WHERE: AT EXPLORIT Science Center, 3141 5th Street, Davis.

Life Cycles of Stars!
Saturday, June 10, 2006
7:30 to 9:30 p.m. at Explorit
Hosts: Vinita & Calvin Domier (530) 756-0191, vcdomier@yahoo.com

Join us Saturday evening, June 10, at 7:30 p.m., when we will discuss the life cycles of stars. We will also look at the planets, stars, and other deep sky objects in the night sky, weather permitting.

Life cycles of stars are predetermined by the size of the stars. All stars are created the same way, and live their infancy, young, and middle age lives in similar ways. Stars of different masses die in different ways. Stars' life spans also depend on their masses, with more massive stars having much shorter lives than less massive stars.

Stars evolve in nebulae, which are giant clouds of gas and dust in space. These clouds are created when older stars shed some of their outer layers or when dying stars explode. Thus, star graveyards are eventually future stellar nurseries!

The size of a star created in a nebula depends on the amount of matter available in it. Gravity pulls the hydrogen gas in the nebula into a clump, which begins to spin. As more and more gas is pulled together, this protostar spins faster and heats up.
Eventually the core of this protostar heats up to 15_106 ∞C and nuclear fusion starts. The giant gas ball is now a star as it shines by its own light created by the process of hydrogen gas fusing into helium gas. The energy emitted is E=mc2, where m is the mass of gasses lost in the fusion process and c is speed of light (c=3_108km/s). The color of the star depends on how hot it is, with blue stars hottest and red stars coolest. Our Sun is relatively cool yellow star.

In the main sequence of its life, the star continues to convert all the hydrogen in the core to helium. When it runs out of fuel, the star's helium core becomes unstable and contracts, but the outer shell of hydrogen expands and cools. The star is now a red giant as it glows red because it is cool and huge because of its expansion. When our Sun becomes a red giant, it will engulf Mercury, Venus and Earth.

In less massive red giant stars, the helium in the core fuses to carbon and the outer hydrogen shell blows away in a planetary nebula. When all the core's helium is used up, nuclear fusion stops and the star collapses inward. It becomes a white dwarf star and then eventually a black dwarf star.

In more massive red giant stars, the helium in the core fuses to carbon, then oxygen, nitrogen and finally to iron. When the core becomes essentially all iron, nuclear fusion stops and energy is released in a cataclysmic super-bright and super-hot (1_109 ∞C) supernova explosion. All elements heavier than iron are synthesized in supernovae explosions and scattered in the universe along with elements from hydrogen to iron. We are truly made up of stardust!

Supernova remnant (the star core left after the supernova) 1.4 - 3 times more massive than our Sun becomes a neutron star that spins rapidly and emits radio waves. Pulsar is a special neutron star that emits radio waves in rapid pulses. A remnant more than 3 times the mass of our Sun collapses into itself, becoming a black hole from which not even light can escape. Black holes are detected only by twin jets of X-rays emanating from matter and energy pulled in.

Planets visible in the sky:
Venus (mag. -3.9, in Aries) is a dazzling bright planet in the eastern sky before sunrise, rising ~ 4am and setting ~5pm. Mars (mag. +1.7, in Cancer) is still visible in the evening sky, but is not very bright. It rises ~ 9am and sets before midnight. Jupiter (mag. -2.3 in Libra) is a very bright planet in the evening sky rising ~ 6pm and setting ~ 4am. It is high in the sky after sunset, and is ideal for nighttime viewing. Saturn (mag. +0.4 in Cancer) is a bright planet in the western sky after sunset, rising ~10am and setting around midnight.

Summer Solstice is on June 21, 2006.
Moon phases: First Quarter: 6/3 & 7/3, Full Moon: 6/11 & 7/10, Last Quarter: 6/18 & 7/17, and New Moon: 6/25 & 7/24.

To Receive These Bulletins via E-mail Contact Explorit at: Explorit Science Center

The Astronomy Club is for everyone - adults, children, knowledgeable or ignorant. Come to listen, look and learn, or to share your expertise or experience.