Welcome to Astra's stellar spectroscopy tutorial!

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Spectroscopy uses the nature of light to learn about the Universe.

While studying the stars, humans began to understand the nature of light.

A prism reveals the source's light wavelengths

When Visible light is passed through a prism it splits into individual colors. The colors are different because light travels in waves of varying length. Red light waves are longer than the blue, the prism bends waves that pass through it and prevents them from blending together again.

Radiation is Energy

That Energy is radiated or transmitted in the form of rays, waves or particles. Light waves were found to have electric and magnetic properties by James Clerk Maxwell in 1865.

The Electromagnetic spectrum is continuous

The tiniest waves are measured in Angstroms, a unit of length equal to one hundred-millionth of a centimeter. Waves of visible light are measured in nanometers (nm), while waves in infrared to radio are measured in more familiar meters.

Milky Way Galaxy Images

The next slides illustrate the Milky Way as it has been mapped by modern astronomers through the new windows of the Electromagnetic Spectrum. False colors are often used to illustrate light at invisible wavelengths. Generally, blue is used for the shorter waves and red for the longer waves.


Many thanks to NASA, the National Radio Astronomy Observatory (NRAO), the National Optical Astronomy Observatory and many others who made these images available for use in this tutorial.

Radio Milky Way

This image shows the Milky Way galaxy as it would appear if we could see the electromagnetic energy the hydrogen in the galaxy emits in the Radio region, specifically the 21-cm wavelength. This image is computer generated from data collected by various radio telescopes.

Microwave Band

This image is part of an all-sky survey taken with the COBE satellite. The red band across the image comes from energy radiated by the Milky Way in the microwave region of the spectrum. Credit for this images goes to the NASA/WMAP Science Team.

Near Infrared

In this near infrared image, the dominant sources of light are stars in the Milky Way. The galaxy appears edge-on to us because our sun is in this plane as well. The image is redder in directions where there is more dust absorbing the light from these more distant stars.

The Milky Way at Normal Wavelength

Here is the Milky Way in visible light, somewhat like what you might see at a dark site, except that a camera collects light longer than your eye is designed to gather it. This is the center of our galaxy, rather than the entire length of it, as are the other images.

Spiral Galaxy

This ultraviolet image of a galaxy called NGC 1365, is similar to how we currently believe our galaxy, the Milky Way, appears from the outside. It is called a "barred spiral type" because of the bar-like quality of its central structure.

X-ray images from the Chandra X-Ray Observatory.

This composite image of Milky Way's galactic center covers an area smaller than the previous visible light image. The central white patch is believed to be the blackhole at the center of our galaxy.

The Milky Way galaxy in the gamma ray region image by Compton Gamma Ray Observatory.

Gamma Waves are very energetic and are often detected in the form of gamma ray bursters. (GRBs).

This is the end of the Spectrocopy module. Click the arrow to restart the lesson

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