What’s Up This Week – May 15 – May 21, 2006

M63: “The Sunflower Galaxy”. Image credit: N.A. Sharp/NOAO/AURA/NSF. Click to enlarge
Greetings, fellow SkyWatchers! It may be raining all over the world, but when the skies do clear there will be plenty to explore as we take a look at bright star systems, distant galaxies, globular clusters and astronomy history. So turn your eyes to the skies, because….

Here’s what’s up!

Monday, May 15, 2006 – While we have a short time before the Moon rises, let’s head towards the stars and revisit the fourth brightest in the sky – Arcturus.

Located some 37 light-years away, the “Watcher of the Bear” was one of the very first stars to be seen during daylight in 1635. It achieved public fame when light from Arcturus activated a photoelectric cell which actuated a relay to turn on floodlights to open Chicago’s “Century of Progress” Exposition in 1933. This nearby star was chosen for the honor because the light reaching Earth that night was thought to have left Arcturus during Chicago’s 1893 Exposition. Here’s to guessing you couldn’t see Arcturus once the lights were on….

But keep your lights off and your eyes on the skies as we explore four celestial “neighbors” of Arcturus. About a fist width east, you’ll see four stars arranged roughly north/south. The northernmost is 4.6 magnitude Xi – a very pretty double with yellow primary and disparate orange secondary. The next star south is 4.7 magnitude Omicron, followed by 4.9 magnitude Pi to the southwest. Pi is a double with a closely matched magnitude companion trailing it to the east. Keep heading south for Zeta – also close to being a matched set. But, beware… It takes at least a larger scope and high magnification to split this pair!

Tuesday, May 16 – With plenty of time before the Moon rises, let’s revisit a galaxy very similar to our own Milky Way – NGC 2903. Located less than two degrees south of Lambda Leonis, this magnificent 9.0 magnitude barred spiral can be spotted with binoculars from a dark location, and is easily seen in a small scope.

While NGC 2903’s size and central bar closely resemble our own galaxy’s structure, the Hubble Space Telescope crossed the 25 million light-year gap and found evidence of young globular clusters in its galactic halo – unlike our own old structures. This widespread star forming region is believed to be attributed to the gravity of the central bar. Small telescopes will show the bar as a lateral concentration across the central structure, while larger apertures will reveal spiral arms and condensed regions of innumerable stars.

Want to try something new? How about the exquisite 9.6 magnitude globular cluster – NGC 5634. Found about halfway between Iota and Mu Virginis and almost due south of Phi, what makes it special is its environs. The little globular shows half its size in smaller scopes, but shares the field but that half with an 8th and a 12th magnitude star. This gives it the appearance of a trinary star system!

Wednesday, May 17 – Today in 1835, J. Norman Lockyer was born. While the name might not be widely recognized, Lockyer was the first to note previously unknown absorption lines in the Sun’s spectrum while making visual studies in 1868. Little he knew that he had correctly identified the electromagnetic signature of the second most abundant element in the universe – helium – an element not discovered on Earth until 1891! Also known as the “Father of Archeoastronomy,” Sir Lockyer was one of the first to note the astronomical nature of ancient structures such as Stonehenge and the Egyptian pyramids.

If you would like to see a helium rich star, look no further tonight than Alpha Virginis – Spica.

Also on this day in 1882, a sun-grazing comet was discovered on photographs of the solar corona taken during a total solar eclipse – but the mysterious comet has not been seen since.

Thursday, May 18 – Before the Moon rises tonight, let’s locate Iota Centauri – another “bright star and galaxy” view. NGC 5102 is a 9.7 magnitude lenticular galaxy which displays a brilliant core. The core region is about all you will see with a 2.9 magnitude star so nearby! A challenge? You bet…

On this day in 1910, Comet Halley transited the Sun, but could not be detected visually. Since the beginning of astronomical observation, transits, eclipses and occultations have provided some very accurate determinations of size. Since Comet Halley could not be spotted against the solar surface, we learned almost a century ago that a cometary nucleus had to be smaller than 100 kilometers in diameter.

Would you like to get a grasp on that concept? Wait until the Moon rises tonight and revisit the most prominent crater of all – Copernicus. In a study done by Shoemaker, this ancient crater was proven to be formed by a gigantic impact. Feature after feature so closely resembles geological impact craters on Earth, that we can say with complete certainty this crater was formed by a large meteoritic body. And just how large is crater Copernicus? Oh, about the size of a certain famous comet’s nucleus – 100 kilometers…

Now let’s head for Omega Centauri. At magnitude 3.7, NGC 5139 is one of the few studies in the night sky receiving a Greek letter despite being decidedly “unstarlike!”

Recorded by Ptolemy as a star, given the designation “Omega” by Bayer, and first noted as non-stellar by Edmond Halley in 1677, J.L.E. Dreyer went on to add three exclamation marks (!!!) to his abbreviated description after including it as entry 5139 in the 1888 New General Catalogue. As the largest globular cluster in our own galaxy, this 5 million solar mass “star of stars” contains more matter than Sagittarius A – the supermassive black hole on which the Milky Way pivots. Omega’s mass is greater than some dwarf galaxies. Of the more than thirty galaxies associated with our Local Group, only the Great Andromeda possesses a globular (G1) brighter than Omega!

Friday, May 19 – Tonight let’s begin by locating the constellation Canes Venatici as we pick out the “Sunflower Galaxy” – M63. Located about a fist width southwest of M51, you can sometimes spot it by scanning the area midway between Alkaid and Cor Caroli.

Originally discovered in 1779 by M?chain, bright M63 is located about 37 million light-years away and believed to be part of a group of galaxies including M51. To binoculars, M63 appears as a faint misty oval, but larger scopes will reveal the galaxy’s spiral arms as a grainy background – brightening considerably towards the center. The most interesting feature of M63 is its arm structure. Most typical spiral galaxies contain two or three distinct arms, yet this structure is multiple – showing short spiral arcs reminding many observers of a “celestial flower.” Studies of M63 reveal that the galactic material at the edges of these arms is moving much faster than normal. Given the amount of visible matter, this additional rotational velocity indicates the presence of significant amounts of dark matter in its overall structure.

If you’re in the mood for a challenge, why not try faint globular cluster – NGC 5466. Located in Bootes, NGC 5466 gives a splendid view in larger scopes. – showing a “pin-cushiony” distribution of its fainter stars. Small instruments might be able to pick this one up on a dark night. The cluster is 52 million light-years away – a value very similar to that of M53 and neighboring globular cluster NGC 5053. To locate NGC 5466, start at M3, about halfway between Arcturus and Cor Caroli. Head due east about five degrees past a lone 6th magnitude star.

Saturday, May 20 – Early evening dark means a good time to look for “the Owl and the Edge-On.”

Start with Beta Ursae Majoris – southwestern star of the Big Dipper. About a finger-width between it and Phecda to the southeast, you’ll catch the 10.1 magnitude Edge-On galaxy first seen by Pierre M?chain on February 19, 1781. Although it was later verified by Charles Messier, it didn’t formally enter the Messier catalog until 1953 when Owen Gingerich entered it. Despite being faint, M108 contrasts well on a good dark night sky and larger scopes will make out irregular patches of detail.

Less than a finger-width further southeast, you’ll spot M97 – the Owl Nebula. But let’s ask a tough question: Which came first, the Owl or the Edge-On? According to Owen Gingerich’s research, the Owl (M97) was discovered by Pierre M?chain three days earlier than the Edge-On – and what an accomplishment that was! Many observers cite M97 as one of the most difficult of the Messier studies to detect – especially through the kind of contrast-robbing skies found near larger cities. Pollution!

The “Owl” gets its name for the vague gray-greenness of its light, and the two curious voids visible through larger scopes. These voids are thought to be the result of looking at a globe of nebulosity whose lowest-density poles lie at an oblique angle to our line of sight. The material making up M97 and the light causing it to glow are associated with a high surface temperature central star in the last stages of life. At the center of M97 is a faint 16th magnitude dying star.

Sunday, May 21 – Are you ready for something new? Then let’s start by locating the two northernmost stars of the Big Dipper – Dubhe and Megrez. Now imagine that these two bright stars are the base of a pyramid. Use lowest power and center at the apex of this pyramid to the north. There you will see a fine, mid-sized spiral galaxy – NGC 4125. Average scopes will see a stellar nucleus in the 9.8 magnitude structure, along with an expansive core region and faint spiral extensions. A “Missed-Messier” perhaps? You bet!

Something old? Return to Omega Centauri and the 7.0 magnitude, almost incomprehensibly structured galaxy NGC 5128. It’s otherwise known as radio-source Centaurus A! NGC 5128 is easily found halfway between Omega and Iota Centauri.

And now for Moon rise…

In 1961, United States President John F. Kennedy launched the country on a journey to the Moon as he made one of his most famous speeches to Congress: “I believe this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to Earth. No single space project in this period will be more impressive to mankind or more important for the long-range exploration of space…”

While the Apollo 11 landing site is hidden behind the terminator tonight, it is still possible to see another: that of Apollo 15. Locate previous northern study crater Plato and look due south past the isolated Spitzbergen Mountains to comparably-sized Archimedes. Spend a few moments enjoying Archimedes’ well-etched terraced walls and textured bright floor. Then look east look for the twin punctuations of Aristillus and the more northern Autolycus. South of Aristillus note the heart-shape of Paulus Putredinus. There you will see Mons Hadley very well highlighted and alone on its northeastern bank. Power up to see that the Mons Hadley area includes a cove known as the Hadley Delta, and there on that plain just north of the brilliant mountain peak is where Apollo 15 touched down.

Be aware that Uranus is also very nearby and will be occulted by the Moon! Check IOTA for specifics in your area.

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