Solar System Stars planets gas in our own Galaxy Other galaxies Tides Tides from differential gravity between 2 points Ex Moon pulls harder on NEAR side of Earth than far side gt stretches Earth out like taffy ID: 636553
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Slide1
The Transient Sky
Things that move, change brightness or color
Solar System
Stars, planets, gas in our own Galaxy
Other galaxiesSlide2
Tides
Tides: from
differential gravity between 2 points
Ex: Moon pulls harder on NEAR side of Earth than far side -> stretches Earth out like taffy!Value of Gravity: F = GMm/r2 (inverse square law)Summed value of tidal force difference between 2 points: ΔF = (2GMm/r3)Δr Δr = difference in distance between 2 points
Δr
Gravitational force of Moon at various pointsSlide3
Tides and Moon Phases
Water stretches much more than rock
water tides bigger Moon much CLOSER than Sun Moon’s tides twice as strong as Sun'sMoon over same spot on Earth every 25 hrs time of high tide changes daily
(strongest)
(weaker)
Tides caused by Earth
’
s shape
deforming as it rotates:
2 high and 2 low tides every 25 hours
-- linked to powerful earthquakes!
1
st
,3
rd
qtrs
new
fullSlide4
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 bulgeEffect: like sideways spinning in a tilted topOne full sideways spin: 26,000 yearsEffect: North Star changes, spring constellations become summer constellations etc.
Astrology doesn
’
t account for precession
Similar process causes Moon
’
s libration (wobbling)Slide5
Lunar Libration (seen from Earth)
(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”)
From Earth, we see 59% of moon’s surfaceSlide6
Fig. 10-3, p. 229Slide7
Convective Zone
In Sun’s core, atoms are so hot they’re ionized (no electrons)
don’t absorb photon energy easily.
85% of way out from core, atoms are cool enough have electrons
absorb energy from high energy photons coming from core heats the gas. It rises, cools, and sinks: convectionSlide8
Granules
Fig. 10-5a, p. 230
Granules (~700 km across) – caused by convection cells coming up from belowSlide9
10.2b Solar Dynamo: winding magnetic field and sunspot numbers
Fig. 10-18b, p. 237
150 yrs
Little Ice Age
CoolingSlide10
Prominence Eruption
Fig. 10-8a, p. 231Slide11
Planetary Motion
We observe Mercury, Venus, Mars, Jupiter and Saturn moving among the “fixed stars” around the sky:
videoSome motion is “retrograde” (backward) confused our ancestors –
led to change our view of Universe Earth is NOT the center! videoSlide12
Asteroids & Comets
Asteroids are EVERYWHERE!
videoNear-Earth asteroidsChance to study some up close with radarOsiris-Rex sample return
Collision warnings!videoComets also are all over – with DIFFERENT orbits! videoSlide13
Fig. 8-28, p. 202
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 12-15km Near Earth Object-- 65 Myr old-- crater 200km wide-- Left iridium layerThe dinosaur-killer!Slide14
Pluto’s Discovery Plates 1930
Fig. 8-2, p. 186
Dates Jan 23 & Jan 29, 1930, moved about 1.4
arcmin (width of a pea at 10 yards)Slide15
Can you spot Eris?
Images taken over 3
hrs
on 21 Oct 2003mag=18.7, taken with Caltech 1.2m Oschin (Mt. Palomar) SchmidtMotion 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 itSlide16
Kuiper Belt Objects
Fig. 8-8a, p. 191
Comets
are out there, too!Slide17
Beyond
Pluto+Eris
- you can help!Kuiper Belt – “outer asteroid belt” of icy/rocky objects, beyond NeptuneSome objects appear “thrown” by unseen, massive objectNeed human eyes to look for moving objects!
Backyard Worlds: Planet 9Slide18
Stars+Planets
Beyond Solar System
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 Earth would be pinhead 1m awaynext star a marble in Indianapolis
Move 1 arcsecond (1 pinhead’s width at a distance of a mile) over 6 months“Parallax” motion detected with invention of photography, 1830sSlide19
Parallax over 1 Year
Fig. 11-8a, p. 250Slide20
Proper Motion
Normally <1 arcsec/yr, often << 1 arcsec/yr
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/yrNeed DISTANCE to convert to km/s
Barnard’s star: moves 50 arcsec (width of Jupiter) in 7 yearsSlide21
Proper Motion of Big Dipper
100,000 BC to 100,000 AD
22
ºSlide22
Proto-planetary disks
Systems are bright in IR due to blackbody emission from cool dust.
HL Tau, ALMA (mm image)
HL Tau, HSTSlide23
Herbig-Haro
Objects: Jet trails from proto or pre-main-sequence-stars
Like water splashes back from pouring water too fast down a drain:
Gas spirals into a forming starGas heats up as it's compressedCentral pressure shoots it out the poles Video explanation
Herbig-Haro (HH) 30, from Hubble, IRSlide24
Visible light: jets bright, star invisible!
Fig. 12-8, p. 280
Shock waves: when a blob of gas hits another blob of gas supersonically
HEAT + LIGHT!
Pre-main sequence star (
hidden by dust
)
Jets strike interstellar gas, make it glow
HH30, HST, visible lightSlide25
IR image of HH object
Fig. 12-9, p. 281
HH46/47 (in dusty
“
Bok globule
”
)
in mid-IR from Spitzer
Pre-main sequence star hidden by dust in visible light, but
BRIGHT in IR!
Dust scatters visible light, but IR light passes right through!
IR: protostars bright!Slide26
11.7 Variable Stars
dec
+10
°
0°
-10°
-20°
RA
3h
2h
1h
0h
N
ESlide27
Variable Stars
Stars vary for all sorts of reasons
Periods from <1 hour to years
Some regular, others irregularEclipsing binariesIntrinsical variables (many classes)Mira: giant pulsating starRR Lyraes – measure distances to star clusters, map out our GalaxyCepheids – measure distances to galaxiesInteracting binaries = novaeExploding stars = supernovaeSlide28
Fig. 11-26, p. 264
Light curve of
Mira
, 1st known variable (1596 by Fabricius)
P=331 days
Naked eye
Need telescope
Variable
Stars
Rev. David
Fabricius
, German, 1564-1617Slide29
Fig. 11-22, p. 261
Eclipsing Binaries: inclination i~0
°:
since we know i ACTUAL masses (rare: ~200 known)
Flat-bottomed light curves: smaller star totally eclipsed.
Round-bottomed light curve: both stars partially eclipsed.
Eclipse type depends on inclination.
Primary eclipse
Primary: hotter star
Secondary: cooler star
Secondary eclipse
Partial eclipses
Total eclipse
Velocities + eclipse curves give relative stellar radii!Slide30
Eclipsing Binary light curve
From
light curve and radial
velocity curve (not shown), we can calculate stars’ radii, relative temperatures, combined masses and mass ratiosSlide31
Transiting Planets
–
like Eclipsing Binary Stars
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° fieldSlide32
Citizen Science: Find Exoplanets
Planet Hunters
Tutorial videoSlide33
Fig. 11-28, p. 265
Period-Luminosity Relation for Cepheid Variables
Measure period -> absolute mag.
Apparent + absolute mag ->
DISTANCE
Bright stars, visible
in our and other galaxies
Good
standard candles!
Video explanationSlide34
Fig. 11-30, p. 266
Hubble key project: pick out Cepheids in other galaxies -> distancesSlide35
Mass
Transfer onto White Dwarf50% (or more) of stars in binary systemsOne becomes white dwarf first; lower mass star become red giant laterLower mass secondary star (red giant, weak gravity) loses mass to white dwarf (strong gravity) Slide36
Dwarf Novae
Roche lobe overflow
from
red giant to accretion disk onto white dwarf (WD)Results in flare-up of factor 102-106 (5-15 mag)Accretion disk instability – hammering star surfaceExtra matter (H) dumps onto WD, gravitational release of energy during dumping causes bright spot
Thermonuclear runaway – fusion bombs
Extra matter (H) reaches critical temperature+density on surface of WD,
undergoes fusion (much brighter than accretion disk instability) – like gasoline on a fire, produces heavy elements like C,O, sometimes Si,SFlare-ups: involve 1/10000th of red giant mass, happen repeatedly (but need not be regular)Slide37
How a Nova Flares UpSlide38
Light Echoes: V838 Monocerotis over 2.4 years
Fig. 13-12, p. 303
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)
1.2pc or 41"
2.1pc or 71"
-----
V838 Mon, HST, blue-green-red lightSlide39
Supernovae
Two main types
physically (IMPORTANT)
:Core Collapse: explosion of supergiant starExplosion of white dwarf (WD)A supernova can briefly shine as bright as an entire galaxy (10 billion stars!)
White Dwarf Supernova Video
NASA Swift satellite
D = 24Mpc
Core collapseSlide40
Core Collapse SupernovaSlide41
Fig. 17-1a, p. 400
normal galaxy
active galaxy
Normal galaxies
: bright nuclei because lots of stars in small volume
Gravity pulled gas to center
lots of star formation happened
Some galaxies: unusually
bright nuclei in
optical/IR – and X-rays/UV/radio
Quasars
and Active GalaxiesSlide42
Active Galaxy Centaurus AFig. 17-4a, p. 401
optical
X-ray – shows jetSlide43
Active Galaxy Jets Blow Bubbles in Surrounding MediumSlide44
Large Synoptic
Survey
Telescope (LSST)
First stone laid 2015 Apr 14Standalone telescope projectSlide45
LSST Key Points
Top-ranked major ground-based facility
by NRC’s Astronomy & Astrophysics decadal survey, 2010
Video introduction to LSSTNSF will pay for construction, operationData analysis paid for by LSST Corp: 30-40 universities and research labs in US and rest of world8 KY universities joined in 2016: UL, UK, EKU, NKU, Morehead St., Murray St., Bellarmine U, Berea CollegeSlide46
Solar Eclipses:
Fig. 4-7, p. 69
Earth goes into Moon's shadow
Solar eclipse
only happens at New Moon
Solar eclipse
lasts only a few minutes
– Moon's shadow is much smaller than Earth
Next total solar eclipses from US:
21 Aug 2017 (Oregon-S Carolina)
08 Apr 2024 (Texas-Maine)
23 Aug 2044 (N Dakota-Montana)
12 Aug 2045 (Cal.-Florida)Slide47
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 descriptionLonger videoSlide48
Great 2017 Eclipse!Slide49
Eclipse in KY: about 1pm CDT
The greatest 2 minutes in astronomy! Slide50
Stages of Eclipse
Partial
– few minutesTotality – 2 minutesPartial – few minutesSlide51
Eclipse Special Effects
Diamond Ring
– 1st/last bit of sun appearsBaily’s Beads
– see bits of sun through moon’s mountainsSlide52
How to View Eclipse
Eclipse glasses
– cost a $1-few
Pinhole or Binocular ProjectionMore expensive solar projectorSlide53
How to photograph Eclipse
Use a tripod!
ONLY during totality: OK to take a normal pictureOUTSIDE of totality: use a filter!See eclipse.gsfc.nasa.gov (Goddard Space Flight Center)Slide54
Deluxe Photography
Glass solar filter on telescope or cameraSlide55
Don’t Miss Eclipse for Photos!
Enjoy your
first experience!Slide56
Some Future Total Eclipses:
2019 Jul 2: northern Chile, Argentina
2020 Dec 14: southern Chile, Argentina2024 Apr 8: Mexico-Texas-Indiana-Quebec2044 Aug 23: North Dakota-Montana-Alberta2045 Aug 12: California-Florida (coast-to-coast)