A100 Solar

System

Today’s APOD

Read Chapter 1 in text – History of Astronomy

Quiz Today (essential facts and scientific notation)

Rooftop Session Sept. 10, 9 PM 1st Homework due Friday (get it on Oncourse)

The Sun Today

Monday, Sept. 8

First Quiz• Bubble and write your name on the

Scantron form• You may consult with your neighbors• No books, notes, papers, internet,

cell phones

What can we see in the night sky?With the naked eye, we can see more than 2,000 stars, as well as 5 planets, the Moon, comets, meteors, the Milky Way, and a few other special objects The Milky Way is a band of light that makes a circle around the celestial sphere

Orion rising

The night sky is familiar, but few people look closely at (or think about) the complex phenomenawe observe in sky.

The Sky!

The brightness of a star is shown by the size of its dot

North

South

Jupiter & the Moon in Sagittarius

Sky chart for 9 PM TONIGHT

Jupiter & the Moon in Sagittarius

Sept 9Sept 8

Just look south… Jupiter is the brightest object in the southern sky

Check out the just south of west, just after sunset

• See Mercury, Venus, and Mars

• You will need to be able to see low on the horizon to the west southwest

ConstellationsA constellation

is a region of the sky

Constellation regions are irregular in

shape

Do the Stars in a constellation belong together?•NO!•The stars in a constellation are not all at the same distance from the Sun

•They do not form a real group in space

The Big Dipper is part of the constellation

Ursa Major

The stars of the Big Dipper are not all at the same distance from the Sun

The Constellations

The 88 official (defined by the International Astronomical Union) constellations cover the celestial sphere

The Celestial Sphere

The stars all appear to lie on a large sphere surrounding the Earth (the celestial sphere)

Really, the stars are all at different distances

Angular Measurement

s

• Full circle = 360º• 1º = 60 (arcminutes) • 1 = 60 (arcseconds)

We measure the sky

using angles

Measure the Angular Size

Image taken by the Galileo spacecraft (Jupiter, 1995-97) during its lunar fly-by in December, 1992

Tycho impact basin

The dark areas are lava rock filled impact basins (mare)

The “real” Moon is ½ degree across

Angular Size distance 2

degrees 360 size physical = sizeangular

An object’s angular size appears smaller if it is farther away

The angular size of Mars changes depending on where Earth and Mars are

in their orbits

angular size

physical size

distance

The Local

Sky

An object’s altitude (above horizon) and direction (along horizon) gives its location in your local sky

Definitions:The Local Sky

Zenith: The point directly overhead

Horizon: All points 90° away from zenith

Meridian: Line passing through zenith and connecting N and S points on horizon

Our view from Earth:• Stars near the north celestial

pole are circumpolar and never set.

• All other stars (and Sun, Moon, planets) rise in east and set in west.

Celestial equator

A circumpolar star never sets

This star never rises in Indiana

Why do stars rise and set?

Stars in the northern sky circle the northern celestial pole (in the southern hemisphere stars circle the southern celestial pole)

The Earth spins under

Polaris

(Polaris is NOTthe brighteststar in the sky!)

Finding Polaris

Find the Big Dipper in the northwestern sky

Sky chart for 9 PM TONIGHT

Find an open area away from nearby lights where you have a good view of the sky

North

South

Big Dipper’s on its side in the northwestern

sky

Finding Polaris

To find Polaris:• find the Big Dipper• follow to Polaris• the Big Dipper is ALWAYS up

in Indiana!

Altitude of the celestial pole

= your latitude

Why do the constellations we see depend on latitude and time of year?

They depend on latitude because your position on Earth determines which constellations remain below the horizon.

They depend on time of year because Earth’s orbit changes the apparent location of the Sun among the stars.

The sky changes as Earth orbits the Sun

As the Earth orbits the Sun, different constellations are visible at night

At midnight, the stars on our meridian are opposite the Sun in the sky

Where on the Earth is it possible to see the most stars through the year?

a) From the north pole b) From latitude 23.5 degrees c) From the equator d) anywhere, since latitude makes

no difference.

Precession!Over time, the

direction of the Earth’s rotation axis drifts around a circle.

At different times, different stars (other than Polaris) are close to the pole

The location of the celestial pole traces out a circle in the sky every 26,000 years

Vocabulary ReviewoConstellationoEclipticoEquatoroCelestial

sphereoLatitudeoLongitude

oMeridianoZenithoHorizonoAltitudeoNorth and

south celestial poles

One question I’ve always had about astronomy is…

ASSIGNMENTSthis week

Read Chapter 1, History of…

Kirkwood Obs. open Weds. Rooftop Sky Viewing Weds. 1st HW due Friday

Dates to Remember