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Q: How did Vera Rubin measure the speeds of stars?

A: Using a device called a spectrometer and a phenomenon called Doppler shift.

This is a great question! Astronomers only have access to the light from stars, so they have to think carefully about how to extract every useful piece of information from that light.

Dr. Vera Rubin and her collaborator Dr. Kent Ford used a spectrometer, a device which separates light into its separate colors and wavelengths. Depending on the direction an object is moving, its light spectrum will be shifted either toward the blue or red end of the spectrum (this is called the Doppler effect). By comparing the spectrum of a moving star to the spectrum of a (relatively) stationary star, Dr. Rubin could measure precisely how fast the star was going. Try it yourself with the activity Measure Star Speeds!

Q: I think it's cool that plants can respond to light using their photoreceptors. Can plants know other things about their environment?

A: YES! Plants can measure and respond to a lot of aspects of their environment!

Plants are constantly collecting information about the world around them. They can respond to gravity, light, and touch! These traits are called "tropisms", and help plants answer the following questions:

  • gravitropism: which way is up or down?

  • phototropism: how can I find the best sunlight?

  • thigmotropism: can I grab onto this for support? 

Photomorphogenesis, the subject Dr. Marie Clark Taylor studied, helps a plant know when and how to grow. "Tropisms" help a plant know where to grow to collect the nutrients it needs to thrive. Check out this explanation from the New York Botanical Garden.

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