Omega Centauri globular cluster 35 degrees below Spica

Springtime is my favorite observing season. In the course of an evening you can face away from our own galaxy and feast your eyes on other Milky Ways, while tracking down some of the most spectacular [...]]]>

Follow the dipper arc to Arcturus, then spike to Spica

Omega Centauri globular cluster 35 degrees below Spica

Springtime is my favorite observing season. In the course of an evening you can face away from our own galaxy and feast your eyes on other Milky Ways, while tracking down some of the most spectacular objects tangled among the stars and dust of our own galaxy.

Omega Centauri is one of them. It’s the largest of the 150+ globular clusters discovered in our own Milky Way Galaxy. There may be even more undiscovered globular clusters hidden behind the gas and dust of our galaxy. Omega Centauri was discovered by Edmund Halley in 1677 as a nebula, but it had been listed in Ptolemy’s catalog 2000 years ago as a star! It’s located about 15,800 light-years from Earth and contains several million Population II stars. The stars in its center are so crowded that they are estimated to average only 0.1 light years away from each other. It is about 12 billion years old, and there is some speculation that Omega Centauri may be the core of a dwarf galaxy which was disrupted, destroyed and absorbed in an encounter with the Milky Way.

This spectacular object is well known to southern hemisphere observers, but it may come as a surprise that it can be seen from many northern hemisphere locations as well. If you are south of the 25th parallel or 25° (degrees) North latitude you should be able to see it 20° above the horizon, and located 35° below Virgo’s great blue-white star, Spica. I’ve observed it from 37° North (Lake Sonoma, CA) several times (from a hill with a negative horizon) and at 33° N in this writeup, where it appeared less than 20° above the horizon definitely! It’s been seen from 42° North as well, from a very flat horizon. It’s a naked eye object, but often the horizon is hazy, so scan with binoculars if you don’t see it with your eyes.

NGC 5128, Centaurus A Galaxy, and NGC 5139 Omega Centauri, the largest Globular Cluster in our Milky Way

To find Omega Centauri, you’ll first have to find Spica, the brightest star in Virgo. It helps right now that golden Saturn is near by. To find Spica, continue the curve of the big dipper handle and “arc to Arcturus, and then spike to Spica”. Spica transits — when it reaches its highest point in the sky — at around midnight daylight saving time. Use this table of transit times for major solar system objects and bright stars and select your observing dates, object (Spica in this case) and your location and press “compute”. “Alt” next to the transit time at your location indicates Spica’s altitude above the horizon. Spica and Omega Centauri transit at the same time, so look about 35° (one clenched fist is 10°) directly below Spica to look for an oval hazy cluster the size of the full moon. Can you see individual stars? Does it look round or oval? Try with your eyes, then with binoculars.

After confirming my view of Omega Centauri and making this little sketch (sketch view as seen through my binoculars), I opened my Herald Bobroff AstroAtlas to the Centaurus constellation pages and looked at what else was in the vicinity of Omega Centauri. I remembered a favorite galaxy, NGC5128, officially named Centaurus A, but nicknamed the hamburger galaxy for obvious reasons. Now I’ve seen both of these objects from Australian skies where they are not hugging the horizon. But even through a partially cloudy horizon, I was able to see this fabulous object, with its dark dust lane bisecting the oval galaxy.

NGC5128 is one of the closest radio galaxies to Earth, so its active galactic nucleus has been extensively studied by professional astronomers, and a supernova was detected in the galaxy’s dust lane in 1986. The Spitzer Space Telescope studies have confirmed that Centaurus A is colliding with and devouring a smaller spiral galaxy! Centaurus A is located approximately 4° north of Omega Centauri, and because the galaxy has a high surface brightness and relatively large angular size (2/3 the apparent size of Omega Centauri), it’s visible to the naked eye under good conditions. My sketch was made with difficulty, by aiming my 14.5-inch reflector (with a 10mm Radian eyepiece for 200x) nearly horizontal and half-perched uncomfortably on the bottom step of my observing ladder.

M68 cluster in Hydra, NGC2903 Galaxy in Leo

Before moving on, I observed another object in the southern sky line between Spica and Omega Centauri, Globular Cluster M68, or NGC4590 in the constellation Hydra. I sketched an oval glow of stars within a diffuse squarish haze of fainter stars.

Now it was time to get vertical and observe some other objects higher in the sky. The beautiful constellation Leo was still well placed in the southwest sky after midnight. I opened my Night Sky Observer’s Guide Volume 2, the Spring and Summer volume to Leo. Gamma Leonis, or Algeiba, is a beautiful deep yellow/orange and pale yellow double star in the sickle (or backwards question mark or lion’s mane) of Leo’s head. Next, I moved to a fascinating red dwarf, Wolf 359, near the famous Leo galaxies M95, M96 and the Leo “trio” of galaxies. Wolf 359 moves 4.71″ (arcseconds) per year or 8′(arcminutes) in a century. It’s the third closest star to the sun, at 7.75 light years away. Only Alpha Centauri and Barnard’s Star are closer. At magnitude 13.6 (similar to Pluto’s magnitude) it’s faint, but the striking red color helps distinguish it from the other nearby stars.

Leo 1 near Regulas, Leo’s heart was my next target. A faint dwarf galaxy overshadowed by bright Regulus is a member of the local group of galaxies, and may be one of the most distant satellites of the Milky Way. Faint NGC2903 — a very pretty magnitude 9 barred spiral galaxy tangled in the starry lion’s mane was worth a sketch. It’s 31 million light years away, local but not attached to any local galaxy group. I had to go and have a look at the supernova in Leo’s M65 galaxy – here is Mojo’s animation of M65,combining two images of M65, one shot on 3/9/13 at Amboy Crater, and one shot on 4/6/13 at Chuckwalla Bench located at N 33° 39′ 37″, W 115° 32′ 26″

Comet C/2011 L4 (PANSTARRS) shot before dawn on 4/7/13, five-minute exposure

It dawned on me I hadn’t observed Saturn yet. Under fabulous steady skies, I was able to pump up the magnification of my 15-inch Litebox reflector to over 300x using a 6mm Televue Radian eyepiece. When I say “my” 14.5-inch Litebox, I mean Mojo’s — I have a 12.5-inch and 17.5-inch version of these fabulous time machines. This image taken by Anthony Wesley the same night shows Saturn as I viewed it. My visual view was not quite this vivid, but the contrast of the colors is very similar to what I saw, including the dark north polar region, so famous in the Cassini North Polar Hexagon images. The distinct band colors and darker north polar area I saw and sketched were varying shades of butterscotch and chocolate.

All that was left now was Comet PanSTARRS, and we had to wait until about 4:00 a.m. for Andromeda to rise in the northeastern sky. I observed it in my 7×50 Carton Adlerblick binoculars quickly and then pooped out and went to sleep until well after dawn. Mojo stayed up and took this lovely image, plus several more including a time sequence showing the comet’s motion. It’s really worth a look and a read and here’s the link. Until next dark sky observing night on May 11, I’m signing off!

Mojo’s images and report from the same night

Astroatlas B Chart page for Grus and Telescopium, well below Capricornus and Sagittarius

NGC131 and 134 and a 5-spot of mag 10 stars

NGC55 image by Morris Jones, used with permission

While Mojo and I were observing at Amboy Crater on October 22, 2011, Cliff, another observer at the site pointed [...]]]>

Herald-Bobroff Astroatlas

Astroatlas B Chart page for Grus and Telescopium, well below Capricornus and Sagittarius

NGC131 and 134 and a 5-spot of mag 10 stars

NGC55 image by Morris Jones, used with permission

While Mojo and I were observing at Amboy Crater on October 22, 2011, Cliff, another observer at the site pointed out the constellation Grus, The Crane, low on the southern horizon. Grus isn’t a constellation I’ve paid attention to before – you need to be able to see down to the southern horizon in the fall, and you need to be observing at +34N Latitude or further south. If you can see well below Capricornus, Sagittarius and Sculptor in the autumn, give it a try!

None of the star charts I brought on that occasion showed Grus, but I had just the startool at home for the following weekends (October 29) outing — the Herald-Bobroff Astroatlas! I hadn’t needed this lovely atlas since my 1999 Ayer’s Rock Australian observing trip with 20 other astronomers, and welcomed reacquainting myself with it. The atlas begins with the A Charts – wide swaths of the sky, showing several entire constellations. From there you are directed to the B Charts (image at your left), showing smaller segments of the sky and bright stars. The C Charts (9th mag stars and 14th mag. deep sky objects) are where I headed for this night’s observing, but in the past I have drilled down to the D (11th mag. stars and 15th mag deep sky objects), E and F charts for detail showing Coma and Virgo galaxy clusters and the Magellanic Clouds.

There aren’t any bright galaxies to hunt for in the constellation Grus, and observing low to the horizon doesn’t afford the best views, either. But even so, I quickly observed the top ten or so – including some lovely galaxy clusters. First I went for NGC7590 and 7599, a pretty pair of spiral galaxies discovered by John Herschel and Charles Dunlop. I didn’t see the distant Abell 1111 cluster, 2 billion light years away, just the two brighter galaxies.

Next I hunted down a group of galaxies near NGC7418 – a face-on spiral galaxy nestled in a pretty string just below Fomalhaut on the Grus Sculptor border. Here’s a photo of the galaxies I observed. 7418 was discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope in 1847. A supernova erupted in this galaxy in 1983. And Allan Sandage (1975, Astrophysical Journal, 202, 563-582) notes that this galaxy is a member of the IC1459 Grus Group.

Well after midnight on this perfect observing night, our friend Dave came over and told me he had just observed some objects he had not logged before. “A pair of galaxies, with a little dice-shaped asterism of five stars next to it”. Soon I was on my own hunt for NGC131 and 134. It’s to the lower left of big open cluster Blanco 1 on the star chart. The smaller 131 was discovered by John Herschel in 1834, and the larger 134 was discovered in 1826 by James Dunlop in Australia. They are part of our local group of galaxies (LGG), and the galaxy group is also known as LGG-007 located 63 to 82 million lights years away. My sketch is to the left.

This part of the sky is littered with easy to find galaxies, and I spent several hours hopping from one to another. I was observing NGC55, an interesting barred irregular galaxy only 7 million light years away. It’s one of the closest galaxies to our own local group! I encouraged Mojo image it, even though it was low to the horizon. I love his image, and it looked a lot like this through the eyepiece, too. I made a rough sketch of the galaxy, and when I looked at Mojo’s image we both showed the pretty lineup of stars outlining the galaxy.

This is just a sample of the dozens of galaxies I looked at in the deep southern sky on a late October evening. Fall offers long nights of darkness for galaxy starved amateur astronomers tired of all the bright milky way objects of summer. So ladies and gentleman, start your telescopes, and point as low as you can go. Aim your telescopes where the wings of the southern birds Grus and Phoenix fly. If you can’t go that low, Sculptor offers dozens of amazing objects to view. Open your atlas to the constellations around the South Galactic Pole near Sculptor, and you’ll enjoy hours of surfing the southern skies.

Here are Mojo’s Astrophotos from October 29, 2011. I enjoyed visually observing these objects, and then seeing these postcards sent from the universe through Mojo’s astrophotography.

Diagram of the Observable Universe

Review of the Herald-Bobroff Astroatlas

Images showing our observing spot at sunset and waiting for moonset