Observing Across the Spectrum with Telescopes

Background

Astronomers are now able to observe broad regions of the electromagnetic spectrum: from gamma rays at the high energy end to long radio waves at the lowest energies. Earth’s atmosphere lets only a narrow range of the spectrum pass through to the surface. In some regions of the spectrum, Earth’s atmosphere totally blocks all light at those wavelengths, meaning it is opaque. at those wavelengths. In some regions, it is partially transparent—it lets some light through at specific wavelengths. In other regions of the spectrum, all light at those wavelengths passes through the atmosphere, what we call the “visible” part of the spectrum. In astronomy terms, transparent regions of the spectrum are called atmospheric windows.

While there were earlier space telescopes, it was the Hubble Space Telescope (HST) that really revealed the universe through the sharp images it provided in visible light and at some infrared wavelengths. There are approximately two dozen space telescopes currently in operation. There are probably over 600 professional ground-based telescopes operating worldwide. The goals are for much larger ground-based telescopes with equipment and technology to bring very sharp images. You will be investigating just a couple telescopes here.

Question: Why is atmospheric “windows” an appropriate name for the regions where the atmosphere is transparent?

Learning Goals

• Successfully gather the information requested for two of the listed telescopes.
• Explain what is meant by opaque and transparent when referring to the atmosphere.
• Correctly identify the parts of the spectrum that can be observed on Earth.
• Correctly identify the parts of the spectrum that can be observed only by using space telescopes.
• Use MLA format to reference the source of the information.

Part 1: The telescopes

Here are some famous telescopes currently in operation or that will soon be:

• Hubble Space Telescope
• James Webb Space Telescope
• Very Long Baseline Interferometry
• Vera Rubin Observatory Telescope
• Fermi Space Telescope
• Keck Twin Telescopes

Using the Internet, answer the following questions for two of the telescopes in the list. Make sure that you use reputable sources for your information.

Figure 1. The top part of this image shows the incoming energy from the Sun and outgoing energy from the Earth relative to the electromagnetic spectrum. The incoming energy intensity replicates the blackbody characteristics, with the peak energy at yellow. The bottom part shows the wavelength regions with total absorption and those with limited or almost no absorption by the atmosphere. [1]

Part 2: Earth’s Atmosphere

1. What does it mean for Earth’s atmosphere to be opaque in certain regions of the electromagnetic spectrum?
2. What does it mean for Earth’s atmosphere to be transparent in certain regions of the spectrum?
3. For which types of electromagnetic radiation is Earth’s atmosphere completely opaque?
4. For which types of electromagnetic radiation is Earth’s atmosphere completely transparent?

Part 3: Telescopes

5. There are telescopes for every band of the electromagnetic spectrum. Which types of telescopes will be able to detect flux from celestial objects if the telescopes are located on Earth?

• 1. gamma ray telescopes
  2. X-ray telescopes
  3. ultraviolet (UV) telescopes—just beyond blue wavelengths
  4. visible-light telescopes
  5. infrared telescopes—if from high mountains
  6. radio telescopes

6. Which types of telescopes must be placed and operated in space, well above Earth’s atmosphere?

• 1. gamma-ray telescope
  2.  X-ray telescopes
  3. UV telescopes—to obtain complete range of the radiation
  4. visible-light telescopes
  5. infrared telescopes—if complete coverage is needed
  6. radio telescopes

7. Briefly describe at least two advantages and two disadvantages for ground-based versus space-based telescopes.
 

Part 4: References

Give the full references for your sources of information given above. List the complete URLs of your sources in proper internet reference form. The example given here for referencing the source for Figure 1 uses the MLA guidelines.

[1] “The Atmospheric Window,” National Oceanic and Atmospheric Administration (NOAA), https://www.noaa.gov/jetstream/satellites/absorb. Accessed 23 May 2023.