Introduction to Introduction to Astronomy: Astronomy:

Size Scales & Size Scales & TaxonomyTaxonomy

Acknowledgements Tyler Nordgren & Julie Rathbun (University of Redlands)Lynne Raschke, Anne Metevier, Scott Seagroves, & Scott Severson (UCSC)

Photo credit: Roger Smith/NOAO/AURA/NSF

Kathy Cooksey

Assignments

• APOD Presentations: July 10 Demo – http://antwrp.gsfc.nasa.gov/apod/ap07071

0.html

• Astronomy Challenge– With every assignment comes a gift…

introduce planisphere– Due Friday July 20– Come to class with questions!! Please!– I’m free for study hall sessions

The Universe …

… from the Solar System…

… to the Stars…

… to the Milky Way …

… and beyond.

• How well do you know your own neighborhood?

• Imagine we shrink our solar system down to the scale where our Sun were the size of a volleyball:

– How big would the Earth be?– How far from the Sun would the Earth be?– How about Jupiter?

Size Scales

Concept Question

What are the sizes of the planets if the Sun were 8” in diameter?

Powers of Ten

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Powers of Homer

D’oh!

Distance Units in Astronomy

• Astronomical Unit– Distance between Earth and Sun– 1 AU = 93 million miles = 150 million km

• Light-year– Distance light travels in one year– Light travels at velocity of 186,000 miles /

second– 1 l-y = 6 trillion miles = 9.5 trillion km

When we observe an object that is 900 light-years away, we see it as it was 900 years ago

One More Distance Unit …

• Parsec– Distance to object

with parallax angle of one arcsecond

– Parallax angle = half of star’s apparent shift in sky when viewed two times, six months apart

– Arcsecond = 1/3600 of degree

– 1 parsec = 3.3 l-y

A Tour of the Universe

The Solar System

An Inventory

What is the Solar System?• Sun and system of objects orbiting Sun• What’s in the Solar System?

One Star

Eight Planets

Dozens of moons

Thousands of asteroids

Trillions of comets

Concept Question

What causes the moon to go through phases?

The Sun, Earth, and Moon

Moon phases are caused by relative positions of Sun, Earth, and Moon

Solar Eclipse

• Sometimes Moon passes between Sun and Earth

• Casts shadow on the Earth

Lunar Eclipse

• Earth passes between Sun and Moon• Earth casts shadow on Moon

Plane of Solar System

• Sun, Earth, and planets all lie in same plane

Planets

• First step to studying planets?– Compare and

contrast

• What are important qualities?

Terrestrial Planets

• Closest to Sun• Small

– Mass– Radius

• High density– Primarily rocky– Solid surface

• Few moons• No rings

Mercury

Venus

Earth

Mars

Jovian Planets

• Far from Sun• Large

– Mass– Radius

• Low density– Primarily gaseous– No solid surface

• Many moons• Many rings

Jupiter

Saturn

Uranus

Neptune

Dwarf Planets

• Eris– 27% larger than Pluto

• Twice as far

• Pluto– 19% radius of Earth

(743 mi)• 40 AU (30-49 AU)

• Ceres– 18% smallerthan

Pluto• 2.8 AU (Asteroid Belt)

Pluto: Eliot Young, APOD 3 Sep 2006

Eris: Keck Observatory, APOD 18 Sep 2006

Ceres: NASA, ESA, APOD 21 Aug 2006

Rings

• Jupiter’s four largest moons

• Similar in size to our moon

• Visible with binoculars

Galilean Moons

Io

Europa

Ganymede

Callisto

Scale Model of the Solar System

Everyone up and out the door…

THE SUNTHE SUN

The Closest Star

Sunspots

• Appear in photosphere

• 11-year sunspot cycle

• Center = Umbra• Edge =

Penumbra

Sunspots

SO

HO

Im

ag

es

20

01

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Solar Flare

Aurora

The Stars

The Solar Neighborhood

The nearest star, Alpha Centauri, is 4.4 light-years away!

Binary Stars

• Most stars in sky are in multiple systems that orbit each other.

• Binaries, triplets, quadruplets, etc…

• Sun is single star--unusual!

Stellar Sizes

Supergiants, Giants, and Dwarfs

Star clusters

Open Clusters

• Loose collection of stars

• Tens to over hundred stars

• Young stars

Globular Clusters

• Spherical shape• Hundreds of

thousands of stars

• Old stars

Interstellar MediumInterstellar Medium

The Stuff Between Stars

Distribution• Picture dust under your bed

– Fairly uniform thin layer– Some small clumps– Occasional big complexes

• Interstellar dust and gas is same

Dark Nebulae

• Dust blocks some light

Copyright: AURA

Reflection Nebulae

• Blue light is scattered by dust.

NGC 1788, Kathy Cooksey

Witchhead Nebula

Emission Nebulae

• Some gas clouds shine because they are heated by young hot stars within them

Lagoon nebula Copyright - Jason Ware

M57 – Ring Nebula Cat’s Eye

Eskimo Nebula Hourglass Nebula

Planetary Nebulae• Clouds of gas thrown off when star stops

burning

Black Holes and Neutron Stars

Dead StarsCopyright – A. Hobart

Neutron Stars• Giant ball of neutrons• Mass : at least 1.4 x

mass of Sun• Diameter: 20 km!• Density: 1018 kg/m3

– Thimble full weighs as much as mountain

• Spin once every 0.0001 to 1 second• Magnetic fields as strong as Sun, but in

space of a city

Black Holes

• When high-mass star’s core is heavier than ~3 x Msun

– It collapses

– Density so high not even light escapes!

• Star collapses to form black hole

Black Holes• Light bent by

gravity of black hole

• Event horizon is boundary inside which even light cannot escape

• Near event horizon, time slows down relative to distant observers

Seeing Black Holes• Can’t see black hole

itself• Can see matter falling

into hole.• Gravitational forces

stretch and rip matter– Matter heats up

• Very hot objects emit in X-rays (e.g., interior of Sun)

• Cygnus X-1

Illustration Credit: M. Weiss

Galaxies

Optical emission from stars and nebulae

Milky Way

Near-Infrared stellar emission – copyright E. L. Wright and COBE

The Milky Way

Your are Here

Other Galaxies

Galaxies come in many shapes and sizes.Milky Way is fairly large, massive galaxy

Ellipticals• Huge• No gas• No dust• No young

stars• Nothing but

old stars.– Random

orbits

M 87 Copyright – Anglo-Australian Telescope

Board

Jets

Spirals

Spirals

• Like Milky Way• Disks and

bulge• Young stars

and old• Gas and dust• Stars forming• Stars dying M81 and M82 – Copyright R. Gendler

M63 Copyright – S. Miyazaki, Suburu

NGC1365 Copyright – VLT

M31 The Andromeda Galaxy Copyright – Jason Ware

NGC 891 – Copyright WIYN

NGC 891 – Copyright J.C. Barentine, NOAO

Irregulars

Galaxy Groups

Local Group

Gala

xy

Merg

ers

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Patrik

Jon

sson

, UC

SC

Interacting Galaxies

M51 Copyright – Tony and Daphne Hallas

Interacting Galaxies

NGC4676: “The Mice” Copyright – ACS Science & Engineering Team, NASA

Interacting Galaxies

Seyfert’s Sextet Copyright – J. English (U. Manitoba), C. Palma (PSU), et al., NASA

Galaxy Clusters

Hubble Deep Field

Hubble Ultra Deep Field

One Last Trip...

Summary

• What new fact did you learn?– About the size of the Universe?– About what’s in the Universe?– About…?