Stars: Crash Course Astronomy #26

Summary

This script delves into the fascinating world of stars, explaining their diverse brightness, colors, and the mystery behind these variations. It explores the advent of astrophotography and spectroscopy, which revolutionized our understanding of stellar composition and behavior. Annie Jump Cannon's classification system and the HR diagram's role in revealing stars' life cycles are highlighted, showcasing how temperature and luminosity are key to deciphering a star's story.

Takeaways

• 🌟 Stars may appear similar at first glance, but they differ in brightness, color, and other characteristics.
• 🔭 The use of binoculars and photography revealed that stars have different colors, adding to their diversity.
• 🌌 In the late 19th century, astrophotography and spectroscopy became significant tools for studying stars.
• 📊 A star's spectrum is a display of its light across different wavelengths, providing physical data about the star.
• 🌈 Stars emit a continuous spectrum, but their atmospheres create gaps in this spectrum due to specific wavelength absorptions.
• 🔠 Annie Jump Cannon introduced a new system to classify stars based on the strengths and appearances of various absorption lines in their spectra.
• 🌡 Max Planck's work explained how stars emit different colors of light based on their temperature, with hotter stars emitting more blue light and cooler stars peaking in the red.
• 🔬 Cecilia Payne-Gaposchkin combined various scientific findings to show that star spectra depend on temperature and atmospheric elements, revealing their composition.
• 💫 Stars are primarily composed of hydrogen and helium, contrary to earlier beliefs that they had a similar composition to Earth.
• 📝 The HR diagram, developed by Ejnar Hertzsprung and Henry Norris Russell, plots a star's luminosity against its temperature, showing a strong trend and helping to understand stellar evolution.
• 🚀 The HR diagram illustrates the life stages of stars, with the main sequence representing most stars' active hydrogen fusion phase, and other groups indicating different stages of stellar evolution.

Q & A

What is the main reason stars appear to be different colors?

Stars appear to be different colors due to their temperatures and the elements in their atmospheres. This results in different amounts of light being emitted at various wavelengths.

Who introduced the new system of star classification in 1901?

Spectroscopist Annie Jump Cannon introduced the new system of star classification in 1901.

What did physicist Max Planck demonstrate about stars in the early 20th century?

Max Planck showed how stars give off light of different colors based on their temperature, with hotter stars emitting more light at the blue end of the spectrum and cooler stars peaking in the red.

What major discovery did Cecelia Payne-Gaposchkin make regarding the composition of stars?

Cecelia Payne-Gaposchkin discovered that stars are overwhelmingly composed of hydrogen, with helium as the second most abundant element, contrary to the previous belief that stars had similar compositions to Earth.

What is the mnemonic used to remember the classification of stars by their temperature?

The mnemonic used is 'Oh Be A Fine Guy, Kiss Me' or 'Oh Be A Fine Girl, Kiss Me,' which helps remember the order: O, B, A, F, G, K, M.

Why are there no green stars, despite the sun's spectrum peaking in the green?

There are no green stars because our eyes mix the green light with other colors emitted by the star, resulting in a white appearance. The sun appears white to our eyes due to this mixing of colors.

How can the distance of a star help determine its luminosity?

By measuring the star's apparent brightness and knowing its distance, astronomers can calculate its actual energy output or luminosity. This helps distinguish between intrinsically faint nearby stars and very luminous distant stars.

What is the significance of the HR Diagram in astronomy?

The HR Diagram, created by Ejnar Hertzsprung and Henry Norris Russell, plots stars' luminosity versus temperature, revealing strong trends and is considered the single most important graph in astronomy for understanding star properties and their life cycles.

What is the main sequence on the HR Diagram?

The main sequence on the HR Diagram is a broad, long line where most stars fall, indicating that they are fusing hydrogen into helium in their cores, which is a major phase in their life cycle.

What determines the rate of hydrogen fusion in a star's core?

The rate of hydrogen fusion in a star's core depends on the pressure in the core. More massive stars have higher core pressures, leading to faster fusion rates and higher temperatures.