PHYS 1062 Midterm Study Guide Extensive study guide for March 2018 exam. Ch. 1 - 9.
● Red = Key terms
● Orange = Possible Trivia Questions
● Yellow = If you memorize it, you won’t have to math.
● Green = Put here because it was a quiz question and I can’t explain it but I got it right.
● Blue = Formulas
○ 1 Light year = 9.461x10^15 meters
○ Earth’s Diameter = 12,756 km = 8.5x10^-5 AU
○ Milky Way Diameter = 80,000 light years
○ 1 AU = 150 million km = 93 million miles
○ The sun’s radius is 100 times the size of Earth’s radius.
○ Astronomers do not measure in MILES.
○ 5K = 3 miles.
● The stars that appear the biggest are the brightest We also discuss several other topics like eku chemistry
● Circumpolar stars never leave the horizon. They would make concentric paths. ● Size
○ Supercluster, galaxy, solar system, planet (from biggest to smallest) ● Scientific Notation
○ 10^(number of zeroes)
○ EX: 0.0000788 = 7.88x10^-5
● Seasons and Tilts
○ We have seasons because of the Earth’s tilt.
○ In the winter, the sun is above the horizon for less than 12 hours and at low angles, so there’s less concentrated solar heating or sunlight.
● It takes 5.8 minutes for the sunlight to reach Venus.
● It takes 8 minutes for the sunlight to reach Earth.
● It takes 4.2 light years for the sunlight to reach Alpha Centauri
○ Alpha Centauri is the closest star to our sun.
● Earth rotates from west to east. (on the HW question, it’s the sunset line on the right)
● When observing a star for a few hours, it moves from east to west. ○ An overhead star will move through the 15* angle in one hour.
● Precession = The Earth moves like a top (imagine the one at the end of Inception) ○ Why does this happen? - The Sun and Moon pull on Earth’s equatorial bulge.
○ It changes the celestial poles, the equinoxes, the solstices, and the celestial equator.
● Greek Letters = Describe the relative brightness within the constellation ○ Alpha - Brightest
○ Beta - Second brightest
● Celestial Sphere = It’s not physically real, but it is still useful.
○ 88 Regions (constellations)
○ Don’t confuse constellations for asterisms.
■ Asterisms are like...The Big Dipper.
○ Zenith = Above your head
○ Nadir = Below your feet
○ North and South Celestial Poles We also discuss several other topics like bul 4310 fiu
○ Celestial Equator
● Milankovitch Hypothesis = Small changes influence Earth’s climate and cause ice ages.
○ If one star is 100 times brighter than the other, the magnitude difference is 5.
○ 1st Magnitude is very bright. 6th Magnitude, not so much.
○ The higher the number the dimmer the star. (-2.7 vs 2.7)
○ Measure of the light energy from a star that hits one square meter in one second.
○ 2.512^(the difference in magnitudes classes)
● The 5 naked-eye and 2 telescopic planets that wander among the stars will always be near the ecliptic.
● It takes the sun 2 minutes to completely set once it touches the horizon.
● Newton If you want to learn more check out ams 210 stony brook
○ 3 Laws of Motion
■ An object in motion will stay in motion. (or at rest will stay at rest) Unless acted upon.
■ F = ma (Force = Mass*Acceleration)
■ Equal and Opposite Reaction.
● So the amount of force on the Sun by the Earth is the same as the amount on Earth by the Sun.
○ There was a force pulling the Moon to Earth
■ The Moon’s orbital motion has a curved fall.
■ Moon has an acceleration towards Earth
■ The force and acceleration in Newton’s second law must have the same direction.
■ (If there’s a question that has all these answers and another, pick all the above)
■ If the gravity was turned off, the moon would fly off into space in the direction it was facing INSTANTLY.
○ What’s necessary about the force exerted by the Sun (to yield elliptical orbits)
■ The force must be attractive and the force must vary inversely with distance squared.
○ Slowed down time
■ Rolled objects down inclines at low angles. Don't forget about the age old question of What do phagocytes produce to kill bacteria?
○ Worked out the law of inertia (Law #1)
○ If two planets orbit the sun (Earth and Q), and Q is five AUs away from the sun, Q has 1/25 the force on Earth. The two planets are identical. ○ Why would a hammer and feather land at the same time?
■ No air resistance.
○ Mass Vs. Weight
■ Mass is the amount of matter
■ Weight is the amount of gravitational force you experience.
○ You’re never weightless, just in constant freefall.
● General Relativity
○ Solved the major orbital problem: The excess precession of Mercury’s perihelion.
○ Verified on May 29, 1919 solar eclipse (bending of light by gravity) ○ Explains the following
■ Light bending in the vicinity of massive objects.
■ Time dilation close to massive objects
■ Gravitational redshift.
■ Mercury’s orbit does not follow Newton’s laws precisely.
● Albert Einstein
○ Proposed that gravity is the bending of space-time due to the presence of matter.
● Circular Motion
○ Acceleration of the object is toward the center of motion.
● Escape Velocity
○ If we shrink the Earth’s radius by a factor of 100, but we keep the mass, the escape velocity will increase by a factor of 10.
● If there’s an alien beam question, it’s the speed of light.
● Speed vs. Velocity vs. Acceleration
○ Speed - how fast are you going?
○ Velocity - how fast are you going and WHERE?
○ Acceleration - something changed and we gonna find out what.
● Law of Universal Gravity
○ F = -G (Mm/r)
● Free Fall
○ G = Fgravity/M = Fgravity/m
● Escape Velocity
● Speed of light = Frequency x Wavelength.
● Speed of light = 3x10^8 m/s
● E = hf
● H = 6.626 x 10^-34 J*s is the Planck Constant
● Light cannot be portrayed as a wave and a particle in the same experiment. ● Infrared telescopes are on mountaintops and ultraviolet telescopes are in Earth’s orbit.
○ Infrared blocker, water vapor, is in the lower atmosphere.
○ Primary ultraviolet blocker, ozone, is in the higher atmosphere. ● Infrared telescopes
○ Must be cooled to a low temperature to reduce interfering heat radiation emitted by the telescope.
● Electromagnetic radiation travel in any medium that does not absorb them. ● PURPOSE OF A TELESCOPE
○ To gather light and bring it to a focus.
○ Width matters, not length. (*winky face*)
● Big telescopes (size does matter?) now.
○ They can be made thinner and lighter.
○ Tracking is computer controlled.
○ Reduced effect of the Earth’s atmosphere.
○ (pick all of the above)
○ A = pi (p/2)^2 Surface area of the primary lense.
● Chromatic Aberration
○ Prisms take advantage of it.
○ It’s a big problem for the primary lenses of refracting telescopes
● Resolving Power
○ Limited by a cloudy night.
○ Expressed as “0.5 seconds of arc.”
● Electromagnetic Spectrum
○ Visible and Radio are the most transparent to Earth’s atmosphere. ○ Visible Spectrum
● Violet’s photons have the greatest energy.
○ X-Ray Telescopes can observe hot gas trapped in galactic clusters better than an infrared telescope.
○ Infrared Telescopes can observe newborn stars in dusty nebulae better than an X-Ray telescope.
○ Rank telescopes designed for the following specific types of electromagnetic waves in order of the minimum altitude at which they would be useful. (least to greatest)
○ Rank telescopes designed for the following specific types of electromagnetic waves in decreasing order of the altitudes at which they would be useful (greatest to least)
● Radio Telescopes vs Optical Telescopes (everything radio does best) ○ Find the location of cool hydrogen gas
○ See through dust clouds
○ Detect dark molecular clouds
○ Observe during the day
○ (so pick all of the above)
● Determined exclusively by the diameter of the primary mirror or lens. ○ Light Gathering Power and Resolving Power.
● Radio Interferometry
○ Overcomes poor resolving power.
■ It’s poor because the wavelengths are so long.
● It’s about light gathering, not magnifying.
● If you were to make a telescope using the two lenses (it’ll show you a diagram with two blue and white looking things)
○ One uses top lens for the primary and bottom lens for the eyepiece.
● Spectral Types
○ Seven Types: OBAFGKM. O is hottest.
○ Red is the lowest surface temperature for a star compared to (Orange, White, Yellow, and Blue)
○ Blue is the color of the hottest stars.
■ Blue star’s emissions peak at shorter wavelengths than red ones. ○ Temperature controls the color of a star.
● Spectral Lines
○ If it’s blueshifted, the radial velocity is directed towards us.
○ If it’s redshifted, the radial velocity is directed away us.
○ Properties of a star that can broaden the width of its spectral lines ■ Rapid rotation of the star
■ High temperature atmosphere
■ High density atmosphere
● Where is the location of the cooler low-density gas that yields the dark line stellar spectra that were studied by Annie Jump Cannon
○ In the star’s lower atmosphere
○ In Earth’s atmosphere
○ Observed when observing radiation from a hot solid or gas under high pressure.
○ Observe from molten lava.
○ Light from a continuous spectrum source passing through a cooler low density gas produces the absorption line spectrum.
○ Observed when observing radiation through a cool gas.
○ Observed if you looked through gases boiling out of molten lava. ● Emission
○ Observed when observing radiation from a hot gas.
● Black Body
○ All stars!
○ Wavelength of maximum intensity that is emitted is inversely proportional to temperature.
○ Amount of electromagnetic energy radiated from every square meter of the surface is proportional to temperature to the fourth power.
● Temperature of a gas is a measure of the
○ Average motion of its atoms
● Atomic Nucleus
○ All the positive charge
○ 99.9% of the mass
○ No electrons
● Ionized atoms = Atoms with more of either electrons or protons than the other ● Stars are mainly hydrogen and helium but they have no lines for hydrogen or helium in their spectrum. Why?
○ The surface temperature is such that the electrons are not at the proper energy levels to produce spectral lines at visible wavelengths.
● The electron making the transition from level 2 to level 3 corresponds to a hydrogen atom absorbing a visible light photon that has a wavelength of 656 nanometers.
○ Determined by the difference in energy between electron energy levels.
● The Sun
○ Maintains its energy output by fusion of hydrogen nuclei.
○ Magnetic field is responsible for the surface and atmospheric activity. ■ Changes because of the differential rotation of the Sun and
convection beneath the photosphere.
○ Changes in the magnetic field heat the chromosphere and corona to high temperatures.
○ The lower photosphere is hotter than the upper photosphere is responsible for “limb darkening.”
○ Photosphere contains the cooler low-density gas responsible for absorption lines in the Sun’s spectrum
○ Corona is a very hot low-density gas.
○ The layers of the Sun below the photosphere are explored by measuring and modeling the modes of vibration of the Sun’s surface.
○ The general trends in temperature and density from the photosphere to the chromosphere to the corona - Temperature increases and density
○ Photosphere is not part of the interior.
● Layers of the Solar Interior Ranking Questions
○ Outermost to innermost
■ Convective Zone
■ Radiative Zone
○ Increasing temperature (least to greatest)
■ Convective Zone
■ Radiative Zone
● Solar Prominence
○ Solar Material from the chromosphere following the arches of the sun’s magnetic field
○ Its spectrum reveals that it is much cooler than its surroundings. ○ The shape suggests that it is following the solar magnetic field.
● Solar Flare
○ Eruption of solar material from the photosphere
○ Observed at Visible, Ultraviolet, and X-Ray wavelengths
○ Can bring auroras and communication blackouts.
● Solar Neutrino Problem
○ Solved by the discovery that neutrinos oscillate between three different types.
● Solar Neutrinos
○ Created during nuclear fusion
○ Very low mass
○ Travel very fast
○ Detected in large underground pools of chemicals
○ They’re hard to detect because they move fast, have low mass, and oscillate between three flavors.
● Supergranules and Granules
○ Both due to convection cells in the layers below.
○ The center of a granule is brighter than its edges because the temperature is higher at the center.
● Nuclear Fusion
○ Happens at the core
○ Requires high temperatures because:
■ Protons repel each other
■ Overcoming the Coulomb barrier
■ (it’s the one that says all of these choices)
● Proton-Proton Chain
○ Produced from the neutrinos
○ Head out of the Sun at nearly the speed of light.
● How constant is the Solar constant? How much has the solar constant been observed to vary?
○ About 0.1% , so pretty darn constant.
○ Spectral Type is G2, Luminosity is Main Sequence (V)
○ If a star with the same type has a luminosity of 50 solar luminosities, it must be larger than the sun.
○ Cool stars can be more luminous than hot stars if the cool star is larger. ○ Supergiants have the lowest density
○ Main Sequence applies the mass-luminosity relation.
○ If a star has ½ the surface temperature of the Sun and is 4 times larger, the star’s luminosity is 1 solar luminosity
○ L = Surface Area (A) * O (that ugly constant) * Temperature in Kelvin (T)^4 ● Distance
○ Parallax Angle of .5 arcseconds = distance of 2 parsecs
○ If a star’s apparent visual magnitude is less than its absolute visual magnitude, the distance to the star is less than 10 parsecs.
○ How to find without parallax angle
■ Spectral Type and Luminosity Class
○ At 10 Parsecs, the apparent magnitude equals the absolute magnitude ● Red Dwarf
○ Most abundant but rarely plotted because they have low luminosity and are hard to detect.
○ Absolute bolometric magnitude gives the most information about the physical nature of a star.
■ Medium surface temperature stars have the least difference
between absolute visual magnitude and absolute bolometric
● Order of brightness from dimmest to brightest
○ Barnard’s Star
○ Sirius B
○ Rigel A
● Brightest to Dimmest
○ Aldebaran A
○ Procyon B
● Hottest to Coolest
○ Aldebaran A
○ Rigel A
Formulas and Other Random Things that May Help you.
d(parsec) = 1/p
Mv is Absolute visual magnitude
Magnitude Distance Formula. 10^(mv-Mv +5)/5 1 Parsec = 3.26 Light Years
1a = Bright Supergiant
1b = SuperGiants
2 = Bright Giants
3 = Giants
4 = Subgiants
5 = Main Sequence