Astrophysics Chapter 1: Stellar Quantities

• Chapter 1 focuses on Astrophysics.
• The term covers from Term 3, S.Y. 2024-2025, at Asia Pacific College.
• The instructor is MC. Benrick B. Porras.

Chapter Agenda

• Stellar Quantities: Solar System, Stars, Astronomical Distances, Luminosity and apparent brightness
  • Cosmology: Redshift and Hubble's Law; The Big Bang model and the age of the universe

What is Astrophysics?

• Astrophysics applies the principles of physics and chemistry to understand astronomical objects and phenomena.
• It explains the nature of celestial bodies like stars, planets, galaxies, nebulae, and the universe.
• Astrophysics Models Celestial Systems using advanced mathematics and computer simulations to model star clusters and multi-planet or multi-moon systems.
• Astrophysics Studies the formation and evolution of astronomical objects.
• Cosmology is explored, investigating the entire universe, including its origins and structure.
• Cosmic History is traced by examining the creation of the universe and the history of stars and galaxies.
• Astrophysics helps people search for Life, to Discover how planetary systems form and search for signs of life on other worlds.

Solar System

• The Solar System contains different planets, moons, asteroids, comets, and other rocky objects.
• These objects are traveling in elliptical orbits around the Sun.
• The Solar System has Inner (Terrestrial) Planets, Outer (Jovian) Planets, Dwarf Planets, Moons, Asteroid Belt and Kuiper Belt.
• The solar system–planetary system includes a central star of the Sun.
• The System Also contains many natural space objects orbiting the Sun, and was formed by gravitational compression of gas and dust cloud about 4.57 billion years ago.
• The Total mass of the Sun is 99.86% of the entire Solar System.
• The Sun is a 4.5-billion-year-old star at the center of the solar system.
• The Sun is hot a glowing ball of hydrogen and helium.
• The Sun is the Solar System's largest object around 93 million miles from Earth.
• Life on Earth without the Sun would not be possible.
• The Sun is approximately 100 times larger than Earth and approximately 10 times larger than Jupiter.
• The Core temperature is approximately 15 million degrees Celsius.
• Everything in the solar system revolves around the Sun.
• Nuclear fusion, including H2, He, C, O, Ne, Mg, Si, and Fe occurs on the Sun.
• The four Terrestrial Planets close to the Sun have high condensation temperatures that remain solid, gradually accreting particles.
• Mars is considered is the Twin Planet of Earth.
• The Gas Giants: Uranus and Neptune - quantity of ice meant that they became huge and produces strong gravitational fields.
• The strong gravitational fields that captured the slow-moving hydrogen and helium.
• Jovian planets are gas and ice giants in the outer solar system.
• Terrestrial planets are Mercury, Venus, Earth, and Mars.

Why Pluto is Not a Planet

• Not all planets have cleared its orbit of objects
• Pluto orbits the sun, and it's spherical, but it shares its orbital space.
• Pluto shares space with other Kuiper Belt objects.
• Dwarf planets are spherical celestial bodies orbiting the Sun.
• Dwarf planets have not cleared their orbital paths of other debris.
• Pluto was classified as the ninth planet, but redefined as a dwarf planet in 2006.
• Eris is the largest known dwarf planet in the outer Solar System, instrumental in Pluto's reclassification.
• Makemake is a bright, icy dwarf planet located in the Kuiper Belt.
• Haumea has an elongated shape due to rapid rotation, also in the Kuiper Belt.
• Ceres is the largest dwarf planet in the Asteroid Belt, positioned between Mars and Jupiter.
• The Kuiper Belt lies beyond Neptune.
• The Kuiper Belt is the source of short-period comets and contains dwarf planets, including Pluto.
• The Solar System's minor bodies include asteroids, dwarf planets, and moons.
• Asteroids are also called "small planets."
• Asteroids Rocky objects that primarily reside in the Asteroid Belt between Mars and Jupiter.
• Meteoroids are fragments of asteroids or comets entering Earth's atmosphere as meteors.
• Comets develop glowing tails in the Sun's approach.
• The Kuiper Belt and Trans-Neptunian Objects are beyond Neptune, home to dwarf planets like Pluto and Makemake.
• Mars has moons Phobos and Deimos.
• Earth has one Moon.
• Jupiter has Ganymede, Europa, Lo and Callisto.
• Saturn's moons are Enceladus and Titan.
• Uranus has Titania, Oberon, Umbriel, Ariel, Miranda and Puck.
• Neptune has Triton, Proteus, Nereid, Larissa, Galatea and Despina.

Stars

• Stars are giant balls of hot gas, mostly hydrogen, with helium and small amounts of other elements.
• Stars have a life cycle for millions to trillions of years, and properties change as they age.
• The process of forming Stars starts with a dark cloud, a prestellar core, a protostar, a T Tauri star, a pre-main sequence star, then a main sequence star
• Stars exist in groups:
  • Binary Stars rotate around a common mass center.
  • Stellar clusters are positioned closely by gravity; contain a few dozen to millions of stars forming simultaneously within the same nebula.
  • Open Cluster contain up to several hundred stars under ten billion years with some gas and dust.
  • Globular clusters contain many stars over eleven billion years with little gas and dust.
  • 80% of the stars in our galaxy are binary stars
• Constellations are different from star clusters.
• Constellations are patterns formed by stars in the same general direction when viewed from Earth and have religious importance.
• There are 88 officially recognized constellations.

Nebulae

• Nebulae are regions of intergalactic cloud of dust and gas.
• Stars are born in nebulae which act like stellar nurseries.

Galaxies

• Galaxies are vast collections of stars, gas, dust, and dark matter bound together by gravity.
• They include spiral types, containing 100-400 billion stars, some are 100, 000 light years across; 12.5 billion years.
• The Supermassive Sagittarius A blackhole is that the center of our galaxy.
• Elliptical galaxies are galaxy with ellipsoidal shape and a nearly featureless image.
• Irregular galaxies have no distinct regular shape unlike spirals.

Astronomical Distances

• Due to vast distances, astronomers use specialized units:
  • Astronomical Unit (AU): Distance between the Sun and Earth, approximately 1.50 x 1011 meters, or 8 light minutes; used within our solar system.
  • Light-Year (LY): Distance light travels in one Earth year, 9.46 x 1015 meters; used for stars and galaxies.
  • Parsec (pc): Unit of distance, equivalent to 3.26 light-years; typically used to express distances outside our solar system.

Parallax effect and its use in measurements

• Parallax is where Visual of an object relative to a background changes, This is based on the viewer's position
• Parallax is the apparent displacement of an object when viewed from different positions - Lebron James, 2025
• The mathematical parallaxes distance of close by stars can be found using parallax effect
• Closer stars have a greater degree of parallax. So the effect can't be used to measure extremely distant stars

Equations

• SOH-CAH-TOA is used to calulate the measure
• TOA stands for Tan= Opposite / Adjacent
• SOH stands for Sin= Opposite / Hypotenuse
• CAH stands for Cos= Adjacent / Hypotenuse

Luminosity

• Luminosity (L) represents the total energy a star or astronomical object emits per second and is an intrinsic property measured in watts (W).
• Apparent Brightness (b) is the brightness of a star/celestial object appears from Earth.
• Apparent Brightness depends on the object's intrinsic luminosity and its distance from the observer.
• Luminosity depends on the observer distance, W/m² or W.m-2
• Luminosity Formula: b = L / 4πd2

Absorption and Emission

• The element composition of a star from absorption spectra known elements.
• There are Continuous Spectra, which shows all of visible light frequencies
• Emission Line Spectra is produced when electrons jump from higher to lower energy levels.
• Electrons jump from lower to higher energy level, creating Absorption Line Spectra
• Thus, the surface elements of a star can be spotted from the absorption spectrum.
• Spectral classes grouping depending on similar spectra and their surface temperature.
• All stars are approximately 74% H, 25% He, and 1% other elements, depending on class.
  • Bluest or 0 is ionized helium.
  • Bluish or B is neutral helium, neutral hydrogen.
  • Blue-white or A is neutral hydrogen
  • White or F is neutral hydrogen, ionized calcium.
  • Yellow-white or G is neutral hydrogen with the strongest ionized calcium
  • Orange or K is neutral metals (calcium, iron), ionized calcium,
  • Red or M is molecules and neutral metals
• Spectral classification include: O, B, A, F, G, K, M.

HR Diagram

• The Hertzsprung-Russell Diagram is a graph plotting stars' absolute magnitudes (intrinsic brightness) against their spectral types (temperatures).
• Main Sequence Stars - ordinary stars, similar to the sun, and make up 90% of all the stars.
• Super giants - very large, and cooler/hotter temperature
• White Dwarfs - much smaller like the earth, hotter temperature to the sun.

Stellar Evolution

• Einar Hertzprung and Henry Norris Roccel have related work on Stellar Evolution
• In the main sequence stars, there is a relationship between luminosity and mass, described by: L ∝ M3.5

Cosmology

• Concerns the Redshift Effect, Hubble's Law, and the Big Bang
• The doppler effect, the frequency of a wave in relation to the observer, due to relative motion.
• REDSHIFT EFFECT where the wavelength of light/electromagnetic radiation from an object are increased to appear more red.
• If an object becomes nearer, it shifts to the color blue but when something becomes further, it will shift from red.
• Hubble's Law is where Edwin Hubble discovered that the amount of redshift changed by the distance.
• The Hubble's Law of Velocity is an equation using Velocity is directly proportional to the distance from us.
• The Big Bang theory is one explanation and standing for the universe origin