Unveiling the Universe: Stars, Planets, and Earth's Dynamic Past

Cosmic and Terrestrial Phenomena Explained

Cosmic Origins: Why We Are Stardust

We are stardust because calcium, oxygen, and almost all elements are compounds derived from the explosion of a star.

Stellar Lifespans: Why Massive Stars Burn Faster

Bigger stars last less time because they deplete their fuel faster than less massive stars. Their greater mass accelerates fuel consumption proportionally.

Evidence for the Big Bang Theory

One of the most important tests confirming the veracity of the Big Bang theory was provided by astronomer Vesto Slipher. He analyzed the light spectrum of the most distant galaxies and observed that their light waves invariably had a peculiar elongation. To understand the significance of these observations, one must understand the Doppler effect.

In 1929, Edwin Hubble established the law of recession of galaxies, which confirmed Slipher's work. According to Hubble's Law, the recession velocity of galaxies is directly proportional to their distance.

Pangea and the Theory of Continental Drift

Pangea was a supercontinent that existed about 100 million years ago. This supercontinent began to split into the present continents, which traveled thousands of miles, eventually reaching their current positions.

The hypothesis was received with the greatest skepticism by scientists. The greatest weakness of the hypothesis of continental drift lay in the fact that no known force was capable of breaking apart and displacing a continent thousands of kilometers. Aware of these criticisms, Wegener tried to find a plausible cause in the gravitational forces exerted by the Sun and the Moon, although other scientists expressed the impossibility of such an idea. Wegener defended his opinion until his death, but won few converts to his cause, and few scientists continued to support continental drift.

Yet, over time, new discoveries provided evidence that allowed his hypothesis to be resumed and appropriate corrections made, leading to the most currently accepted theory of plate tectonics.

Protostar vs. Star: Key Differences

A protostar has not reached thermonuclear fusion, while a star has.

Rocky Inner Planets: Solar Radiation's Role

The planets nearest the Sun are rocky because solar radiation causes the formation of denser materials.

Plate Tectonics: Obduction and Subduction

Subduction is when, at a convergent plate margin, one plate passes below the other. Obduction is when, at a convergent plate margin between an oceanic plate and a continental plate, the oceanic plate is mounted onto the continental plate.

Understanding Stellar Evolution

Stars form out of nebulae (clouds of gas and dust) which condense due to gravitational action. As temperature rises, the protostar emits light but has not yet begun thermonuclear fusion. When the temperature rises sufficiently, a star is born.

The primary process is fusion, converting hydrogen into helium (always losing some mass, which is converted into energy). Main sequence stars are in equilibrium. Smaller stars live longer because their gravity is less, and they consume fuel more slowly. When a star runs out of hydrogen, it begins to fuse helium into carbon.

The braking force in a star (like the Sun) is due to neutron degeneracy pressure. The nucleus continues to shine even without fusion and eventually cools, becoming a white dwarf. In larger stars, when iron fusion occurs, the star begins to collapse. If it swells, it can become a supernova. Massive stars can form black holes.

Key Facts About Stars and Our Galaxy

• How many stars in our galaxy? Approximately 400 billion.
• Most abundant chemical element in stars? Hydrogen.
• Force initiating star formation? Gravity.
• Diameter of the Sun? Approximately 1.5 million km.
• What holds a main sequence star in equilibrium? Avoiding gravitational collapse.
• Color of cooler stars? Red.
• Color of hotter stars? Blue.
• Smallest, coolest stars? Red dwarf.
• When will the Sun consume all its hydrogen? In about 5 billion years.
• What is a planetary nebula? Bright gas masses around the nucleus of a dying star.
• What can occur in a white dwarf belonging to a binary system? A white dwarf can accrete material (hydrogen) from its companion star, increasing its mass until it explodes in a thermonuclear reaction (Type Ia supernova).