What Is a Spectroscope?

What is a Spectroscope?

Our sun is a star. Everyone knows this now. But the early scientists did not believe this. There was no proof! The key to the proof came in 1850 with the invention of the spectroscope (SPECK-truh-scope).

A spectroscope identifies elements by the colors they give off.

Every substance gives off light when it becomes hot enough. Every element gives off its own special color. A spectroscope separates the light into colored lines. We call these lines a spectrum. A spectrum is like a fingerprint. No two people have the same finger prints. And, no two elements have the same spectrum. But the spectrum is always the same for a particular element.

For example:

1. This is what a sodium spectrum looks like.
   

Only sodium looks like this. No other element looks exactly like this.

1. This is what a potassium spectrum looks like.
   

Only potassium looks like this. No other element looks exactly like this.

There are 92 naturally occurring elements. We know the spectrum for each one. About 67 of them have been found in sunlight. This means that the sun contains at least 6 elements that are found on earth.

How do we know that the sun is a star? Simple! The spectroscope patterns of the sun and the stars are very similar.

Understanding the Spectroscope

The most important part of a spectroscope is a prism. A prism is glass shaped like a wedge or a triangle.

A prism can break up white light into a rainbow of colors. This is the spectrum of white light.In a spectroscope, a prism forms spectrums of individual elements.

Identifying Spectrums

Figure B shows the spectrums of 9 elements. The numbers represent wavelengths of color.

Figure C shows 3 spectrums coming from a heavenly body. Use figure B to find out which element is shown by each spectrum. Write your answer in the chart.

Spectrum 1

Spectrum 2

Spectrum 3

Spectrum / Element
1
2
3

Matching: Match the two lists. Write the correct letter on the line next to each number.

1. _____astronomy A) key part of a spectroscope
2. _____ optical telescope B) band of colors
3. _____ spectroscope C) analyzes light
4. _____ prism D) gathers light
5. _____ spectrum E) study of the heavens

How a Spectroscope is Used

How is a spectroscope used to study light from objects in space?

1. The spectroscope is connected to the telescope.
2. A camera is connected to the spectroscope. The camera photographs the spectrum.
3. Astronomers study and identify the spectrum.

The spectroscope does more than identify the chemical makeup of the sun and the stars. The spectroscope tells us:

1. The makeup of the atmosphere of the planets.
2. How fast a heavenly body moves and in which direction (red shift/blue shift).
3. How hot a star is.
4. If a star is rotating.
5. If a star has a magnetic field

Analyzing Red Shift & Blue Shift Spectrums

Light can be described as traveling in the form of waves. Each color that the human eye can see has a different wavelength. The longest visible wavelengths are in the red end of the spectrum. The shortest visible wavelengths are in the blue end.

The wavelength of light that an observer sees coming from an object depends on the motion of the object relative to the observer. If either the object or the observer moves, the wavelength will change. The relationship between motion and observed wavelength is called the Doppler effect.

When a blue shift occurs

If a star is moving toward Earth, the wavelength will be smaller than if the star were at rest relative to Earth. In this example, the light has shifted toward the blue end of the spectrum, making what is called a blue shift.

When a red shift occurs

If the star is moving away from the observer, the observer sees light of a longer wavelength than it had when it was emitted. In this case, the observed light has made what is called a red shift.

1. An astronomer discovers two stars. Both stars appear red, but Star A appears redder than Star B. What can the astronomer conclude?

2. If an astronaut in a spacecraft saw a star ahead that seemed to be growing bluer as time passed, what might she assume about the motion of the object relative to the spacecraft? List four possibilities.

Shifting Spectra & Speed

The greater the shift the faster the object is moving towards or away from Earth.

Galaxy / Rank
A
B
C
D

Based on the spectrums below, rank the four galaxies in order of the speed with which they are moving away from Earth, from slowest (1) to fastest (4).

1. Based on Hubble’s Law, which of the galaxies is farthest from Earth?

1. Are any of the galaxies moving toward Earth? Explain