ASTR-1010ASTR-1010Planetary AstronomyPlanetary Astronomy

Day - 16

AnnouncementsAnnouncements

Homework Chapter 3: Due Wednesday Feb. 24

Smartworks Chapters 4 & 5 are also posted

Exam 2 will cover chapters 3, 4, & 5

Ranking Task (Gravity) due now.

1st quarter observing night: Wednesday!!

Photograph of a Star ClusterPhotograph of a Star Cluster

Spectra of a Star ClusterSpectra of a Star Cluster

ClassAction StuffClassAction Stuff

• Hydrogen atom simulator

• Splash page warm up

But, what is light?But, what is light?• Newton, Remember Newton? He did more than

just calculus and mechanics.

• In the 17th Century, Isaac Newton argued that light was composed of little particles while Christian Huygens suggested that light travels in the form of waves.

• In the 19th and 20th Century Maxwell, Young, Einstein and others were able to show that Light behaves both like a particle and a wave depending on how you observe it.

Thomas Young’s interference experiment

Scottish physicist James Clerk Maxwell Scottish physicist James Clerk Maxwell

showed mathematically in the 1860s that light showed mathematically in the 1860s that light

must be a combination of electric and magnetic must be a combination of electric and magnetic

fields.fields.

In 1905 Einstein calculated the energy of In 1905 Einstein calculated the energy of

a particle of light a particle of light ((photon)photon) and and

proposed the photoelectric effect. proposed the photoelectric effect.

EEphotonphoton = hc/ = hc/

e-photon

But, where does light actually But, where does light actually come from?come from?

Light comes from the Light comes from the acceleration of charged acceleration of charged

particles (such as particles (such as electrons and protons)electrons and protons)

electron

Accelerating charges produce light – electromagnetic radiation!

But, where does light actually come from?

The Electro-Magnetic (EM) Spectrum

• The EM spectrum covers the entire range of wavelengths.

• All waves travel at one speed (c, the speed of light).

Tutorial:Tutorial:– p.45 – p.45 EM Spectrum of Light EM Spectrum of Light

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one

another. Take time to understand it now!!!!

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask

another group.

• Work with a partner!

• 5 minutes

An atom consists of a small, dense

nucleus (containing protons and neutrons)

surrounded by electrons

- Model Proposed by Niels Bohr 1913

A nucleus is about 10-15

m in size and the first electron orbits out at

10-10 m from the center of the atom – The size of the electron orbit is 100,000 times greater

than the size of the nucleus

Atoms are mostly empty space

So if a nucleus the size of an orange (10 cm) was located at the center of the football

field, where would the electron be?End Zone?

Grandstands?On Campus?In Clarksville?

If the electron’s orbit is 100,000 times bigger than the nucleus then the electron would be

10,000 m or 6.21 miles away from the center of

the Football Field!

Still in Clarksville, but near exit 11.

The electron should be thought of as a

distribution or cloud of probability around the

nucleus that on-average behave like a

point particle on a fixed circular path

Nucleus

Photons (light-waves) are emitted from an atom when an electron moves from a higher energy level to a lower energy level

Nucleus

Photons (light-waves) can also be absorbed by an atom when an electron moves from a lower energy level to a higher energy level

Nucleus

ClassAction StuffClassAction Stuff

• Hydrogen atom simulator

Tutorial:Tutorial:– p.63– p.63Light & AtomsLight & Atoms

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one

another. Take time to understand it now!!!!

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask

another group.

• Work with a partner!

• 15 minutes