Astronotes-Jun-Jul-2009

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June-July, 2009 Astronotes

Ottawa Centre Meeting Report - May 1, 2009

Recorder’s Notes by Estelle Rother Meeting chair Attilla Danko opened the May meeting with an announcement. Al Seaman will be presented with the RASC National Services Award at the GA. He has worked on mailing lists, served on council and has looked after FLO for many years. He is passing care of the observatory to Byran Black.

The meeting continued with Tim Cole's presentation on Ottawa Skies for May. It is an urban myth that Mercury is difficult to see but it is just tends to be low in the sky. The best way to see Mercury is when it is near something that can act as a reference. Early in May, that reference will be the Pleiades. Saturn's rings are starting to open. A transit of Tethys would be visible May 17. Jupiter would be at its brightest on May 31. But you would need to be out at 4 am. All the Galilean moons would also be visible.

Richard Alexandrowich followed with a discussion of Stellar Death of Stars with Medium to Low Mass. Stars go through the stages of birth, life and death. The most massive stars will go supernova and become a neutron star or a black hole. Stars with less than 8 times the sun's mass will become a white dwarf. Planetary nebulae are very popular with astronomers. They provide a link between a red giant and a cooling white dwarf. They can also be used as standard candles to determine the size and age of the universe. Tracking the velocity of a planetary in its galaxy can show the distribution of dark matter in the galaxy. For amateur astronomers, they are beautiful to look at and can also be challenge objects.

More than 2500 planetary nebulae are currently catalogued. They are difficult to see because of their small angular size, distance from us and the intervening gas and dust. In spite of studies at all wave-lengths, many aspects of planetary nebulae are not well understood, including their many shapes. At optical wavelengths, we see 3 basic shapes: round, elliptical and butterfly. The central star becomes a degenerate white dwarf.

As they enter the planetary nebula stage, they cast off shells of gas. So when a star puffs up, astronomers know it is nearing the end of its life. An Earth sized lump of carbon forms at the star's core. Hydrogen has been depleted and helium fusion begins. In stars that will become planetary nebulae, carbon is the final fusion product. There is not enough mass above the core to continue the fusion into heavier elements. Then the star's core begins to cool while 2 layers above the core continue with fusion. The inner layer burns helium and the outer layer burns hydrogen. Helium fusion is very sensitive to temperature. A 2% rise in temperature more than doubles the reaction rate and the star becomes unstable. Carbon in the star's atmosphere begins to settle and adds mass to the core. The helium burning layer expands and cools, the star becomes reddish and reaction rate diminishes. The final events of helium fusion eject the star's envelope into the interstellar medium (ISM). Each event creates a bubble of gas with an escape velocity of about 36,000 miles per hour.

The final helium flash creates a dense spray if gas and dust particles. This dust causes the dark lanes we see. There are also major axis bipolar flows. About 1% of the dust mixes with the ISM and reflects light from the dying star. The shape of each nebula is different and this makes them interesting to us. When a star becomes a red giant and starts to burn helium, it becomes unstable, variable and will start to pulsate. This will give rise to ejections of gas from the star. A planetary nebula will only last for about 10,000 years as the cloud of gas expands and disperses into the ISM. The remaining white dwarf shrinks and cools from an initial temperature of 100,000 Kelvin. Collisions between electrons halts further collapse and the white dwarf ends up with a diameter of 12,000 kilometres. A spectrum of a planetary shows lines of hydrogen alpha, hydrogen, helium and doubly oxidized oxygen. This dispersing gas allows light to shine through and we can now see the nebula.

The sun is 5 billion years old and currently on the main sequence of the HR diagram. In about 5 billion years from now its supply of hydrogen in the core will run out and it will become a red giant. The sun will swell to 100 times its current radius and it will swallow Mars and maybe even Jupiter.

Attilla commented that knowing the physics gives him an appreciation of what he is seeing. Richard Taylor also appreciates the physics of astronomy. He is a physics teacher; he likes calculus and is he a left-brain kind of person. He shows his students the names of things and the physics of what they are seeing. In his talk Take Time to Observe he talked about just laying back and observing. Physics is not the only thing in astronomy. A good example of the art and beauty of the night sky was the Talefmusik presentation of the music of the spheres. We should all try to just enjoy the beauty of the night sky.

Several years ago he spent the summer getting in touch with the artistic side of things with the help of Drawing on the Right Side of the Brain. There are 2 sides to your way of thinking. The left side of the brain is associated with naming things, language, scientific analysis and mathematics. The right side is more creative, associated with spatial perception and emotion. When we use the left side of out brain, we seem to be carrying on a conversation with ourselves. We are naming things and describing what is going on. At star parties we point out things in the night sky and answer questions. Sometimes, we should just enjoy looking at the night sky. When we see familiar things we usually name them and replace them in out head with a standard picture. That prevents us from noticing anything new. It helps to turn the image upside down and see it in a new way. Richard has looked at the sky from different places on Earth. In the southern hemisphere, the northern constellations are upside down and he invented new constellations.

Richard teaches grade 9 astronomy. He showed his students an image of the Big Dipper and his students called it the Shopping Cart. And it does look like a shopping cart. The myths and creatures they do not really see in the sky can overwhelm people new to astronomy. And that is not really important. What matters is knowing your way around the sky and recognizing that the same shapes are always in the same relationships with each other. Appreciating these shapes helps us to find our way around star maps and using a telescope.

Star Hop Through Sagitta is a web page Richard created that is available on the Ottawa RASC web site. When he star hops, he is looking for shapes. He is trying to find a shape on the map that matches what he sees in his finder scope.

The shapes on the map are not standard shapes. So at the telescope do not name things. Just look for a pattern in the sky.

Mike Moghadam then talked about upcoming IYA Events. On Saturday June 6 Dr. Roberto Abraham will speak at Carleton University. His topic will be Cosmic Dawn and Monster Telescopes. The event will begin at 1 pm. There will also be other activities and displays.

The Cube Gallery has a show called Nocturne until June 28. This is a group show of contemporary painting and sculpture dedicated to the beauty of the night sky. The Ottawa Centre was asked to participate in 3 events. The first would be held on May 22. On June 4 Rob Dick will a discussion of light pollution called The Dark Side of Light. And a star party is planned for June 11.

The meeting continued after a short break and the distribution of door prizes. Attilla mentioned that Canada Post had issued 2 stamps for the IYA. Tim Cole made a few Museum announcements. International Astronomy Day would take place on May 2. There would be a stargazing evening on May 15 (so bring your umbrella?). And have some fun launching water rockets on the evening of May 22.

Simon Hanmer has given many interesting presentations about the geology of the inner planets, the outer planets, and their moons using 2 dimensional Power Point slides. Since this is the IYA, he decided to go 3D, or 4D since he would also be moving through time to fly through the various parts of the solar system. Simon used a program by Software Bisque. It is similar to Celestia, a program that is available for free on the Internet. We will be in a spaceship moving around the solar system. Space is big so Simon speeds up time so we can do a tour at the meeting.

In a previous talk, Simon took us on a tour of the inner planets. In this talk, Being There: Jupiter and Saturn, he used Mars as the jumping off point to tour Jupiter and some of its moons. From Jupiter the sun is just a tiny dot. We watched some of Jupiter's moons crossing its disk. We then entered a polar orbit and saw the Jovian moons from above. Europa was the first moon we approached. It has a very young dynamic surface with few impact craters. Ganymede is an icy moon with dark older ice and a lighter colored younger ice. We can tell the lighter ice is younger because there are long veins where it cuts into the darker ice. Callisto's surface is much older. Io was the final moon on this tour. And instead of being icy like the other moons, Io is rocky. It is also the most volcanically active body in the solar system. We saw a volcano surrounded by a red ring of ash. Io has no atmosphere so the ash comes out of the volcano on a ballistic trajectory. The ash forms an umbrella shape and it all falls to the surface at the same distance from the volcano.

Observation Reports followed. Paul Comision remarked that with all his equipment, he still makes mistakes. And even Hubble made mistakes.

In April, Brian McCullough and his wife attended the science fiction spectacular at the NAC. It featured the music of science fiction movies and George Takei, Mr. Sulu from the original Star Trek series, narrated segments. Brian had brought a book of his autobiography and was hoping to have it signed. But George Takei had already returned to his hotel. One of the NAC employees offered to get the book autographed and the following Monday Brian had his book. He left a package of astronomy material for the NAC employee. When he returned home, Brian noticed the moon was not in the sky. Now what? Instead he observed M58 and showed the sketch he had made.

Last month's lunar challenge was to find the cross of death in Lacus Mortis. Gordon Webster actually located 3 crosses, including the real one from the challenge. He showed sketch of his find.

Bob Olson showed a mosaic of M86 that he created by stitching together 4 images. There were many galaxies visible in the image. And more details became visible in the reverse image. M51 is his favourite galaxy to photograph. He showed an image taken with a new telescope Peter Ceravolo had loaned him after he had collimated the telescope properly.


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Negative Image of M86 (labeled) by Bob Olson
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M51 – Image by Bob Olson (his favourite galaxy)

Sanjeev Sivarulrasa used a Canon 40D and an 85 mm refractor to image the Horsehead area, M45 and M13.

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Image of M13 by Sanjeev Sivarulrasa

Richard Alexandrowich is also president of the Glengary Stargazers, a small astronomy club in Alexandria. On his way home from work at 2 am one morning he got the idea of inviting someone from the Canadian Space Agency to give a talk. After a lot of hard work, the club succeeded. The event was held on April 5 at the Best Western in Cornwall. The speaker was Tara Hillebrandt, the real time support manager for the Canadian space arms on the ISS. She talked about Canada's involvement with the ISS.

Simon Hanmer told us about NASA's new press release on its Messenger mission to Mercury. The most exciting thing in the release was at the end. Mercury is a peculiar planet. Like all rocky planets, it has a core of nickel iron. The other rocky planets have an outer part, called the crust on Earth, and stuff in between, called the mantle. Mercury's core is huge in relation to the planet's size. Two theories have been proposed. A collision early in the history of the solar system blew off the outer layers. Or since Mercury is so close to the sun, the sun blew off the outer layer during Mercury's formation.

It is important to know what the outer part of Mercury is today. Initially it looked like this was anorthosite, the same composition as the light parts of the Moon (the same composition as the original Coffee Mate). However the press release stated there are no felsic rocks on Mercury (no Coffee Mate on the surface). But there is basalt. Basalt forms the ocean basins on Earth. It is a very common rock in the outer parts of normal planets. So NASA will eventually say there is something wrong with the models explaining Mercury's large core. You heard it here first.

May Observing Challenges:

Deep Sky: Gary Susick's Pick

  • NGC4631, NGC4656 and their neighbours. Observe the galaxies in the neighbourhood of NGC4631 in the constellation. This group of galaxies is in Canes Venatici, below the handle of the Big Dipper.

Gary also recommended a book: Atlas of the Messier Objects.

Thanks to Ann and Art Fraser for the after meeting refreshments.

A Primer to Planetaries

Richard Alexandrowich Glengarry Stargazers

All that we see in the heavens has an evolutionary tale to tell. Objects ranging from grain-sized meteoroids to massive galaxy clusters have their stages of existenance. The birth, life, and death of stars present their stories as well. Let us skip the first two chapters of a star's life and examine the mysteries of stellar death. Nothing can be more picturesque or beautiful as a snapshot of a dying star. However, one thing is clear, not all stars meet fate in the same fashion. The key element that determines how a star will die lies in its mass. Stars about eight times heavier than our Sun explode in a catastrophic event known as a supernova. The smallest of stars, the red dwarfs disappear gradually with a whimper. And stars similar to our Sun die in a "middle-of-the-road" fashion. They undergo a series of smaller explosions, puffing off layers of their material into space. In the aftermath, a small degenerate white dwarf is left to hang in space. Only the most massive stars will yield a compact object such as a neutron star or a black hole after they go ka-boom. Visually through our telescopes observers see them as colourful, star-like, planetaries. The majority of planetary nebulae reside along the galactic plane. In fact four globulars are known to harbour these enigmatic objects. With that said, it is logical to assume that planetaries are found in all galaxies.

In 1784, English astronomer, William Herschel coined the term 'planetary” when he likened these stellar corpses to his newly-found planet, Uranus. Since then the name stuck. Astronomers love exploring these ghostly apparitions. They are a popular object for study. As more and more images of these nebulae were beamed down to Earth from the Hubble space telescope, the intensi for curiousity became more apparent.

Only decades ago it was a popular myth that all stars in the heavens went supernova. Tools like the Hubble proved this was not the case. Since the mid-1990fs the exploration of planetary nebulae went into full throttle. We know that there are hundreds out there waiting to be discovered. According to my latest information, about 1,500 have been snared. Stellar astronomers estimate that as many as 10,000 are strewn throughout the galaxy all in various stages of development. Some we will probably never see due to intervening gas and dust. Size is also a problem. Since some are so tiny and distant (in arc-seconds) it is often a challenge to find one, let alone see it.

It is much easier to spot a full-grown planetary when the envelope of material expands enough to a size we can detect. The hot central star must shed its outer layers and begin ionizing it. Astronomers dissect these objects into several wavelengths. But there are aspects about them that are poorly understood. Looking at them in optical light, we note that they come in three basic forms: round, elliptical, and butterfly shaped. It is in the final "helium flash" that a planetaries' shape is determined. The dying phase of a sun-like star begins at the end of a distended red-giant's life. Unfortunately, for Earth, our Sun will meet a similar fate. In a nutshell, these stars are beginning to exhaust their supply of fuel necessary for the continuation of thermonuclear reactions and then cast off shells of gas we see in those colourful Hubble snapshots. We must note that the star slips off the main-sequence branch and enters the realm of the red-giants.

During the main-sequence phase of its life, a sun-like star is burning hydrogen into helium. As the star begins to age, the helium is converted into carbon and oxygen. It is at this point that the fusion comes to a halt. If the mass of the core is less than 1.4 solar masses, the collapse abruptly stops and a white dwarf is born. All nuclear burning stops at the star’s core.

Over a period of several thousand years the ill fated red-giant begins to belch out material and pulsates like a Mira-type variable. The star has now become unstable. A large part of a star's mass is ejected into space in an expanding shell. These puffs of stellar debris provide evidence that the star is aging and facing a mortal chapter in its life. To understand the fate of stars like the Sun, astronomers must look back in time several hundred years. Our natural galactic laboratory comprised of several hundreds of billions of stars provides us with specimens in different stages of evolution. Having many samples to work with is a big plus for astronomers.

After the star ejects it's outer layers, it wraps itself in a dusty cocoon shrouding itself from optical light. If a young planetary begins to shine, it is only because newly formed dust particles reflect light in our direction. It will take some time before the dust can expand sufficiently to create pathways for light to reach our eyes. Meanwhile as we divert our attention to the stars core, the fusion process has converted it's heart into a lump of carbon about the size of our planet. In stars that are destined to become planetary nebulae, carbon is the ultimate fusion byproduct. There simply is not enough mass to continue fusing elements into calcium, silicon, and iron.

Since heat cannot be replenished, the tiny star begins to cool like an ember in a fireplace. Thermonuclear fusion continues to take place in the outside layers. The forces of gravity persist by squeezing hydrogen and helium, but only for a brief period. Carbon that is found in the star's atmosphere begins to settle and as it does, adds mass to the already inert carbon core. What fuel remains lies too far from the core and there is not enough mass above it to compress it to its fusion point. And then the drama begins. The final spasmodic fits of helium cooking and whatever is left of it, flings these outer layers into the interstellar medium. Each hiccup creates a new bubble of gas having an escape velocity matching that of some of our space-probes, or about 36,000 mph.

The final helium flash will determine the nebula’s artistic shape. This event will form the dust lane and luminous lobes found along the major axis. A small percentage of this new dust will mingle with the interstellar medium and in the process will begin to reflect light from the dying star. Areas close to the budding planetary will become enriched with carbon-and silicate-rich particles. The scaffolding for living organisms, those carbon-based molecules, will also compliment the interstellar medium.

Time spans for those nebulous glories are relatively short, about 10,000 years, so astronomers must capitalize on these celestial moments. It won't be too long before a planetary will expand and disperse into the vacuum of space.

We have collected many images of classes of these objects in various stages of development, but they are still shrouded in mystery. One conundrum relates to their anatomy or structure that has scientists scratching their heads. Why are the outflows asymmetrical and not round? Should not a round star produce circular debris of material? What is the mechanism that is responsible for the shapes we see in telescopes? Is it possible that the dying star has an unseen orbiting companion that will ultimately dictate the shape of the nebula? Magnetic outflows may be more complicated than we can envision. Perhaps we don't fully understand magnetohydrodynamic (MHD) models that apply to dying stars.

When astronomers examined these nebulae in ultraviolet light, they discovered gas flows that were impressively fast, much faster than their manuals had predicted. This "fast wind" slams into the slower wind that was ejected in earlier spasmodic episodes. In doing so, it clears the gas and incinerates whatever lies in its path. This creates a cavity between the star and the surrounding nebula.

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M57 – Image by Gary Boyle

A classic visual example is the famous Smoke-Ring Nebula (M57) in Lyra. Astronomers suspect that Earthlings are gazing down the throat of a face-on cone in M57. From our vantage point, it only appears as a nebulous ring around a star. The collision process from the fast wind heats up the gas and as a consequence instruments on Earth begin to detect x-rays emanating from the nebula. Whatever gas is left is scooped up into a tenuous membrane. Beyond this rim we find the slow wind that has since decelerated from earlier episodes. Finally the gas bubble is breached as it reaches the outer edge of the slow wind. This cosmic stew then empties into the ISM. From this recipe a new generation of stars, planets, and people are created. The halos or bubble-like lobes we see in Hubble images are the end result of this process. The central star, usually dim or invisible in backyard scopes, eventually glows very hot and casts a bluish light. Intense heat from the star emits ultraviolet radiation stripping electrons from their atoms. At this time, observers begin to note the variety of hues and intricate shapes associated with these nebulae.

The challenge for amateur astronomers is to resolve some detail in these stellar corpses. Planetaries fall under two general categories, they are either bright but small, or large distended objects resembling ghostly apparitions. High power, good optics, and dark skies are a must to view these stellar denizens.

Imagine this scenario. Perhaps one day in the very distant future, we may have a ringside view of the fate that awaits our closest star, the Sun. For now, we can look into the eyepiece and marvel in the beauty of a star's death.

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