astronomy homeworks ( Astronomy of the Universe AST 101) !!
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AST101Ch5.docxElectromagnetic Spectrum
Components:
Light behaves as both a particle and a wave. At this moment we are only going to focus on the wave properties.
There are two major divisions for waves:
1) Transverse: A distortion that is perpendicular to the direction of travel. Be comfortable with understanding that waves at the beach coming toward the shore are transverse waves.
2) Longitudinal: A distortion that is parallel to the direction of travel.
Shorter wavelength corresponds to higher energy.
Also know the colors of visible light in order of decreasing wavelength
1) Red
2) Orange
3) Yellow
4) Green
5) Blue
6) Indigo
7) Violet
There are three different types of spectra:
1) Continuous
2) Emission
3) Absorption
Is the speed of light constant? NO
The correct way to think of this is “All observers measure the speed of light in a vacuum to have the same value.”
A prism changes the medium through which the light is traveling. This causes the light to slow down and change direction. When the light leaves the prism it speeds up again. The change in angle due to the change in speed is dependent on the wavelength (color) of the light.
A continuous spectrum occurs when light at all wavelengths (within the visible light portion of the spectrum) is present.
Consider hydrogen as the simplest example for all elements (and molecules, etc.).
Hydrogen has a proton for the nucleus and an electron that orbits around the nucleus at various distances. These are referred to as the orbital shells.
1) The laws of physics are the same everywhere in the Universe. This cannot be proven (with current technology and understanding of physics). However, we have observational data that supports this. A consequence of this is that all protons (in reality all particles) in the Universe must have exactly the same properties. This verifies that all interactions between protons will have the same results. Expanding on this idea requires that all electrons in any given hydrogen molecule orbit at the same distance.
2) The Universe is lazy. This means that the Universe tries to do everything using as little energy as possible, and entities (molecules, systems of particles, etc.) try to remain in their lowest energy state. For our hydrogen molecule, this means that the electron wants to be in the first orbital shell (closest to the nucleus).
Any interaction between charged particles that results in the release of energy will release that energy in the form of photons.
When electrons move toward a nucleus, energy is released and photons are observed. These are called “transitions” and are categorized by where the electron lands.
These transitions are defined by the electron landing on shell
1) First shell Lyman transition UV photons given off
2) Second shell Balmer transition Visible light photons
3) Third shell Paschen transition IR photons
4) Fourth shell Brackett transition IR photons
This gives me the information needed to create “fingerprints” for emission spectra to use for comparison with observation.
The Doppler effect applies to waves and changes the apparent wavelength based on motion.
Applying this to light, if a light source is moving toward an observer then the light’s wavelength appears shorter than it really is and this is referred to as a blue shift. Conversely, if the light source is moving away from an observer then the light’s wavelength appears longer than it really is and this is referred to as a red shift.
Overall the effect is the same whether the light source and/or the observer are moving. If the distance between them is decreasing then there is a blue shift. If the distance between them is increasing then there is a red shift.
