Announcements

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Announcements

Observing on the roof of Van Allen Hall has started and will run Tuesday to Thursday from 9-11 pm this week.

The first hour exam will be on Friday, September 17.

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Temperature and Color, Classifying Stars

Spectrum of light

How the eye sees color

Temperature and color/spectrum

Colors/spectra of stars

Classifying stars

Reading: sections: 16.5-16.6, 6.2

Slide 3

Electromagnetic spectrum

The “spectrum” of a particular star is how much light it produces at each wavelength.

Slide 4

How your eye sees light and color

Slide 5

Rods and cones on the retina sense light

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Rods and cones

Cones are color sensors

There are cones for red, green, and blue

The color ones perceives depends on the firing rates of the red vs. green vs. blue cones

Cones need relatively bright light to work

Rods give finer, more detailed vision

Rods can work with less light

At night, color vision is less effective because only the rods function

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Sensitivity of cones

Slide 8

A star will produce light overlapping the response of all three cones. The color of the star depends on how strong its spectrum is in the ranges covered by the different cones.

Slide 9

A star will produce light overlapping the response of all three cones. The color of the star depends on how strong its spectrum is in the ranges covered by the different cones.

Slide 10

A star will produce light overlapping the response of all three cones. The color of the star depends on how strong its spectrum is in the ranges covered by the different cones.

Slide 11

What can we learn from a star’s color?

The color indicates the temperature of the surface of the star.

The same is true for the filament in a light bulb or any other hot object. In general, we call radiation from a hot body `black body’ radiation (do demonstration 6B40.10).

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