Final Exam: Sun 1 Flashcards
How far is the sun? What is it’s diameter?
The sun is 150 Million kilometres from earth and is 109 times the diameter of earth
What did the sun begin as? What did this cause?
The sun began as a cloud of gas that underwent a gravitational collapse. This caused the core of the sun to become hot enough to start nuclear fusion reactions.
What did the suns nuclear fusion generate? What did this pressure create?
The nuclear fusion generated an energy that provided OUTWARD PRESSURE. This pressure perfectly balances the inward force of gravity. This is called GRAVITATIONAL EQUILIBRIUM.
What is the PHOTOSPHERE?
The visible surface of the sun.
Most visible light comes from here.
~5,800 K
What is the composition of the sun? How do we know this?
70% Hydrogen 28% Helium 1.5% Oxygen 0.3% Carbon 0.2% Iron
We know the composition by identifying the ABSORPTION LINES in the suns spectrum.
How is light the cosmic messenger? (Answers in slides)
What is Spectroscopy?
Light travels from all parts of the universe
MATTER in the universe interacting with light leaves FINGERPRINTS in the light
SPECTROSCOPY is the process of dispersing light into its spectrum (different wavelengths)
CONT: how is light the cosmic messenger?
Through study of how atoms absorb and emit ELECTROMAGNETIC RADIATION
By observing the spectral lines formed in different elements and comparing these with spectra from astronomical objects it can be determined the chemical composition of these objects
what is the E M spectrum? What does this do?
Electromagnetic spectrum
All radiation from Gamma to Radio
Blue (violet) light with {weird A symbol} (in vacuum) of 434 nm (nanometers) to
Red light with {weird A symbol) = 768 nm
Radiation with longer wavelength than Red light is INFRARED and wavelength shorter than Blue light is ULTRAVIOLET
Types of spectra
Continuous (thermal) spectrum = Hot blackbody passing through prism
Absorption line spectrum = Hot blackbody passing through cloud of gas and through prism
Emission line spectrum = hot blackbody passing through cloud of gas and through a prism (like Absorption line spectrum)
What is continuous (thermal) spectrum?
Spectrum of the common (incandescent) lightbulb. Spans all visible wavelengths with light interruption.
Continuous spectra are from hot dense objects due to the motion and collisions of particles
What is Thermal Radiation?
Nearly all large or dense objects emit thermal radiation, including starts, planets, and you
The radiation emitted by an opaque abject is called BLACKBODY RADIATION
A blackbody’s continuous thermal radiation spectrum depends on only one property: it’s TEMPERATURE
What are the properties of thermal radiation? (The laws)
1) Stefan-Boltzman law:
Hotter objects emit higher energy than cooler objects
2) wien’s law:
Hotter objects emit photons with a higher average energy. The wavelength of peak intensity decreases (shifts towards blue) as the temperature increases.
Hence the thermal spectrum can tell us the temperature of a star.
What is hotter?
A) blue star
B) Red star
C) a planet that emits only infrared light
A) blue star
What is Emission Line Spectrum?
A thin or low-density cloud of gas when HEATED emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
SIMPLY PUT: thin/low-density cloud of gas when heated emits specific wavelengths of light. This depends on the composition of the cloud
What is Absorption Line Spectrum?
A cloud of gas between us and a light source can absorb light of a specific wavelengths, leaving dark absorption lines in the continuous spectrum
What are the chemical fingerprints in light?
Each type of atom has a unique spectral fingerprint of absorption or emission lines
Observing the fingerprints in a spectrum tells us which kinds of atoms are present
What is an atom?
Building block of matter, composed of positively charged protons and neutral neutrons in the nucleus and is surrounded by negatively charged electrons
What is a Ground State?
The lowest energy state an electron can have within an atom
What is an excited state?
State of an atom when one of its electrons is in a higher energy orbital than the ground state. ATOMS CAN BECOME EXCITED BY ABSORBING A PHOTON OF A SPECIFIC ENERGY OR BY COLLIDING WITH A NEARBY ATOM
What does Ionized mean?
State of an atom that has had at least one of its ELECTRONS removed
What is the Bohr model of the hydrogen atom?
In the hydrogen atom, an electron circles the nucleus (proton) only in allowed orbits.
N = 1, 2, 3, …………
Where N = 1 is the smallest orbit
What is the Structure of atoms?
The number of PROTONS determines what element it is
Neutral atom: the same number of protons and electrons
PROTONS and NEUTRONS roughly have the same mass, while ELECTRON mass is 2000 times less
While planets are kept in their respective orbits by gravitational force, electrons keep orbiting the nucleus due to attractive electric force between protons and the electrons
How can an electron “jump” from one orbit to another?
By gaining or losing the correct amount of energy
To jump from an INNER orbit to an OUTER orbit the electron must absorb a specific amount of energy
Electron must EMIT (loose) a specific amount of energy to jump from an outer to an inner orbit
What is an electron shell?
The number of protons in the nucleus is unique to each element.
Each kind of element has its own pattern of permitted orbits
What happens to an “excited” atom?
And excited state: when an electron is in a higher orbit than ground state n = 2, 3, …….
When an atom absorbs energy beyond a certain maximum value the electron(s) are no longer bound to the nucleus and can roam free.
- atom has one (or more) less electron(s)
- atom is positively charged
- such an atom is called an ION
CONT: excited atoms
The longest-wavelength (reddest) photon has only enough energy to excite the electron from n=1 to n=2
The shorter the wavelength (higher energy, bluer) photons can excite electrons to higher levels
A photon with too little energy cannot be absorbed
- the hydrogen atom has many more levels than shown, it can absorb many different wavelengths
What happens in the emission of light by atoms?
In the hydrogen atom, the electron jumps from orbit 3 to orbit 2 by emitting a photon.
The energy of the photon emitted exactly equals the difference in energy between the two orbits.
Chemical Fingerprints in light
Each type of atom, ion and molecule has a unique ladder of energy levels that electrons can occupy
The only changes allowed are those corresponding to a transition of an electron between energy levels
Each transition corresponds to a unique photon energy, frequency and wavelength
Because those atoms/ions/molecules can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths
What is the formation of spectra?
The hydrogen atom produces many spectral lines from the ultraviolet to the infrared. However only 3 hydrogen lines are visible to human eyes.
How does light tell us what things are made of?
Electrons in atoms have distinct energy levels
Each chemical element, ion, molecule has a unique set of energy levels
Spectral fingerprints of molecules
Molecules have additional energy levels because they can vibrate and rotate
The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated
Many of these molecular transitions are in the infrared part of the spectrum
Why is the sky blue during daytime?
Mall particles scatter blue light more effectively
Since air molecules are smaller than visible light they scatter blue light
