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May 2, 2024 · The movement of Mars was problematic – it didn’t quite fit the models as described by Greek philosopher and scientist Aristotle (384 to 322 B.C.E.) and Egyptian astronomer Claudius Ptolemy (about 100 C.E to 170 C.E.). Aristotle thought Earth was the center of the universe, and that the Sun, Moon, planets, and stars revolved around it.
- Stage 1: A Giant Cloud of Gas
- Stage 2: The Protostar
- Stage 3: The T-Tauri Star
- Stage 4: The Main Sequence
- Stage 5: The Red Giant
- Stage 6: White Dwarves and Supernovas
Above: The Helix Nebula, located 700 lightyears away from Earth. Image Credit: NASA Stars begin their life cycles as clouds of gas and dust within a vast expanse of stellar debris called a nebula, formed from the gas and dust expelled by the explosion of a dying massive star. Once formed, a nebula becomes a region in space, often several times larg...
Above: A protostar forms an hourglass as the gas cloud contracts into the protostar's core. Image Credit: NASA In the second stage of a star's life cycle, the giant gas cloud collapses in on itself forming a protostar. The matter at the center of the cloud compresses into a hot, dense core. This core continues to pull in matter from the surrounding...
Above: Artist's rendition of a T-tauri star. Image Credit: Wikipedia The T-tauri stage, named for a star discovered in the Taurus constellation way back in 1852, begins once a protostar has collected enough material from the surrounding dust cloud to trigger a process called gravitational collapse. At this point, the gravitational pull of the proto...
Above: The sun entered the main sequence stage over 4.5 billion years ago. Image Credit: NASA After a hundred million years of gravitational collapse a T-tauri star's core reaches one million degrees Kelvin, igniting a fusion reaction. In the fourth stage of its life cycle, a Main Sequence star is sustained by the fusion reaction of hydrogen into h...
Above: The size of a red giant relative to the size of our sun. Image Credit: Daniel Huber Eventually, after billions and billions of years, a main sequence star runs out of hydrogen fuel and can no longer sustain the fusion reaction taking place inside its core. The hydrogen fuel runs out, the hydrogen-helium fusion reaction stalls, and the core s...
A star can remain a red giant until the remaining supply of helium in its core runs out. Then it transitions into the final stage of its life cycle. Depending on the size and solar mass of the star, its life will end in one of two ways: as a white dwarf star or as a supernova explosion. Above: Image of a white dwarf star. Image credit: BBC Sky Maga...
Scientists think planets, including the ones in our solar system, likely start off as grains of dust smaller than the width of a human hair. They emerge from the giant, donut-shaped disk of gas and dust that circles young stars. Gravity and other forces cause material within the disk to collide. If the collision is gentle enough, the material ...
Kepler’s First Law describes the shape of an orbit. The orbit of a planet around the Sun (or a satellite around a planet) is not a perfect circle. It is an ellipse—a “flattened” circle. The Sun (or the center of the planet) occupies one focus of the ellipse. A focus is one of the two internal points that help determine the shape of an ...
The night sky over New Zealand's Southern Alps gives a spectacular view of the Milky Way, the galaxy in which our own solar system resides. Mike Mackinven / Getty Images. Our planet Earth is part of a solar system that consists of eight planets orbiting a giant, fiery star we call the sun. For thousands of years, astronomers studying the solar system have noticed that these planets march ...
After a supernova, some stars leave behind a super dense neutron star, while the heaviest stars leave a black hole. Based on our understanding of stellar evolution, the Sun will start to run out of core hydrogen in about 5 billion years. The Sun will expand, engulfing several of the inner planets, including Earth.
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Apr 11, 2022 · This process is called the triple-alpha process, so named because physicists call the nucleus of the helium atom an alpha particle. When the triple-alpha process begins in low-mass (about 0.8 to 2.0 solar masses) stars, calculations show that the entire core is ignited in a quick burst of fusion called a helium flash .
