Astronomy Study Guide #1
1. Be able to define wavelength, frequency and photon. Given the relationship between
frequency, speed and wavelength (the wave equation) and the relationship between
photon energy and wavelength, be able to identify regions of long and short wavelength,
regions of high and low frequency, and regions of high and low photon energy on a
spectral curve (a graph of intensity vs wavelength).
Wavelength is the distance between
adjacent peaks of a wave. Frequency is the rate at which peaks of a wave pass a certain point
every second. A photon is an individual particle of light. The wave equation is wavelength x
frequency = speed. The longer the wavelength, the lower the frequency and the shorter the
wavelength the higher the frequency. The relationship between intensity and wavelength is that
the higher the intensity the bluer and shorter wavelength the object has. The lower the intensity,
the longer the wavelength and the more red the object is. Also, the brighter the object, the higher
photon energy is, then the higher the intensity level is.
2. As an object heats up, what two things happen to its spectral curve? Given a
continuous radiation spectrum for an object of a certain temperature, be able to identify
the spectrum of an object that is slightly warmer or cooler based on these principles. Be
able to sketch a graph (intensity vs wavelength) of a warmer or cooler object given a
spectral graph of an object with a certain temperature.
As an object heats up, its spectral
lines are more intense which shows that it is emitting more light and the shorter the wavelength
is. Therefore, according to continuous radiation, the hotter the object, the shorter its wavelength
and the more radiation there is.
3. How do we use the information from question 2 to estimate the temperatures of stars?
Why do objects appear more red, then more yellow, then more blue as they get hotter?
From a graph of intensity vs wavelength, be able to identify which of two stars appears
redder or bluer and which is giving off more blue or red light.
The hotter the star, the more
blue it is; the cooler the star is, the redder it is. We know this because of the spectral lines of the
object. If the object appears red than it is less intense and the wavelength is shorter. So, as an
object moves from red to blue, it is getting hotter because of the relationship between wavelength
and intensity. Stars with a peak that is closer to the bluer part of the spectrum, appear more blue.
However, if that star is more intense than another, but it's peak is closer to the blue, it is giving off
more red light as well, compared to the star with a peak closer to the red part of the spectrum that
is less intense.