Astronomy Archives

September 12, 2008December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast – September 12 -14, 2008

Greetings, fellow SkyWatchers! It’s big… It’s bright. It’s undeniably the Moon. So what are we going to do this weekend? Why, study of course! We’ll take a look at some history, some mystery and even some cool variability that can be studied without any special equipment. Are you ready to journey into the night?

Friday, September 12, 2008 – Arthur Auwers was born today in 1838. His life’s work included unifying the world’s observational catalogs. He specialized in astrometry, making very precise measurements of stellar positions and motions and he also calculated the orbits of Sirius and Procyon long before their companions were discovered. Auwers also directed expeditions to measure the transits of Venus and began a project to unify the all available sky charts, an interest that began with his catalog of nebulae which he published in 1862. There’s even a lunar crater named for him!

Also today, in 1959, the USSR’s Luna 2 became the first manmade object to hit the moon. It was the first spacecraft to reach the surface of the Moon, and it impacted the lunar surface west of Mare Serenitatis near the craters Aristides, Archimedes, and Autolycus. Scientifically, Luna 2 is most famous for confirming the earlier detection of the solar wind by Luna 1. However, it’s most famous for what it did after it launched! When it separated from its third stage, the spacecraft released a bright orange cloud of sodium gas, which aided in spacecraft tracking and acted as an experiment on the behavior of gas in space. Can you imagine the sight? Today also celebrates the 1966 Gemini 11 launch – the highest Earth orbit ever reached by an American manned spacecraft (1374 kilometer altitude).

Tonight our primary lunar study is crater Kepler. Look for it as a bright point, slightly north of lunar center near the terminator. Its home is the Oceanus Procellarum – a sprawling dark mare composed primarily of minerals of low reflectivity (low albedo), such as iron and magnesium. Bright, young Kepler will display a wonderfully developed ray system. The crater rim is very bright, consisting mostly of a pale rock called anorthosite. The “lines” extending from Kepler are fragments that were splashed out and flung across the lunar surface when the impact occurred. The region is also home to features known as “domes” – seen between the crater and the Carpathian Mountains. So unique are Kepler’s geological formations that it became the first crater mapped by U.S. Geological Survey in 1962.

Saturday, September 13, 2008 – Today in 1922, the highest air temperature ever recorded on the surface of the Earth occurred. The measurement, taken in Libya, burned in at a blistering 136Â° F (58Â° C) – but did you know that the temperatures in the sunlight on the Moon double that? If you think the surface of the Moon is a bit too warm for comfort, then know that surface temperatures on the closest planet to the Sun can reach up to 800Â° F (430Â° C) at the equator during the day! As odd as it may sound, and even as close to the Sun as Mercury is, it could very well have ice deposits hidden below the surface at its poles.

Get out your telescope, because tonight we’re going to have a look at a lunar feature that goes beyond simply incredible – it’s downright weird. Start your journey by identifying Kepler, and head due west across Oceanus Procellarum until you encounter the bright ring of crater Reiner. Spanning 30 kilometers, this crater isn’t anything showy…just shallow-looking walls with a little hummock in the center. But, look further west and a little more north for an anomaly – Reiner Gamma.

Well, it’s bright. It’s slightly eye-shaped. But what exactly is it? Having no appreciable elevation or depth, Reiner Gamma could very well be an extremely young feature caused by a comet. Only three other such features are known to exist – two on the lunar far side and one on Mercury. They are high albedo surface deposits with magnetic properties. Unlike a lunar ray, consisting of material ejected from below the surface, Reiner Gamma can be spotted during the daylight hours – when ray systems disappear. And, unlike other lunar formations, it never casts a shadow.

Reiner Gamma is also a magnetic deviation on a barren world that has no magnetic field, so how did it form? Many ideas have been proposed, such as solar storms, volcanic activity, or even seismic waves. But the best explanation? It is the result of a cometary strike. Evidence exists that a split-nucleus comet, or cometary fragments, once impacted the area, and the swirl of gases from the high-velocity debris may have somehow changed the regolith. On the other hand, ejecta from such an impact could have formed around a magnetic “hot spot,” much like a magnet attracts iron filings.

No matter which theory is correct, the simple act of viewing Reiner Gamma and realizing it is different from all other features on the Moon’s Earth-facing side makes this journey well worth the time!

Sunday, September 14 – With a nearly Full Moon, skies are light-trashed tonight, so if you’d like to visit another object that only requires your eyes, then look no further than Eta Aquilae (RA 19 52 28 37 Dec +01 00 20), about one fistwidth due south of Altair…

Discovered by Pigot in 1784, this Cepheid variable varies by over a magnitude in a period of 7.17644 days. During this time it will reach of maximum of magnitude 3.7, and then decline slowly over five days to a minimum of 4.5… Yet it only takes two days to brighten again! This period of expansion and contraction makes Eta unique. To help gauge these changes, compare Eta to Beta on Altair’s same southeast side. When Eta is at maximum, it will about equal Beta in brightness.

Wishing you clear skies and a super weekend!!

This week’s awesome images are Kepler Crater by Wes Higgins, Luna 2 courtesy of NASA, Reiner Gamma from the Clementine Lunar Browser and Eta Aquilae – Credit: Palomar Observatory, courtesy of Caltech. Many thanks!

September 11, 2008September 13, 2016 by Fraser Cain

Ten Interesting Facts About the Sun

The Sun as viewed by the Solar and Heliospheric Observatory (NASA/SOHO)

Think you know everything there is to know about the Sun? Think again. Here are 10 facts about the Sun, collected in no particular order. Some you might already know, and others will be totally new to you.

1. The Sun is the Solar System
We live on the planet, so we think it’s an equal member of the Solar System. But that couldn’t be further from the truth. The reality is that the mass of the Sun accounts for 99.8% of the mass of the Solar System. And most of that final 0.2% comes from Jupiter. So the mass of the Earth is a fraction of a fraction of the mass of the Solar System. Really, we barely exist.

2. And the Sun is mostly hydrogen and helium
If you could take apart the Sun and pile up its different elements, you’d find that 74% of its mass comes from hydrogen. with 24% helium. The remaining 2% is includes trace amounts of iron, nickel, oxygen, and all the other elements we have in the Solar System. In other words, the Solar System is mostly made of hydrogen.

3. The Sun is pretty bright.
We know of some amazingly large and bright stars, like Eta Carina and Betelgeuse. But they’re incredibly far away. Our own Sun is a relatively bright star. If you could take the 50 closest stars within 17 light-years of the Earth, the Sun would be the 4th brightest star in absolute terms. Not bad at all.

4. The Sun is huge, but tiny
With a diameter of 109 times the size the Earth, the Sun makes a really big sphere. You could fit 1.3 million Earths inside the Sun. Or you could flatten out 11,990 Earths to cover the surface of the Sun. That’s big, but there are some much bigger stars out there. For example, the biggest star that we know of would almost reach Saturn if it were placed inside the Solar System.

5. The Sun is middle aged
Astronomers think that the Sun (and the planets) formed from the solar nebula about 4.59 billion years ago. The Sun is in the main sequence stage right now, slowly using up its hydrogen fuel. But at some point, in about 5 billion years from now, the Sun will enter the red giant phase, where it swells up to consume the inner planets – including Earth (probably). It will slough off its outer layers, and then shrink back down to a relatively tiny white dwarf.

6. The Sun has layers
The Sun looks like a burning ball of fire, but it actually has an internal structure. The visible surface we can see is called the photosphere, and heats up to a temperature of about 6,000 degrees Kelvin. Beneath that is the convective zone, where heat moves slowly from the inner Sun to the surface, and cooled material falls back down in columns. This region starts at 70% of the radius of the Sun. Beneath the convection zone is the radiative zone. In this zone, heat can only travel through radiation. The core of the Sun extends from the center of the Sun to a distance of 0.2 solar radii. This is where temperatures reach 13.6 million degrees Kelvin, and molecules of hydrogen are fused into helium.

7. The Sun is heating up, and will kill all life on Earth
It feels like the Sun has been around forever, unchanging, but that’s not true. The Sun is actually slowly heating up. It’s becoming 10% more luminous every billion years. In fact, within just a billion years, the heat from the Sun will be so intense that liquid water won’t exist on the surface of the Earth. Life on Earth as we know it will be gone forever. Bacteria might still live on underground, but the surface of the planet will be scorched and uninhabited. It’ll take another 7 billion years for the Sun to reach its red giant phase before it actually expands to the point that it engulfs the Earth and destroys the entire planet.

8. Different parts of the Sun rotate at different speeds
Unlike the planets, the Sun is great big sphere of hydrogen gas. Because of this, different parts of the Sun rotate at different speeds. You can see how fast the surface is rotating by tracking the movement of sunspots across the surface. Regions at the equator take 25 days to complete one rotation, while features at the poles can take 36 days. And the inside of the Sun seems to take about 27 days.

9. The outer atmosphere is hotter than the surface
The surface of the Sun reaches temperatures of 6,000 Kelvin. But this is actually much less than the Sun’s atmosphere. Above the surface of the Sun is a region of the atmosphere called the chromosphere, where temperatures can reach 100,000 K. But that’s nothing. There’s an even more distant region called the corona, which extends to a volume even larger than the Sun itself. Temperatures in the corona can reach 1 million K.

10. There are spacecraft observing the Sun right now.
The most famous spacecraft sent to observe the Sun is the Solar and Heliospheric Observatory, built by NASA and ESA, and launched in December, 1995. SOHO has been continuously observing the Sun since then, and sent back countless images. A more recent mission is NASA’s STEREO spacecraft. This was actually two spacecraft, launched in October 2006. These twin spacecraft were designed to watch the same activity on the Sun from two different vantage points, to give a 3-D perspective of the Sun’s activity, and allow astronomers to better predict space weather.

We have recorded an episode of Astronomy Cast all about the Sun called The Sun, Spots and All.

References:
NASA Science
NASA SOHO
NASA Stereo

September 10, 2008December 24, 2015 by Nancy Atkinson

Star Endured Unique Explosion That Didn’t Destroy

Eta Carinae Credit: Gemini Observatory artwork by Lynette Cook

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There’s ‘smoked but didn’t inhale,’ ‘promised but didn’t deliver,’ and now there’s ‘exploded but didn’t destroy.’ Eta Carinae, the galaxy’s biggest, brightest and perhaps most studied star after the sun, appears to be driven by an entirely new type of stellar explosion that is fainter than a typical supernova and does not destroy the star. Astronomer Nathan Smith proposes that Eta Carinae’s historic 1843 explosion was, in fact, an outburst that produced a fast blast wave similar to, but less energetic than, a real supernova. This well-documented event in our own Milky Way Galaxy is probably related to a class of faint stellar explosions in other galaxies recognized in recent years by telescopes searching for extragalactic supernovae.

“There is a class of stellar explosions going off in other galaxies for which we still don’t know the cause, but Eta Carinae is the prototype,” said Smith, a UC Berkeley postdoctoral fellow.

Eta Carinae (Î· Car) is a massive, hot, variable star visible only from the Southern Hemisphere, and is located about 7,500 light years from Earth in a young region of star birth called the Carina Nebula. In 1843, observers saw Eta Car brighten immensely. Visible now is the resulting cloud of gas and dust, known as the Homunculus nebula, wafting away from the star. A faint shell of debris from an earlier explosion is also visible, probably dating from around 1,000 years ago.

But these shells of gas and dust are moving relatively slowly at 650 kilometers per second (1.5 million miles per hour) compared to the blast shell of a regular supernova.

Presumably blown off by the star’s fierce wind, the shells of gas and dust are moving slowly – at speeds of 650 kilometers per second (1.5 million miles per hour) or less – compared to the blast shell of a supernova. But new observations by Smith show filaments of gas moving five times faster than the debris from the Homonuculus, which would equal speeds of materials accelerated fast blast wave of a supernova explosion.

The fast speeds in this blast wave could roughly double earlier estimates of the energy released in the 1843 eruption of Eta Carinae, an event that Smith argues was not just a gentle surface eruption driven by the stellar wind, but an actual explosion deep in the star that sent debris hurtling into interstellar space. In fact, the fast-moving blast wave is now colliding with the slow-moving cloud from the 1,000-year-old eruption and generating X-rays that have been observed by the orbiting Chandra Observatory.

“These observations force us to modify our interpretation of what happened in the 1843 eruption,” he said. “Rather than a steady wind blowing off the outer layers, it seems to have been an explosion that started deep inside the star and blasted off its outer layers. It takes a new mechanism to cause explosions like this.”

If Smith’s interpretation is correct, supermassive stars like Eta Carinae may blow off large amounts of mass in periodic explosions as they approach the end of their lives before a final, cataclysmic supernova blows the star to smithereens and leaves behind a black hole.

“Looking at other galaxies, astronomers have seen stars like Eta Carinae that get brighter, but not quite as bright as a real supernova,” he said. “We don’t know what they are. It’s an enduring mystery as to what can brighten a star that much without destroying it completely.”

Source: EurekAlert

September 10, 2008December 24, 2015 by Tammy Plotner

The Dragon Slayer – NGC 5985, NGC 5982, NGC 5981 by Ken Crawford

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There are wonderful tales which surround the circumpolar Draco constellation. According to Greek legend, Draco represents the dragon killed by Cadmus before founding the city of Thebes – or perhaps it represented the dragon which guarded the golden fleece and was eventually killed by Jason and his famous Argonauts. To the Romans, it was simply a creature killed by Minerva and tossed into the sky as stars to be remembered. The Egyptians called it Tawaret. But the most famous of all representations of Draco was one of the twelve labors that Hercules had to overcome. Many of us will never see the jewels that hide within the boundaries of this sprawling constellation, but thanks to the Herculean efforts of Ken Crawford – we can share in its mysteries…

To deep sky observers, the group of NGC 5985, NGC 5982 and NGC 5981 is commonly known as the “Draco Trio”. Two barred spirals at different angles and a face on elliptical all in the same field of view is a rare sight and makes for a beautiful celestial portrait. The beautiful spiral is NGC 5985. The proper designation for the elliptical galaxy is NGC 5982. The catalog number for the edge-on is NGC 5981. While these galaxies span huge amounts of light years apart, they share telescopic space at RA: 15h 38m 40s Dec: +59Â°21’22” as a center and share photons in the eyepiece at around 25 arc minutes. While the Draco group is far too small to be considered its own galaxy cluster and has never been classified as a compact group, oddly enough all three are around 100 million light years away from the Sol System.

I did mention there were mysteries here, didn’t I? Then let’s explore them…

Take a closer look at the grand spiral, NGC 5985. It’s a Seyfert. According to research done by SimÃµes Lopes (et al) it may also harbor a wonderful black hole right in there with its active galactic nucleus. “This result demonstrates a strong correlation between the presence of circumnuclear dust and accretion onto the central, supermassive black hole in elliptical and lenticular galaxies. Current estimates suggest the dust settling or destruction time is on order of 108 yr, and therefore the presence of dust in ~50% of early-type galaxies requires frequent replenishment and similarly frequent fueling of their central supermassive black holes. The observed dust could be internally produced (via stellar winds) or externally accreted, although there are observational challenges for both of these scenarios. Our analysis also reveals that approximately one-third of the early-type galaxies without circumnuclear dust have nuclear stellar disks. These nuclear stellar disks may provide a preferred kinematic axis to externally accreted material, and this material may in turn form new stars in these disks. The observed incidence of nuclear stellar disks and circumnuclear dust suggests that episodic replenishment of nuclear stellar disks occurs and is approximately concurrent with the fueling of the central AGN.”

But that’s not all, because there’s a quasar there, too. According to a 2001 study done by one of my heroes – Halton Arp and David Russell; “The distribution on the sky of clusters of galaxies shows significant association with relatively nearby, large, active galaxies. The pattern is that of clusters paired equidistant across a central galaxy with the apparent magnitudes and redshifts of their constituent galaxies being closely matched. The clusters and the galaxies in them tend to be strong X-ray and radio emitters, and their redshifts occur at preferred redshift values. The central, low-redshift galaxies often show evidence of ejection in the direction of these higher redshift clusters. In all these respects the clusters resemble closely quasars which have been increasingly shown for the last 34 years to be similarly associated with active parent galaxies. New, especially significant pairings of quasars are presented here, which are, at the same time, associated with Abell clusters of galaxies. It is argued here that, empirically, the quasars are ejected from active galaxies. They evolve to lower redshift with time, forming stars, and fragmenting at the end of their development into clusters of low-luminosity galaxies. The cluster galaxies can be at the same distance as their lower redshift parents because they still retain a component of their earlier, quasar intrinsic redshift.”

Now, let’s take a look at the quiet little elliptical – NGC 5982. Just this year it was studied by Del Burgo (et al) for its dust shell. According to the report: “Shells in Ellipticals are peculiar faint sharp edged features that are thought to be formed by galaxy mergers. We use Spitzer data in the wavelength range from 3.6 to 160 Î¼m and HST/ACS optical data. After subtracting the galaxy models, residual images are used to identify the shells. We detect for the first time shells from mid-infrared data. The very different distributions of dust, warm gas and HI gas together with the presence of shells and a kinematically decoupled core suggest a minor merger in NGC 5982.”

Ah, ha! So, it’s always the quiet ones that get ya’, huh? Then it might interest you to know that NGC 5982 may also contain its own black hole, a peculiar population of stars, a low luminosity active galactic nucleus and may have even been a product of a black hole merger! What more, new globular clusters may have formed during these interactions without the benefits of gaseous materials. Simply too cool…

Now… How about the wild looking edge-on, NGC 5981? Science loves to examine what it just can’t quite see and in the case of this highly inclined spiral, we’ve found out that the stellar disc just might be cut off – or foreshortened. According to a 2007 work done by Florido (et al); “This is the first work reporting observations of the truncation of a stellar disc, in both the optical and the NIR spectral ranges. No galaxy has been observed at both wavelengths with the required depth. The optical radial profiles of spiral galaxy discs seem to suggest a double exponential behaviour, whilst NIR profiles seem to show a real truncation. NGC 6504 has a real truncation in both the optical and the NIR radial profiles. A double exponential does not fit the observed optical profile. The truncation radius is larger in the V band than in the NIR by ~10 arcsec, about 3 kpc (equivalent to about 10%).”

But, just because its equipment is a little shorter than most, does that mean it doesn’t produce as many stars? Not hardly. It just means its peanut-shaped central bulge may be embedded in a dark halo. Thanks to the work of Joop Schaye who also took a look at NGC 5981, we know a little more about these properties. “We study global star formation thresholds in the outer parts of galaxies by investigating the stability of disk galaxies embedded in dark halos. The disks are self-gravitating, contain metals and dust, and are exposed to UV radiation. We find that the critical surface density for the existence of a cold interstellar phase depends only weakly on the parameters of the model and coincides with the empirically derived surface density threshold for star formation. Furthermore, it is shown that the drop in the thermal velocity dispersion associated with the transition from the warm to the cold gas phase triggers gravitational instability on a wide range of scales. The presence of strong turbulence does not undermine this conclusion if the disk is self-gravitating. Models based on the hypothesis that the onset of thermal instability determines the star formation threshold in the outer parts of galaxies can reproduce many observations, including the threshold radii, the column densities, and the sizes of stellar disks as a function of disk scale length and mass.”

While we’ll never see the Draco Trio in the telescope eyepiece as well as what this incredible image by Ken Crawford presents, we welcome the Dragon Slayer for the opportunity it gives us to take a closer look at another cosmic mystery. Is the Draco Group really a galaxy group? Perhaps. According to independent research papers done by both Giuricin and Garcia, this small group of friends collectively known as the NGC 5866 Group (because it’s the brightest) is located to the northwest of both the M101 Group and its companion galaxies which makes it proximity. Also nearby is the M51 Group, home to the Whirlpool Galaxy, the Sunflower Galaxy, and several others. The distances to these three groups was gathered by studying their individual members and science has found they are similar – and perhaps part of a much larger, more loose association than we’ve yet discovered.

But we’re learning…

Many thanks to AORAIA member Ken Crawford for the use of the spectacular image and the awesome research challenge it posed! My gratitude for the inspiration and the learning challenge…

September 6, 2008April 26, 2016 by Tammy Plotner

The Fire Cracker Galaxy – NGC 6946 by Dietmar Hager

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It’s time to take a look back to what was happening 210 years ago on the night of September 9th. Sir William Herschel was at the eyepiece of his telescope in Slough. While he was viewing in real time, what he was viewing occurred more than 10 million years ago – the fireworks that ignited in NGC 6946.

At one time, it was widely believed that NGC 6946 was a member of our Local Group; mainly because it could be easily resolved into stars. There was a reddening observed in it, believed to be indicative of distance – but now know to be caused by interstellar dust. But it isn’t the shrouding dust cloud that makes NGC 6946 so interesting, it’s the fact that so many supernova and star-forming events have sparkled in its arms in the last few years that has science puzzled! So many, in fact, that they’ve been recorded every year or two for the last 60 years…

Most normally, bursts of star formation happen in galaxies which have nearby companions to lend materials. Yet, NGC 6946 appears to be alone in the field. According to a 2000 study done by Pisano (et al) ” Such gas-rich companions could include material left over from the galaxy assembly process which could persist into the current day around an isolated galaxy such as NGC 6946. NGC 6946 is prolifically forming stars, has a nuclear starburst, and has widespread high-velocity clouds associated with the disc. All of these features could be explained by the accretion of low-mass Hi clouds by NGC 6946. Our survey recovered two previously detected dwarf galaxies associated with NGC 6946, but otherwise found no signatures of interactions in the NGC 6946 system. The companions are small enough, and distant enough from NGC 6946 that they should have minimal effect on the main galaxy. Some tidal debris may be expected due to interaction between the two dwarf galaxies, but none is observed. This could be because it is at low column densities, or because the dwarf galaxies are more separated than they appear on the sky. This study of the system suggests that NGC 6946 is a gravitationally bound system with two dwarf galaxies in stable orbits about the larger primary galaxy.”

But, that was some 8 years ago and 16 events into the past. According to studies done by Eva Schinnerer (et al) in 2006, NGC 6946 has been “Caught in the Act” as a Bar-driven Nuclear Starburst Galaxy. “The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner ~10” (270 pc) with a large concentration of molecular gas (MH2~1.6Ã—107 Msolar) within the inner 60 pc. This nuclear clump shows evidence for a ringlike geometry with a radius of ~10 pc as inferred from the position-velocity diagrams. Both the distribution of the molecular gas and its kinematics can be well explained by the influence of an inner stellar bar of about 400 pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC 6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar.”

Now, for the really cool part – understanding barred structure. Thanks to the Hubble Space Telescope and a study of more than 2,000 spiral galaxies – the Cosmic Evolution Survey (COSMOS) – astronomers understand that barred spiral structure just didn’t occur very often some 7 billion years ago in the local universe. Bar formation in spiral galaxies evolved over time. A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts. This makes NGC 6946 very rare, indeed… Since its barred structure was noted back in Herschel’s time and its age of 10 billion years puts it beyond what is considered a “modern” galaxy.

Science believes bars in galaxies have been forming steadily over the last 7 billion years, more than tripling in number. “The recently forming bars are not uniformly distributed across galaxy masses, however, and this is a key finding from our investigation,” Sheth explained. “They are forming mostly in the small, low-mass galaxies, whereas among the most massive galaxies, the fraction of bars was the same in the past as it is today.” The findings, Sheth continued, have important ramifications for galaxy evolution. “We know that evolution is generally faster for more massive galaxies: They form their stars early and fast and then fade into red disks. Low-mass galaxies are known to form stars at a slower pace, but now we see that they also made their bars slowly over time,” he said. Bars form when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. “The tiny elongations in the stars’ orbits grow and they get locked into place, making a bar,” explained team member Bruce Elmegreen of IBM’s research Division in Yorktown Heights, N.Y. “The bar becomes even stronger as it locks more and more of these elongated orbits into place. Eventually a high fraction of the stars in the galaxy’s inner region join the bar.”

Added team member Lia Athanassoula of the Laboratoire d’Astrophysique de Marseille in France: “The new observations suggest that the instability is faster in more massive galaxies, perhaps because their inner disks are denser and their gravity is stronger.” Bars are perhaps one of the most important catalysts for changing a galaxy. They force a large amount of gas towards the galactic center, fueling new star formation, building central bulges of stars, and feeding massive black holes. “The formation of a bar may be the final important act in the evolution of a spiral galaxy,” Sheth said. “Galaxies are thought to build themselves up through mergers with other galaxies. After settling down, the only other dramatic way for galaxies to evolve is through the action of bars.” (HubbleSite News Release)

Yet the studies of NGC 6946 haven’t stopped. In 2005, Gemini II also took a look at this crazy galaxy. “In order to sustain this rate of supernova activity, massive, quickly evolving stars must form or be born at an equally rapid rate in NGC 6946,” said Gemini North Associate Director, Jean-RenÃ© Roy. “Its stars are exploding like a string of firecrackers!” And with it in 2007, hydrogen halos… Says Rense Boomsma: “A halo of neutral hydrogen is found around an increasing number of spiral galaxies. It is not well understood how hydrogen halos are formed. The orientation of nearby spiral galaxy NGC 6946 enables us to measure vertical gas velocities in the disk of the galaxy and therefore measure how the gas gets into the halo. We find hydrogen with high velocities toward regions where stars are formed. This correlation suggests that the formation of a hydrogen halo is related to massive star formation. A similar close connection is seen in the nearby spiral galaxy NGC 253. For some hydrogen clouds in NGC 6946 we have indications that they have been accreted from outside the galaxy.”

Will we ever understand everything there is to know about galaxies like NGC 6946? Perhaps not in our lifetimes. However, one of the best parts is knowing that it is a galaxy that you can observe and study with larger backyard telescopes. Located in the constellation of Cepheus (RA 20:34.8 Dec +60:09) and billed at magnitude 8.9 (but beware, it’s low surface brightness!), this small barred spiral will show some structure in 10″ or larger scopes with decent skies. Who knows what your night may reveal?

Our many thanks to AORAIA member, Dr. Dietmar Hager of Stargazer Observatory for the use of this incredible image and the challenge of researching the information!

Link to original full size image.

September 5, 2008December 24, 2015 by Ian O'Neill

Kuiper Belt Object Travelling the Wrong-Way in a One-Way Solar System

Artist impression of two KBOs and Neptune eclipsing the Sun (Mark A. Garlick)

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A strange Kuiper Belt Object (KBO) has been discovered orbiting the Sun in the wrong direction. The object, designated as 2008 KV42 but nicknamed Drac (after Dracula, as vampires are fabled to have the ability to walk on walls), has a highly inclined orbit of 103.5°. Drac is a rarity as very few objects in the Solar System have retrograde orbits; in fact this kind of orbit is usually exclusive to Halley-type comets that have orbits that take them very close to the Sun. Drac on the other hand travels through the Kuiper Belt in a stable orbit at a distance of between 20-70 AU from the Sun. This finding has puzzled astronomers, but Drac may provide clues as to where Halley-type objects originate…

When an object has an inclination of more than 90° from the ecliptic, its direction of motion becomes retrograde when compared with the majority of the Sun’s satellites that share a common, or “prograde” orbital direction. This type of orbit is usually reserved for long-period comets thought to originate from the mysterious Oort Cloud. However, Drac stands out from the crowd as it orbits the Sun from the distance of Uranus to more than twice that of Neptune. Halley-type comets come much closer to the Sun.

Researchers led by Brett Gladman of the University of British Columbia observed the 50 km (30 mile) diameter object in May. Drac (or 2008 KV42) appears to have an extremely stable orbit, and its possibly been that way for hundreds of millions of years. Although Drac orbits through the Kuiper Belt, astronomers do not believe it originates there. “It’s certainly intriguing to ask where it comes from,” says Brian Marsden of the Minor Planet Center in Cambridge, Massachusetts.

Gladman believes the object originated far beyond the Kuiper Belt, possibly from the same volume of space believed to breed Halley-type comets with highly tilted (often retrograde) orbital periods of between 20-200 years. Gladman and his colleagues believe Drac came from a region beyond the Kuiper Belt, but it didn’t come from the Oort Cloud (some 20,000 to 200,000 AU from the Sun). The researchers believe 2008 KV42 was born in a region 2000-5000 AU from the Sun, a theorized volume of the Solar System called the inner Oort Cloud.

It seems likely that Drac was gravitationally disturbed from its home in the inner Oort Cloud by a passing star, or some other disturbance in its local space. It then fell toward the inner Solar System where it found its new home near the Kuiper Belt. Gladman believes that 2008 KV42 may be a “transition object” on its way to becoming a Halley-type comet. However, it will need to be disturbed again before it breaks free of its current stable orbit to fall closer to the Sun.

The British Columbia team have found a collection of 20 KBOs with steeply inclined orbits, but Drac, the vampire of the Solar System, is the only one orbiting in the wrong direction…

Source: New Scientist

September 5, 2008December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast – September 5 – 7, 2008

Greetings, fellow Skywatchers! The weekend has arrived at last and with it… more lunar challenge studies. Are you ready to dance with the pie-eyed piper as we seek out Piccolomini? You’ll find it to the southwest of the shallow ring of Fracastorius on Mare Nectaris’ southern shore. How about seeing double as we take on a few binary stars? It’s time to get out your binoculars and telescopes as we head to the Moon because… Here’s what’s up!

Friday, September 5, 2008 – Tonight let’s discover beauty on our own Moon as we have a look at one of the last lunar challenges of the year which occurs during the first few days of the Moon’s appearance – Piccolomini. You’ll find it to the southwest of the shallow ring of Fracastorius on Mare Nectaris’ southern shore. Piccolomini is a standout lunar feature – mainly because it is a fairly fresh impact crater. Its walls have not yet been destroyed by later impacts, and the interior is nicely terraced. Power up and look carefully at the northern interior wall where a rock slide may have rumbled toward the crater floor. While the floor itself is fairly featureless, the central peak is awesome. Rising a minimum of two kilometers above the floor, it is even higher than the White Mountains in New Hampshire!

When you’ve caught up on your studies, let’s have a look at Beta and Gamma Lyrae, the lower two stars in the “Harp.” Beta is actually a quickly changing variable which drops to less than half the brightness of Gamma in around 12 days. For a few days the pair will seem of almost equal brightness; then you will notice the star closest to Vega begins to fade away. Beta is one of the most unusual spectroscopic stars in the sky, and it is possible that its eclipsing binary companion may be a prototypical “collapsar” (Yep – a black hole!) rather than an actual luminous body.

Now use the telescope for a pair of stars which are very close – Epsilon Lyrae (RA 18 44 20 Dec +39 40 12). Known to most of us as the “Double Double,” look about a fingerwidth northeast of Vega. Even the slightest optical aid will reveal this tiny star as a pair, but the real treat is with a telescope – because each component is a double star! Both sets of stars appear as primarily white, and each pair is very close in magnitude. What is the lowest power that you can use to split them?

Saturday, September 6, 2008 – Today celebrates the founding of the Astronomical and Astrophysical Society of America. Started in 1899, it is now known as the American Astronomical Society. Also on this date, in 2006, the milestone 1500th episode of Jack Horkheimer’s Star Gazer series aired. The long-running short program on public television has led thousands of people, young and old, to “keep on looking up!” For a lifetime of achievement in public outreach, we salute you, Mr. Horkheimer!

Tonight when you have had a look at the Serpentine Ridge, drop south along the terminator and see if you can identify the very old crater Abulfeda, west of Theophilus.

This charming crater was named for Prince Ismail Abu’l Feda, who was a Syrian geographer and astronomer born in the late thirteenth century. Spanning 62 kilometers, its rocky walls show what once was a great depth, but the crater is now filled-in by lava, and drops to a mere 3110 meters below the surface. While it doesn’t appear very large to the telescope, that’s quite big enough to entirely hide Mt. Siple – one of the highest peaks in Antarctica! If conditions are steady, power up and take a look at Albulfeda’s smooth-appearing floor. Can you see many smaller strikes? If the lighting is correct, you might even spot one far younger than the others!

Sunday, September 7 – For binoculars and telescopes, tonight’s Moon will provide a piece of scenic history as we take an in-depth look at crater Albategnius. This huge, hexagonal, mountain-walled plain will appear near the terminator about one-third the way up from the south limb. This 136 kilometer wide crater is approximately 4390 meters deep, and its west wall will cast a black shadow on the dark floor. Albategnius is a very ancient formation, which partially filled with lava at one point in its development. It is home to several wall craters like Klein (which will appear telescopically on its southwest wall). Albategnius holds more than just the distinction of being a prominent crater – it holds a place in history. On May 9, 1962 Louis Smullin and Giorgio Fiocco of the Massachusetts Institute of technology aimed a red laser toward the lunar surface and Albategnius became the first lunar object to be illuminated by a laser and then detected from Earth!

On March 24, 1965 Ranger 9 took this “snapshot” of Albategnius (in the lower right of the lunar image) from an altitude of approximately 2500 kilometers. Companion craters in the image are Ptolemaeus and Alphonsus, which will be revealed for us tomorrow night. Ranger 9 was designed by NASA for one purpose – to achieve a lunar impact trajectory and send back high-resolution photographs and high-quality video images of the lunar surface. It carried no other scientific experiments, and its only destiny was to take pictures right up to the moment of final impact. It is interesting to note that Ranger 9 slammed into Alphonsus approximately 18.5 minutes after the lunar photo was taken. They called that…a “hard landing.”

As the week progresses, watch as the Moon draws closer for a near event with Jupiter by Wednesday. While the pair will still be separated by around two degrees it will still be an awesome sight that doesn’t require a telescope to enjoy!

Wishing you clear skies…

This week’s awesome images are Crater Piccolomini – Credit: Oliver Pettenpaul (LPOD), Beta Lyrae – Credit: Palomar Observatory, courtesy of Caltech, Beta Lyrae – Credit: Palomar Observatory, courtesy of Caltech, Crater Abulfeda – Credit: Wes Higgins, Ranger 9 Image of Lunar Surface and Image of Lunar Surface – Credit: NASA. We thank you!!

September 3, 2008December 24, 2015 by Tammy Plotner

Observing Alert: Possible New Dwarf Nova In Andromeda

[/caption]According to AAVSO Special Notice #122 prepared by M. Templeton, there’s a possible new WZ Sge-type dwarf nova located in Andromeda. The alert was posted yesterday and intial observations were sent in within the last 48 hours. For more information, read on…

AAVSO Special Notice #122

Multiple observers have confirmed the detection of an optical transient in Andromeda whose photometric behavior is thus far consistent with its classification as a WZ Sge-type dwarf nova system. The object was submitted to the CBAT unconfirmed objects list (D. Green, editor) by an unidentified observer on 2008 September 01.6.

A comprehensive list of the numerous follow-up observations made in Russia was published and an announcement of apparent very short period superhumps (P ~ 0.055 days) was made in vsnet-alert 10478. A comparison of the field with archival POSSII plates by D. Denisenko et al suggests the progenitor is very faint, with a blue magnitude of 21 or fainter. The reported outburst magnitudes of approximately V=12.5 then suggest an amplitude of at least 8 magnitudes.

M. Andreev (Terskol, Russia) obtained the following coordinates for the object using a 28-cm telescope:

RA: 02h 00m 25.42s , Dec: +44d 10m 18.4s (J2000)

Several other sets of coordinates have been published by Russian observers on the page noted above, and most are within a few tenths of an arcsecond.

Observations of this new object, including time-series photometry, are encouraged. The object has not been formally named, and the WZ Sge classification has not been definitively confirmed. Observers are asked to follow the object during the next several weeks. The object may fade and rebrighten, so please submit all observations including “fainter-than” estimates. Instrumental time-series observations are also encouraged to confirm the presence of superhumps and (if possible) define the period.

Please submit all data to the AAVSO using the name and/or AUID pair VSX J020025.4+441018 , AUID 000-BFT-799.

Nova Andromeda Photo courtesy of AstroAlert.

September 3, 2008December 24, 2015 by Tammy Plotner

NGC 7023 – ‘Iris From The Dust’ by Kent Wood

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As the very last of the summer flowers bloom in the dusty grasses of the northern hemisphere, so a cosmic flower blooms in the dusty star fields of the northern constellations. While this image conjures up a vision of an iris delicately opening its 6 light year wide petals some 1300 light years away in Cepheus, this bit of flora is anything but a pretty little posey…

NGC 7023 was first discovered by Sir William Herschel on October 18, 1794 and since that time it has had a rather confusing catalog history. As usual, Herschel’s notes made the correct assumption of “A star of 7th magnitude. Affected with nebulousity which more than fills the field. It seems to extend to at least a degree all around: (fainter) stars such as 9th or 10th magnitude, of which there are many, are perfectly free from this appearance.” So where did the confusion come in? It happened in 1931 when Per Collinder decided to list the stars around it as a star cluster Collinder 429. Then along came Mr. van den Berg, and the little nebula became known as van den Berg 139. Then the whole group became known as Caldwell 4! So what’s right and what isn’t? According to Brent Archinal, “I was surprised to find NGC 7023 listed in my catalog as a star cluster. I assumed immediately the Caldwell Catalog was in error, but further checking showed I was wrong! The Caldwell Catalog may be the only modern catalog to get the type correctly!”

But what isn’t wrong is the role molecular hydrogen plays in formations like the Iris nebula. In a gas rich interstellar region near a a hot central object such as the Herbig Be star HD 200775, atomic and molecular excitation occurs. The resulting fluorescence produces a rich ultraviolet and infrared spectrum… and interstellar emissions. Just what kind of interstellar emissions might occur from a region like the Iris Nebula? According to the 2007 Micron Spitzer Spectra Research done by Sellgren (et al) at Ohio State: “We consider candidate species for the 18.9 Âµm feature, including polycyclic aromatic hydrocarbons, fullerenes, and diamonds.”

Now, we’re not only bringing you space flowers… but diamonds in the rough.

The discovery of aromatic hydrocarbons, diamonds, and fullerenes in interstellar space is a new puzzle to space science. According to the work of K. Sellgren; “Emission from aromatic hydrocarbons dominates the mid-infrared emission of many galaxies, including our own Milky Way galaxy. Only recently have aromatic hydrocarbons been observed in absorption in the interstellar medium, along lines of sight with high column densities of interstellar gas and dust. Much work on interstellar aromatics has been carried out, with astronomical observations and laboratory and theoretical astrochemistry. In many cases, the predictions of laboratory and theoretical work are confirmed by astronomical observations but, in other cases, clear discrepancies exist that provide problems to be solved by a combination of astronomical observations, laboratory studies, and theoretical studies. …Studies are needed to explain astrophysical observations, such as a possible absorption feature due to interstellar â€˜diamondsâ€™ and the search for fullerenes in space.”

What this comes down to is carbon nanoparticles are out there in the interstellar medium. Polycyclic aromatic hydrocarbons – or PAHs – are molecules constructed of benzene rings that look like segments of single layers of graphite. If you were here on Earth? You’d find them everywhere… coming out of your car’s exhaust, stuck to the top of your grill, coating the inside of your fireplace. Apparently we’re picking up the signature of PAHs in Unidentified Infra-Red emission bands, Diffuse Interstellar Bands and a UV extinction bump in NGC 7023 – but what the heck is it doing there?

According to research, it’s entirely possible these PAHs may have formed in the dust when the grains collided and fractured – releasing free PAHs. They could have grown between smaller unsaturated hydrocarbon molecules and radicals in the remnants of carbon rich stars. Science just doesn’t really know. But one thing they do know… Once a PAH is there, it is extremely stable and extremely efficient at rapidly re-emitting the absorbed energy at infra-red wavelengths.

Take the time to view the Iris Nebula yourself. Located in Cepheus (RA 21:00.5 Dec +68:10) and around magnitude 7, this faint nebula can be achieved in dark skies with a 114-150mm telescope, but larger aperture will help reveal more subtle details since it has a lower surface brightness. Take the time at lower power to reveal the dark dust “lacuna” around it reported so many years ago, and to enjoy the true beauty of this Caldwell gem. Remember your astronomy lesson, too! According to O. Berne, who also studied NGC 7023 just this year, “Unveiling the composition, structure and charge state of the smallest interstellar dust particles remains one of todayâ€™s challenges in astrochemistry.”

We would like to thank AORAIA member, Ken Wood for this incredibly inspiring image!

September 2, 2008December 24, 2015 by Nancy Atkinson

New Eye to the Universe Under Construction

The LSST, or the Large Synoptic Survey Telescope is a large survey telescope being constructed in northern Chile. When operational in 2015, it will be the widest, fastest, deepest eye of the new digital age, providing timelapse digital imaging across the entire night sky every three days, mapping the structure of our dynamic universe in three dimensions and exploring the nature of dark matter and dark energy. LSST hit a major milestone in its construction when the primary mirror blank was recently created. Project astronomers say the single-piece primary and tertiary mirror blank cast for the LSST is “perfect.”

The 51,900 pound (23,540 kg) mirror blank was fired in the oven at the University of Arizona’s Steward Observatory Mirror lab in Tucson, Arizona. It consists of an outer 27.5-foot diameter (8.4-meter) primary mirror and an inner 16.5-foot (5-meter) third mirror cast in one mold. It is the first time a combined primary and tertiary mirror has been produced on such a large scale.

LSST will have three large mirrors to give crisp images over a the largest field of view that will be available. The two largest of these mirrors are concentric and fit neatly onto a single mirror blank.
LSST was recently the recipient of two large gifts: $20 million from the Charles Simonyi Fund for Arts and Sciences, and $10 million from Bill Gates. The finished mirror is scheduled to be delivered in 2012.

More information about LSST.

News Source: LSST press release