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The Life Cycles of Stars

November, 2009

By Tom Koonce

Antelope Valley Astronomy Club, Inc.

Lancaster, California

“The bigger they are, the harder they fall…?  This is certainly true of stars.  When single stars condense from a star forming nebula, their life history is pre-written based upon their initial mass and the cloud’s composition.  High mass stars burn very hot, have very short stellar lifetimes then explode in spectacular Supernovae, forming either Neutron Stars or Black Holes.  On the other end of the mass scale, low mass single stars have relatively cool temperatures, but live extremely long lifetimes and may radiate dimly for many, many billions of years

Image1Over time, higher density regions within giant nebulae like the Orion Nebula or the Eagle Nebula begin to contract gravitationally, and as they do, the cloud rotates.  As the gas contracts and rotates faster, the gas begins to heat up to become a Protostar.  Once its temperature reaches approximately 15,000,000 Celsius, nuclear fusion initiates in the cloud’s center causing the Protostar to begin to radiate brightly.   The smallest stellar objects that form in the star forming regions are called Sub-Stellar Objects.  These form with masses between 0.013 and 0.08 times the mass of our own Sun (our Sun = one solar mass).  These stars radiate briefly as a dim star, but gradually collapse, cool as they evolve further into Brown Dwarf stars.  Eventually the Brown Dwarf will cool further and it will cease radiating at all.

The stars known as “Red Dwarf? stars have between 0.08 and 0.4 solar masses when they form.  These are the most common type of stars in the observable universe and have lifetimes longer than 13 billion years.  As these small, long living stars eventually cool, they die and become Black Dwarf stars.

Stars approximately the size of our Sun with 0.4 to 8 solar masses are called “Intermediate? stars and will swell into Red Giant stars as their fuel is expended.  Eventually, these stars will end their lives as White Dwarf stars.

Image2Nebulae and stars are typically composed of 74% hydrogen, 25% helium and 1% everything else in the periodic table by mass.  A star’s initial mass is determined by the amount of material available within the nebula from which the star forms.  Very dense nebulae can produce the most massive stars – true giants with 8 times (or greater than) our Sun’s mass.  Those stars with between 8 and 25 solar masses will expand into Super Giant stars then explode as supernovae and end their lives as Neutron Stars; those stars with greater than 25 solar masses will expand into Super Giant stars, explode as supernovae and become Black Holes.  It isn’t known what the upper limit is to a star’s initial mass is, but in the early 1990’s, a star nicknamed the “Pistol Star? was discovered by the Hubble Space Telescope near the center of the Milky Way galaxy with a mass of 100 solar masses and a radius of 100 million miles, comparable to the Earth-Sun distance of 93 million miles.  The Pistol Star is called a Blue Hyper Giant and is so hot that its gravity can’t stabilize it and it is expected to go supernova within only 1 to 3 million years.  A great deal of gas and matter is expelled during these supernovae explosions which then give rise to future generations of stars, repeating the cycle of stellar birth.

Smaller stars burn dimly, but may burn for billions and billions of years.  Giant stars burn with incredible intensity, but go through their hydrogen and helium fuel in as little as millions of years, and then end their lives in dramatic supernovae explosions.  I can think of a few analogous Hollywood situations…but that’s for another type of “Star? article altogether.

References and image credit: NASA StarChild initiative, NASA Hubble Space Telescope, Wikipedia.

Other Newsletter inserts:

The zodiac names we use today are actually the names our ancestors gave to special star groups known as constellations. How many of the ancient constellation names can you correctly identify? Place the constellation’s letter on the line next to its description.

A. Gemini _____ The Water Carrier
B. Cancer _____ The Crab
C. Aries _____ The Goat
D. Libra _____ The Twins
E. Ursa Major _____ The Dragon
F. Capricornus _____ The Winged Horse
G. Leo _____ The Scorpion
H. Draco _____ The Bull
I. Pegasus _____ The Archer
J. Taurus _____ The Fish
K. Pisces _____ The Hunter
L. Aquarius _____ The Lion
M. Sagittarius _____ The Scales
N. Scorpius _____ The Ram
O. Orion _____ The Great Bear

STAR SIGNS ANSWER KEY

A. Gemini – The Twins

B. Cancer – The Crab

C. Aries – The Ram

D. Libra – The Scales

E. Ursa Major – The Great Bear

F. Capricornus – The Goat

G. Leo – The Lion

H. Draco – The Dragon

I. Pegasus – The Winged Horse

J. Taurus – The Bull

K. Pisces – The Fish

L. Aquarius – The Water Carrier

M. Sagittarius – The Archer

N. Scorpius – The Scorpion

O. Orion – The Hunter

How many star terms can you find hidden in the puzzle below? Words may be written

horizontally, vertically, diagonally, left to right or right to left. Circle each word as you

find it.

Star Terms:

hot, atoms, nebula, supernova, neutron, red giant, cycle, sphere, energy, fusion,

core, galaxy, hydrogen, evolve, gas, cloud, glow, x-ray.

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The Galileoscope In Action

When I first heard about the Galileoscope project which seeks to get a ‘good’ telescope into people’s hands for $20, I was, to say the least, a bit dubious about their claims.  I wasn’t expecting much, but for $20 and an acknowledged addiction to telescopes, I took a chance and ordered one from their website:   https://www.galileoscope.org/gs/

The Galileoscope™: An IYA2009 Cornerstone Project

The Galileoscope™ is a high-quality, low-cost telescope kit developed for the International Year of Astronomy 2009 by a team of leading astronomers, optical engineers, and science educators. No matter where you live, with this easy-to-assemble, 50-mm (2-inch) diameter, 25- to 50-power achromatic refractor, you can see the celestial wonders that Galileo Galilei first glimpsed 400 years ago and that still delight stargazers today. These include lunar craters and mountains, four moons circling Jupiter, the phases of Venus, Saturn’s rings, and countless stars invisible to the unaided eye. The Galileoscope costs just US$20 each plus shipping for 1 to 99 units.

Production and distribution are managed by Galileoscope, LLC, a new company established by the Galileoscope project team with the express purpose of ensuring delivery of the best possible product at the lowest possible price.

Sounds great right?  But we all know that “talk is cheap.?  Well, I am now a believer in this product!  I ordered my Galileoscope in early March and didn’t receive delivery until mid July.   But as I said, I wasn’t expecting much for my $20, and the delay turned out to be caused by the sheer number of orders they had.

Image3The telescope arrived in kit form, and thanks to outstanding online directions, it only took 30 minutes from the box to mounting the completed two inch refractor, with two 1 ¼ inch eyepieces being mounted onto my existing photo tripod!  It went together easily and probably would for ages 8 and up with adult supervision and for ages 12 and up, building it by themselves.  Also, despite the name, the telescope is NOT a model of Galileo’s telescope.  He would have loved to have an instrument of this quality and capability!

You have to supply your own mount for the scope, but the scope has a standard tripod mount thread on it and the instructions describe how to make a poor-man’s cardboard box mount that would work fine.  I mounted mine on an inexpensive photo tripod  I already had.

The two inch, two element objective lens produces well color-corrected imagery of the Moon and Venus, and the eyepieces produce 18X and 25X images when used individually or by combing these into a Barlow arrangement, you can get up to 50X.  I have left it at 25X.  First light for the scope was a daylight terrestrial object, the top of a power pole located 1 mile from my house that I frequently use to sight in telescopes and finder scopes.  I’m glad I did this during the day because I was able to get familiar with the drawtube focusing of the Galileoscope and get focus set close to infinity before I used it later that night.  The daylight images of the mountains we very sharp, but I was trying to not be too anxious in case the night-time views were less spectacular.  The first object I looked at later in the evening was the gibbous Moon.  Wow!  It was tack sharp and I could see all details which I wasn’t expecting to see for a $15 dollar telescope.  I could also see subtle shade differences and crater details that made me smile.  I remembered the views through my very first Tasco two inch refractor with its “75X Zoom? eyepiece that had to cost $50 in the 1960’s.  You probably had similar experiences with fuzzy imagery and chromatic aberration that made looking at the Moon poorly surreal experience.  The Galileoscope is a breath of fresh air.

What can be seen?  After studying the Moon with both eyepieces, I decided I liked the 25X view better, made sure the focus was still sharp before I pointed it at Jupiter, about thirty degrees above the eastern horizon.  The very first thing I noticed about Jupiter were the four sharply focused moons, one just emerging from behind the planet.  I guess I wasn’t expecting to even see the Moons very well, not the two primary and one set of secondary bands on the planet.  But there they were!  I can imagine the inspiration that the Galileoscope will provide youngsters around the world.  I observed the beautiful gold and blue double star Albireo at the head of Cygnus next.  Great color, nice view.  The globular cluster M13 was a nice fuzz ball and I could tell it was a globular and not a comet.  The next morning I got up at 4:30 am to point the scope at the Orion Nebula and was not disappointed.  I resolved everything I expected a two inch telescope to reveal, and the contrast was pretty darn good!  I had to kneel on the ground while looked nearly overhead at the nice view of the Andromeda Galaxy M31, ($20 folks!  This scope is sooo cool!), then I got the entire Pleiades cluster in the field of view.  I saved Venus for last, since it is typically a big problem for inexpensive scopes because Venus appears small, white and very bright.  I immediately noted two things.  I was looking at a gibbous Venus and that I saw an afterimage from internal reflection between the front two elements and a faint afterimage reflection between the two elements of the eyepiece.  The front reflection was a bit distracting, but not overwhelmingly so.

The Moon, major planets, the brighter deep sky objects – all for one twenty dollar bill.  Better yet, buy one for yourself and in the spirit of the International Year of Astronomy 2009, buy a second scope for just $12.50 to donate to someone around the world who otherwise would never get an opportunity to see the sky in such detail.

Observe Pluto This Year!

September, 2009

By Tom Koonce

Antelope Valley Astronomy Club

Lancaster, California

How many planets have you observed?  How many minor planets and dwarf planets?   Even though this month’s IYA theme is “Planets and Moons? our new Dwarf Planet, Pluto, offers an interesting challenge.  Let’s not debate the terms “Planet? or “Dwarf Planet?, but instead ask if you have you ever observed faint Pluto?  It’s a difficult object to see and to verify.

Pluto can be observed through an 8? telescope, but in my opinion it is HARD to do for an intermediate-level observer.  In Greek mythology, Pluto was named after Hades, the God of the underworld, and you’ll think about sending this challenge to the same location, but stick with it because spotting Pluto on your own for the first time is an extremely rewarding experience.

You need exceptionally dark skies, a decent telescope and a lot of patience!  There is an equation to help you work out how far down the magnitude scale you can get with a telescope (Remember big magnitudes = fainter objects):

There is an equation to help you work out how far down the magnitude scale you can get with a telescope (Remember big magnitudes = fainter objects):

Telescope Limiting Magnitude = (Visual Limiting Magnitude) – (5*log d) + (5*log D)

where d is the aperture of the human eye in meters and D is the aperture of the telescope in meters.  So to give some examples, let’s consider a normal sky where the visual limit is around Magnitude 4.5 and using a 3-inch (76 mm) refractor telescope.  We’ll use 6 mm as an example aperture of the dark-adapted human eye (young eyes can get to 7 mm):

Telescope Limiting Magnitude = 4.5 – (5*log(0.006)) + (5*log(0.076)) = 10.0

So with a small refractor you can theoretically see down to a limit of about Magnitude 10.0 under these conditions.  Pluto however is at Magnitude 13.8 so this is well out of the range of such a small telescope.  Under very good skies with a limiting Magnitude of 7.0 and using a telescope of 10 inches (254 mm) aperture, the limiting magnitude becomes.

Telescope Limiting Magnitude = 7.0 – (5*log(0.006)) + (5*log(0.254)) = 15.1

This puts Pluto easily into “realistically observable? status.  Why not set the goal of observing all the planets, and Pluto – just for fun?

Depending upon the type of telescope you have and if you have astrophotography skill, you may choose to image Pluto instead of working on the drawing recommended here.  Either way you’ll have to know where to look.  It’s recommended that you determine (and memorize) the field of view that you will use during your observation.  You can utilize the “12DString FOV Calculator? online here: (http://www.12dstring.me.uk/fov.htm) to help figure out the field of view you will see in the eyepiece.  You can use a Go-To scope or you can star-hop to the location of Pluto.  Either way you must use your telescopes’ clock drive to keep the field around the suspected position of Pluto and carefully draw the field of stars.  It is critical to spend a lot of time making this drawing because you’ll use it over the next two nights to determine which of the faint dots of light is moving and which are static.  Fixed = background stars… moving = Pluto!

You will see something like this in your eyepiece:

Amateur astronomer Chris Peterson, 12-inch telescope, Cloudbait Observatory, Guffey, CO

NOT something like this:

Pluto Image from Bill Dirk

Take the Pluto Observing challenge!  Try to observe all of the planets and at least one dwarf planet within the next twelve months!  Maybe you’ll be able to see or image Charon, Pluto’s moon!