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