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UNT / Physics / PHYS 1062 / ohad shemmer

ohad shemmer

ohad shemmer


School: University of North Texas
Department: Physics
Course: Stars and the Universe
Professor: Ohad shemmer
Term: Winter 2016
Tags: physcs, astronomy, phys, stars, universe, sun, and temperature
Cost: 50
Description: Covers everything possible from Chapters 1 to 9, excluding 3 and 4 since they won't be on the test. I did my absolute best and drew influence from all the sources I could. Hopefully this helps and you don't have to go searching through all your quizzes, homeworks, or resort to reading. Enjoy!
Uploaded: 03/04/2018
10 Pages 14 Views 14 Unlocks

PHYS 1062 Midterm Study Guide Extensive study guide for March 2018 exam. Ch. 1 - 9.

in meters how long is a 1 ​Light year​?

Key Terms:

● 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

Ch. 1

● Conversions/Units

○ 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

in diameter how big in the Earth?

If you want to learn more check out umass math 235
If you want to learn more check out nanuet egyptian goddess

○ 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.

Ch. 2

● 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.

in diameter how big in the Milky Way?

○ 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.

○ Horizon

○ 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.

● Magnitude 

○ 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)

● Flux 

○ 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.

Ch. 5

● 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.

● Galileo

○ 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)

● Force

○ 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 

○ (2GM/r)^(½) 

Ch. 6

● 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) 

■ Radio 

■ Visible 

■ Infrared 

■ X-Ray 

○ 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) 

■ Ultraviolet 

■ Infrared 

■ Visible 

■ Radio 

● 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.

○ Pupils

○ Telescopes.

● 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.

Ch. 7

● 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 

● Continuous 

○ Observed when observing radiation from a hot solid or gas under high pressure.

○ Observe from molten lava.

● Absorption 

○ 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. 

Ch. 8

● 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 

■ Core 

○ Increasing temperature (least to greatest) 

■ Convective Zone 

■ Radiative Zone 

■ Core 

● 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.

Ch. 9

● Sun

○ 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.

● Luminosity 

○ 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.

● Magnitude

○ 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 

○ Sun 

○ Canopus 

○ Rigel A 

● Brightest to Dimmest 

○ Antares 

○ Polaris 

○ Aldebaran A 

○ Altair 

○ Procyon B 

● Hottest to Coolest 

○ Aldebaran A 

○ Altair 

○ Antares 

○ Mira 

○ 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

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