Astronomy: Life of Stars, Big Bang, and Orbital Mechanics

Flashcards covering astronomical topics including stellar evolution, Big Bang cosmology, nuclear fusion, Newton's laws of motion, Kepler's laws of planetary motion, and space exploration.

What is a light year, and what distance does light travel in one Earth year?

A light year is the distance light travels in one Earth year, which equals approximately $5.88\text{ trillion miles/year}$ (or $300{,}000\,\text{km/s}$, $136\,\text{miles/s}$).

According to the Big Bang Theory, when and how did the universe begin?

The universe began approximately $13.7\text{ billion years}$ ago with an enormous explosion, and galaxies continue to expand from this initial event.

What are the three main lines of evidence supporting the Big Bang Theory presented in the lecture?

1. Color of light (redshift)\n2. Existence of microwaves (cosmic microwave background)\n3. Evidence from telescopes

How does the color of light indicate whether an astronomical object is moving towards or away from an observer?

Blue light indicates the object is moving towards the observer (waves are bunched together with shorter wavelengths), while red light indicates it is moving away (waves are stretched out with longer wavelengths).

What is the Doppler effect?

The change in frequency of a wave relative to an observer, applicable to both sound waves and light waves.

What major change occurred in the universe approximately $380{,}000\text{ years}$ after the Big Bang?

The universe cooled down sufficiently for atoms to form, allowing light to travel freely rather than scattering randomly.

What is a spectroscope and how do astronomers use it?

A spectroscope is an instrument that spreads light into different wavelengths, allowing scientists to examine spectra and determine how far light has traveled through redshift.

What does Hubble's Law state?

The further away a galaxy is from Earth, the faster it is moving away, as observed by its redshift.

Where was the physical center of the Big Bang explosion?

The Big Bang had no central point; it was not an explosion in space, but an expansion of space itself occurring everywhere simultaneously.

How do stars begin their life cycle, and what triggers nuclear fusion?

Stars begin as giant clouds of Hydrogen ($\text{H}$) gas; when they grow massive enough, they collapse under gravity, causing Hydrogen atoms to fuse into Helium.

What is a supernova, and what role does it play in the formation of elements?

A supernova is the explosion of a red supergiant star. The energy and collisions of atoms during this explosion create the elements on the periodic table beyond iron ($\text{Fe}$) and scatter them throughout the universe.

In what form does energy from nuclear fusion in the Sun travel through space to Earth?

Energy reaches Earth as radiation (not heat) and is experienced on Earth as heat and light.

What are the three steps of the nuclear fusion reaction that powers stars?

Step 1: Two $\text{H}$ atoms fuse to form Deuterium (Hydrogen with a mass of $2$), releasing $+1\text{ energy}$.\nStep 2: Deuterium fuses with another proton to become Helium-3, releasing $+4\text{ energy}$.\nStep 3: Two Helium-3 nuclei fuse to form Helium-4 and release two protons, producing $+9\text{ energy}$.

What is an isotope?

An atom of the same element that has the same number of protons (atomic number) but a different number of neutrons, resulting in a different mass number.

What causes sunspots on the photosphere of the Sun?

Sunspots are caused when intersecting magnetic fields block radiation from being emitted, creating localized areas that are cooler and appear darker than the surrounding surface.

What are solar flares, and what causes them?

Solar flares are explosive releases of energy from the core of the Sun that occur when the magnetic fields causing sunspots snap.

How are mass and inertia related according to Newton's First Law?

Mass is solely dependent on inertia, which is the resistance to a change in motion; greater mass means greater inertia.

How do mass and distance affect the force of gravitational attraction between objects?

Gravitational attraction increases when mass increases and when distance decreases.

How does Newton's Second Law ($F_{\text{net}} = ma$) explain the stable orbit of a planet around a star?

The star's gravitational pull acts as the net force ($F_{\text{net}}$), continuously accelerating the planet toward the star and curving its path away from straight-line inertia into an orbit.

What does Kepler's First Law of Planetary Motion state?

Planets orbit the Sun in ellipses (ovals) with the Sun located at one focus, meaning the distance between a planet and the Sun varies throughout its orbit.

Which of Kepler's laws is represented by this orbital diagram, and what principle does it illustrate?

Kepler's Second Law; it illustrates that an orbiting planet sweeps out equal areas in equal intervals of time ($\text{Area } 1 = \text{Area } 2$ over one month).

What does Kepler's Third Law (Law of Harmony) describe regarding planetary orbits?

Planets closer to the Sun have shorter orbital periods ('years') than those farther away; the square of the orbital period is proportional to the cube of the semi-major axis.

What milestone marked the beginning of satellite technology in 1957?

The launch of the first artificial satellite into orbit by the former Soviet Union.

What is astrobiology?

The study of life in the universe, including life on Earth and the possibility of extraterrestrial life.