Download Chapter 6: Terrestrial Planets - Department of Physics and Astronomy

The Transient Sky
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Things that move, change brightness or
color
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Solar System
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Stars, planets, gas in our own Galaxy
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Other galaxies
Tides and Moon Phases
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Water stretches much more
than rock water tides
bigger
Moon much CLOSER than
Sun  Moon’s tides twice
as strong as Sun's
Moon over same spot on
Earth every 25 hrs  time
of high tide changes daily
1st,3rd qtrs
(weaker)
new
(strongest)
Tides caused by Earth’s shape deforming as it
rotates: 2 high and 2 low tides every 25 hours
-- linked to powerful earthquakes!
full
Precession
• Earth: equatorial bulge – (equator spins
faster than poles)
• Moon's orbit inclined to ecliptic by 5º,
thus to equator by 18-28°, pulls on bulge
Astrology
doesn’t
account for
precession
– Effect: like sideways spinning in a tilted top
– One full sideways spin: 26,000 years
• Effect: North Star changes, spring
constellations become summer
constellations etc.
• Similar process causes Moon’s libration (wobbling)
Lunar Libration (seen from Earth)
From Earth, we see 59% of moon’s surface
• (1) Seeing moon
from opposite
sides of Earth
every 12 hrs, (2)
elliptical orbit
(variable orbital
speed), (3) orbit
inclined to Earth’s
equator cause
libration (N-S
“nodding”)
Fig. 10-3, p. 229
10.2b Solar Dynamo:
winding magnetic field
and sunspot numbers
Little Ice
Age
Cooling
150 yrs
Fig. 10-18b, p. 237
Prominence Eruption
Fig. 10-8a, p. 231
Planetary Motion
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We observe
Mercury, Venus,
Mars, Jupiter and
Saturn moving
among the “fixed
stars” around the
sky: video
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Some motion is
“retrograde”
(backward)
confused our
ancestors – led to
change our view of
Universe
 Earth is NOT the
center! video
Asteroids & Comets
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Asteroids are
EVERYWHERE! video
Comets also are all over
– with DIFFERENT
orbits! video
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Near-Earth asteroids
Chance to study
some up close with
radar
Osiris-Rex sample
return
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Collision warnings!
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video
Barringer Crater, Arizona
Diameter 0.7 mi, 50000 yrs
old
Impactor: iron-nickel, 50yd
diameter, 300000 tons
Estimated speed: 27,000
mph
Explosion: 150x Hiroshima
Meteorite melted, scattered
See
www.barringercrater.com/science
Chicxulub: result of 1215km Near Earth Object
-- 65 Myr old
-- crater 200km wide
-- Left iridium layer
The dinosaur-killer!
Fig. 8-28, p. 202
Pluto’s Discovery Plates 1930
Dates Jan 23 & Jan 29, 1930, moved about
1.4 arcmin (width of a pea at 10 yards)
Fig. 8-2, p. 186
Can you
spot Eris?
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Images taken
over 3 hrs on 21
Oct 2003
mag=18.7, taken
with Caltech
1.2m Oschin (Mt.
Palomar)
Schmidt
Motion is 1.75
arcsec/hr (width
of a BB at 10
yards/day)
Don’t feel bad if
you can’t see it –
a computer
found it
Kuiper
Belt
Objects
Comets
are out
there, too!
Fig. 8-8a, p. 191
Beyond Pluto+Eris- you can help!
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Kuiper Belt – “outer asteroid belt” of icy/rocky objects,
beyond Neptune
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Some objects appear “thrown” by unseen, massive object
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Need human eyes to look for moving objects!
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Backyard Worlds: Planet 9
Stars+Planets Beyond Solar System
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Q. If Earth moves around sun, why
not see stars move over year?
A. The stars are too far away to
see motion easily!
If sun were marble
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Earth would be pinhead 1m away
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next star a marble in Indianapolis
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Move 1 arcsecond (1 pinhead’s
width at a distance of a mile)
over 6 months
“Parallax” motion detected with
invention of photography, 1830s
Parallax over 1 Year
Fig. 11-8a, p. 250
Proper Motion
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Normally <1 arcsec/yr, often << 1 arcsec/yr
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Fastest: Barnard’s Star (7.1 arcsec/yr) (~8 arcmin or ~¼ diameter
of Moon in a human lifetime)
α Cen (nearest star system): ~3.6 arcsec/yr
Need DISTANCE to convert to km/s
Barnard’s star: moves
50 arcsec (width of
Jupiter) in 7 years
Proper Motion of Big Dipper
22º
100,000 BC to
100,000 AD
Proto-planetary disks
Systems are bright in IR due
to blackbody emission from
cool dust.
HL Tau,
ALMA (mm
image)
HL Tau,
HST
Herbig-Haro Objects: Jet
trails from proto or premain-sequence-stars
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Like water splashes back
from pouring water too
fast down a drain:
Gas spirals into a forming
star
Gas heats up as it's
compressed
Central pressure shoots it
out the poles
Video explanation
Herbig-Haro (HH) 30, from Hubble, IR
Visible light: jets bright, star invisible!
Jets strike interstellar
gas, make it glow
Pre-main sequence
HH30, HST,
star (hidden by dust)
visible light
Shock waves: when a blob of gas hits another
blob of gas supersonically  HEAT + LIGHT!
Fig. 12-8, p. 280
11.7 Variable Stars
dec
+10°
N
0°
E
-10°
-20°
RA
3h
2h
1h
0h
Variable Stars
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Stars vary for all sorts of reasons
Periods from <1 hour to years
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Eclipsing binaries
Intrinsical variables (many classes)
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Some regular, others irregular
Mira: giant pulsating star
RR Lyraes – measure distances to star clusters,
map out our Galaxy
Cepheids – measure distances to galaxies
Interacting binaries = novae
Exploding stars = supernovae
Variable Stars
Rev.
David
Fabricius,
German,
1564-1617
P=331 days Naked eye
Need telescope
Fig. 11-26, p. 264
Light curve of Mira, 1st known variable (1596 by Fabricius)
Eclipsing Binaries: inclination i~0°: since we
know i  ACTUAL masses (rare: ~200 known)
Primary:
hotter star
Secondary:
cooler star
Partial
eclipses
Total
eclipse
Velocities + eclipse curves
give relative stellar radii!
Primary eclipse
Secondary
eclipse
Flat-bottomed light curves: smaller star totally eclipsed.
Round-bottomed light curve: both stars partially eclipsed.
Eclipse type depends on inclination.
Fig. 11-22, p. 261
Eclipsing Binary
light curve
From light curve and
radial
velocity curve (not
shown), we can
calculate stars’ radii,
relative temperatures,
combined masses and
mass ratios
Transiting Planets – like Eclipsing Binary Stars
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Planet transiting star  dip in star brightness of ~0.01-1%
ex: DJupiter~0.1DSun, so AJupiter/Asun~(0.1)2=0.01 -> Jupiter
would block out 1% of Sun’s light if aliens watched it transit
If we see planet transiting its star  MUST have inclination
i~0 deg  if we know true velocity  get accurate mass!
Advantage: distance-independent!
Kepler 10°x10° field
Citizen Science: Find Exoplanets
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Planet Hunters
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Tutorial video
Period-Luminosity
Relation for Cepheid Video
explanation
Variables
Bright stars,
visible in our and
other galaxies
Measure period ->
absolute mag.
Apparent + absolute
mag -> DISTANCE
Good standard candles!
Fig. 11-28, p. 265
Hubble key project: pick
out Cepheids in other
galaxies -> distances
Fig. 11-30, p. 266
Mass Transfer onto White Dwarf
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50% (or more) of
stars in binary systems
One becomes white
dwarf first; lower mass
star become red giant
later
Lower mass secondary
star (red giant, weak
gravity) loses mass to
white dwarf (strong
gravity)
How a Nova Flares Up
Light Echoes: V838
Monocerotis over 2.4 years
1.2pc
or 41"
V838 Mon, HST,
blue-green-red light

2.1pc or
71"
-----
Progressively larger shells of gas and dust are
illuminated as light goes out from nova in all directions.
In outburst, central star brightened 600,000x (14.4 mag)
and swelled to as big as Jupiter's orbit. Then it faded.
Distance to V838 Mon is about 6.1 kpc (6100 pc)
Fig. 13-12, p. 303
Supernovae
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Two main types physically
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D = 24Mpc
Core collapse
(IMPORTANT):
Core Collapse: explosion of supergiant star
Explosion of white dwarf (WD)
NASA Swift
satellite
A supernova can briefly shine as bright as an entire galaxy (10
billion stars!)
White Dwarf Supernova Video
Core Collapse Supernova
Normal galaxies: bright nuclei
because lots of stars in small
volume
Gravity pulled gas to center 
lots of star formation happened
normal galaxy
Quasars and Active
Galaxies
Some galaxies: unusually
bright nuclei in optical/IR –
and X-rays/UV/radio
active galaxy
Fig. 17-1a, p. 400
Active Galaxy Centaurus A
optical
X-ray – shows jet
Fig. 17-4a, p. 401
Active Galaxy Jets Blow Bubbles
in Surrounding Medium
Large Synoptic Survey
Telescope (LSST)
First stone laid 2015 Apr 14
Standalone telescope project
LSST Key Points
Top-ranked major
ground-based facility by
NRC’s Astronomy &
Astrophysics decadal
survey, 2010
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Video introduction to LSST
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NSF will pay for construction, operation
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Data analysis paid for by LSST Corp: 30-40 universities
and research labs in US and rest of world
8 KY universities joined in 2016: UL, UK, EKU, NKU,
Morehead St., Murray St., Bellarmine U, Berea College
Solar Eclipses: Earth goes into Moon's shadow
Next total solar eclipses
from US:
21 Aug 2017 (Oregon-S
Carolina)
08 Apr 2024 (Texas-Maine)
23 Aug 2044 (N DakotaMontana)
12 Aug 2045 (Cal.-Florida)
Solar eclipse only happens at New Moon
Solar eclipse lasts only a few minutes – Moon's
shadow is much smaller than Earth
Fig. 4-7, p. 69
Aug 11, 1999 solar eclipse from space
From Mir space
station. Shadow
moves 2000
mph.
Only observers
near center of
shadow see
total eclipse.
Those in outer
shadow see
partial eclipse.
Video description
Longer video
Great 2017 Eclipse!
Eclipse in KY: about 1pm CDT
The greatest 2 minutes in astronomy!
Stages of Eclipse
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Partial – few
minutes
Totality – 2
minutes
Partial – few
minutes
Eclipse Special Effects
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Diamond Ring – 1st/last
bit of sun appears
Baily’s Beads – see bits of
sun through moon’s
mountains
How to View Eclipse
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Eclipse glasses – cost a $1-few
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Pinhole or Binocular Projection
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More expensive solar projector
How to photograph Eclipse
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Use a tripod!
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ONLY during totality: OK to take a normal picture
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OUTSIDE of totality: use a filter!
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See eclipse.gsfc.nasa.gov (Goddard Space Flight Center)
Deluxe Photography
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Glass solar filter
on telescope or
camera
Don’t Miss Eclipse for Photos!
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Enjoy your
first
experience!
Some Future Total Eclipses:
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2019 Jul 2: northern Chile, Argentina
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2020 Dec 14: southern Chile, Argentina
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2024 Apr 8: Mexico-Texas-IndianaQuebec
2044 Aug 23: North Dakota-MontanaAlberta
2045 Aug 12: California-Florida (coastto-coast)