can rise as high as 2 kilometers above the surface, casting unusual shadows on the lava covered floor. At around 3 million years old, Plato is more ancient than Mare Imbrium to its south. For 300 years astronomers have been keeping a watchful eye on this crater. Hevelius called it the “Greater Black Lake,” due its low albedo (surface reflectivity). Despite its dark appearance, Plato is well known as a home for lunar transient phenomena such as flashes of light, unusual color patterns and areas that could be outgassing. Enjoy this lunar feature which will point the way to others in the future!

Before you put your telescope away for the evening, be sure to head towards the constellation of Leo and take a look at Mars! Right now it’s shining at +0.2 magnitude and has an apparent size of 9.0”. Why so bright? Maybe because it’s close. Right now the red planet is 1.03957 AU (155.5 million km) away from Earth… And about to get closer!

Monday, January 2 - In 1959, the USSR launched the very first Moon probe. Named Luna 1, it became the first extraterrestrial spacecraft. The spacecraft carried no propulsion system of its own, but after having reached escape velocity, its third stage released a payload of sodium gas, which left a glowing trail that reached a brightness of sixth magnitude, allowing astronomers to trace it. Luna 1 made outstanding contributions to science, including the first confirmation that the Moon had no magnetic field. The probe was designed to impact the surface, and although it failed to do so, it did achieve another first with its flyby.

Hmmmm… Is that a fly by the Moon? Nope. It’s Jupiter! No telescope is necessary to see the splendid pairing of Jupiter and the Moon! Look for the bright and mighty Jove just a couple of degrees away from our nearest astronomical neighbor and enjoy this bit of celestial scenery!

Now, turn your eyes towards the Moon as we perform a "flyby" of our own! Let's begin our lunar studies tonight with a deeper look at the "Sea of Rains." Our mission is to explore the disclosure of Mare Imbrium, home to Apollo 15. Stretching out 1123 kilometers over the Moon's northwest quadrant, Imbrium was formed around 38 million years ago when a huge object impacted the lunar surface creating a gigantic basin.

The basin itself is surrounded by three concentric rings of mountains. The most distant ring reaches a diameter of 1300 kilometers and involves the Montes Carpatus to the south, the Montes Apenninus southwest, and the Caucasus to the east. The central ring is formed by the Montes Alpes, and the innermost has long been lost except for a few low hills which still show their 600 kilometer diameter pattern through the eons of lava flow. Originally the impact basin was believed to be as much as 100 kilometers deep. So devastating was the event that a Moon-wide series of fault lines appeared as the massive strike shattered the lunar lithosphere. Imbrium is also home to a huge mascon, and images of the far side show areas opposite the basin where seismic waves traveled through the interior and shaped its landscape. The floor of the basin rebounded from the cataclysm and filled in to a depth of around 12 kilometers. Over time, lava flow and regolith added another five kilometers of material, yet evidence remains of the ejecta which was flung more than 800 kilometers away, carving long runnels through the landscape.

Tuesday, January 3 - We start tonight's lunar tour with a northern landmark that can even be spotted with unaided vision - Plato. Located in the northern hemisphere of the Moon, its dark ellipse is unmistakable. Plato's floor consists of 2700 square miles of lava fill and is considered by some observers as the darkest single low-albedo feature on the Moon. Because of its low reflectivity, this crater has the distinction of being one of the only mountain-walled plains that doesn't "disappear" as the Moon grows full. With Plato in the center of the field note the pyramid-like peak of Pico due south in northeastern Mare Imbrium. East of Pico is an unnamed dorsum - or lava wave - terminating just above crater Piazzi Smyth to the south. Power up in a telescope and check out the triangular peak near its end.

Today is the birth date of Russian astronomer Grigori Neujmin (1886.) His important discovery was the rotating asteroid Gaspra. This is also the date that Stephen Synnot discovered Juliet and Portia, two additional moons belonging to Uranus.

Although skies will be bright, be sure to keep a watch for members of the Quadrantid meteor shower. Its radiant belongs to an extinct constellation once known as Quadran Muralis, but any meteors will seem to come from the general direction of bright Arcturus and Bootes. This is a very narrow stream, which may have once belonged to a portion of the Aquarids. As Jupiter's gravity continues to influence it, in another 400 years of so this shower will become as extinct as the constellation for which it was named.

Wednesday, January 4 - Tonight we'll begin in the lunar north as we explore another challenging region - Sinus Roris. "The Bay of Dew" is actually a northern extension of the vast region of the Oceanus Procellarum. Extending for about 202 kilometers, many lunar maps aren't quite true to Sinus Roris' dimensions. Its borders are not exactly clear given the curvature on which we see this feature, but we do know the eastern edges join Mare Frigoris. This area is much lighter than most features of this type. If you seek answers, then look further north as Roris' high albedo can be attributed to the ejecta from many nearby impacts. It also holds a fanciful place in history, as seen in this excerpt from the science fiction story "Man on the Moon" by Wernher van Braun:

"We can't land where the surface is too rugged, because we need a flat place to set down. Yet the site can't be too flat, either-grain-sized meteors constantly bombard the moon at speeds of several miles a second; we'll have to set up camp in a crevice where we have protection from these bullets. There's one section of the moon that meets all our requirements, and unless something better turns up on closer inspection, that's where we'll land. It's an area called Sinus Roris, or "Dewy Bay," on the northern branch of a plain known as Oceanus Procellarum, or "Stormy Ocean" (so called by early astronomers who thought the moon's plains were great seas). Dr. Fred L. Whipple, chairman of Harvard University's astronomy department, says Sinus Roris is ideal for our purpose - about 1000 kilometers from the lunar north pole, where the daytime temperature averages a reasonably pleasant 40 degrees and the terrain is flat enough to land on, yet irregular enough to hide in."

Today is also the birthdate of Wilhelm Beer (1797), an amateur astronomer who with Johann Madler created an exhaustive and first of its kind map of the Moon - Mappa Selenographia. Tonight discover for yourself what Galileo and Beer saw. Using any type of optical aid, trace the bright lunar rays extending from the brilliant Tycho.

But, if you hear a wolf howl...perhaps it might be the "Dog Star" on the rise. Alpha Canis Majoris, better known as Sirius, is the fifth nearest star known and has played an important role throughout the history of astronomy. Although Sirius is a "moving star," belonging to the Ursa Major moving group, there is historical evidence that it was seen from the island of Zylos in the Persian Gulf on the 29th of April - in the year 11,542 BC!

Watch its dazzling appearance while it is still fairly low and flashing all colors of the rainbow. The light you see from this main sequence star left almost 9 years ago and was seen by Ptolemy, Homer and Plutarch. The ancient Egyptians revered it and the Greeks and Romans feared it. Enjoy it tonight and we'll be back to study...

Thursday, January 5 - We start our observing evening with the beautiful Moon as we begin with the ancient and graceful landmark crater Gassendi standing at the north edge of Mare Humorum. The mare itself is around the size of the state of Arkansas and is one of the oldest of the circular maria on the visible surface. As you view the bright ring of Gassendi, look for evidence of the massive impact which may have formed Humorum. It is believed the original crater may have been in excess of 462 kilometers in diameter, indenting the lunar surface almost twice over. Over time, similar smaller strikes formed the many craters around its edges and lava flow gradually gave the area the ridge- and rille-covered floor we see tonight. Its name is the "Sea of Moisture," but look for its frozen waves in the long dry landscape.

Now let's turn our attention towards the constellation of Orion and a binocular and small telescope cluster known as Collinder 69. While many of us have looked at Orion's triangular head before, what we may not have realized is that the area surrounding third magnitude Lambda is an open cluster. Containing approximately 19 stars that range from fifth to ninth magnitude, look for a southward extending chain that gives this collection its signature.

As you look at the brightest star, let me introduce you - its name is Meissa. The cluster itself is considered young, and probably formed no more than 10 million years ago. On a dark night, look again to see if you can spot some nebulous filaments that remain from its birth! Now look at Orion's belt. Almost all of us have seen these three stars time and again, but did you know they are also part of an open cluster? Turn your binoculars there and have a look. In an area spanning about three degrees are around 100 stars known as Collinder 70. Look for many mixed magnitudes, chains and pairings. This area has been used in the search for brown dwarfs!

Friday, January 6 - As the Moon nears Full, it becomes more and more difficult to study, but there are still some features that we can take a look at. Before we go to our binoculars or telescopes, just stop and take a look. Do you see the "Cow Jumping over the Moon"? It is strictly a visual phenomenon—a combination of dark maria which looks like the back, forelegs and hind legs of the shadow of that mythical animal. Maybe he’s running across the skies to chase Mars! Right now the celebrated planet is less that 1 AU away and getting brighter!

Today in 1949, the first atomic clock built on theoretical work by Isidor Rabi and Norman Ramsey went into operation. This model used ammonia as its "pendulum," but only 8 years later the first cesium beam device was built. Clocks using this primary standard are now keeping time to about one-millionth of a second per year. Like clockwork, objects that we can view also keep incredibly accurate time. Tonight return again to Orion's belt as we have a closer look at its westernmost star - Mintaka.

Located around 1500 light-years away, Delta Orionis usually holds a magnitude of 2.20, but orbiting it in a clockwise orbit of 5.7325 days is a nearly equal star around 8 million kilometers away. Mintaka is a prime example of an eclipsing binary star, and although visually you won't really notice a .2 magnitude drop in light, let's take a closer look with binoculars. As one of the few easy binocular double challenges, Mintaka will easily reveal its 6.7 magnitude companion star to its north. For over 100 years, the eclipsing physical AB pair has been closely watched and no movement between the half light-year apart physical pair has been detected. For those with larger telescopes - power up - and see if you can discover the 13th magnitude C star southwest of the primary.

No matter how you look at Mintaka, this fascinating star has been a part of history. It was the very first to display stationary spectral lines which proved the existence of interstellar matter!

Saturday, January 7 - Tonight the Moon will look nearly full and it is a good time to spot yet another lunar asterism, “The Rabbit in the Moon.” Since the dawn of mankind, we have been gazing at the Moon and seeing fanciful shapes in large lunar features. Tonight, as the Moon rises, is your chance to catch a lunar challenge - "The Rabbit in the Moon." The "Rabbit" is a compilation of all the dark maria. The Oceanus Procellarum forms the "ear" while Mare Humorum makes the "nose." The "body" is Mare Imbrium and the "front legs" appear to be Mare Nubium. Mare Serenitatis is the "backside" and the picture is complete where Mare Tranquillitatis and Mare Fecunditatis shape the "hind legs" with Crisium as the "tail." See the Moon with an imaginative mind and new eyes -- and find the "Rabbit." It's already out of the hat and in the heavens…

Despite bright skies, let's take a brief look towards the three stars that form Orion's "belt". Starting with just our eyes, look around a thumb's length south to discover an asterism of stars referred to as the "sword." On a clear, dark night away from city lights you can spot a glowing cloud of dust and gas surrounding Theta that has long held a place in astronomy history. It was first noted only one year after Galileo first used his telescope, and the discovery is credited to Nicholas Peiresc in 1611. It wasn't until Christian Huygens sketched it in 1656 that it became well known for containing a "heart of stars."

Now, take out your binoculars and have a look. Stars are still being born in a dense cloud behind the nebula, and hundreds of them are less than a million years old. Compared to our own Sun's age of over four billion years, these would seem almost new! But think again at what you are looking at...the light you see tonight left this area around 1900 years ago.

So magnificent are the many details that can be seen in the Orion Nebula, that chapter upon chapter could be devoted to its riches. For now, feast your eyes upon this 30 light-year expanse of dust, neutral and ionized hydrogen, and doubly-ionized oxygen illuminated by the ultraviolet starlight of this stellar nursery. It is more than 20,000 times larger than our own solar system and its mass could form 10,000 stars like our own Sun!

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