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Astronomical light

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Grades 8–12 · Astronomical light

Which is electromagnetic radiation used in astronomy?

  1. Ocean waves
  2. Sound waves in vacuum
  3. Radio waves
  4. Seismic S waves
Answer and explanation

Radio waves

Radio waves are electromagnetic, like visible light.

Grades 8–12 · Astronomical light

Using c=3×10^8 m/s and wavelength 3 m, find frequency in MHz.

Answer and explanation

100 MHz

f=c/λ=10^8 Hz=100 MHz.

Grades 8–12 · Astronomical light

At fixed vacuum speed, reducing wavelength increases what?

  1. Vacuum light speed
  2. Time per cycle
  3. Mass of the observer
  4. Frequency
Answer and explanation

Frequency

Frequency and wavelength are inversely related.

Grades 8–12 · Astronomical light

A signal travels 600000 km at 300000 km/s. Find travel time.

Answer and explanation

2 s

Time equals distance divided by speed.

Grades 8–12 · Astronomical light

An absorption feature indicates what most directly?

  1. Distance is exactly zero
  2. Some wavelengths are removed relative to neighbouring light
  3. The source has no temperature
  4. Every atom has been photographed
Answer and explanation

Some wavelengths are removed relative to neighbouring light

Interpretation of the feature requires a model of absorbing material.

Grades 8–12 · Astronomical light

Why do astronomers combine observations from different wavelength bands?

Answer and explanation

Different processes, temperatures or obscuring material affect bands differently. Combined observations can constrain models more strongly than a single band.

Credit complementarity rather than claiming more images guarantee truth.

Study notes

Light, spectra and astronomical evidence

Radio, infrared, visible, ultraviolet, X-rays and gamma rays are electromagnetic radiation. Astronomy uses more than the light visible to human eyes.

Grades 8–12

Blackbody peak wavelength

This is the peak of spectral radiance per wavelength; a frequency-spectrum peak is a different definition.

Grades 9–12

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