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The Transient Sky Things that move, change brightness or color The Transient Sky Things that move, change brightness or color

The Transient Sky Things that move, change brightness or color - PowerPoint Presentation

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The Transient Sky Things that move, change brightness or color - PPT Presentation

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

eclipse star stars fig star eclipse fig stars earth light moon solar video bright gas mass tides sun motion

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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

°

-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)