Introduction To Stars

You are looking at the star Promixa Centauri. "What?" you might ask ... "which one is Proxima Centauri?" Proxima Centauri is the star in the very center of this image ... the reddish star with the nice point starlike projections from the length of the photograph time. This nondescript star is our closest neighbor star, and a mere 4.3 light years distance. But, as you can see, this little star is hardly alone. Proxima Centauri is just one of an estimated 200 billion stars that make up our galaxy, the Milky Way. Notice too that the stars in this image are not all white dots, but colored from blue, yellow, orange, red, and white. Some stars are very dim, and others bright, as evidenced by the size of their images. It is the purpose of this unit to introduce to you stars and their interesting lives.

First, there are two pictures above these words. Both are photographs taken by David Malin (David Malin Images) and are copyrighted and cannot be reproduced by you without permission. He pointed his telescope at the constellation Sagittarius, opened the shutter of his camera, and allowed the light from the stars to reach his camera film. To the left is a general region about M17, and to the right is a close-up of that same area. The number of stars is absolutely incredible.

Below is an image of the Omega Centauri Globular Cluster. This is a collection of stars that is orbiting our galaxy in the same way that a planet orbits our Sun. Click on the image to see what the Hubble Space Telescope sees when it looks into the interior of this dense cluster of stars.


If not, then check out this image below. These are the three stars in the belt of constellation Orion. Notice the small figure of a horsehead below the far left major star in the belt. This is the famous "Horsehead Nebula."

One of the most obvious features people see in Orion is the three stars that make up what most people consider the belt of the giant. Mintaka , the westernmost (far left) star in the belt, comes from the Arabic word for belt. Alnilam, the center star in the belt, means "a belt of pearls". And Alnitak, the eastern-most star (far right), means the girdle. All three are at the same distance from us and, with Rigel, Saiph, and Meissa (other stars in the constellation Orion ), probably formed at about the same time some ten million years ago from the molecular clouds astronomers have found in Orion.

Name Alnitak - Super Giant Distance 1500 light years Brightness 35,000 times greater than the Sun Surface Temperature 60,000 F
Color White-blue Mass 20 times the mass of the Sun

Name Alnilam - Super Giant Distance 1500 light years Brightness 40,000 times greater than the Sun Surface Temperature 50,000 F
Color White-blue Mass 20 times the mass of the Sun

Name Mintaka - Super Giant Distance 1500 light years Brightness 20,000 times greater than the Sun Surface Temperature 60,000 F
Color White-blue Mass 20 times the mass of the Sun

To me, there are few things I have enjoyed as much as my trips to Hawaii. If I were asked to rank my top experiences in my life (and since this is my course, I can do anything I want, so I choose to rank those things here right now), I would list: 1) Standing at the edge of a lake of lava near the base of Pu u'O o' and watching molten lava churn and bubble from a nearby distance of only 1 foot; 2) Watching lava pour into the ocean at night, once again standing right next to the flows; 3) Walking on a knife-edge glacier in Alaska while wearing crampons, roped to be friend, and using an ice ax. To be sure, my wedding to my wife and the birth of my daughters far outweigh these experiences, but those are family experiences, so they fit into a category separate from the nature ones. So, the top two things were done while visiting Hawaii with my Uncle. After those heady volcano trips, I would return to his home in Pahala and look at the stars through his telescope. It was so dark there, and I could see so much detail that the city lights obliterate here in Minnesota. It is a shame that we have to light up our streets, but public safety is a real issue, so I understand it. However, the entire island of Hawaii uses sodium vapor lamps for street lighting, and all are pointed at the ground with shielding to prevent any excess light from scattering up into the air. This certainly helps the Mauna Kea observatories, but it also makes it possible to see the beauty of the night sky from a backyard over there.

During my most recent trip to the Big Island in the summer of 2002, I participated in the Spring Meeting of the AAVSO (American Association of Variable Star Observers) and these spent a few more days at the HEA (High Energy Astrophysics) Symposium. While this is a fantastically impressive conference to tell others that I was present at, I admit that I was quite unprepared for the depth of the presentations and my own shortcomings as an Astronomy teacher soon became very obvious to me. During that six day conference, I began to synthesize into a more complete picture just what a study of stars is all about. I am now attempting to write a new curriculum based on what I learned at those meetings, as well as from information found in a wonderful resource "Extreme Stars," written by James Kaler and published by Cambridge University Press in 2001. He has developed a wonderful internet resource for stars that I would encourage you to look at, as well as its terrific connecting links.

This Unit on Stars will be a work in repeated progress. I suppose that I will never be content with the content (nice play on words, eh?) of this unit, and I will be very interested in your opinions, but I am going to make the best effort I can to teach a little about stars from a perspective of normal and abnormal ... from the average to the extreme. Our Sun is considered the average and serves as the baseline to which we compare everything else. You should have completed the Sun Unit before you try your hand at this one, for from this point on, we look at stars that are unlike ours.

The Star Unit is divided into:

The place to start The Big Picture - this is a general overview

Measuring the Distance to Stars - something that we will look at later.

Spectral Classes of Stars - a general review of the different kinds of stars based on their spectra.

Star Lifecycles - a general look at the lifecycles of stars

Main Sequence Dwarf Stars like our Sun

The Faintest and Coolest Stars - Red Dwarfs, Brown Dwarfs & Red Giants

Hot Stars - White Dwarfs

The Brightest Stars

The Largest Stars - Supergiants

The Smallest Stars -

Supernova 1987A Lab

Do not forget, there is a Star Quiz at the end of this Unit.

Each section was designed to be relatively short and introductory in nature. I struggled to grasp the complexity of what I was trying to present. However, the more time I spent in research, the more interesting stars became, and the more in depth if dug myself into an attempt to better understand their natures. I now have material in here that might rival a solid college level Astronomy course. My hope is to convey to you some of the real wonder of what is out there. If ever you want to see some of the complexity, click on Electronic Sky to see some star names, classifications, and other interesting stuff.

Please move forward first to the Big Picture, and then to Spectral Classes , or to the Syllabus.

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