Stars, Milky Way, Cosmology

[Jim Colyer]

Posted: 9/30/12 at 8:07pm

A THOUSAND STARS - KATHY YOUNG and THE INNOCENTS
http://www.youtube.com/watch?v=_Fri2I16x88

Stars
Stars are always there, even in the daytime when they are washed out by the sun. As the earth revolves in its orbit, different parts of the stellar panorama are exposed in the night sky. Constellations become identified with seasons.

Constellations are illusions. They are two dimensional. They existed in the minds of ancient Greeks. Stars are at various distances. They are three dimensional. Some appear bright because they are close. Others appear dim because they are far away.

The most recognizable constellations are Ursa Major (Big Dipper), Orion and Scorpius.

The pointers in the bowl of the Big Dipper point to the North Star. Polaris is overhead at the north pole and maintains its position as the earth spins. It is slightly off. Over 26,000 years, the earth wobbles like a top. This explains precession of the equinoxes and a shift away from Polaris as the North Star.

The Zodiac consists of Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. The sun, moon and planets stay against the background of the Zodiac because of the flatness of the solar system. Everything is in the same plane.

The most elaborate story in the sky is that of Perseus and Andromeda, told by the fall constellations. There are Andromeda's parents, Cepheus and Cassiopeia, and the monster Cetus. Pegasus is the winged horse ridden by Perseus. Perseus holds the head of Medusa, represented by the variable star Algol.

Constellations are tied to Greek and Roman mythology. Stars forming the constellations are in our own star cloud and close to the sun when we think in terms of the whole Milky Way.

The Greeks explained the Milky Way in poetic fashion. Legend had it that Hercules was born from an affair between Zeus and a mortal. When Zeus wanted his wife, Hera, to suckle the baby, she pushed it away and her milk flowed across the sky.

Visible stars range from 1st to 6th magnitude. The brightest are Sirius, Canopus, Alpha Centauri, Arcturus, and Vega. Arabs named the stars. We see 4,000 at any one time. Stars twinkle because of the atmosphere. They are so far away that they appear as points of light even through large telescopes.

Stars are trillions of miles away. Their distances are measured in light-years. A light-year is the distance light travels in a year: 6 1/2 trillion miles. Light is the fastest thing in the universe at 186,000 miles per second. The closest star is Alpha Centauri: 4 light-years, or 25 trillion miles, away.

Double stars are the rule. Mizar, the second star in the handle of the Big Dipper, is a double. So is Albireo at the head of Cygnus. The contrast between its blue and yellow components is striking.

Astronomers like to compare stars to people. Stars are born. They age. They die. Stars are born when gaseous nebulas shrink under their own gravity. Mass determines whether a celestial body will become a star. If there is enough mass, the pressure and temperature at the core will be great enough for nuclear reactions to start.

Stars form in clusters. The Pleiades are condensing from surrounding gas. Likewise, the Orion Nebula is a stellar nursery. Nebulas glow when they reflect starlight. The Horsehead Nebula is dark, outlined by the starlight behind it.

Stars come in colors. Blue-white stars are young and hot. Yellow stars like the sun are in the mid-temperature range. Red giants are old and cool.

Stars die in two ways. Average stars like the sun become red giants. They die peacefully by exhausting their fuel. Antares and Betelgeuse are red giants.

When a star burns all of its hydrogen, it burns helium to form carbon. Elements are made inside stars. Our bodies are made from the remnants of ancient stars.

A dying star giving off a shell of gas is called a "planetary nebula". It is a bad name because it has nothing to do with planets. The Ring Nebula in Lyra is a dying star.

A dying star shrinks to become a white dwarf. A white dwarf is the core of a red giant. They can be brown or red but are still called white dwarfs.

Massive stars die by becoming supernovas and blowing up. A supernova was seen in the Large Magellanic Cloud in 1987. Supernovas become pulsars and may become black holes. Black holes are collapsed stars whose gravity is so great that even light cannot escape.

Milky Way
The Milky Way is our galaxy, and we are inside it. This is not apparent right away as we look at the glimmering arch across the sky. The Greeks saw milk. But the Milky Way consists of 200 billion suns 100,000 light years across and 2,000 light-years thick. If we could stand outside the Milky Way, we would see a disk with a bulge at its center, shaped like a fried egg or a flying saucer. Our solar system revolves two-thirds of the way from the center toward the outer rim. It takes 200 million years to revolve around the galaxy, a period known as a cosmic year. The last time our solar system was in this place, dinosaurs roamed the earth. In the desert in 1979, there was a moment when I felt myself revolving around the galactic center.

Because we are inside the galaxy, trying to figure out its shape is like someone in a house trying to determine the shape of the house. The structure of the Milky Way and the sun's position in it was ascertained by Harlow Shapley in 1917. We understand it when we know what we are looking at. The Milky Way circles the sky. Its bulging center is in the direction of Sagittarius where the star clouds are thick. The thin part of the circle, visible in winter, is in the direction of the outer rim. When we look at right angles to the Milky Way, we look through the top or bottom of the disk. Stars are sparse. As we might expect, more galaxies can be seen through the top or bottom.

Patches of dust and gas like the Coalsack and Cygnus Rift obscure parts of the Milky Way. People once thought these were holes. Because of the dust and gas, we use radio telescopes to study the center of the galaxy. The Milky Way is 10 billion years old.

Cosmology
The universe is 13.7 billion years old. 13.7 billion years ago, all the stuff in the universe was concentrated in a speck of infinite density, a singularity, a mathematical concept. It exploded. This is what we call the Big Bang, the point at which time began.

Primordial energy and matter flew in all directions. They cooled. Gas clouds condensed into galaxies. Galaxies are aggregates of stars, the building blocks of the universe. There are 250 billion galaxies. Some are distinctive. The Whirlpool and Sombrero look like works of art. Galaxies can be categorized according to their structures. The Milky Way is a spiral. M87 is elliptical. The Magellanic Clouds are irregular.

The Milky Way belongs to a Local Group of 35 galaxies. The Andromeda Galaxy M31 is in this group. M31 is a spiral similar to the Milky Way, but larger. It is 2.3 million light-years away and the fartherest visible object.

Charles Messier assigned numbers to fuzzy patches in the sky. He cataloged 110 objects so he would not mistake them for comets. He lumped galaxies and nebulas together. The more detailed New General Catalog (NGC) dates from the 19th century.

Galaxies form in clusters which in turn make up superclusters. The Virgo supercluster is vast. The Local Group is in the Virgo supercluster. The universe is mostly empty.

Proof of the Big Bang was provided by Edwin Powell Hubble. By applying the Doppler Effect to light, Hubble found that light from galaxies showed a red shift. This suggested that galaxies are receding, moving away from each other. This is what we mean by the Expanding Universe. If we run it backwards, there is a point at which all galaxies converge. Furthermore, the farther apart galaxies get, the faster they travel. The question becomes whether expansion will continue forever or whether there is enough gravity in the universe to pull it back together. This would be the Big Crunch and suggests an oscillating universe, one that alternately expands and collapses. Black holes may provide the gravity for a Big Crunch. The universe is not expanding in space. Space is being created as it expands. The balloon analogy is used, blowing up a balloon with dots on it to represent galaxies.

We ask what was before the Big Bang. The answer is nothing. There was no space, no time and no events. It was the beginning in the truest sense.

E. P. Hubble was the greatest astronomer of the 20th century. Shapley thought that external galaxies were inside our own.

Cosmology was the step I was trying to take since I was a teenager. Carl Sagan's Cosmos was a breakthrough. To paraphrase Sagan, "The Cosmos is everything that has been, everything that is and everything that will be." The terms "cosmos" and "universe" are interchangeable.

[Jungle Red]

Posted: 9/30/12 at 8:14pm

I don't understand these threads. I know that this is the "off topic" board, but these are only interesting to Jim.

He shouldn't use a super gay, theatre message board to air these kind of things. Frankly, I don't give a damn.

[Wynbish]

Posted: 9/30/12 at 8:22pm

Jim, don't you have Youtube videos to spew racist, inhuman hatred on?

[Jungle Red]

Posted: 9/30/12 at 8:30pm

I guess he's hated on enough Michael Jackson videos.

[Huss417]

Posted: 9/30/12 at 8:31pm

What the Hell was that all about? I only saw the name so didn't bother reading it.

[Jungle Red]

Posted: 9/30/12 at 8:42pm

It shows that it's locked on my screen but I can still read and respond.