• In just one second the Sun emits more energy than humans have used in the last 10,000 years. •The Sun has been shining relatively steadily for 4.6 billion years. Until the early 20th century, humans did not know of any process that could explain the energy production of the Sun. •Even if a fire, such as those that occur on Earth, were as large as the Sun, the fire would consume the mass of the Sun in a few thousand years.

Scale of the Sun's Energy

The Sun's Energy• The Sun produces an amazing amount of light and heat through nuclear reactions.•The process that produces the Sun's energy is called nuclear fusion. •In nuclear fusion, two atoms come together to produce a heavier atom. •Fusion reactions release energy and tiny elementary particles.

• The Sun is a massive amount of hydrogen, the lightest and most abundant element in the universe.

• All matter inside the Sun is gravitationally attracted to all the other matter in the Sun.

•This inward pull creates high pressures and temperatures inside the Sun.

• The center is so violent and hot that collisions between atoms break the hydrogen atoms apart into their subatomic ingredients.

How does fusion happen?

Observing X-rays from the sun.

•A hydrogen atom is made up of a proton, and a electron that orbits the proton.

•In the Sun, collisions separate Hydrogen’s electron from the proton, freeing each to move about the solar interior.

•A gas in which particles are ionized, or have electric charges, is called plasma (the fourth state of matter).

• The separation of hydrogen nuclei from their electrons makes nuclear fusion possible at the Sun's core, producing the Sun's light and heat.

Hydrogen particles in Helium out (mostly)

Nuclear Fusion in the Core•With their electrons gone, hydrogen nuclei (protons) can be packed much more tightly than complete atoms.

•At great depths inside the Sun, the pressure of overlying material is enormous, the protons are squeezed tightly together, and the material is very hot and densely concentrated. •At the core, the temperature is 15,600,000oC and the density is morethan 13 times that of solid lead.

•This is hot and dense enough to achieve FUSION!

The nuclear fusion reaction that powers the Sun involves four protons that fuse together to make one nucleus of helium. Two of the original protons become neutrons. The result is a helium nucleus, containing two protons and two neutrons. The helium nucleus has less mass, by 0.7 %, than the four protons that combine to make it. The fusion reaction turns the missing mass into energy, and this energy powers the Sun.The relationship between energy and the missing matter was explained in 1905 by a German-born American physicist Albert Einstein.

E = mc2

.Energy equals mass times speed of light squared

The rate of nuclear reactions in the Sun is relatively low, because protons repel each other. Only a tiny fraction of the protons inside the Sun are moving fast enough to overpower this repulsive electrical force.

The nuclei that are moving fast enough can get very close together, and strong nuclear force, very powerful, but only over very short distances. takes over, pulls the nuclei together and holds them together.

In this way, nuclear reactions proceed at a relatively slow pace inside the Sun. If the pace were much quicker, the Sun would explode like a giant hydrogen bomb.

Spectroheliograph image of the sun, taken aboard Skylab in 1973, using the extreme ultraviolet radiation from ionized helium, 304 Angstrom wavelength.

http://library.thinkquest.org/C001124/gather/ssun.html

star mass (sol m.) time (years) Spectral type60 3 million O330 11 million O710 32 million B43 370 million A51.5 3 billion F5

1 10 billion G2 (Sun)0.1 1000's billions M7

http://www.astronomynotes.com/evolutn/s2.htm

The stages a star will go through and how long it will last in each stage depends mainly on the mass

Color-enhanced Clementine satellite image of the sunrise and Venus over the moon.

What is the Sun made of?

Spectroscopy shows that hydrogen

makes up about 94% of the solar

material, helium makes up about

6% of the Sun, and all the other

elements make up just 0.13% (with oxygen, carbon, and nitrogen the three most abundant ``metals''---they make up 0.11%).

In astronomy, any atom heavier than helium is called a ``metal'' atom. The Sun also has traces of neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, potassium, and iron. The percentages quoted here are by the relative number of atoms. If you use the percentage by mass, you find that hydrogen makes up 78.5% of the Sun's mass, helium 19.7%, oxygen 0.86%, carbon 0.4%, iron 0.14%, and the other elements are 0.54%.

For example, Helium was first discovered in the spectrum of the Sun (the name helium derives from helios, which is the Greek name for the Sun).

The spectral lines observed in the Solar emission spectrum could not be associated with any known element and must belong to a new element.

Helium was then discovered on the Earth (helium occurs in certain very deep gas wells on the Earth) and a new element was confirmed.

Helium spectrumHelium spectrum

How do we know? Spectroscopy!

Hydrogen Emission Spectrum

chemed.chem.purdue.edu/.../bp/ch6/bohr.html

When an electric current is passed through a glass tube that contains hydrogen gas at low pressure the tube gives off blue light.

When this light is passed through a prism, four narrow bands of bright light are observed against a black background.

So who figured this out? •Not Dalton: His model of the atom assumed the atom to be an indestructible mass, explaining most chemical reactions. • The idea of indivisible atoms was shattered by Thomson and Rutherford.•Those guys who figured out there weresubatomic particles namely the electrons and protons and a nucleus.• Further Rutherford created an atomic modelof a positively charged nucleus surroundedby electrons that explained some properties of atoms, but not emission spectra. •Yet neither Rutherford nor Thomson’s models could explain why the electrons of elements and compounds emit specific wavelengths of light, rather than a complete spectrum.

JJ and Ernie talking about old times

For most of the 19th century, spectroscopists puzzled over these lines for a wide variety of substances, with little to show for it.Then a very perceptive Dane came on the scene. Modern atomic theory begins with Niels Bohr (1885-1962). And his explanation for spectra.

Dr. Bohr, young and old

1. An energy level is the region around the nucleus where an electron is likely to be moving.

2. According to Bohr, electrons cannot exist between the energy levels – they have to jump from one level to another. To do this, they must gain or lose a specific amount, or quantum of energy. (losing emits light!)

• The term “quantum leap” comes from this idea.

Hydrogen atom and emission spectrum

http://outreach.atnf.csiro.au/education/senior/astrophysics/images/spectra/bohrhydrogen.gif

Spectroscopy

Emission Spectroscopy

Wavelengths and intensity an excited sample emits

Absorption spectroscopy

Wavelengths and intensity of light passing through a sample showing what the sample absorbs

Sample A

Sample B

http://library.thinkquest.org/19662/images/eng/pages/model-bohr-3.jpg

http://www.astrocappella.com/background/doppler_background.shtml

• MH is that of the most common variety of metal halide lamp, which is basically a mercury vapor lamp enhanced with iodides of sodium and scandium.

• High Pressure mercury vapor, typical of a mercury vapor lamp. Low pressure mercury vapor has a similar spectrum except the green line is slightly dimmer and the yellow lines are significantly dimmer.

• Next one after that is a mercury lamp with the common Deluxe White phosphor.CFL is compact fluorescent lamp of the 2700K color.