6.4 Flashcards
Learning Intentions Describe stars: formation, brightness and life cycle Use Hertzsprung-Russell diagrams to classify stars in terms of absolute magnitude and temperature
What do all stars begin as?
A nebula (collection of dust and gas).
What is the Great Orion Nebula?
A nebula visible from Earth with the naked eye.
What forms when a nebula collapses due to gravity?
A dense cloud, forming visible globules.
What is a protostar?
A dense cloud not yet hot enough for nuclear fusion.
What triggers nuclear fusion in a protostar?
High temperatures from increased pressure.
What is nuclear fusion?
The fusion of hydrogen isotopes (deuterium and tritium) to form helium, releasing a neutron and energy.
What do larger stars fuse?
Larger atomic nuclei to form heavier elements.
Why are larger stars hotter?
They fuse heavier elements, increasing gravity and pressure.
What does apparent magnitude measure?
The brightness of a star as seen from Earth.
Why might some stars appear brighter than others?
They may be closer to Earth, not necessarily brighter.
What is the scale range for apparent magnitude?
-30 (brightest) to +30 (dimmest).
What is the apparent magnitude of the full moon and the Sun?
Full moon: -13; Sun: -27.
What does absolute magnitude measure?
The actual brightness of a star.
How is absolute magnitude calculated?
By determining the star’s distance from Earth.
What two factors are used to categorize stars?
Absolute magnitude and temperature.
What does a red star indicate about temperature?
A red star is cooler.
What does a blue or white star indicate about temperature?
A blue or white star is hotter.
How do scientists classify stars?
By analyzing the spectrum of light and photographs of the stars.
What do dark lines in a star’s light spectrum indicate?
They correspond to colors of light absorbed by substances in the star.
Why do different substances show different dark lines in a spectrum?
Different substances absorb different colors of light.
How can astronomers identify elements in a star?
By identifying the wavelengths of the colors missing from the spectrum.
What is a red shift in a star’s spectrum?
A shift to lower frequencies, indicating the star is moving away from the observer.
What is a blue shift in a star’s spectrum?
A shift to higher frequencies, indicating the star is moving toward the observer.
What happens to light waves when a star moves toward Earth?
The waves are squeezed together, shortening the wavelength and shifting spectral lines toward blue.
What happens to light waves when a star moves away from Earth?
The waves are stretched out, increasing the wavelength and shifting spectral lines toward red.
What is red shift?
A shift of spectral lines toward the red end of the spectrum (lower frequencies) when the source moves away from the observer.
What is blue shift?
A shift of spectral lines toward the blue end (higher frequencies) when a light source moves rapidly toward the observer.
What did Edwin Hubble observe in 1929?
Some galaxies were moving toward Earth, while most were moving away.
What relationship did Hubble discover?
A relationship between the size of the red shift and the distance from Earth.
What is the relationship between a galaxy’s distance and its red shift?
The further a galaxy is from Earth, the greater its red shift and the faster it is moving away.
What explains the movement of most objects away from each other in the Universe?
The expansion of space.
How does the expansion of space resemble a balloon?
Like a balloon’s surface increasing in size as it inflates, increasing distance between objects.
What happens to the speed of objects moving apart as distance increases?
The further apart two objects are, the faster they move apart.
What is the Hertzsprung–Russell diagram (HR diagram)?
A scatter plot showing the relationship between stars’ absolute magnitudes or luminosities and their stellar classifications or effective temperatures.
Who created the HR diagram, and when?
Ejnar Hertzsprung and Henry Norris Russell, around 1910.
What does the HR diagram help scientists understand?
Stellar evolution.
What do some scientists use in the HR diagram aside from luminosity?
Stellar classifications (e.g., white dwarf, supergiant).
What is luminosity in astronomy?
An absolute measure of radiated electromagnetic power (light) from an object.
How is luminosity often expressed in astronomy?
In terms of the luminosity of the Sun (L⊙).
What is a stellar nebula?
A cloud of gas and dust where stars are born.
What is a main sequence star?
A stable phase where a star fuses hydrogen into helium in its core.
What is a red giant?
A phase where a star expands and cools after exhausting hydrogen in its core.
What is a red supergiant?
A massive star that expands further and cools, leading to eventual collapse.
What is a planetary nebula?
The outer layers of a star expelled after the red giant phase, surrounding a white dwarf.
What is a white dwarf?
The remnant core of a low to medium mass star after it has shed its outer layers.
What is a black dwarf?
A theoretical stage where a white dwarf has cooled and no longer emits significant heat or light.
What is a supernova?
A powerful explosion marking the death of a massive star, resulting in either a neutron star or black hole.
What is a neutron star?
A dense remnant of a supernova, composed mostly of neutrons.
