<< TO DO >>: Notes in ROUGH DRAFT ...

The information in these notes should not duplicate what is found under the specific objects observed during this program ... rather, these notes should supplement the objects' information with regards to the topic of this program... and provide hyperlinks to the object pages that will be used during this program:

These notes are still in DRAFT... edited/reviewed to "TO BE COMPLETED..." below...

Life Story of A Star

During this program we will look at objects that represent stars at different stages of their lives. We will begin each program by taking a look at Saturn which has the same composition as a star but is not massive enough to actually become one. A contrast double star will be the next object as we discuss the relationship between the color, temperature, and mass of stars. We will look at a cloud of interstellar gas and dust from which stars are being born known as a diffuse nebula. We will also observe an open star cluster to see what a diffuse nebula looks like after most of the gas and dust has been made into stars. And we will also look at the remains of a star similar to our Sun called a planetary nebula, to give our visitors a look at what happens at the end of a Sun-like star’s life.

Suggested Observing List

Life Story of a Star Program Information

Planet

  1. Saturn will appear as a yellowish ball with a ring around it. The dark line visible within the rings is called Cassini’s division. It is about 3,000 miles wide and separates two of the major rings as seen from Earth. Up to four of Saturn’s moons can usually be seen with the telescope.

  2. Saturn is a large ball of hydrogen and helium gas, the same material that our sun is made of, with a solid rocky core two to three times the size of Earth. If Saturn had gathered 300 times more of this material, it might have become a star.

  3. Saturn is the second largest planet in the solar system, the fifth planet from the Sun and the farthest planet known to ancient stargazers before telescopes were invented.

Diffuse Nebula

  1. Diffuse nebulae are huge clouds of hydrogen and helium gas. Over the course of a few hundred thousand to a few million years the cloud will break up into a few hundred smaller clouds each of which will eventually become a star system.

  2. A diffuse nebula contains very little matter compared to the amount of space it takes up. It is a better vacuum than any vacuum we can make on Earth. An Earth-sized piece of a nebula contains the same amount of matter as a thimble full of Earth's atmosphere. If you blow up a balloon one foot across, it contains as much air (matter) as a diffuse nebula contain in a box 500,000 miles on each side.

  3. The next object we will observe (an open cluster) will show what this diffuse nebula will look like in a few hundred million years.

  4. The Hubble Space Telescope, with its amazing resolution has captured pictures of newly forming stars within the churning expanses of gas and dust in many nearby diffuse nebulae. These images suggest that the gas and dust disks of newly formed star systems form disks of debris and planets between 2 and 8 million years after the new stars are born.

  5. This helps confirm that other planetary systems form in ways similar to how we believe our solar system formed 4.5 billion years ago.

  6. The clouds of gas in this nebula glow because they are heated and irradiated by the newly forming, young stars hidden deep within the interstellar gas and dust of the nebula.

Open Star Cluster

  1. Through the telescope the open cluster will appear as a large group of individual stars; much like sugar or salt sprinkled on a black tablecloth.

  2. The diffuse nebula we looked at before will look like this open cluster 250 million years from now. Or to put it another way, 250 million years ago the area of space we are now looking at would have been occupied by a diffuse nebula instead of this open cluster of stars.

  3. The stars you see here were all formed out of the same cloud of gas and dust. You might say that these stars are members of the same family.

  4. Because they are only loosely bound by their mutual gravity, the stars in open clusters eventually drift apart and after a billion years or so are no longer recognizable as a star cluster.

  5. Open clusters lie in the plane of the galaxy containing between a few hundred to a few thousand stars. The typical separation between the stars in an open cluster is 2-3 light years. The stars in our solar neighborhood are 4-5 light years apart.

  6. Our star, the Sun, spent the first 2 to 3 billion years of its life as part of an open cluster of stars similar to this one.

  7. Star clusters are important to astronomers because they can be used to test theories of stellar evolution. Astronomers are able to do this because all the stars in the cluster can be assumed to have formed at about the same time and out of the same material.

    Theories of stellar evolution are based on computer models that are based on what we know about stars and the laws of physics. One of the things these models tell us is that stars of different masses evolve differently.

    To test their theories, astronomers model the stars that would be found in an open cluster and then compare the appearance of their model cluster with observations of real clusters. If there are significant differences, the astronomers change their model until it matches the observed real cluster.

  8. M11, also known as the Wild Duck Cluster, is one of the richest and most compact of the known open clusters. It contains about 2,900 stars with the average separation of the stars being about 1 light year. The age of this open cluster is estimated to be about 220 million years old so it is considered relatively young.

  9. All of the bright stars in this cluster are very luminous giants with the total brightness of the cluster being about 10,000 times the brightness of the sun.

TO BE COMPLETED...

Contrast Optical Double Star

! An optical double star is two (or more) stars that appear to be close to each other in space however one is much farther away than the other, they just lie in the same line-of-sight. They do NOT actually orbit each other like a binary star. ! Like Beta Cygni, some optical double star systems are special because their stars are different colors and these different colors can tell us a lot about the stars. ! The colors of the stars indicate their temperatures. Which star is hotter, the blue or yellow? (blue). Which star looks brighter through the telescope? In the case of Beta Cygni, the yellow star’s surface is about 6,500 ºF, much cooler than the blue star which is about 21,000 ºF. ! Why is the cooler star brighter than the hotter star? It could be because it’s bigger or because its closer. ! As it turns out, the yellow star is bigger than the blue one, so although it emits less energy per square foot, than the blue star, it has a lot more square feet. Thus the total amount of energy emitted by the yellow star is greater. ! Since the yellow star is bigger than the blue star but it’s also cooler, this tells us that the yellow star is beginning to run out of fuel to fuse in its core. It’s becoming a red giant and is in the final phases of stellar life The blue star is still middle-aged or still on the main sequence. ! We know that the more mass a star has the faster it ages. Since the yellow star has started running out of fuel and is becoming a red giant, it must, therefore, have more mass than the blue star. ! This star is also known as Albireo. It is one of the best known contrast optical double stars. ! The yellow star is actually a multiple star system; the star that we see along with an unseen companion orbit each other. CONTRAST OPTICAL DOUBLE STAR BACKGROUND INFORMATION: BETA CYGNI BACKGROUND INFORMATION FOR EXPLAINERS: 104 LIFE STORY OF A STAR - PROGRAM INFORMATION: RING NEBULA (M57) PLANETARY NEBULA Right Ascension: 18h 53m 36s Best Seen: 6/15-11/15 Declination: 33º 02' 00" Magnitude: 8.8 Computer File: m57 Constellation: Lyra Actual Compared to Sun Distance 2,300 l.y. -- Diameter ~ 1 l.y. -- Actual Brightness of central star -- 3 Magnitude of central star 14.4 -- Spectral type of central star -- -- Surface Temperature of star ~ 180,000 ºF ~ 18 Age -- -- Density (gram/cubic cm) -- -- Recommended eyepiece: 26 mm or 40mm. ! M57 looks like a faint whitish, hazy smoke ring when seen through the telescope. ! As stars the size of our sun begin to die, they expand to become red giants. At the end of the red giant phase, they will gently puff off their outer layers. These outer layers of gas form the planetary nebula we see. ! The planetary nebula gas is moving away from the remaining stellar core called a white dwarf, at speeds of 12 to 20 miles per second (20 to 30 km/sec). After 50-100 thousand years, the shell of gas will have moved far enough from the white dwarf so that it no longer shines. The remaining white dwarf core is 1.2 times the mass of our Sun. 105 ! Only about 10% of the original star’s mass gets puffed off. The rest gets compressed by gravity until it is about the size of Earth and the resulting star is called a white dwarf. White dwarfs are no longer generating internal fusion energy so they eventually cool off and become dark. ! White dwarfs contain as much matter as the sun but are Earth-sized. One teaspoon of white dwarf star stuff brought back to Earth would weigh as much as a couple dozen elephants. ! Stars with masses greater than about four times our sun's mass will not form a planetary nebula and white dwarf. Instead they will end their stellar life cycle in a spectacular explosion called a supernova. ! Our sun will begin this process in about 4 - 5 billion years when it will expand to become a red giant. It will cause the Earth’s atmosphere and oceans to evaporated into space and there is a chance that the entire Earth will itself evaporate. What remains of the sun will then become a white dwarf. ! There are between 20 to 50 thousand planetary nebulae in our galaxy. ! Discovered in 1779, the Ring Nebula was the second planetary nebula ever discovered after the Dumbell Nebula. ! We are looking at the Ring Nebula from its end, like looking through a barrel. If we were to view it from a different angle, say from the “side,” it would probably appear to be shaped more like an hour glass. PLANETARY NEBULA BACKGROUND INFORMATION FOR EXPLAINERS: M57 BACKGROUND INFORMATION FOR EXPLAINERS: