Lecture 1: What is Astronomy? - University of...
Transcript of Lecture 1: What is Astronomy? - University of...
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Lecture 1: What is Astronomy?
![Page 2: Lecture 1: What is Astronomy? - University of Arizonaatropos.as.arizona.edu/aiz/teaching/a250/Lecture1.pdfOur Cosmic Address: Classroom N210, Tucson, US, Sol 3 (Earth), Solar System,](https://reader034.fdocuments.in/reader034/viewer/2022051919/600b4dfbfb9396015c674ed6/html5/thumbnails/2.jpg)
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
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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
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Astronomy
• inter-disciplinary technologies as well!
◦ solid state, electrical, and mechanical engineering
◦ imaging
◦ optics
◦ computer science
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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!
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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
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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
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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
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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
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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?
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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...
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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
![Page 14: Lecture 1: What is Astronomy? - University of Arizonaatropos.as.arizona.edu/aiz/teaching/a250/Lecture1.pdfOur Cosmic Address: Classroom N210, Tucson, US, Sol 3 (Earth), Solar System,](https://reader034.fdocuments.in/reader034/viewer/2022051919/600b4dfbfb9396015c674ed6/html5/thumbnails/14.jpg)
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