Doppler Effect

In Matt Williams article, “Here’s How to Follow the De-orbit of Tiangong-1, Now Estimated to Happen Between March 30 and April 2,” talks about the space station that is expected to fall to Earth. Williams’ mentions the predictions that satellite trackers have in regards to the space station descending into Earth.
The image above is included in the article showing the possibilities of where the space station could land on Earth where blue has “zero probability,” green has “lower probability,” and yellow are the areas at “higher risk.”
The article relates to the objective due to the Doppler shift which is “the effect that shifts the wavelengths of spectral features in objects that are moving toward and away from the observer.” In this case, the space station is moving towards the observer (us).
As you can see by the image below from the lecture-tutorial the space station would be considered blueshifted because it is moving towards the observer causing it to have shorter wavelengths.
I found the article to be incredibly interesting because who would have said that a space station would be falling into Earth within the days. I also found it interesting learning about the Doppler effect because “light emitted by an object can appear to change wavelength due to its motion.”

One Shift, Two Shift, Red Shift, Blue Shift

In class, we learned that astronomers are able to study the light emanating from a star and determine its chemical composition and the speed and direction at which it travels. A photon is a particle which carries light energy. These are the particles which astronomers study to determine composition, speed, and direction. Different types of light produce different types of photons. Each photon holds a specific amount of energy, and this measurement of energy is known as a quantum.

The spectrum of different types of light (from shortest to longest) are as follows: gamma rays, x-rays, UV rays, visible light, infrared light, and radio waves. The light rays with a shorter wavelength (gamma, x, and UV) have higher energy an higher frequencies. Light with longer wavelengths (infrared and radio) have lower energy and lower frequencies. Although the frequencies may differ, all light travels at the same speed.

Planck’s law describes the relationship between energy and frequency as such:

E = h * v

where E is energy, v is frequency, and h is the constant 6.6 * (10^-34) joules.

By studying the wavelengths emitted by a star, we can determine their temperature and classify them by “spectral type.” Hotter stars emit bluer light while cooler stars emit redder light. The spectral types, beginning with the hottest, are O, B, A F, G, K, and M. Within each of those classes, scientists then use the numbers 0-9 (0 being coolest and 9 being hottest) to sub-divide them within their class. Categorizing stars into certain spectral types also helps determine the chemical composition because certain materials ionize at different temperatures. For example, “O” stars include ionized helium and some hydrogen, A stars have lots of hydrogen, and K stars only have neutral/singly ionized metals.

Studying light waves also allows us to conclude the direction and speed at which a star is travelling. Here is a diagram of the varying wavelengths of the spectrum of visible light:

light wavelength

As you can see, red light has a much longer wavelength and lower frequency than blue light. When a star moves farther away from us, the wavelengths emitted become longer, or “red-shifted.” When a star moves towards us, the wavelengths become shorter, or “blue-shifted.” This phenomenon is known as the “doppler effect.” The doppler effect also tells us the speed at which a star is moving. Stars moving more quickly will experience a greater shift than slower moving stars. For example, if two stars are both moving away from us, both of their wavelength emissions become red-shifted. However, if Star A is moving away  more quickly than Star B, Star’s A wavelengths are even more elongated than Star B’s are. The doppler effect does not apply stars that remain at a constant distance or stars moving left or right across the sky; it only applies to stars moving closer or farther away.


REVISION: I found an article on titled, “Surprise! 3 Planet-Forming Disks Spotted Around Young Double Star.” As you can imagine, the article discusses a recent discovery of three planet-forming disks all revolving around a young binary star system. Each of the three disks are misaligned, staggered over one another. Each star seems to have one disk to itself, with the third disk that is much larger and crosses over the other two. The stars are both relatively young and they’re located about 400 light years from Earth.

The article connects to what we learned in class because scientists using the ALMA telescope measured the light waves emitted by the disks, and figured out that there were 3 distinct disks by using the doppler effect to discern which gases are moving away from us and which are moving towards us.

REFLECTION: I thought this would be a great article to use for this conceptual objective because the discovery of the three different disks relies on the use of the doppler effect. Without measuring the shift in light waves, the scientists studying this binary system never would have resolved the three separate disks because frankly, it is quite unusual the way this system is composed. I really liked this article because it exemplifies the importance of measuring doppler shifts. If the scientists had not done this, they would not have realized there were three different disks and they would have been looking at the binary system & studying it under false pretenses. The doppler effect gives us very important information about celestial objects.

Using Light to Identify

Nearby Comet Has a Big Heart, Radar Reveals

The seventh conceptual objective, I can explain how astronomers use light to determine the chemical composition, the speed and direction of an astronomical object’s motion, has been discussed frequently in class as of late. In class, we discussed the properties of light; speed and energy. We also discussed and defined electromagnetic radiation. Electromagnetic radiation includes radio-waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays. We then discussed light as electromagnetic waves. Wavelength, frequency and speed were all talked about in class as well. We also learned that the photon carries electromagnetic radiation. Each photon has a specific amount of energy known as a quantum. We then went into depth on Planck’s Law. Planck’s Law says that the frequency of an electromagnetic wave is related to the energy of the photon. This expressed mathematically with the equation: E=hv. Towards the end of the conceptual objective, in class, we learned that since gases ionize at different temperatures, the lines also tell the temperature of a certain star. The hotter a gas gets, the electrons will be in higher energy states. In order to practice and clarify this conceptual objective, we spent time in the Lecture-Tutorial book. We did a Lecture-Tutorial on the electromagnetic spectrum of light as well as the Doppler shift. These Lecture-Tutorials we exercised in class represented a clear representation of the seventh conceptual objective. All of this information discussed and exercised in class can be used to clarify the seventh conceptual objective. The article I chose, “Nearby Comet Has a Big Heart, Radar Reveals”, relates closely to our seventh conceptual objective. A series of delay-Doppler images of the comet were taken. The Doppler effect is a shift in the frequency of wavelength of radiation emitted from an object as it moves with respect to an observer. This concept has been discussed and exercised in class. Studying a comet using radar technology can prove to be rare. Because of the close proximity this comet flew to Earth, it was able to be studied using Doppler images. As stated in the Lecture-Tutorial book, ” Because of the Doppler Effect, light emitted by an object can appear to change wavelength due to its motion toward or away from an observer. This recent news story regarding Comet 45P/HMP relates closely to the seventh conceptual objective. In order to assume the speed, composition and direction of this comet, astronomers used Doppler images to make observations. Ultimately, light was used to make these observations. The concept of using light to characterize certain astronomical objects has been exercised in class as well as applied in my chosen article. The article clearly demonstrates this concept and applies it to a real world situation, a comet fly-by. This article and conceptual objective has furthered my understanding on light and has taken it to the next step. I am now aware of how light can be used to make identifications and observations of objects in space. The article I chose was very informative and interesting. After reading this article, my understanding of the seventh conceptual objective was clarified.