Can you guess why I am showing you this picture?

Longer wavelengths (left side) have less energy Longer wavelengths (left side) have less energy. Think of these waves a strings that are being shaken. Rapidly shaken (high energy) strings look like the ones on the right.

The Electromagnetic Spectrum Visible light is just a small segment of the continuum. The “red end” of the spectrum has longer wavelengths. The “blue end” has shorter wavelengths. Shorter wavelengths have higher energy, so we know that a red star is cooler and a blue star is hotter.

Why there are no green stars…

Infrared Radiation Mostly visible light

Stars emit many different wavelengths of “light.” Light refracts (turns) when it passes through materials of different density (such as a glass prsim. Different wavelengths refract different amounts, so a prism can separate light into a color spectrum. Correct Refraction Incorrect Refraction,but it shows light from a star.

A spectroscope separates radiation into its component wavelengths in an organized way that can be easily analyzed.

When elements are in gas state, they absorb or emit specific wavelengths of radiation. The wavelengths of radiation an element emit or absorb depend on their electron configurations. Those wavelengths can be used as a “fingerprint” to identify elements in distant stars.

When gases absorb light, their electrons orbit faster, causing them to jump out to more distant energy levels (orbiting farther from the nucleus). When electrons release energy (by giving off light), they slow down. This causes them to fall inward to an orbit closer to the nucleus.

“Fingerprints” of different elements Are these absorption spectra or emission spectra? Emission

Neon Absorption Spectra Example The black lines are wavelengths of radiation that are absorbed by Neon. If we see these black lines when we analyze starlight with a spectroscope, we know that neon is in the star. Neon Absorption Spectra

In the sun, nuclei fuse. When they do this, the products of fusion have less mass than the nuclei that fused. This “lost” mass is actually converted to energy, according to Einstein’s famous equation… E = Energy produced by nuclear fusion C = Speed of light M = Mass that’s “lost” when nuclei fuse.

Most stars are “Main Sequence” stars Most stars are “Main Sequence” stars. These stars are powered by hydrogen fusion proceeding at a steady pace. Luminosity vs. Surface Temperature Luminosity = energy radiated each second

In an average star, like our sun, most of its energy comes from the fusion of Hydrogen. Hydrogen produces helium when it fuses. This helium is heavier, so it sinks to the sun’s core and pushes the hydrogen outward. As our sun ages, this outward movement of fusing Hydrogen will cause the sun to expand. This outward movement also causes the rate of hydrogen fusion to diminish (due to lower pressure away from the core), thus cooling the sun. Cooling will turn it red.

Sun is running out of fusable Hydrogen. Switching to Helium fusion. At some point, fusion will no longer occur in the sun’s core. The sun will cool, and that cooling will cause it to shrink. This shrinkage will create compression, which will, in turn, cause the sun to heat back up (and turn from a cooler red to a hotter white). This stage is called a white dwarf. Sun is running out of fusable Hydrogen. Switching to Helium fusion. With no fuel remaining, the star will eventually radiate its heat into space and turn to a cold, dark “black dwarf.” This stage is called a “planetary nebula.” The super hot core creates a “solar wind” that blasts away and “lights up” the outer layer of gases.

In a massive star, there is enough pressure to cause more fusion. Simply put, the elements in the inner layers come from fusion of the elements in the outer layers. It all starts with hydrogen fusion… The fusion process continues until iron is created. Even in a massive star there is not enough pressure for iron nuclei to fuse.

Life Cycle of a massive star (25 times the size of the sun) When a massive star runs out of fuel, it collapses. The collapsing outer material speeds toward the star’s center at an extremely high velocity. This outer material then slams into the core and “bounces” back outward. This bounce is an explosion called a supernova.

Our solar system formed from a nebula like this one, but smaller. Life Cycle of a massive star (25 times the size of the sun) A supernova produces such high pressures that elements even heavier than iron are formed by fusion. Many of these elements are scattered into space and “recycled.” They form new nebulas that create new stars. Scientists believe that all of the earth’s heavy elements were created in a massive star that exploded long ago. Our solar system formed from a nebula like this one, but smaller. Scientists believe the heavy elements in our solar system came from a supernova.

Life Cycle of a massive star (25 times the size of the sun) The outer portions of the star are blasted outward and scattered through space. If the material remaining in the core is greater than 3 solar masses, its gravitational force is strong enough to cause the collapse of neutrons. The mass compresses itself into an infinitely small point whose gravity is so intense that not even light can escape from it. Ultimate Fate of A Massive Star The core becomes so compressed that protons (+) and electrons (-) fuse to create neutrons… If the material remaining in the core is between 1.4 and 3 solar masses, a very dense “neutron star” is created.

Less than 1.4 times the mass of our Sun More than 1.4 times the mass of our Sun Recycling into new nebula

Star life cycles

In Main Sequence stars, the energy is being produced by fusion of hydrogen into helium About 90% of all stars are main sequence stars.

The “Singularity” The “Event Horizon”

The Big Bang Theory suggests that the universe exploded outward from an infinitely small point, called the “cosmic singularity” – and that the universe has been expanding ever since. As the universe expands, that radiation (emitted by the early 2000 degree universe) stretches with the universe, so its wavelength lengthens and energy decreases. Today, the wavelength of that radiation is so long that it corresponds to matter at about 2.76 degrees Kelvin (degrees above absolute zero). This is the most distant light that we can see. As space has expanded, this radiation has stretched along with space. Universe is now transparent to light, so suddenly, light can travel. Temperature of matter filling the universe about 3,000 degrees Kelvin. Universe is a plasma, which is opaque to light. Hydrogen and Helium Formed

Radiation emitted just after the big bang has stretched along with the expanding universe. 13.7 billion years ago, the background radiation was consistent with radiation from a 3000 K degree body. Today, the background radiation has a longer wavelength, consistent with radiation from a 2.76 K degree body.

Evidence supporting the Big Bang Theory: 1) Cosmic Microwave Background Radiation: Space is filled with low-energy microwave radiation of same temperature that scientists predicted would be left over from the Big Bang.

More Big Bang Evidence: The Doppler Effect Waves emitted by a moving object are compressed in front of the object and stretched out behind the object. When a star moves toward us, we see shortened wavelengths. This is called a “blue shift,” because the blue end of the light spectrum has shorter wavelengths. 2) All distant galaxies, and most nearby galaxies, have red-shifts (stretched waves), indicating that they are moving away from us, and that, therefore, the universe is expanding.

Hubble’s Law The farther away a galaxy is, the faster it is moving away from us. We can tell this by applying knowledge of the Doppler effect. The more distant the galaxy, the more extreme its red shift. This is consistent with an expanding universe.

Is this diagram showing an emission spectrum or an absorption spectrum? Absorption – the dark aras show the wavelengths of light that are being absorbed by the star.

http://periodictable. com/Properties/A/UniverseAbundance. ssp. log http://periodictable.com/Properties/A/UniverseAbundance.ssp.log.html

Balloon Model of The Universe’s Expansion (coins = galaxies; balloon surface = universe; the outside and inside of the balloon are not part of the universe) The universe is inflating like the surface of a balloon. Galaxies (pennies in diagram) are not moving through space, the space between them is expanding. Every galaxy is moving away from every other galaxy, and more distant galaxies are separating faster. The space within galaxies is not expanding, because gravity is holding it together.