July 16 , Lecture 5, AST201H1
How do we get knowledge about astronomical data. All we know about the universe
is from the light we receive. What happens at the micro-level. What happens
between the atoms. Nucleus, made of protons and neutrons, electrons. Move around
the nucleus. Very specific. Specific amount of energy, specific orbital. From one level
to another, it can only happen if the electron has the energy to the correspond to the
difference between which that transition happens. The further away from the
nucleus, the energy goes up.
Possible transitions (on the slide) are different/ highlighted for different colors.
Number of these orbitals, the energy (how far the space). Circular representation,
more horizontal representation (cut the circle and level it out). Each transition,
whether it happens in emission or absorption, correspond energy, wavelength, and
Light of how many colors approaches. All of these different wavelengths. Of all these
photons, only the green one will have that specific energy. Allow electron to move
from lower to higher. Absorption. Gain the energy to move from lower level to
higher level. All other light aside from the green. Later, the green light is re-emitted.
Another type of representation, strips of colors. More of what we get from
astronomical data. Spectrum. How do we get these bright lines? Emitted certain
energy, is certain wavelength and frequency, all we get is the spikes, thus color. The
dark lines are absorbed. Hit with all the colors, see the background of rainbow
colors that continue, but dark lines are interrupted when absorbed.
The set of spectral lines that we see in the star’s spectrum depends on the star’s:
This is why we call spectral lines chemical composition
Energy levels of molecules:
Made of atoms.
Molecules have additional energy levels, because they can vibrate and rotate. Many
more energy levels. If look at spectrum of molecules, there are more black lines.
The large number of rotational or vibrational energy levels can make the spectra of
molecules very complicated. Many of these molecular transitions are in the infrared
and radio part of EM Spectrum.
Interpreting an Actual Spectrum
Spike up = emission
Going low = absorption
Mass per unit volume. Density equals mass divided by volume. Within a certain
volume, certain amount of matter, if you have more matter compared to the same
volume where you have way less matter, higher density. Water has higher density to Gas. Compare within the same area, small in size but
can be more massive. Density and area are related to the mass.
Cat’s Eye Nebula. A planetary nebula. Give away emission lines (insert slide). Gas
that is fairly hot. When something is hotter, it moves faster. Has more energy. Has
more energy, electrons are already going to be on excited levels, and what they
produce are the emission levels. Peaks at very specific wavelengths.
Low density gas (not a lot of interactions, no chance to interact each atom emits
or absorbs light independently of the others.
Hot gas. Atoms more excited, electrons can go to higher levels, particles will be more
excited. Lines are higher (amount of light are high).
Warm gas. Amount of light that comes is not as strong
Cool gas, less electrons are higher levels, not as many transitions. So less light
Temperature decreases, less and less light comes.
Low density gases produce emission spectra.
Dense objects. Solid objects. Sun, way more particles than interstellar mediums.
A gradient, a continuous graph. Peak at certain point and drop down.
Dense objects emit some light at all wavelengths.
The particular continuous spectrum emitted by dense objects is called a blackbody
spectrum. We have a certain blackbodies (stars), but these are the type of objects
that absorb all the light that comes into them. Most dense objects