lecture 1: what is astronomy? - university of...
TRANSCRIPT
Lecture 1: What is Astronomy?
Our Cosmic Address:
Classroom N210, Tucson, US, Sol 3 (Earth), Solar System, Milky Way Galaxy (2/3's of the way outside center), Local Group of Galaxies, Virgo Supercluster of Galaxies, Universe
Astronomy
• study of light and matter beyond Earth
• inter-disciplinary science
◦ physics: how material interacts and behaves
◦ geology: composition of planets
◦ chemistry: elements combine in rocks and space
◦ biology: can life evolve elsewhere?
◦ mathematics: language of science
Astronomy
• inter-disciplinary technologies as well!
◦ solid state, electrical, and mechanical engineering
◦ imaging
◦ optics
◦ computer science
What we know is subject of this class, plus at least 5 more full years of coursework.
No one is able to know it all --> specialization.
What don’t we know? A whole lot!
What does an astronomer actually do? • background: love of science --> math, physics, astronomy
classes --> research training --> grad school --> post-doctoral years --> professional astronomer
• guild-like system
• observational, theoretical, instrumental
• proposals for money for students, telescope time, instrument supplies, big computer access
• lots of teaching, computer work, travel to telescopes and conferences
• committees, politics
How we do we collect evidence?direct: moon rocks, meteorites, planet landers, retrieval missions, particle detectors
indirect: observations of the electromagnetic spectrum
Magellan
MMT
LBT
Things you should know (but aren’t covered here)
what causes the seasons
basic motions of stars & planets on the sky
basic nomenclature (meridian, zenith, north celestial pole, ecliptic)
cause of lunar phases
cause of solar and lunar eclipses
check out reference materials on website
Things you should know (and are reviewed here)
Classical Mechanics1st law: when !F = 0 , !p = m!v = constant
2nd law: when !F != 0 ,d!p
dt= !F ;
usually written as !F = m!a becausedm
dt= 0
So, if forces known to be acting on body, then acceleration is introduced.
Conversely, if body undergoes acceleration, a force must be acting.
!a != 0 even if |v| = 0 but changes direction e.g., circular motion
Gravitational Force
m1m2!F12
!F21
r12
F12 = Gm1m2
r2
!F12 = !!F21
G = 6.67 ! 10!8gm!1cm3sec!2
m1!a1 = !m2!a2
Why is Fg so great near a black hole?
Conservation Laws
energ
y
kinetic
potentia
l
bound states have E < 0, what are orbits?
binding energy (energy required to move boundparticle to infinity)
total energy =1
2m1v
2
1 +1
2m2v
2
2 + (!Gm1m2
r) = constant
end of review...
Felectric
Fgravity=
e2/r2
Gm2e/r2
=e2
Gm2e
! 1042
stationary charges produce only fields!E
moving charges produce and fields!E !B
accelerated charges emit EM radiation
force exerted on charge q1 by charge q2 :
F12 =
q1q2
r212
Felectric
Fgravity=
e2/r2
Gm2e/r2
=e2
Gm2e
! 1042
Coulomb’s law
Electromagnetism
So why is gravity important?
mass comes only in one sign (positive)
matter is electrically neutral in bulk (electric forces cancel)
so gravity generally dominates over large scales formacroscopic objects