Transcript A105 Stars and Galaxies - Department of Astronomy

A105
Stars and Galaxies
Today’s APOD
News quiz today
Moon worksheet due Thursday
Finish units 5, 6, 10 in text
Office hour/Solar Lab at Kirkwood
Obs. TODAY, 11:00 – noon
The Sun Today
Solar
Orbiting
Heliospheric
Observatory
(SOHO)
Orbits between the Sun and
Earth, about a million miles away
– a constant view of the Sun
Last Thursday
First News Quiz
• Put your USERNAME on the scantron
form
• You may consult with your neighbors
• No books, notes, papers
• 2 minutes per question
Modern science relies on
observations and experiments!
Understanding Science
Purpose – to understand the universe
well enough to figure out the basic
relationships that govern it
A process for understanding and
predicting
What about facts?
will it rain tomorrow?
what will be on the quiz?
what will happen if…?
new discoveries
better data
new theories
facts change!
An Ongoing Process
The process of science has been
so successful because
results are widely shared and
evaluated
experiments are reproduced and
checked
value of ideas based on observation
and usefulness, not authority
Debating Scientific Issues
How do we tell who is correct?
Majority vs. minority opinions
Majority isn’t always right
Debate is a poor technique for deciding
EVIDENCE and DATA
How was the experiment done?
Was it repeated by others
Is a new theory TESTABLE?
Warning Signs of Bad Science
How is it announced? Is the source reliable?
How good is the evidence?
is it anecdotal? does it appeal to authority?
does it fit what you already know?
does it violate widely-accepted laws or theories?
is contrary evidence ignored?
What kind of reasoning is used?
Can the claim be tested?
The Baloney Detection Collection
Phil Plait's Bad Astronomy: Home Page
A Little Review….
Sound travels at a speed of 300 meters per
second. In analogy to the light-year, what
does 1 sound-minute equal?
a) The time sound takes to travel 300
meters.
b) The time delay of a sound heard 300
meters away.
c) The distance traveled by sound in 1
minute.
d) The speed of sound 1 minute later.
The
Sky!
The brightness
of a star is
shown by the
size of its dot
From wunderground.com
Getting
Started
1.Which way is north?
2.To find Polaris:
• find the Big Dipper
• follow to Polaris
Orion
rising
The night sky is familiar, but few people look
closely at (or think about) the complex phenomena
we observe in sky.
Patterns in the Sky
• What does the universe look like from Earth?
• Why do stars rise and set?
• Why do the constellations we see depend on latitude
and time of year?
• What causes the seasons?
What does the universe look like
from Earth?
With the naked eye,
we can see more than
2,000 stars, as well
as the Milky Way
The Milky Way is band
of light making a circle
around the celestial
sphere.
What is it? Our view
into the plane of our
galaxy.
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
The Celestial Sphere
The 88 official
(defined by the
International
Astronomical
Union)
constellations
cover the
celestial sphere.
Constellations
A constellation
is a region of the sky.
The regions of
the
constellations
are irregular
in shape
Investigating a Constellation
• 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
Review: Coordinates on the Earth
• Latitude: position north or south of equator
• Longitude: position east or west of prime
meridian (runs through Greenwich, England)
Angular
Measurements
• Full circle = 360º
• 1º = 60 (arcminutes)
• 1 = 60 (arcseconds)
We measure
the sky using
angles
Angular Size
An object’s
angular size
appears smaller
if it is farther
away
360 degrees
angular size = physical size 
2  distance
The
Local
Sky
An object’s altitude (above horizon) and direction
(along horizon) gives its location in your local sky
Explore_Celestial_Sphere.swf
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
Why do stars
rise and set?
Earth rotates east to
west, so stars appear
to circle from west to
east.
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.
A
circumpolar
star never
sets
This star
never rises
in Indiana
Celestial Equator
Your Horizon
The Earth spins
under Polaris
(Polaris is NOT
the brightest
star in the sky!)
Altitude of the celestial pole =
your latitude
The North Star (Polaris) is 50°
above your horizon, due north.
Where are you?
A.
B.
C.
D.
E.
You are on the equator.
You are at the North Pole.
You are at latitude 50°N.
You are at longitude 50°E.
You are at latitude 50°N and
longitude 50°E.
The sky changes as Earth orbits the Sun
• As the Earth
orbits the Sun,
the Sun appears
to move
eastward along
the ecliptic
• 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)
b)
c)
d)
From the north pole
From latitude 23.5 degrees
From the equator
anywhere, since latitude makes
no difference.
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.
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
Vocabulary Review
o Constellation
o Ecliptic
o Equator
o Celestial
sphere
o Latitude
o Longitude
o Meridian
o Zenith
o Horizon
o Altitude
o North and
south celestial
poles
Moon worksheet due Thursday
Finish units 5, 6, 10
News Quiz on Tues., Sept. 12