Thursday, March 31, 2011

Weekend Observing Alert – Nova Saggitarii 2011 #2

Submitted by Tammy Plotner

If you think you’re looking a a star studded field, you’d be right. But take a close look at the full size image done by Joe Brimacombe and you’ll see a faint circle with the latest of sky phenomena in its center – Nova Sagitarii 2011… #2!

According to the latest AAVSO press release done by Elizabeth Waagen, “We have been informed by the Central Bureau for Astronomical Telegrams (Central Bureau Electronic Telegram 2679, Daniel W. E. Green, ed.) that Koichi Nishiyama, Kurume, Japan, and Fujio Kabashima, Miyaki, Japan, report their discovery of a possible nova at magnitude 11.7 on two unfiltered CCD frames taken around March 27.832 UT. They confirmed the object on images taken on March 27.832 UT. After posting on the Central Bureau’s Transient Objects Confirmation Page (TOCP) webpage, the object was given the provisional name PNV J18102135-2305306.

Low resolution spectra taken March 28.725 UT by A. Arai, M. Nagashima, T. Kajikawa, and C. Naka, Koyama Astronomical Observatory, Kyoto Sangyo University, suggest that N Sgr 2011 No. 2 is a classical nova that is reddened by interstellar matter.”

At magnitude 12.5, one tiny star is hard to pick out of a huge field, especially when it’s so close to our galactic center. As Joe said, “It is quite close to the Cat’s Paw and Lagoon Nebulae, so the wide field image is neat even though its only a single 10 minute exposure.” For those of us who would take more than ten minutes just to find it, the celestial coordinates are: R.A. 18:10:21.35 Dec. -23:05:30.6. N Sgr 2011 No. 2 has been entered into VSX and assigned the identifier VSX J181021.3-230530. Finder charts for N Sgr 2011 No. 2 may be plotted by entering the coordinates above in the International Variable Star Plotter. Please report observations to the AAVSO International Database as N SGR 2011 NO. 2.

It might be an early morning adventure, but then… Aren’t the skies always the darkest just before dawn?

Many thanks to Joe Brimacombe and AAVSO for waking us up!

Saturday, March 12, 2011

Jupiter and Mercury Pair Up in Twilight March 13–16

Submitted by Tammy Plotner

According to a Sky & Telescope press release, two bright planets will shine close together low in the western twilight from Sunday to Wednesday, March 13th to 16th. Anyone can see them with the naked eye. You’ll just need a clear sky and an open view toward the west roughly 40 minutes after sunset, as twilight fades.

Jupiter is the brighter of the two. “Mercury is pretty hard to spot most of the time, so a lot of people have never recognized it in their lives,” says Alan MacRobert, a senior editor of Sky & Telescope magazine. “With Jupiter guiding the way, now’s your chance.”

Jupiter has dominated the evening sky for several months, but now it’s on its way down and out for the season. It’ll be gone in another couple of weeks. Mercury, on the other hand, will climb a little higher in the western twilight by late March. (This refers to viewers in the world’s mid-northern latitudes, including the United States, Canada, southern Europe, and elsewhere between about 30° and 50° north latitude.)

The graphic here shows where to look.

Find a spot with a clear, open view low to the west, and you can watch Mercury passing Jupiter in twilight from March 13 to 16, 2011. Credit: Sky & Telescope magazine

The two planets will appear closest together on Monday and Tuesday, March 14 and 15, when they’ll be only about 2° apart — about the width of your thumb held at arm’s length.

Although the two planets appear close together, they’re not. Jupiter is more than 5 times farther away, at a distance of 550 million miles compared to Mercury’s 102 million miles. That means the light we see from them takes 49 and 9 minutes, respectively, to reach us.

“Don’t miss this chance to do a little astronomy from your backyard, balcony, or rooftop,” says Sky & Telescope associate editor Tony Flanders. “It’s a big universe, and planets await.”

For more skywatching information and astronomy news, visit or pick up Sky & Telescope, the essential magazine of astronomy since 1941.

Wednesday, March 9, 2011

Capturing Thor's Helmut

Written by Tammy Plotner

It spans nearly 30 light years of space… and resides approximately 15,000 light-years from Earth. Its heartbeat is an extremely hot giant star thought to be in a brief, pre-supernova stage of evolution. Interactions with a nearby dense, warn and large molecular cloud are what may have contributed to its complex shape and curved bow-shock structure. Step back into mythology and see if you have what it takes to capture “Thor’s Helmut”…

Unlike many nebula, this unusual character is the product of the central Wolf-Rayet star, its stellar winds, and the surrounding interstellar matter. The powerful star emits a high velocity wind, pushing matter ahead of it. This process both compresses and expands its ring-like shell. As it grows, it collects even more gas and dust from the interstellar medium. But how many times and how many events?

“We have detected three different velocity components, and determined their spatial distribution and physical properties. The kinematics, morphology, mass and density are clearly stratified with respect to the W-R star.” says JR Rizzo (et al). “These features allow us to learn about the recent evolutionary history of HD 56925, because the multiple layers could be associated to several energetic events which have acted upon the surrounding circumstellar medium. Hence, a careful study of the different shockfronts contain clues in determining the present and past interaction of this evolved massive star with its surroundings.”

While most planetary nebulae contain old stars nearing the end of their lives, the central Wolf-Rayet star in NGC 2359 is very young. Its ultraviolet photons are the fueling source of the emission nebula. Wolf-Rayets are evolved, massive and extremely hot – up to ~50,000 K. Not only that, but their luminosity is incredible, too… up to 10L to the fifth or sixth power. Their surface composition is extremely exotic, being dominated by helium rather than hydrogen and the stars themselves are rare, simply because they are so short-lived. It was only three short decades ago that astronomers also realized that WRs suffered from heavy mass loss as well. Their ejecta bursts outward at speeds comparable to a nova. The whole process of formation simply isn’t clearly understood yet. The layers may be from differential rotation – but they could be the results of the exposed stellar core.

“The overall emission in the nebula is dominated by the overwhelming contribution of the H II region and is characteristic of photoionization processes. The embedded, photoevaporating cloud contributes enough mass over a dynamical lifetime to account for the shell mass of 5.0 solar mass.” says TE Jernigan. “In NGC 2359, imagery reveals variations in density, temperature, and ionization structure on scales ranging from the size of the nebula down to the seeing limit of approximately 2.1 seconds. The structure of the H II region can be understood in terms of a photoionized conical cavity protruding into the surrounding molecular cloud. The emission in the bubble region is characteristic of that produced in the incomplete cooling region behind a stellar-wind shock wave.”

No matter what explanation lay behind it, observing “Thor’s Helmut” is a pure pleasure. You’ll find it located about a fistwidth east-northeast of Sirius (07h 18m 30s, ?13° 13′ 48″). This Herschel object is a delightful 8th magnitude and well worth the effort!

And many thanks to John Chumack of Galactic Images for making the effort and sharing it with us!

Saturday, March 5, 2011

A New Spin On NGC 2403

Written by Tammy Plotner

No. You're not looking at a Hubble image. This incredibly detailed photo was taken with a 14.5" telescope from right here on the surface of planet Earth. When Allan Sandage turned the Hale telescope its way, he discovered the first Cepheid variables beyond our local galaxy group. At the time he concluded its distance as about 8,000 light years away, but today it is believed to be as distant as 8,000,000. What's its name? NGC 2403...

Discovered in 1788 by Sir William Herschel, this intermediate spiral galaxy is part of the M81/M82 group... and like its contemporaries, is a product of a galaxy merger. Its northern spiral arm connects to NGC 2404 - riddling the halo with young stars. In this masterful astrophoto done by Warren Keller, the pink and red regions denote active star formation, while clusters of neophyte suns gather in the blue OB associations. Like a fine piece of Irish lace, holes appear where dark regions of dust block the light. But NGC 2403 doesn't follow the rules. Here the galaxy's arms rotate at a different speed.

"High sensitivity H I observations of the nearby spiral galaxy NGC 2403 obtained with the VLA are presented and discussed. The properties of the extended, differentially rotating H I layer with its H I holes, spiral structure and outer warp are described. In addition, these new data reveal the presence of a faint, extended and kinematically anomalous component. This shows up in the H I line profiles as extended wings of emission towards the systemic velocity. In the central regions these wings are very broad (up to 150 km/s) and indicate large deviations from circular motion." says F. Fraternali (et al). "We have separated the anomalous gas component from the cold disk and have obtained for it a separate velocity field and a separate rotation curve. The mass of the anomalous component is 1/10 of the total H I mass. The rotation velocity of the anomalous gas is 25-50 km/s lower than that of the disk. Its velocity field has non-orthogonal major and minor axes that we interpret as due to an overall inflow motion of 10-20 km/s towards the centre of the galaxy. The picture emerging from these observations is that of a cold H I disk surrounded by a thick and clumpy H I layer characterized by slower rotation and inflow motion towards the center. The origin of this anomalous gas layer is unclear. It is likely, however, that it is related to the high rate of star formation in the disk of NGC 2403 and that its kinematics is the result of a galactic fountain type of mechanism. We suggest that these anomalous H I complexes may be analogous to a part of the High Velocity Clouds of our Galaxy."

Does this different rotational curve have an cosmological implications? According to the work of E. Battaner and E. Florido: "We review the topic of rotation curves of spiral galaxies emphasizing the standard interpretation as evidence for the existence of dark matter halos. Galaxies other than spirals and late-type dwarfs may also possess great amounts of dark matter, and therefore ellipticals, dwarf spirals, lenticulars and polar ring galaxies are also considered. Furthermore, other methods for determining galactic dark matter, such as those provided by binaries, satellites or globular clusters, have to be included. Cold dark matter hierarchical models constitute the standard way to explain rotation curves, and thus the problem becomes just one aspect of a more general theory explaining structure and galaxy formation. Alternative theories also are included. In themagnetic model, rotation curves could also be a particular aspect of the whole history of cosmic magnetism during different epochs of the Universe."

Yet on the other hand, perhaps the differing rotations were caused by the merger itself - with no dark matter involved. "Quite a point has been made about deviations of some galaxies from flat rotation curves, specifically the decreased velocity in outer parts of the curves. Such cases can be explained under the diffusion model by considering collisions and tidal interactions between galaxies. In this explanation, the excess gravitational force is considered to be caused by a “cloud” of the agent that carries gravitational force that always is diffusing freely, although more concentrated in some regions than others as a result of the time required for the diffusion process and the size of the regions involved." says Roy J. Britten. "When tidal interactions have occurred between galaxies, some momentum could be transferred between stars, gas, and dust that would not be shared by the diffusing clouds, and therefore, asymmetries in the gravitational forces would result. For example, the cloud and galaxies could separate if the two galaxies merged because the galaxies would share their momentum and the clouds would remain independent and continue to diffuse. Then, new gravitational clouds would be built slowly by diffusion from the merged galaxy."

Dark matter or no dark matter, NGC 2403 (07h 36m 51.4s, +65° 36′ 09″) is a pleasure to observe. Located in the northern constellation of Camelopardalis, this 8.4 magnitude spiral galaxy can be spotted under dark sky conditions with ordinary 10X50 binoculars. In 1954 Fritz Zwicky reported a supernova event and 50 years later it happened again, keeping astronomers wondering about this galaxy with the low-luminosity "dwarf" Seyfert nucleus. SN2004 is the bright yellow "star" in this portrait and it is the closest - and brightest - stellar explosion discovered in more than a decade...

As close as your eyepiece on the next dark night!

Many thanks to Warren Keller of Billions and Billions for sharing his incredible work!

Tuesday, March 1, 2011

Sky & Telescope Magazine Editor Emeritus, Leif J. Robinson, Passes Away

Submitted by Tammy Plotner

For those of us who have dreamed over the stars for years while reading Sky & Telescope magazine, we respectfully remember Leif J. Robinson, who served for 20 years as Editor in Chief. He passed away Sunday, February 27, at the age of 71 at his home in Costa Rica.

According to the S&T Press release, Robinson worked 38 years on the staff of Sky & Telescope and served as Editor in Chief from 1980 to 2000. Sky & Telescope is a monthly magazine based in Cambridge, Massachusetts. First published in November 1941, the magazine is approaching its 70th anniversary, and it remains the world’s most influential popular magazine about astronomy.

“Leif was a towering figure in the history of Sky & Telescope, and he tirelessly promoted the capabilities and achievements of amateur astronomers,” says current S&T Editor in Chief Robert Naeye. “During his tenure, S&T’s circulation grew significantly, and the magazine’s stature grew by leaps and bounds in the amateur and professional communities.”

“Every one of us who worked with Leif was inspired by his strong leadership, which emphasized journalistic and ethical principles of accuracy and integrity. These core values continue to guide everything we do at S&T,” adds Senior Editor Dennis di Cicco, who worked with Robinson at S&T for more than 25 years and remained in close contact after his retirement.

Robinson was born May 21, 1939, in Connecticut. He moved to Southern California in 1954 and became an active member in the Los Angeles Astronomical Society. Shortly thereafter he began writing articles for Sky & Telescope about lunar cartography.

While visiting his grandparents in Connecticut in 1962, he received a telegram offering him a job at S&T. Robinson initially planned to reject his offer so he could complete his studies at UCLA. But he decided to accept it after talking with S&T office staffer Caroline Nason, whom he would later marry. Robinson held several editorial positions until 1980, when he was named S&T’s third Editor in Chief following the sudden death of Joseph Ashbrook.

During his 38-year tenure on the editorial staff, Robinson became a champion of professional-amateur collaborations. S&T’s tradition of promoting such partnerships continues to this day. Seeing the potential of rapidly evolving digital technology in the 1980s, Robinson lobbied professionals to take amateur observations seriously, an effort that has been amply rewarded with major amateur contributions in many different fields, from discovering asteroids, comets, and supernovae to hunting for and characterizing planets around other stars. “I was one of the few people to walk in both communities with equal facility,” said Robinson. “I could relate CCD cameras to the amateur and I could relate science to the amateur.”

Robinson officially retired on December 31, 2000. But he remained active until the very end of his life. He wrote the popular “50 & 25 Years Ago” column for Sky & Telescope, and he continued to give talks to general audiences and amateur astronomers. From 2001 to 2005 he served on the Board of Directors of the Astronomical Society of the Pacific. Besides his career at S&T, Robinson was a world-class birdwatcher, and he authored the book Outdoor Optics.

“Today is a day of mourning at S&T, but we are also celebrating his life and contributions. Leif’s legacy will always remain a part of who we are and what we do,” says S&T Senior Editor Alan MacRobert, who worked with Robinson for 18 years.

Robinson is survived by his second wife “Ollie,” son Leif, Jr., and daughter Kara.

Image Credit: Leif J. Robinson courtesy of Sky & Telescope / Dennis di Cicco