Curiosity to Land on the Red Planet

Curiosity: A model at the Discovery Science Center

The Mars Rover Curiosity will land on the Red Planet on August 5, 2012 (Pacific Time).

A collaboration between JPL (Jet Propulsion Laboratory) and NASA, Mars Rover Curiosity (SUV), otherwise known as Mars Science Laboratory (MSL), has technology that succeeds its predecessors, Spirit and Opportunity (golf carts) and Sojourner (microwave). NASA launched Curiosity on November 26, 2011 at the Cape Canaveral Air Force Station. Curiosity is expected to land on August 5, 2012 on the Aeolis Palus region of the Gale crater. Curiosity‘s four objectives are: 1) determine whether Mars is suitable for life; 2) study Mars’ climate; 3) study Mars’ climate; 4) plan future human mission to Mars.

THE BASICS

  • Weight: 2,000 lbs.
  • Length: >9.8 ft.
  • Distance Covered (per day): ~600 ft
  • Lifetime: >687 Earth days (1 Martian year)

SPECIFICATIONS

  • Power: Radioisotope Thermoelectric Generator (RTG) – uses the decay of plutonium-238 to generate 2.5 kilowatt hours per day
  • Heat Rejection System: To keep Curiosity at optimal temperatures since temperatures on Mars vary dramatically (30°C  to -127°C)
  • Computers: “Rover Compute Element” – tolerates extreme radiation from space; Inertial Measurement Unit (IMU) – rover navigation
  • Communications: X band transmitter – communicate directly with Earth; UHF Electra-Lite software defined radio – communicate with Mars orbiters
  • Mobility: 6 wheels in rocker-bogie suspension – serve as landing gear

COOL GADGETS

  • Cameras: 1. MastCam – multiple spectra and true color imaging; 2. Mars Hand Lens Imager (MAHLI) – microscopic images of rock and soil; 3. MSL Descent Imager (MARDI) – color images to map the  surrounding terrain and landing location
  • ChemCam: laser to vaporize samples up to 7 meters away for analysis, with the laser-induced breakdown spectroscopy (LIBS) and micro-imager (RMI)
  • Alpha-particle X-ray spectrometer (APXS): map the spectra of X-rays to elemental composition of samples
  • Chemistry and Mineralogy (CheMin): identify and quantify abundance of minerals on Mars
  • Sample Analysis at Mars (SAM): analyze organics and gases from atmospheric and solid samples
  • Dynamic Albedo of Neutrons (DAN): measure hydrogen, ice, and water at and near Martian surface
  • Rover Environmental Monitoring System (REMS): measure atmospheric pressure, humidity, wind currents and direction, air and ground temperature, UV levels
  • MSL Entry Descent and Landing Instrumentation (MEDLI): measure aerothermal environments, sub-surface heat shield response, vehicle orientation, atmospheric density; detect heat shield separation
  • Hazard Avoidance Cameras (HazCams): use light to capture 3-D image to protect the rover from crashing
  • Navigation Cameras (Navcams): use visible light to capture 3-D images for navigation

LANDING

Landing Sequence

  • EDL (Entry, Descent, Landing): also called the “7 minutes of Terror,” because any malfunction or any misstep means failure of the mission
  • Landing Sequence: “6 vehicles, 76 pyrotechnic devices, 500,000 lines of code, zero margin of error”; from 13,000 miles an hour to 0 miles and hour; 1,600 degrees upon entry
  • Mar’s atmosphere is 100 times thinner than Earth’s so it is harder for MSL to slow down
  1. Guided Entry: control the craft to approximate landing site region
  2. Parachute Descent: supersonic parachute (can withstand 65,000 lbs of force but only weighs 100 lbs.) deploys at 10 km altitude
  3. Powered Descent: cut parachute off and rocket thrusters (Mars Lander Engine, MLE) extend out and slow the descent
  4. Sky Crane: lower the rover with a 21-foot tether wheels down onto the Martian crater to prevent the rockets from making dust clouds; the bridle is cut and the rock thrusters fly away to a safe distance

INTERESTING FACTS

  • Each wheel on Curiosity has a specific traction pattern that is Morse code for “JPL”
  • It takes 13 minutes and 46 seconds to relay signals from Earth to Curiosity

References

Grecius, Tony, ed. “Mars Science Laboratory.” NASA. NASA, July 2012. Web. 27 July 2012.

Albert Einstein’s Legacy

ALBERT EINSTEIN (1879-1955)

Albert Einstein

Legacy

  • Reformulated the concept of time and space (E = mc² => special relativity)
    • Time is not an absolute quantity but appears to flow at a different rate depending on relative motion
  • Opened the road to quantum mechanics
    • Light “hits” like a particle
    • Light waves have “quantized” and “discrete” energies, depending on their wavelengths
  • Presented a revised theory of relativity
    • General relativity: space is curved
    • Foundation of modern cosmology

Einstein’s World

  • Reality of atoms and molecules in hot debate
  • Light poorly understood: “What was the medium light traveled in?”
  • Phenomena of radiation
  • Absorption lines in the Sun were observed, but could not be explained

Einstein helped clear these mysteries and began the era of modern physics.

Einstein’s Early Life and Career

Born in Ulm, German Empire in 1879, Albert Einstein excelled in physics and mathematics but failed in other subjects. Einstein dropped out of high school in 1895 and restarted school in Aarau, Switzerland, where he studied Maxwell’s works (~1870), which stated that electricity and magnetism obeyed the same set of physical laws — hence, electromagnetism. Einstein discovered that the velocity of light remained constant no matter the media. Although Einstein was brilliant, he irritated professors as he was too independent. In 1902, Einstein became a patent office clerk at the Swiss Patent Office in Bern. By 1905, Einstein had written six scientific papers, three of which explored the existence of molecules and the “kinetic theory.” For his other three papers, one published in March explained his light-quantum hypothesis (light hits like a particle), a fundamental step of quantum mechanics. For this, Einstein received a Nobel Prize in 1921. Another paper published in June was Einstein’s first paper on Special Relativity that explored light contraction and time dilation approaching the speed of light. In September of 1905, Einstein published his second paper on special relativity, in which he included the famous equation E = mc².

* General relativity includes gravity, while special relativity does not.

General Relativity and Special Relativity

Special Relativity

  1. The laws of physics are the same in all uniformly moving reference frames, or in all directions
  2. In any uniformly moving reference frame, the velocity of light (c) is the same whether emitted by a body at rest or a body in motion

Time Dilation and Length Contraction

Time Dilation: Time itself doesn’t tick at the same rate approaching the speed of light; instead, the time synchronization veers off; so approaching the speed of light, time appears to tick much slower.

Length Contraction: The lengths of moving objects are contracted when viewed by a stationary viewer

Mass and Energy

  • The mass of a moving body increases compared to its “rest mass” because it takes a bigger force to accelerate
  1. Acceleration: speed gained in a given time
  2. An object accelerating up is smaller because of time dilation; acceleration is harder the more massive the object is
  • Energy is responsible for powering stars, nuclear decay, and nuclear energy

Einstein’s Impact

  • At first, the scientific community met Einstein’s special relativity theory with silence, but Max Planck, who won the Nobel Prize for explaining black body radiation, realized the importance of Einstein’s work and publicized it; from 1906, scientists took notice and visited Einstein to talk about science
  • Einstein’s scientific circles grew stating 1908; became associate professor in 1911 and a professor of the Swiss Federal Institute of Technology in 1912
  • Einstein’s findings demanded a new way of thinking as Newton’s Law of Gravity was only valid from speeds much smaller than light
  • Einstein named the “birth of special relativity” “The Step”
  • 1907: The Equivalence Principle – gravity corresponds to acceleration
  • 1911: Bending of light in a gravitational field, a consequence of the Equivalence Principle, could be checked with astronomical observations
  • 1912-1915: Extend relativity to objects moving in an arbitrary way with respect to one another
  • 1915: General Relativity “Gravity curves space”: there’s no need for the “force” of gravity; all motion is along “straight lines” in curved space-time and matter tells space how to move
    • Evidence: starlight bends around the Sun; Mercury’s orbit will precede at a different rate than Newton predicted
  • 1919: Arthur Eddington leaders solar eclipse expedition and confirms special relativity
  • 1929: Edwin Hubble observes expansion of the Universe
    • Friedmann said that Einstein’s equations supported an expanding Universe, but Einstein proposed the “cosmological constant” to keep the Universe static

COSMOS: UCI – Part 2

UCI Observatory

The UCI Observatory is located about a mile from the UCI campus. Though relatively small compared to famous observatories such as Keck Observatory in Hawaii or Kitt Peak Observatory in Arizona, the UCI Observatory serves basic viewing purposes. UCI Observatory dome houses a 24-inch telescope with a CCD camera and a 8-inch portable telescope. UCI professor Dr. Tammy Smecker-Hane and TAs Liuyi Pei, John Phillips, and Shea Garrison-Kimmel adjusted the telescopes and pointed them toward objects of interest, among which were the Ring Nebula, Mars, Saturn, star clusters, and a binary star system.

“As a bumpy, seat-wrangling dirt road emerges, a muddy, night-black SUV launches itself past ironclad gates. City lights twinkle to the left; hills lined with sharp grasses cast shadows to the right. Music blasts from speakers; Cosmonauts chatter nonstop, voices intermixed. A gray-white dome emerges and four shadows await, silently calibrating the 24 and 8-inch ocean-blue telescopes. As the sun dips beneath the horizon, night blankets the earth and icy air tackles my vest and slacks. First the moon, then Vega and Ursa Major— the true celestial sphere has appeared.” – Tianjia Liu

COSMOS: UCI – Part 1

In Remembrance: Sally Ride (1951-2012)

SALLY RIDE (May 26, 1951 – July 23, 2012)

Sally Ride, First Woman Astronaut in Space

Sally Ride, the first woman astronaut to travel to space, passed away today at the age of 61 from her 17-month battle with pancreatic cancer. At Stanford University, Ride earned her master’s degree and Ph.D in physics. Ride joined NASA in 1978 and rode the Challenger to space on June 18, 1978 at the age of 32 and again in 1984. She spent 14 days in space!  After NASA, Sally Ride worked at the Stanford University International Security and Arms Control and taught physics at the University of California, San Diego. She later became the director of the California Space Institute and the founder and CEO of Sally Ride Science. Today, President Obama remembered Sally Ride as “a national hero and a powerful role model.”

References

Borenstein, Seth, and Alicia Chang. “Sally Ride, first US woman in space, dies at 61.” Boston.com. Boston.com, 23 July 2012. Web. 23 July 2012.

COSMOS: UCI – Part 1

COSMOS Cluster 2 as Saturn and Its Moons

COSMOS Cluster 2 as Higgs Boson

This past month (June 24, 2012- July 21, 2012), I attended the COSMOS (California State Summer School for Mathematics and Science) at the University of California, Irvine, with brilliant minds from Northern and Southern California, as well as other states. The 152 students were divided into 8 clusters. I was part of Cluster 2: Astronomy and Astrophysics. With 22 other COSMOS students, I ventured into the world of astronomy and astrophysics unraveled by UCI professors Dr. Tammy Smecker- Hane, Dr. James Bullock, Dr. Aaron Barth, Dr. Erik Tollerund, TAs John Phillips, Liuyi Pei, and Shea Garrison-Kimmel, and Teacher Fellow Lisa Taylor. I discovered that all students shared a strong passion for astronomy and high aptitudes for learning. It has been my honor to learn with the students, listen to the professors’ lectures, and follow the TAs’ instructions for CLEA (Contemporary Laboratory Experiences in Astronomy) Labs.

For a cumulative final, the TAs divided the class into 8 groups for Project Labs:

“Deriving the Mass of Saturn” (By: Angel Guan, Francisco Terrones, and Luis Loza; Directed By: Liuyi Pei)

1. Deriving the Mass of Saturn

“Finding the Angular Velocity of an Asteroid” (By: Rachel Banuelos and Luis Salazar; Directed By: John Phillips)

2. Finding the Angular Velocity of Asteroids

3. Properties of an Eclipsing Binary Star System

  • By: Carlin Liao, Matthew Thibault, Sara Sampson; Directed By: Shea Garrison-Kimmel

4. Determining Stars’ Properties Using Stellar Spectra

  • By: Tina Liu, Noemi Urquiza, John Cabrera; Directed By: John Phillips

“Determining the Properties of Open Cluster M11″ (By: Luzanne Batoon, Julian Rose, Janet Lee; Directed By: Tammy Smecker-Hane)

5. Determining the Properties of Open Cluster M11

“Determining the Properties of Globular Cluster M13″ (By: Dennis Feng, Maricruz Moreno, Collen Murphy; Directed By: Tammy Smecker-Hane)

6. Determining Properties of Globular Cluster M13

7. Dark Matter in the Universe: Measuring the Rotation of Spiral Galaxies

  • By: Emma MacKie, Danny Tuthill, Michael Cox; Directed By: Shea Garrison-Kimmel)

8. Number Counts of Distant Galaxies and the Shape of the Universe

  • By: David Wong, Thomas Purdy, Joshua Heck; Directed By: Liuyi Pei

“Determining Stars’ Properties Using Stellar Spectra” (By: Tina Liu, Noemi Urquiza, John Cabrera)

- The red, white, yellow, and blue dots in the background represent stars of the H-R Diagram, including main sequence stars, red giants, and white dwarfs.

My Project: Determining the Properties of Stars Using Stellar Spectra (By: Tina Liu, John Cabrera, and Noemi Urquiza; Directed By: John Phillips)

ABSTRACT: Stellar spectra are fundamental in understanding properties — temperature, spectral type, chemical composition, and mass — of stars.  A spectrum is the amount of light that a star emits through narrow slit about 1 Angstrom in width. With the UCI Observatory’s 24-inch telescope and its photograph and ST-8 CCD camera, images of stars’ spectra — those of Arcturus, Vega (HD172167), and HD142780— were taken. Using the software program IRAF, the spectra were extracted, calibrated, and analyzed. Since stars are classified by spectral types, stellar spectra help distinguish a more massive and hotter star from a less massive and cooler star. Analyzing the strengths of absorption lines shows the stars’ compositions of elements such as hydrogen, helium, and calcium. While hotter stars such as Vega are more massive and have strong hydrogen absorption lines, cooler stars such as Arcturus are less massive and have strong neutral metals lines. Understanding stars’ properties leads to a better grasp of the past, present, and future of the Universe.

QUESTION: How can we use stellar spectra to determine the properties of stars such as spectral type, temperature, mass, and chemical composition?

Spectra of different elements including hydrogen, helium, and neon

BACKGROUND INFORMATION: Stars, actually infinitesimally small points of light, appear to twinkle because light refracts at Earth’s atmosphere. Held by gravity, stars shine due to nuclear fusion, its source of fuel. Their lifetimes depend primarily on mass; for their prime of life, stars, travel along the main sequence on the Hertzsprung- Russell, or Color- Magnitude Diagram. A stellar spectrum is the amount of light a star emits at a narrow wavelength interval (about 1 Angstrom, or 10^-10 meters). Each element has a distinguishable pattern of absorption lines (dark bands along the spectrum). Spectral types are a classification scheme developed by Annie Jump Cannon in the late 1800s and early 1900s. The spectral types are ordered in decreasing surface temperatures: O, B, A, F, G, K, M. Originally the classification scheme was A, B, C, D, etc. and stars were ordered according to the strengths of their Balmer (hydrogen) lines. Since stars with the strongest Balmer lines are not necessarily the hottest stars (hotter temperatures caused electrons to be excited and the atom to be ionized- lose electrons), the scheme was rearranged. The two stars analyzed were two variable stars: Arcturus of the constellation Boötes and Vega of the constellation Lyra.

MATERIALS:

  • 24-inch telescope, ST-8 CCD camera
  • Needed Files on Linux (software):
    • uciobs_fear_lowres.dat (from observatory website): List of arc lines used for wavelength calibration
    • arc_red.jpg (from website): Plots of arc images, with wavelengths of prominent lines
    • plotspec.pro : Plots the reduced spectrum and marks absorption lines that are found in LINES.UCI file
    • wave : File containing wave limits of reduced spectra. Needed to run plotspec.pro
    • LINES.UCI : Input file for plotspec.pro that contains prominent absorption lines to be marked on the final, reduced spectrum

PROCEDURES: Independent Variable: Wavelength (Angstroms); Dependent Variable: Intensity

  1. Take pictures of stars using a 24 inch telescope and ST-8 CCD camera
  2. Use DS9 on Linux to analyze and crop the portion of the image planned on using
  3. Edit parameters
  4. Label absorption lines according to reference, with each element specific to its wavelength
  5. Graph the spectrum
  6. Change “pixel” on the x-axis to “wavelength”
  7. Analyze the star’s properties by comparing them to predetermined spectral types.

RESULTS:

Arcturus Spectrum

Arcturus: “K” type star, 4,290 K, 1.5 solar masses, absence of hydrogen lines and abundance of neutral metal lines

Vega spectrum

Vega: “A” type star, 9,600 K, 2.14 solar masses, strong hydrogen lines

HD142780 spectrum

HD142780: “M” type star, 3,000 K, 0.2 solar masses, absence of hydrogen lines and abundance of neutral metal lines.

CONCLUSION: By analyzing the absorption lines on the stars’ spectra, we determined the spectral types of each, thus allowing us to find their respective properties. The absence of hydrogen lines and prevalence of neutral metals in Arcturus’ spectrum allowed us to identify it as a K type star (Figure 1) . Vega’s spectrum contained strong hydrogen and ionized metal lines. Therefore we classified it as an A type star (Figure 2). Because the spectrum revealed absent hydrogen lines and visible neutral metals, we classified it as a M type star (Figure 3).

DISCUSSION: WHY DO STELLAR SPECTRA MATTER FOR THE FUTURE OF ASTRONOMY?

  • Map galaxies
  • Map the Universe
  • Learn about the lifetimes of different stars
  • Use information on old stars to learn about conditions after the Big Bang
  • Learn about what has happened in the Universe since the Big Bang

REFERENCES:

Blumenthal, G., Burstein, D., Greeley, R., Hester, J., Smith, B., & Voss, H. G. (2007). Light, The Tools of the Astronomer, Taking the Measure of Stars. In 21st Century Astronomy. (2nd ed.). (pp. 92-128, 134-158, 380-385). New York, New York, U. S. A.: W. W. Norton & Company.

Kaler, J. B. (2010, July 30). Spectra. University of Illinois. Retrieved July 13, 2012, from http://stars.astro.illinois.edu/sow/spectra.html

Special Thanks to: COSMOS, UCI Professors and Graduate Students, our Teacher Fellow, and Cluster 2: Astronomy and Astrophysics!

COSMOS: UCI – Part 2

Nuclear Fusion: What Fuels Stars

CONTRACTION OF PRE-MAIN SEQUENCE STARS

  • The interior heats due to gravitational contraction and radiates away this energy as black-body radiation
  • At 10K, fusion starts, pressure increases, and the star establishes hydrostatic equilibrium (the balance between gravity and gas pressure)
  • As gravity pulls inwards (fusion releases energy, and maintains the core’s high temperature), gas pressure pushes outwards (high temperature prevents the star from collapsing under its own weight)
  • When a star reaches hydrostatic equilibrium, it enters main sequence

* Energy produced more efficiently at core’s center

Difference Between Fission and Fusion

Nuclear Fission vs. Nuclear Fusion

Fission: splitting heavy nuclei into lighter ones (e.g. atomic bombs and nuclear reactors derive their energy from fission of uranium or plutonium)

Fusion: merging light nuclei into heavy nuclei (e.g. how stars shine, hydrogen bombs, “nuclear burning” – different from ordinary chemical burning processes)

Strong Nuclear Forces: protons in the nucleus repel by electrical forces, but strong nuclear forces, which can only occur at close distances, keep the atom together. As temperature rises, protons move faster. When 2 protons fuse, the output is 1 neutron, 1 positron, and 1 neutrino.

How Fusion Works: Proton-Proton Chain & CNO Cycle

Common Elements (and Their Isotopes) Involved in Fusion: ¹H (hydrogen) [1 proton], ²H (deuterium) [1 proton, 1 neutron], ³H (tritium) [1 proton, 2 neutrons], ³He (helium-3) [2 protons, 1 neutron], 4He (helium-4) [2 protons, 2 neutrons]

Proton-Proton Chain

Proton-Proton Chain

Step 1: 2 hydrogen nuclei –> deuterium nucleus => releases positron + neutrino

  • Positron (e+): antimatter of electron
  • Neutrino (ν): unchanged particle that only interacts very weakly with normal matter

Step 2: deuterium + hydrogen nuclei –> helium-3 => releases gamma ray

-> Repeat first two steps.

Step 3: 2 helium-3 –> helium-4 => releases two protons

Summary

Input: 6 protons

Output: 2 positrons, 2 neutrinos, 2 gamma rays, 1 helium nucleus, 2 protons

Net Output: 4 protons –> 1 helium-4 => releases 2 positrons, 2 neutrinos, 2 gamma rays

0.7% of the total mass of 4 protons is converted into energy, while 99.3% results in 1 helium nucleus. Some of the mass is converted into energy. Since E = mc², a little mass and release tremendous energy. While at rest, however, energy is equal to mass.

CNO Cycle

CNO (Carbon-Nitrogen-Oxygen) Cycle

The CNO Cycle is the main nuclear burning chain in main sequence stars hotter than the Sun. Using carbon as a catalyst to convert hydrogen into helium, the CNO cycle also converts 7% of hydrogen’s mass into energy; hydrogen fuses with carbon to form helium. 10% of the Sun’s nuclear fusion reactions is from the CNO Cycle. In 1967, Hans Bethe theorized on the energy production in stars.

Nebulae and Star Formation

Orion Nebula

Nebulae: a cloud of dust and gas that we see in light

  1. Emission Nebulae or Bright Nebulae: a glowing gas (hydrogen); e.g. Great Nebula in Orion, heated by the Trapezium
  2. Absorption Nebulae or Dark Nebulae: dark dust clouds; e.g. Horsehead Nebula
  3. Reflecting Nebulae: reflecting dust cloud; e.g. Pleiades in Taurus
  4. Planetary Nebulae: excited by central star; e.g. Dumbbell Nebula
  5. Cirrus

STAR FORMATION

Trapezium

Stars form in Giant Molecular Clouds about 100,000 to 1 million solar masses. A few thousand in the Milky Way Galaxy, Giant Molecular Clouds break into denser bits, contract, and eventually form stars. The Orion Molecular Cloud has about 500 stars. The Trapezium and the Orion Nebula have solar masses of matter with young stars.

  1. Non-stellar galactic objects reside in HII regions with molecular clouds of pre-main sequence stars and dense clumps of dust.
  2. Protostars and newborn stars about 1/2 to 1 solar mass reside in Molecular Clouds.

Interstellar Medium – The Material Between Stars

WHAT LIES BETWEEN STARS IN GALAXIES?

- Interstellar Medium

Interstellar Medium

Interstellar Medium is gas and dust between stars, nebulae, and giant molecular clouds (basic building blocks of galaxies in star formation). The four types of matter in interstellar medium are: interstellar dust, interstellar atoms, interstellar molecules, and interstellar snowballs.

Interstellar Dust

  • Interstellar Reddening: dust that scatters blue light and causes stars to look redder
  • Extinction of Obscuration: high dust content that diminishes the brightness of stars, by as much as 25 magnitudes
  • Can be smaller than smoke particles
  • Consists of graphite, silicates, or ices
  • In core of heavy elements (e.g. iron, magnesium), mantle of organic compounds (oxygen, carbon, nitrogen), and outer mantle of ice

RADIO ASTRONOMY

  • Radio waves = longest wavelength of electromagnetic waves
  • Brightest optical objects not necessarily the brightest radio objects
  • e.g. Taurus A (Crab Nebula) and Sagittarius A (center of the Milky Way Galaxy)
  • Radio Spectral Line: the frequency or wavelength at which radio noise is slightly more or less intense
    • Hydrogen: 21 centimeter line
    • Radio spectra lines of molecules
      • OH (hydroxide): 1963
      • H20 (water): 1968
      • NH3 (ammonia): 1968
    • Over 50 molecules in interstellar space
    • Gives information on temperature, density, and motion
    • Molecular absorption line in UV

Interstellar Molecules

  • Molecules: two or more atoms bound together (e.g. H2O, CO, CH4, OH, H2, NH3)
  • Give absorption or emission bands
  • Observable in very cold, low density interstellar environments

Interstellar Snowballs

  • Between the sizes of  grains and comets
  • Composed of water, carbon, silicates, and other molecules

Interstellar Regions

  1. HI region: 200 K
  2. HII region: 10,000 K
  3. Molecular clouds: 50% gas in our galaxy
  4. Hot interstellar medium: 1 million K, super-heated gas from expanding supernova blasts (up to 90% of total volume)
  • HI Region
    • High density of neutral hydrogen atoms about a million atoms per cubic centimeter (e.g. Orion Nebula)
    • ~ 200 K
  • HII Region
    • Hydrogen with electron removed; e.g. ionized hydrogen gas (in emission nebulae)
      • Average density of hydrogen elsewhere is 1 atom per cubic centimeter
    • ~ 10,000 K

The Solar System: Basics

The Solar System

COMPARATIVE PLANETOLOGY

  • Eccentricity of Orbit: measures the ellipticity of orbit (ranges 0-1, with 0 as spherical and 1 as very elliptical)
  • Density: mass per unit volume; mass in grams and volume in cubic centimeters
  • Oblateness: measures how much the middle section of the planet bulges
  • Surface Gravity: the larger the surface gravity, the thicker the atmosphere as gravity pulls in more gases
  • Albedo: measures the fraction of light reflected compared to the amount of light received from the Sun; the higher the albedo, the more reflective the surface
  • Escape Velocity: minimum speed or velocity needed to escape the planet’s gravitational pull
  • Rotation: most planets rotate in counter-clockwise direction (prograde); others rotate in the clockwise direction (retrograde)
    • Rotational period is shortest for gaseous planets and longest for Venus
  • Roche Limit: about two and a half times the radius of the planet; within the Roche Limit, matter cannot accretes to form moons because the tidal force of the planet tears matter apart to form rings

Giant Planets: Giant planets have lighter elements such as hydrogen and helium in their atmospheres. They have stronger gravity and are at larger distances from the Sun. Jupiter, Saturn, and Neptune are stormy with great spots of lasting storms and belts and zones. However, Uranus is comparatively bland and uniform. All giant planets are home to convection, or hot gases rising and cold gases falling.

Terrestrial Planets: Terrestrial planets have heavier elements such as carbon, oxygen, and nitrogen. Mercury is most heavily cratered while Earth is least cratered. Larger terrestrial planets have plate tectonics. Earth has a sizable magnetic fields that can protect it from solar wind particles and Van Allen Belts. Earth has the “Goldilocks phenomenon,” or the right conditions for the development of life.

For more information: THE SUN, THE PLANETS, PLANETESIMALS

Stellar Properties

Stars: Stellar Properties

Stars are balls of gas held together by force of gravity and generate energy and light by nuclear fusion.

A star’s “color,” or wavelength gives information on:

  1. Temperature
  2. Composition
  3. Conditions
  4. Motion (Doppler Shift)
  5. Classification Scheme

What to Measure and How to Classify Stars:

  1. Spectroscopy
    • To determine composition
      • Absorption line produced when an electron absorbs a photon; emission line produced when an electron emits a photon
      • Dual nature of light: light behaves as waves (electromagnetic waves) or as particles (photons)
      • High energy electromagnetic waves are high energy photons, low energy electromagnetic waves are low energy photons
      • Energy of a photon defined by: E = hf, where h is Planck’s constant (h = 6.63 x 10 ^ – 34 joules sec) and f is the frequency of the electromagnetic wave
      • Three Types of Spectra:
        • Continuous Spectrum: appears as a rainbow spectrum
        • Emission Spectrum: appears as distinct color lines, characteristic of chemical elements
        • Absorption Spectrum: appears as black lines on a rainbow background, reverse of emission spectrum
    • To determine temperature
      • All objects give off thermal radiation
      • Peak wavelength corresponds to maximum intensity of radiation
      • Peak wavelength of electromagnetic radiation is related to temperature
      • Wien’s Law: W = 0.00290/T
      • As temperature increases, wavelength decreases
      • The hotter an object, the bluer the radiation
    • To determine density
      • The thicker the spectral line, the greater the abundance of the chemical element present
    • To determine motion
      • Doppler shift of spectral lines
      • Red Shift = moving away
      • Blue Shift = moving closer
    • To determine distance
      • Measured in light years (ly) – distance light travels in one year and parsecs (pc) – one parsec is 3.26 light years
      • Parallax: the only direct measure of stellar distance, the angle across the sky that a star seems to move with respect to a background of distant stars) between two observation points at the ends of a baseline of one astronomical unit (A.U.); a star one parsec from Earth has a parallax of one arc second
  2. Brightness
    • Apparent Brightness
      • Affected By: absolute (true) brightness, distance, intervening space, Earth’s atmosphere, and eyes’ visual response
      • Measured by apparent magnitude “m,” relative brightness as seen on Earth; brightest star (m=1) to faintest (m=6); a 1st magnitude star is 100 times brighter than a 6th magnitude star
    • Absolute Brightness
      • Measured by absolute magnitude “M”
      • The magnitude of a star observed from a distance of 10 parsecs (1 parsec = 3.26 light years)
      • Stars further than 10 parsecs would “appear” brighter; M increases
      • Stars closer than 10 parsecs would “appear” dimmer; M decreases
    • m-M = 5 log (r/10)
  3. Distances
    • Distance as the primary factor in the decrease of stellar brightness as perceived on Earth, used to determine absolute brightness
    • Inverse Square Law: the intensity of light varies inversely with the square of the star’s distance from the Earth
  4. Mass and Size
    • MASS: For binary stars, both the period of revolution of one star orbiting the other and the distance between the two stars can be measured
    • SIZE: Diameters of stars can be determined from temperature and luminosity (calculated from absolute brightness) =>  L  =   σ  T^4  A, where L = luminosity, σ = distance, T = temperature, and A = absolute brightness
  5. Classification Scheme
    • Spectral Types: O, B, A, F, G, K, M; subtypes 0 to 9 (e.g. B1, A4, G2, and M0)
    • O stars are more than 10 times hotter than M stars
    • Developed by Annie Jump Cannon in the late 1800′s
  6. H-R Diagram: to study evolutionary tracks