Star Temperature and Spectra

• Star colors are crucial for understanding their temperature.
• Size, color, temperature, and age influence each other in stars.
• Stellar classification categorizes stars based on their spectra.
• Nuclear fusion fuels stars; larger stars undergo this process faster.
• Stars evolve in color and size throughout their existence.
• The sun will eventually become a red giant with a cooler surface.
• Spectra classifications for main sequence stars depend on temperature.

Measuring Star Temperature

• Astronomers use Kelvin to measure star temperature.
• Kelvin uses absolute zero as its base.
• Stars range from 2500 K to 50,000 K.

Spectra Categories

• Stellar spectra categorize stars via O, B, A, F, G, K, and M.
• O-class stars are hottest (over 40,000 K).
• M-class stars are coolest (around 3,000 K).
• Blue stars are the hottest.
• O to A stars appear blue to white with decreasing temperature.
• F to K stars appear light yellow to orange with decreasing temperature.
• M stars are red.
• L-class includes brown dwarfs (under 2500 K), which are not technically stars due to lack of fusion.
• The sun is a class-G yellow dwarf at about 5800 K.

Stellar Spectra

• The visible light spectrum is what humans can see, but there also exists infrared and ultraviolet which are not visible.
• All electromagnetic energy produces radiation (light) and transfers heat.
• Star temperature and color are closely related.
• A star's spectra is based on observed photon intensity over time.
• Spectra reveal a star's atmosphere's temperature, density, and chemical makeup.
• More intense stars burn hydrogen quickly, raising temperature, increasing brightness and have a higher photon intensity.

Wavelengths

• Wavelength is the distance between waves.
• Frequency is how often a wave repeats.
• Shorter wavelengths have greater frequency.
• Higher energy output shortens the wavelength of electromagnetic energy affecting visible color.
• Determining the dominant wavelength requires a blackbody curve.

Blackbody Curve

• Blackbody curves graph wavelength and intensity for a theoretical object that absorbs all light.
• Peak height indicates temperature.
• Higher peaks represent higher temperatures and intensities.
• Blackbodies re-emit a star's electromagnetic energy based on temperature.
• Lightbulbs emit mostly in the infrared spectrum, but a small portion is in the visible spectrum.
• Hotter stars emit more short wavelength energy, cooler stars emit more long wavelength energy.
• Blackbody graphs visualize these temperature differences.

Wien's Law

• Wien's Law dictates that emitted energy shifts to shorter wavelengths as temperature rises.
• Hotter objects appear blue (shorter wavelength).
• Cooler objects appear red (longer wavelength).
• Maximum emitted wavelength is inversely proportional to absolute temperature.
• Astronomers can determine a star's temperature just by identifying the wavelength of emitted light via blackbody curves.

Color and Temperature

• Stellar spectra classify stars into O, B, A, F, G, K, or M.
• O stars are hottest, most intense, and blue.
• M stars are coolest, dimmest, and red.
• Blackbody curves measure temperature and intensity by showing the relationship between intensity and wavelength.
• Less intense stars emit longer wavelengths, appearing red or orange.
• Moderately intense stars emit shorter wavelengths, appearing yellow or white.
• The hottest stars emit the shortest wavelengths, appearing blue.