1. How do we know that the sun is a star (and bonus: when and
how did we learn this in history? Note I mentioned this in class,
but it was a long time ago) This is basically a review of all
properties of a star 2. What color is the sun? (Interpret color how
you wish.) Explain the answer fully (not 1-word answer :) 3. By
what means do we know how far the sun is? 2 / 14 Activities
Slide 4
The sun is a yellow, G-class star on main sequence Can actually
be called a yellow dwarf, but informally As all stars, nearly
spherical, and fuses hydrogen into helium in its core as means of
balancing out gravity 4.567 billion years old, so about halfway
through life Over 100x the earths diameter, but over 300,000x the
mass. Accounts for 99.86% of mass of solar system Mean density
works out to 1.4 g/cm 3, slightly >water Ball of plasma (a gas
hot enough to be composed primarily of ions instead of atoms.
Electrons stripped!) Temperature (surface) ~5,500-6,000 K/C (10 4
F) Our Sun: Facts 3 / 14
Slide 5
Earth is 1 A.U., 149.6 million km, away (93 million mi.), while
sun 27,200 light years from galactic center Orbits elliptically
once per 365.256 days (sidereal year) Light travel time of 8
minutes, 19 seconds in vacuum Moving around the galaxy (once every
2-250 million years) while earth and rest of planets move around it
220 km/s relative to black hole at center of the galaxy 20 km/s
relative to mean speed of the closest stars 370 km/s relative to
Cosmic Microwave Background Completes own full rotation once every
~25-35 days Helioseismology : bell-like ringing turbulence (
sunquakes? ) Distance and Motion 4 / 14
What particle did we think we were missing many of from the sun
until we understood their nature better? A. Neutrino B. X-ray C.
Gamma-ray D. Nucleon The most common EM emission from the sun is A.
Light (visible) B. Microwaves C. Heat (infrared) D. Ultraviolet
Questions CHALLENGE 6 / 14
Slide 8
Absolute magnitude of 4.83 (so, at the same distance from earth
that Vega is, 25 light-years away, sun would be quite faint. ~5-6
is the limit of naked eye) 3.8 x 10 26 W(atts). Relative magnitude
in sky of -26.7 Even though looks yellow, that is only because that
is peak in emission. It produces light at all visible wavelengths
(called white light) + below/beyond Atmospheric effects
(refraction, optical depth, angle), plus psychology, change
apparent size or color Reddens at sunrise, sunset. More air:
scatters blue Prismatic differential angle of refraction/scatter
leads to the famous sunset green flash (is real, but NASA images in
the UV for instance employ false colors) Visual Appearance 7 /
14
Slide 9
Blackbody Spectrum Graph courtesy of Berkeley Lab Heat Island
Group 8 / 14
Slide 10
The solar wind causes high- energy, electrically-charged
particles to bombard earths atmosphere all the time Planetary
magnetic field leads to spiraling paths around (magnetic) poles
Aurora borealis in north, australis in south (is same) Color: from
e - energy levels Also: coronal mass ejection, a massive burst of
magnetic gas carried on solar wind EM Phenomena While docked and
onboard the International Space Station on March 21st 2008, an
STS-123 Endeavour crewmember, looking northward across the Gulf of
Alaska, captured the glowing green beauty of the Aurora Borealis
over the Earth An artist's conception of what an aurora would look
like from space 9 / 14 Yellowish- green= oxygen
Slide 11
10 / 14
Slide 12
The sun has an 11-year cycle in sunspot activity (periodic)
Magnetic field oscillations Controversially linked to global
warming, as opposed to human activities (CO 2 ) Solar maximum was
in 2013 BUT weakest in >century CMEs, solar flares can also have
effects: aurora; disrupt communication, electronics An Effect on
Our Weather This image was created by Robert A. Rohde from the
published data listed below and replaces an image created by
William M. Connolley. It is part of the Global Warming Art project.
Leland McInnes 11 / 14
Slide 13
Recall that when two protons fuse to form a larger nucleus, one
of them is forced to decay: neutron, e +, neutrino From pp, other
processes (Boron-8, etc.) a certain number of neutrinos expected
(predicted) from our Sun But, fewer: only one-third observed! A
mystery for decades, with particle physicists accusing the
astronomers of not having the correct solar model Correct answer
only achieved after realizing neutrinos oscillate in flavor There
are 3 types, but also 3 masses Solar Neutrino Problem Homestake
Solar Neutrino Experiment 4,850 depth (4,300 m.w.e. or meters of
water equivalent) at the S anford U nderground R esearch F acility
(SURF) in Lead in South Dakota, the site (back then) of the
Homestake gold mine. Noble Prize winning results. (LUX detector is
installed in the Ray Davis cavern!) 12 / 14
Slide 14
A. Red supergiant, then supernova B. Red supergiant, then black
hole C. Red giant, then neutron star D. Red giant, then white dwarf
A. Nitrogen B. Helium C. Iron D. Oxygen Future Fate = ? Sequence of
events brought on by the beginning of the burning of 13 / 14
Slide 15
Homework #10 passed out (again) now due Monday NASA Probe
Captures Images of Pluto and Its Moon Charon
http://www.scientificamerican.com/article/nasa-probe-
captures-images-of-pluto-and-its-moon-charon-video/
http://www.scientificamerican.com/article/nasa-probe-
captures-images-of-pluto-and-its-moon-charon-video/ New Horizons
spacecraft set to make first flyby of Pluto in July Dawn spacecraft
gets an eyeful of dwarf planet Ceres
http://www.bbc.com/news/science-environment-30888818
http://www.bbc.com/news/science-environment-30888818 Both to be
read by this coming Monday also please Homework 14 / 14