AnnouncementsAnnouncements

Class’s web site no live!Class’s web site no live! www.astro.umass.edu/~mauro/astro100www.astro.umass.edu/~mauro/astro100

Syllabus is on line, check it!Syllabus is on line, check it! Lectures #1 and 2 are on lineLectures #1 and 2 are on line

Scales of the UniverseScales of the Universe

Course Web Site:Course Web Site:

www.astro.umass.edu/~mauro/www.astro.umass.edu/~mauro/astro100astro100

Today’s Assigned ReadingToday’s Assigned Reading

Chapter 1, allChapter 1, all Chapter 2, allChapter 2, all Appendix AAppendix A

Now… on to scales in the Now… on to scales in the Cosmos…Cosmos…

Let’s explore the universe in Let’s explore the universe in steps of increasing steps of increasing

magnification, from small to bigmagnification, from small to big

At each step, let’s change scale At each step, let’s change scale by TWO orders of magnitude at by TWO orders of magnitude at a time and see what happens.a time and see what happens.

52 feet across

1 mile across

= 6000 feet

=1.6 km

160 kilometers across

1 mile = 1.61 kilometers

Infrared photo

12,756 km

1,600,000 km

=1.6 x 106 km

Moon

1.6x108 km =1.6x1011m

1AU = 1.5x1011 m

AU is a distance unit

1.6 x 1010 km, or a trillion (1012) times wider than the first picture!

32 AU

100 AU

10,000 AU

Stars are so far apart from each other!If the Sun is a golf ball in NYC, the nearest star is a golf ball in Chicago!!!

106 AU = 17 ly

1 ly =63,000 AU = 1013 km

1700 ly

170,000 ly

1.7 x 107 ly

The local group of galaxies

1.7 x 109 ly

AnnouncementsAnnouncements

Class’s web site is live!Class’s web site is live! www.astro.umass.edu/~mauro/astro100www.astro.umass.edu/~mauro/astro100

Syllabus is on line, check it!Syllabus is on line, check it! Lectures #1 and 2 are on lineLectures #1 and 2 are on line

Basic classes of celestial objects:

Comets and Asteriods

Planets Earth as one

Stars Sun as one

Galaxies Milky Way as one

Their sizes

Comets and Asteroids: 10-100 km dust

Earth: 104 km poppy seed

Sun: 106 km grape fruit

Milky Way 1018 km Earth-Sun distance

Universe 1023 km 100,000 Earth-Sun distance

A Sense of SpaceA Sense of Space

1. The Sun would hold 1.3 million Earths. i.e. the radius of the Sun is about 100 times that of the Earth.

2. There are ~100 billion "Suns" in a galaxy like our own Milky Way Galaxy.

3.Astronomers can see billions of galaxies.

Your local address:Your local address:

What is our address in the What is our address in the Universe?Universe?

•UMass, Amherst, Massachusetts, USA•Earth, •Solar System•Milky Way Galaxy, •Local Group, •Local Supercluster•Our Universe•Are there other universes? Most likely yes!

•Multi-verses as opposed to Uni-verse

So…How Big is the So…How Big is the Observable Universe Observable Universe

anyway?anyway?……about 14 billion-billion-billion centimeters in diameterabout 14 billion-billion-billion centimeters in diameter

oror14,000,000,000,000,000,000,000,000,000 cm14,000,000,000,000,000,000,000,000,000 cm

oror1.4x101.4x102828 cm cm

oror14 billion ly14 billion ly

oror6000 Mpc6000 Mpc

The finite speed of light lets us “look” into the past!

100,000 l-years

EarthSupernova

now 97,997 BC

Consider this:If you had friends throughout the galaxy, how could youcreate a “live” TV show?

If If the the Sun were a grapefruit on one side Sun were a grapefruit on one side of the room, what would be Earth?of the room, what would be Earth?

1) 1) A poppy seed on the other side. A poppy seed on the other side.

2) 2) Another grapefruit on the other side.Another grapefruit on the other side.

3) 3) A poppy seed in my office.A poppy seed in my office.

4) 4) An apple on the other side.An apple on the other side.

If If the the Sun were a grapefruit on one side Sun were a grapefruit on one side of the room, what would be Earth?of the room, what would be Earth?

1)1) A poppy seed on the other side. A poppy seed on the other side. (Earth-Sun distance~100x radius of Sun~ 100 radius of Earth) (Earth-Sun distance~100x radius of Sun~ 100 radius of Earth)

2) 2) Another grapefruit on the other side.Another grapefruit on the other side.

3) 3) A poppy seed in my office.A poppy seed in my office.

4) 4) An apple on the other side.An apple on the other side.

What would then be What would then be the nearest star?the nearest star?

1) 1) A poppy seed at the Amherst downtown.A poppy seed at the Amherst downtown.

2) 2) A poppy seed on the west coastA poppy seed on the west coast

3) 3) A grapefruit at the Amherst downtown.A grapefruit at the Amherst downtown.

4) 4) A grapefruit on the west coast.A grapefruit on the west coast.

What would then be What would then be the nearest star?the nearest star?

1) 1) A poppy seed at the Amherst downtown.A poppy seed at the Amherst downtown.

2) 2) A poppy seed on the west coastA poppy seed on the west coast

3) 3) A grapefruit at the Amherst downtown.A grapefruit at the Amherst downtown.

4) 4) A grapefruit on the west coast.A grapefruit on the west coast.

(Nearest star is 4Ly ~ 300,000 AU)(Nearest star is 4Ly ~ 300,000 AU)

A Sense of TimeA Sense of Time

If we were to compress the time since the Big Bang into one year, and make the time of the Big Bang January 1, The Earth was formed in mid-September. The mammals appeared on December 26. All human prehistory (from the first known stone tools) and history have occurred in the last ½ hour of New Year's Eve.

All of human history is but a fleeting instant on the cosmic timescale.

So MANY objects….How Do We Make Sense of it ALL??

Our investigation of the universe has become quite sophisticated…Here is the NASA/ESA Hubble Space Telescope (HST)

The Sky and its CyclesThe Sky and its Cycles

Goals:Goals:

To describe and locate objects in the sky To describe and locate objects in the sky

To understand the apparent motions of celestial To understand the apparent motions of celestial objectsobjects

To introduce the seasonsTo introduce the seasons

How Do We Locate Objects on the How Do We Locate Objects on the Sky? Sky?

The Celestial Sphere (C.S.)Stars, planets, the Sun , external galaxies, are at different distances from us, yet for studying patterns in the sky, we represent them in projection onto the C.S.

The Sun is physically 400 times larger than the Moon.Why is their angular size is the same?

Angular SizeAngular Size

Angle diameter (in radians) = diameter/distanceFull circle = 2 (in radians)=360 degrees=360o

1o=60 arminutes = 60’1’ = 60 arcseconds = 60” ; 1 rad = 206,264.81”

rad= S/D

D

S

Angular SizeAngular Size Some Examples: Horizon to zenith (point overhead) 90o Your fist at arm's length 10o Your fingernail at arm's length 1o = 60' Sun or Moon seen from Earth 0.5o = 30' Smallest detail visible to naked eye 1' = 60'' Smallest detail visible by a single telescope from Earth's surface: 1''

Angular size of Pluto: 0.15”

Betelgeuse (largest star) seen from Earth 0.004''

The Orion Constellation

ConstellationsConstellations88 official constellations divide the sky into areas with clearly boundaries.

The names of constellations are in Latin. But most bright star names derived from ancient Arabic.

The original constellations were invented by farmers over 5000 years ago.

Remember that the constellations are not real!

They are just imaginative figures “invented by ancient cultures

Projection

Big Dipper ---- an asterism

Humans have logarithmic sensesHumans have logarithmic senses

Our senses are logarithmic, i.e. respond logarithmically to Our senses are logarithmic, i.e. respond logarithmically to stimuli.stimuli.

If a stimulus I is exerted on our senses (vision, hearing, If a stimulus I is exerted on our senses (vision, hearing, touch, all work the similarly)…touch, all work the similarly)…

… … our body DOES NOT sense I, but sense Log(I) insteadour body DOES NOT sense I, but sense Log(I) instead For example, if one doubles I (e.g. turn the volume of the For example, if one doubles I (e.g. turn the volume of the

sound from 3 to 6), we only perceive an increment of sound sound from 3 to 6), we only perceive an increment of sound of Log(2)=0.3, i.e. 30% louderof Log(2)=0.3, i.e. 30% louder

Same thing for visionSame thing for vision

Luminosity and MagnitudeLuminosity and Magnitude

mmVV = -2.5*Log(I) + C = -2.5*Log(I) + C

mm11 – m – m22 = -2.5*Log(I = -2.5*Log(I11/I/I22)) If IIf I11=2xI=2xI22, then m, then m11 – m – m22 = -2.5*Log2 = -0.75 = -2.5*Log2 = -0.75

If IIf I11=10xI=10xI22, then m, then m11 – m – m22 = -2.5*Log10 = -2.5 = -2.5*Log10 = -2.5

If IIf I11=100xI=100xI22, then m, then m11 – m – m22 = -2.5*Log100 = -5 = -2.5*Log100 = -5

II11/I/I22 = 10 = 10-0.4*(m-0.4*(m11

– m – m22

)) = 2.512 = 2.512(m(m11

– m – m22

))

I is the true intensity of the light

Log(I) is what we sense we our eyes

The Motions of EarthThe Motions of Earth

1. The Earth rotates – this leads to day and night.

2. The Earth revolves around (orbits) the Sun – this leads to the seasons. 3. The Earth and Sun revolve around (orbit) the center of the Galaxy.

4. The Galaxy moves through the Universe.

Latitude and longitude make aconvenient coordinatesystem for locatingobjects on the Earth.

Altitude and Azimuthgive us the directionto look on the celestialsphere.

Time Zones and Universal TimeTime Zones and Universal Time

Time Time

We live on a rotating sphere (Earth) that receives lights only from one source (the Sun).

If here is day, on the other side of Earth it is night. So, how do we synch the time across the planet?

The time for many astronomical events is given in Universal Time (UT), which is (approximately) the local time for Greenwich, England --- the Greenwich Mean Time or GMT.

Earth's rotation causes the sun and stars to rise in the east and set in the west daily.

Cycles of the SkyCycles of the Sky

But stars and the Sun do not set and rise daily everywhere!

Near the poles, the sun rises and sets every half year,and circumpolar constellations such as Ursa Major, never set.

What other cycles do you know?

There are two ways to think about the motion of the skey: - the C.S. rotates - or the Earthrotates while the sky sits still.

Sometimes one works better thanthe other …

The altitude of Polaris The altitude of Polaris above the horizon is above the horizon is approximately the approximately the

same as the observer's same as the observer's latitude in the latitude in the

Northern Hemisphere.Northern Hemisphere.

Are there stars in the sky during the daytime?

How long to go all the way around?

d. 1 year

c. 1 month

b. 1 week

1 day

Earth also orbits around the Sun. Takes 1 year for one round.Note the tilt between the ecliptic and Earth’s rotation axis

Ecliptic

The constellations along the ecliptic are called the zodiac

Everything in the Universe is Everything in the Universe is Moving! … but …Moving! … but …

the further away from us something is, the more it has the further away from us something is, the more it has to move to be noticeable.to move to be noticeable.

the motion of the Earth rotating on itself (day/night) the motion of the Earth rotating on itself (day/night) is the easiest to seeis the easiest to see

Followed by the motion of the Moon around the Followed by the motion of the Moon around the Earth (~29 days)Earth (~29 days)

followed by the motion of the Earth around the Sunfollowed by the motion of the Earth around the Sun and finally the motion (over tens or hundreds of and finally the motion (over tens or hundreds of

years) of close starsyears) of close stars

What causes the seasons?What causes the seasons?

What are the differences between days in summer and winter?

Longer days

stronger Sun

in summer than in winter

Seasons are due to the tilt of the earth.

Are the seasons due to the Are the seasons due to the changing distance from the sun? changing distance from the sun?

NO!NO!

The Earth-Sun distance does NOT matter with the seasons!

(Not to scale)