Transcript The Celestial Sphere

Welcome to
The Solar
System and
The Universe
Eighth Grade Elective
What Is Astronomy?

Answer the following question in
your notebook:


What do you think the term
“astronomy” means?
Astronomy: the branch of
science that deals with celestial
objects, space, and the physical
universe as a whole
What Do Astronomers Do?

Study planets and the sun in our
own solar system, as well as
other stars, solar systems,
galaxies, and the whole
universe.

Try to understand how the
universe works

Study the evolution of stars in an
attempt to understand how our
own star, the sun, and our solar
system of planets were created
and what will happen to them as
they age
Types of Astronomers

Most astronomers concentrate on a
particular question or area of astronomy: for
example, planetary science, solar
astronomy, the origin or evolution of stars, or
the formation of galaxies.

Observational astronomers design and
carry out observing programs with a
telescope or spacecraft to answer a question
or test the predictions of theories.

Theorist work with complex computer
models of a star’s interior, for example, to
understand the physical processes
responsible for the star’s appearance.
What Does It Take To Be An
Astronomer?

One of the most important
sciences astronomers must
learn is physics

Physics is the study of the laws
of nature and how particles
interact with one another

They also study chemistry,
computer science, and
mathematics
Why Study Astronomy?

Think It- Write It: Take a few
minutes to write down why you
decided to take this course.

Practical Uses:


Knowledge of astronomy
allows us to keep track of time
and seasons and predict the
tides
Intellectual Interest

Astronomy is a fun and
interesting science to study

It allows you to leave
everyday life behind, to
expand your horizons and to
explore the conditions of
human existence
The Celestial
Sphere
The Night Sky

Activity: Close your eyes and imagine
looking up at the night sky. What do you
see?

Questions:


Have you ever visited a planetarium?

Do you know how to find the north star?
Have you ever tried to locate a
constellation?
Is The Sky Moving?

If you pay close attention to the night sky
you will notice that the stars appear to move
over time

Question: So, is the sky really moving?
What do you think?

Answer: No, it is actually Earth that rotates
on its axis (once every 24 hours), making
the stars, as well as the Sun and Moon,
appear to rise and set
The Celestial Sphere

Close your eyes again and imagine a huge
hollow sphere that surrounds Earth. Think of
all the stars as dots painted on the sphere

Note: we know this analogy isn't really
correct—some stars are much further away
than others—but the visual image presents a
handy way of thinking about the sky.

The imaginary hollow sphere is called the
celestial sphere.
Longitude and
Latitude
Latitude

Latitude lines run horizontally

Degrees latitude are
numbered from 0° to 90° north
and south, with 0° degrees
being the equator
Longitude

Longitude lines run vertically

The Earth is divided into 360°
longitude

Zero degrees longitude is
located at the Prime Meridian
(0°)

The degrees continue 180°
east and 180° west where
they meet and form the
International Date Line
How Do Latitude and
Longitude Work Together?

To precisely locate points on the earth's
surface, degrees longitude and latitude have
been divided into minutes (') and seconds (”)

There are 60 minutes in each degree. Each
minute is divided into 60 seconds

To locate the latitude and longitude of a
specific place check out this site :

http://universimmedia.pagespersoorange.fr/geo/loc.htm
The Celestial
Sphere
What is the Celestial Sphere?

The celestial sphere is an imaginary
projection of the Sun, Moon, planets, stars,
and all astronomical bodies upon an
imaginary sphere surrounding Earth

It is a useful mapping and tracking remnant
of the geocentric theory of the ancient Greek
astronomers

It provides an important tool to astronomers
for fixing the location and plotting
movements of celestial objects
How Does It Work?

The celestial sphere describes an extension of
the lines of latitude and longitude

Projections of lines of latitude and longitude
are transformed into declination and right
ascension

Just as every point on Earth can be expressed
with a unique set of latitude and longitude
coordinates, every object on the celestial
sphere can be specified by declination and
right ascension coordinates.

A direct extension of Earth's equator at 0°
latitude is the celestial equator at 0° declination
Declination

Declination- the angular distance of a point
north or south of the celestial equator

Declination is further divided into
arcminutes and arcseconds

In 1° of declination, there are 60 arcminutes
(60’)

In one arcminute there are 60 arcseconds
(60”)
Right Ascension (longitude)

Right ascension- the distance of a point
east of the First Point of Aries, measured
along the celestial equator and expressed in
hours, minutes, and seconds

Instead of longitude, right ascension is
measured in hours

Corresponding to Earth's rotation, right
ascension is measured from zero hours to
24 hours around the celestial sphere

One hour represents 15 angular degrees of
travel around the 360° celestial sphere
Important Points on the
Celestial Sphere
The Celestial Poles

The stars on the celestial sphere seem to
rotate around the north and south celestial
poles

Celestial poles- points on the celestial
sphere that are directly above Earth's North
and South Pole
The Celestial Poles
The North Star

If you live in the Northern
Hemisphere, you’ve probably
heard of the north star

The North Star, also known as
Polaris is bright star that's very
close to the north celestial pole!
The Celestial Equator
Celestial Equator

Another important imaginary line
on the sky is the celestial
equator

This line is actually an imaginary
circle on the celestial sphere,
directly above Earth's equator

It is always exactly 90 degrees
from the celestial poles, just like
Earth's equator is 90 degrees
from its poles
The Horizon

The horizon is the edge of our
local sky

Since we are located on the
surface of Earth we can see only
half of the celestial sphere at
one time
Zenith

The point straight overhead on
the celestial sphere is called the
zenith

The zenith is the point you'll see
if you lie on your back and look
straight up at the stars

It is always 90 degrees from the
horizon.
The Meridian
Since the sky rotates from east to west above us, the meridian marks
the halfway point of the celestial sphere.
Fun Facts

In the morning, the Sun is east
of the meridian (because the
Sun rises in the east).

At local noon, the Sun is right
on the meridian

In the afternoon the Sun moves
past the meridian to the west

In Latin, the morning is ante
meridiem, which is abbreviated
a.m. and means “before
meridian”

After noon, it is post meridiem,
or p.m., which means “after
meridian”
Is the Sky
Really
Moving?
The Sun

You know that planets orbit the Sun, but
planets do not orbit at uniform velocity.

Because of the elliptical shape of Earth's
orbit, Earth moves faster when closet to the
sun (perihelion) and slower when it is
furthest away (aphelion)

This difference in Earth's orbital velocities
(speed of an object in a specific direction)
makes the Sun appear to move at different
speeds at different times
Why Stars Appear To Move

All the stars in the sky are pretty much
standing still - they only look like they're
moving

There are two different reasons why stars
appear to move across our sky:


The Earth is spinning
The second is because the Earth itself is
moving around the Sun.
Why We See Different Stars

Standing on the surface of Earth we see the
stars passing by until after a whole
revolution around the Sun


So, it would take a year for us to see all
the stars pass by
At the same time as the Earth is moving
around the sun it is spinning on it own axis
(once a day)

So, we see some different stars coming
into view as the Earth spins from night to
night and other stars move out of view
The Moon Is
Following Me!

Unlike the stars, the moon is actually moving
in orbit around the earth

The Moon’s motion has two parts:

It looks like it's moving around the earth
once per day along with everything else

In addition, it is actually moving around
the earth once per month- this is what
makes it move to a different place on the
sky
Moon Phases
http://www.brainpop.com/science/space/moonphases/preview.weml
Key Points

A new moon occurs when the moon is
positioned between the earth and sun with
the illuminated portion of the moon facing
away from earth

At a full moon the moon is between the
earth and sun, but the moon is on the
opposite side of the earth, so the entire
sunlit part of the moon is facing us
Eclipses
Eclipses

An eclipse is caused by the casting of a
shadow of one heavenly body on another

Recall that the Earth is in constant motion



It rotates around its own axis
It revolves around the sun
The moon is also in constant motion


It orbits around the Earth
It rotates around its own axis
Lunar Eclipse
Solar Eclipse
Constellations
Constellations

http://www.brainpop.com/science/space/con
stellations/preview.weml

Ancient cultures celebrated heroes, gods,
and mythical beast by giving their names to
groups of stars

The oldest constellations named by Western
cultures originated in Assyria over 3000
years ago

Babylonian and Greek astronomers added
others in the classical age

48 of these ancient constellations are still
in use
Constellations (cont)
Alpheratz belongs to Andromeda

To the ancients, a constellation was a
loose grouping of stars

Constellation boundaries, when they
were defined at all were only
approximate
 Star Alpheratz could be part of
Pegasus or Andromeda.
 To correct gaps and ambiguities, in
1928 the International Astronomical
Union established 88 official
constellations

Constellation now represents not a group
of stars but an area of sky and any star
within the region belongs to on and only
one constellation

Asterisms= less formally
defined groupings of stars
Important to remember:

The Big Dipper is a well
known asterism that is part of
the constellation Ursa Major
•
Constellations and asterisms are
groups of stars that appear close
together in the sky.
•
Most are made of up of stars that
are not physically associated with
one another
•
•
Some stars may be many times
farther away than othere and
moving in other directions.
The only thing they have in common
is that they happen to lie in
approximately the same direction to
Earth.
Names of Stars

Ancient astronomers gave individual names to
the brightest individual stars

Naming stars however is not very helpful.
Why?

Simple names give you no clues to the
location of the star in the sky or to its
brightness.

Assign letters to the bright stars in a
constellation in approximate order of
brightness

Greek Alphabet or Letter used (Alpha,
beta…)
Constellation of The Hand

According to the Lakota, the Constellation of the
Hand, namely the bottom half of the constellation
Orion, represents the arm of a great Lakota chief.
The gods wanted to punish the Lakota's chief for his
selfishness and made the Thunder People rip out his
arm. The chief's daughter offered to marry anyone
who would recover her father's arm.

Fallen Star, a young warrior whose father was a star
and whose mother was human, returned the arm and
married the daughter. The return of the arm to the
chief symbolizes harmony between the gods and the
people with the help of the younger generation.
What are some myths about
Constellations?
Your task:
1.
Read the Myth story given
to you about a specific
constellation.
2. Write a retelling of the story.
3. Draw the constellation large
enough so it can be hung in
our classroom.
Parallax
How Astronomers Measure Stars
Brightness of Stars

Astronomers measure brightness of stars
using the magnitude scale
 System first appeared in the writings of
Ptolemy in AD 140
 Probably originated earlier by Greek
astronomer Hipparchus.
 Hipparchus compiled the 1st known star
catalog

The ancient astronomers divided the stars
into six classes
 Brightest = first-magnitude
 The larger the magnitude number, the
fainter the star
Magnitude of Star

Ancient astronomers could only
estimate magnitudes

Modern astronomers can
measure the brightness of stars
to high precision. Adjustments
were made to the scale of
magnitude

Favorite Star Vega = .04

Favorite Star Sirius= -1.47
"The Sun is just one among a hundred billion stars in the Milky Way
Galaxy, each with its own cosmic tale to tell."
— Timothy Ferris, in the film Seeing in the Dark
The Light Year

If you could travel at the speed of light it would take you 8
minutes to reach the sun

The next nearest star, Proxima Centauri, would take you
4.2 years to reach!!

A light year is based on the distance light travels in a year

At 300, 000km/sec a light year works out to be 9.5
million million kilometers! (this can also be written as
95. trillion km)
Parallax

Astronomers use parallax to measure star distances

Parallax is the apparent change in position when you look
at an object from a different position
Your View
Parallax at the movies…
Your Friend’s View
Parallax in Astronomy

To measure a star’s distance astronomers do the
following:

1.) Look at a nearby star when Earth is on one side of
the sun

2.) Look at the same star six months later, when Earth
is on the opposite side of the sun

3.) Measure how much the star appears to have
moved against a background of stars that are much
further away

The less a star appears to move, the further away it is
Lab: How Far is That Star?
What you’ll need

Masking tape

Paper clips

Black and red pencils, plus a pen to write with

Metric ruler

Paper

Meter stick

Calculator

Lamp without a shade

Copy paper box without the lid
Objectives

Infer the apparent change in position of the
dots of light for each star

Calculate the distance to an objects by using
ratios of measured values

Predict the parallax of an object at different
distances