EXOPLANETS!

EXOPLANETS!

EXOPLANETS!

USING LIGHT, COLOR, AND TEMPERATURE TO FIND EXOPLANETS

Our bodies are constantly taking in information. Everything we sense around us, from the colors that we see to the heat that we feel, is information that we use to interpret the world around us. It is our ability to interpret this information that allows us to find out about the world around us.

Let's think of an example of using our senses to take in information and interpret that information to determine the properties of an object.

A coil on a kitchen oven top can emit heat energy. We can turn the oven coil on and you can sense the changes that occur to it from touch (not too close!) and by sight. By turning it on you immediately sense it get warmer, and as energy is continually being added to the coil, its temperature rises and more heat energy can be felt coming off of the coil. You can also see the energy being added by watching the color of the coil change. It will go from black to red as the heat increases.

But what if you were trying to get the coil to a particular temperature, and no thermometer was available to take its temperature? You don't want to touch the coil to figure out how hot it is. What if we could determine the temperature just by its color? The light that is emitted (given off) from an object can tell us about the energy being emitted. So if we know how much light is being emitted, and what color that light is, we should be able to predict the approximate temperature of the coil.

Light has known characteristics that can help us make predictions about the temperature of an object without touching that object. This idea goes much farther than just determining the temperature of a kitchen coil. Astronomers will never be able to touch the objects they study to determine their temperatures. The stars they look at can be in different galaxies, hundreds of light years away. They must use the light these stars emit to determine their temperature. And stars are much hotter then any coil you would use to cook something, so we can expect that stars would emit different color light than a stovetop coil. The different colors that stars emit range from red at their coolest to blue at their hottest. This probably at first doesn't seem possible. We constantly use the color blue to represent cool, or downright cold. But when we study the nature of light, we will see that blue light is more energetic than red light, and therefore corresponds to a higher temperature.

The astronomers you are learning about are actively searching the sky for a particular type of star. They use the light that is emitted from the star and create a picture to determine its temperature. By measuring the light, color, and temperature emitted by a star, astronomers are able determine an assortment of characteristics about the star. The information that you will be given in this lesson will give you the basic skills astronomers use in their search for exoplanets.

Consider the picture below of a planet/star system.

What is the difference in these two objects? What information can be inferred from the following picture? Which do you think is hotter and why?

 

 

Take another look at the picture of the two objects above. This picture was produced from light emitted from the infrared (IR) part of the light spectrum, which our eyes aren't able to interpret; however, IR follows the same energetic trend as visual light--it has a more energetic part and a less energetic part. Because this image was taken using IR light, scientists had to re-interpret this information in a way such that we could actually see it.

Map of the US with each county colored re, blue, or purple, to indicate whether the county voted as a majority for Obama (blue) or Romney (red), or if it was closer to 50-50 (purple).

It is similar to looking at an electoral map to see how many people voted and whether they voted for President Obama or Mr. Romney. The true picture of the map is not blue or red. But to represent the voting information based in different regions, the map was recolored with voting data to help visualize this information.

Similarly, the IR image was "recolored" to colors that we could see. This image was then false colored to provide visual representation of the energetic information from the light coming from the stars.

Let's look at some more familiar pictures utilizing the scientific technique of false coloring. Look at these pictures of US map from a satellite using data taken from visible light, infrared light, and water vapor.


Images' source: http://nasa.gov

What are the differences in the pictures and what are the same? Which of these are "true colored" and which are "false colored", and why?

 

 

The light that we see is only a part of the light spectrum (also called the electromagnetic spectrum). Other waves of light include radio waves and x-rays. The visible light on the spectrum runs in color from violet, with shorter wavelengths, to red, with longer wavelengths. Just beyond the visible red light is infrared light. That first picture is a photo taken in infrared and false colored based on where the light emitted from the star falls on the light spectrum.


The scales here show the wavelength of the light in that area of the spectrum in either meters or nanometers.
1 nm = 10-9 m, or 1 one-billionth of a meter.

 

Based on the scale provided above which of the following statements is false?

 

 

Objects radiate infrared light in the form of thermal energy or heat. We can determine the relative "hotness" or "coolness" of an object by observing it in the infrared part of the spectrum. But, since we can't see infrared light, we have to transpose the information from that observation by matching up the infrared part of the spectrum with the visible part.

The infrared part of the light spectrum can be scaled out using color in the same manner as the visible light part of the spectrum. The higher energy visible light has a shorter wavelength and appears blue, so really hot objects appear blue when we scale out the infrared. If that is true, then the lowest temperatures would show as which of the following colors?

 

 

So here's a visible-light image of the man holding a scorpion as though it's no big deal.


Image source: Cool Cosmos' Infrared Zoo

If we were to take an infrared picture of the man and the scorpion, and then false-color that picture using the visible spectrum, what parts of the picture should be blue?

 

 

 

So here's an infrared picture of the man with the scorpion. What can you infer about the differences between the temperatures of the man and the scorpion? (The scale shows temperature in Fahrenheit.)


Image source: Cool Cosmos' Infrared Zoo


 

 

How can we use light to determine what is happening on distant objects in space? Let's look at the picture of the planet/star system again.

Utilize the new information that you have gained about the light spectrum and determining the temperature of stars that are very far away.