Starlight What is it? What does it tell us? Write down all notes in RED.

Not all of these light sources emit the same kind of light Incandescent Bulb Fluorescent light The Sun! Halogen bulb

Each part of the Electromagnetic Spectrum (abbreviate EMS) provides us with different information. Draw the wavelength below and label. Electromagnetic Spectrum

Astronomers classify light waves by their energies (wavelengths). LONG wavelengths LOW energies SHORT wavelengths HIGH energies

Electromagnetic Waves

If you pass white light through a prism, it separates into different colors. ROYGBIVROYGBIV spectrum

What can we learn by analyzing starlight? A star’s temperature Its composition

An atom consists of a small, dense nucleus (containing protons and neutrons) surrounded by electrons. - Model Proposed by Niels Bohr 1913 Atoms are mostly empty space.

If the total atom was the size of a football field, then the nucleus would be the size of a marble in the middle of the field.

Nucleus Moving outward from the nucleus, electrons exist at different energy levels. n = energy level

When the electron drops to a lower energy level, it releases (emits) a photon (light-waves). Nucleus Draw this picture and label.

Photons (light-waves) can also be absorbed by an atom when an electron jumps to a higher energy level. Nucleus Draw this picture and label.

If an element gets heated, its electrons become excited and they jump an energy level. When they leave an excited state they fall down an energy level, emitting (or producing) its own unique set of spectral lines.

Spectroscopy Is the study of light and its wavelengths. Different atoms absorb or emit specific wavelengths of light These spectral lines allow astronomers to infer physical properties of stars: – Chemical composition – Temperature – Mass – Luminosity (brightness)

Three types of spectra Continuous Spectrum Hot/Dense Energy Source prism Emission Line Spectrum prism Hot low density cloud of Gas Absorption Line Spectrum Cooler low density cloud of Gas Hot/Dense Energy Source prism

3 Types of spectra: Continuous, Emission Line, Absorption Line Some light sources emit all colors (appears as white light). Others emit just a few colors. Some are missing a few colors.

Pictorial Graphical Emission Line Spectrum:

Absorption Line Spectrum: Pictorial Graphical

Absorption spectrum: atmosphere of stars

Absorption of light: electrons excited to higher energy levels. Photon is gone!

H He Ne Kr Atomic Fingerprints

Which of the 3 spectrums would you see with these lights.

Spectral Lines are Affected By: Electrical and Magnetic Fields Number of Electrons Atoms Have Lost (Indicates Temperature and Pressure) Motion (Doppler Effect) – Blue-shifted if motion is Toward Observer – Red-shifted if motion is Away From Observer

The Doppler Effect

Doppler Shift of Spectral Lines By studying how much the pattern of spectral lines is shifted, we can measure the speed of the light source towards or away from us.

Remember this saying: RED Ahead Blue Towards You