11: Stellar Properties
- Page ID
- 64061
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Upon completion of this module, the student will be able to:Upon completion of this module, the student will be able to:
- Identify the basic stellar characteristics
- Describe how astronomers use parallax
- Identify terms, such as light-year, parsec, stellar luminosity, and magnitude system
- Detail Stellar Types and those responsible for the development of the stellar types
- Describe how the H-R Diagram works and what it shows
- Identify the different types of binary stars and variable stars
- Differentiate between globular and open clusters
- 11.1: Module Introduction
- This page discusses the waning popularity of children's lullabies, especially "Twinkle, Twinkle, Little Star," a poem from 1806. It explores the poem's relevance to both children and modern astronomy. Additionally, it outlines an educational module aimed at teaching students about stars, including their characteristics, classifications, and the H-R Diagram, with objectives focused on identifying stellar traits, understanding parallax, and differentiating star types and groups.
- 11.2: Variable Stars
- This page discusses variable stars, which exhibit brightness changes due to intrinsic characteristics rather than eclipses, numbering over 150,000. These changes vary in magnitude and duration and are classified into two main types: Pulsating Variables, which expand and contract, and Cataclysmic Variables. A significant subgroup of pulsating variables is Cepheid Variables.
- 11.3: Cepheids
- This page discusses Cepheids, which are massive variable stars characterized by their pulsation periods of one to 70 days and light variations of 0.1 to 2 magnitudes. They are important as standard distance indicators in astronomy due to the correlation between their luminosity and pulsation period. By calculating a Cepheid's luminosity and period, astronomers can determine its distance using the inverse square law, highlighting their significance in measuring galactic distances.
- 11.4: Cataclysmic Variables
- This page discusses cataclysmic variables, which are binary star systems consisting of a white dwarf and a secondary star that supplies matter. This transfer causes the primary star to exhibit irregular brightness outbursts, known as novae, followed by a dimming phase until the cycle repeats, contingent on the availability of stellar fuel.
- 11.5: Star Clusters
- This page explains star clusters, dividing them into two types: Open Clusters (OC) and Globular Clusters (GC). OCs are irregular, consist of 50 to over 100 young stars, and have a loose gravitational association. GCs are spherical, contain 10,000 to a million older stars, and are tightly bound. The page highlights their visual differences, noting that OCs are less organized and contain fewer stars compared to the dense, symmetrical GCs.
- 11.6: Consider this…
- This page features Dr. Neil deGrasse Tyson discussing the significant influence of the night sky on his life and his path to becoming an astrophysicist during an interview with Stephen Colbert on January 29, 2010.
- 11.7: The Unknown in Astronomy
- Astronomers analyze stars by comparing them to the Sun, exploring what constitutes an atypical star, especially regarding brightness and energy output. Abnormal stars, noted for their unique variations in brightness, are particularly intriguing. Studying these variations enhances understanding of how they differ from normal stars, like the Sun.
- 11.8: Star and Celestial Object Characteristics
- This page discusses key characteristics of stars, including stellar mass, size, surface temperature, and luminosity. Stellar mass is paramount as it influences a star’s fuel consumption and lifespan. Newton's application of Kepler's Third Law is used to measure binary star systems. Surface temperature affects a star's color and is determined by its diameter and energy output, while luminosity represents the energy emitted, relying on size and temperature.
- 11.9: Distances to the Stars and other Celestial Objects
- This page discusses the challenges astronomers encounter in measuring the distance and brightness of distant stars. Traditional tools like radar are ineffective due to energy loss over vast distances. Instead, they use stellar parallax, which involves measuring a star's apparent shift against distant stars as Earth orbits the Sun. This method helps in calculating distances to nearby stars, similar to perceiving the shift of a finger when viewed from different angles.
- 11.10: Stellar Distances
- This page discusses Earth's orbit around the Sun and stellar parallax, which measures distances to nearby stars. It features diagrams illustrating Earth's two positions and the apparent shift of a star over six months. The text notes challenges with parallax measurements, effective only for closer stars, and compares two stars to show how distance influences the angle of parallax, with nearer stars exhibiting larger angles than those farther away.
- 11.11: Everything is Moving
- This page discusses the complexities of measuring a star's position due to the movements of the Sun, Solar System, and other stars. It emphasizes the need for multiple measurements that account for these motions to achieve precise results.
- 11.12: How Close are the Close-by Stars?
- This page explains that the closest star to Earth is the Sun, with Proxima Centauri being the next closest at about 25 trillion miles away, part of the Alpha Centauri system. It clarifies that Proxima Centauri is often confused as the second closest star. To illustrate distances, it suggests that a stack of toilet paper 50 miles high represents one million miles, providing a relatable scale for understanding astronomical distances.
- 11.13: Light-Years
- This page explains why astronomers use light-years for measuring vast distances in space, as it simplifies figures significantly. A light-year represents the distance light travels in one year, making astronomical distances more comprehensible, such as the Sun being 8.33 light minutes away. Proxima Centauri is noted as 4.
- 11.14: Parsec Vs. Light-Year Measurement
- This page explains the parsec (pc) as a distance measurement in astronomy, defined by a parallax angle of 1 arcsecond, equating to roughly 3.261 light years or 1.9174 trillion miles. The term derives from "parallax of one arcsecond," and its use simplifies astronomical distance calculations, making it favored by astronomers over the light-year in scientific literature and general use.
- 11.15: Stellar and Celestial Object Brightness
- This page explains the distinction between luminosity and apparent brightness in stars. Luminosity, measured in watts, indicates a star's total power output, using the Sun as a reference (3.846×10^26 watts). Apparent brightness, on the other hand, is the light received per unit area, which decreases with distance according to the Inverse Square Law. The summary highlights that as one moves away from a light source, such as while driving at night, the perceived brightness diminishes significantly.
- 11.16: Magnitude System
- This page explains the magnitude system of ranking stars by brightness, initiated by Hipparchus and later revised by Pogson. It establishes a scale from 1 (brightest) to 6 (faintest), with Polaris rated at 2. Pogson's 1856 revisions quantified brightness differences and included the Sun and Moon, introducing the concept of Apparent Magnitude (M v) for measuring how celestial objects appear from Earth.
- 11.17: Celestial cartography
- This page discusses celestial cartography, emphasizing its role in astronomy for creating star maps. It parallels the challenges faced by early terrestrial cartographers, highlighting the complexities of depicting the numerous stars in the sky. Artistic elements were often incorporated into these maps, blending scientific knowledge with artistic skill for effective representation.
- 11.18: Planispheres
- This page explains celestial objects' brightness through formats like planispheres and star charts, illustrating apparent vs. absolute magnitude. Apparent magnitude reflects perceived brightness, while absolute magnitude offers a comparison of intrinsic brightness at a standard distance of 10 parsecs. For example, the Sun's apparent magnitude is -26.74, and its absolute magnitude is 4.83, highlighting the distinction between subjective observation and true brightness.
- 11.19: Star Colors
- This page discusses star colors determined by surface temperatures, classifying them into Spectral Types. Hotter stars appear blue-white, while cooler ones appear red. The classification system was refined by Annie Jump Cannon, and Cecilia Payne Gaposchkin established the temperature link in her 1925 dissertation. Her findings faced initial controversy regarding the Sun's composition but were later recognized, though overshadowed by Henry Norris Russell, who published similar conclusions.
- 11.20: Spectral Type
- This page details how Annie Jump Cannon created the spectral type classification system for stars, organizing them into types based on color and temperature. She streamlined the classification process by eliminating certain letters and numbers, resulting in the system widely used today.
- 11.21: Sample Spectral Types
- This page summarizes the spectral types of stars using the mnemonic "Oh Be A Fine Girl/Guy, Kiss Me" for O, B, A, F, G, K, and M categories. It details their temperature ranges, colors, and examples, with O stars being extremely hot and blue, and M stars being cooler and red. Additional star types such as carbon RNS stars and low-temperature L, T, and Y stars are also included, complete with their own mnemonics.
- 11.22: The Hertzsprung-Russell Diagram
- This page describes the Hertzsprung-Russell diagram (H-R Diagram), a graph plotting stellar luminosity against temperature and spectral type, created by Ejnar Hertzsprung and Henry Norris Russell around 1910. It shows patterns in stars, their groupings, and evolutionary changes, with color coding: blue-white stars on the left, yellow in the center, and red to purple on the right. Brighter stars are positioned higher on the Y-axis, indicating greater luminosity or absolute magnitude.
- 11.23: The Four Hertzsprung-Russell Diagram Stellar Groups
- This page explains the H-R Diagram, which classifies stars into four categories: Supergiants, Giants, White Dwarfs, and the Main Sequence. It highlights stellar evolution and the relationship between mass, luminosity, and diameter in stars with similar chemical compositions. The diagram can also represent other stellar classes like protostars and brown dwarfs, along with color index and magnitude data.
- 11.24: Types of Star Systems and Stars
- This page explores different star systems, including Optical Doubles, which are not physically related despite appearing double, and Binary Stars, which are physically associated pairs. It also covers Eclipsing Binary Stars (EBS), where one star's orbit causes periodic eclipses of another, with frequency variations based on the stars' proximity.