Transcript NATS 1311-From the Cosmos to Earth

NATS 1311 - From the Cosmos to Earth
Scientific approach to the study of nature
•
Copernicus and Galileo introduced observation and
experimentation in the 16th century.
•
Science is not a set of facts.
•
It is a way of conducting a dialogue about our physical
surroundings.
•
The scientific method consists of careful observation of
nature and an open-minded creative search for general
ideas that agree with and predict those observations.
•
To be scientific, a statement must be capable of being
proven wrong.
NATS 1311 - From the Cosmos to Earth
Scientific approach to the study of nature.
•
Observation and experimentation set science apart from other
ways of knowing - ways that are not less important - just different
– Philosophy – Reason – Logic
– Art – Appreciation of form – Beauty
•
Pseudoscience statements:
– Hypothesis that cannot be tested with reproducible results;
Cold fusion, ufo's, astrology. . .
NATS 1311 - From the Cosmos to Earth
Scientific approach to the study of nature.
•
•
•
Scientific Law:
– Statement of observed regularity in nature - attempts to describe the
observations
– has a well documented history of successful replication and
extension to new conditions
Scientific Theory:
– Statement of observed regularity in nature - attempts to explain the
observations
– General principle offered to explain a set of phenomena or observed
facts.
– Not all scientific predictions can be tested directly
•
Core of earth
•
Sun—energy
•
Expansion of the universe
Require models—creative thought
– No ultimate truths—all Provisional
•
Ok as long as they are not contradicted
NATS 1311 - From the Cosmos to Earth
Scientific approach to the study of nature.
•
Model:
– Simplified version of reality used to describe
aspects of nature.
– Not synonymous with reality.
– Based on assumptions that may simplify some
aspects of nature, or may be incomplete
statements about nature
– Useful to make predictions that can be verified by
experimentation or observation.
NATS 1311 - From the Cosmos to Earth
The Scientific Method
NATS 1311 - From the Cosmos to Earth
Hallmarks of Science
• Modern science seeks explanations for observed phenomena that rely
solely on natural causes.
• Science progresses through the creation and testing of models of
nature that explain the observations as simply as possible.
• A scientific model must make testable predictions about natural
phenomena that would force us to revise or abandon the model if the
predictions do not agree with observations.
NATS 1311 - From the Cosmos to Earth
Occam’s Razor
The idea that scientists should prefer the simpler of two models that agree
equally well with observations - the second hallmark - after medieval
scholar William of Occam (1285 - 1349).
For instance, original model of Copernicus (Sun-centered) did not match
the data noticeably better than Ptolemy's model (Earth-centered). Thus, a
purely data-driven judgment based on the third hallmark might have led
scientists to immediately reject the Sun-centered idea. Instead, many
scientists found elements of the Copernican model appealing, such as the
simplicity of its explanation for apparent retrograde motion. Was kept alive
until Kepler found a way to make it work.
NATS 1311 - From the Cosmos to Earth
The most exciting words in science are
not “Eureka (I found it)” but “Now that’s
funny”.
NATS 1311 - From the Cosmos to Earth
MOTIONS OF EARTH
1. ROTATION ON ITS AXIS - Day
2. REVOLUTION ABOUT SUN - Year
3. PRECESSION - Wobble of spin axis
NATS 1311 - From the Cosmos to Earth
Motions of Earth
Motion
Typical Speed
rotation
1,000 km/hr or more around axis, with
one rotation taking 1 day
orbit of Sun
100,000 km/hr around Sun, with one
orbit taking 1 year
motion within local solar
neighborhood
70,000 km/hr relative to nearby stars
rotation of the Milky Way
Galaxy
800,000 km/hr around galactic center,
with one galactic rotation taking about
230 million years
motion within Local Group
300,000 km/hr toward Andromeda
Galaxy
universal expansion
more distant galaxies moving away
faster, with the most distant moving at
speeds close to the speed of light
NATS 1311 - From the Cosmos to Earth
Rotation
The Earth rotates about its axis axis
once per day - one rotation equals
one day. The axis goes through the
north and south poles and through
the center of the Earth. It rotates
counterclockwise when looking
down on the north pole which
means that the sun rises in the east
and sets in the west.
NATS 1311 - From the Cosmos to Earth
The Rotation of the Earth From Space
Earth Rotation Movie
NATS 1311 - From the Cosmos to Earth
Earth’s rotation causes the stars
- the celestial sphere - to
appear to rotate around the
Earth. Viewed from outside, the
stars (and the Sun, Moon, and
planets) therefore appear to
make simple daily circles
around us. The red circles
represent the apparent daily
paths of a few selected stars.
NATS 1311 - From the Cosmos to Earth
The Celestial Sphere
Envisioned by the ancients, the celestial sphere had Earth at the
center with the stars emblazoned on the sphere. They thought the
stars rose and set because the celestial sphere (the sky) rotated,
carrying the stars from east to west. All stars appear to move
around two points on the celestial sphere, the north and south
celestial poles—projections of earth’s axis of rotation. Earth's
equator projected on the celestial sphere becomes the celestial
equator.
NATS 1311 - From the Cosmos to Earth
Our lack of depth
perception when
we look into space
creates the illusion
that the Earth is
surrounded by a
celestial sphere.
Thus, stars that
appear very close
to one another in
our sky may
actually lie at very
different distances
from Earth.
NATS 1311 - From the Cosmos to Earth
Constellations
Constellations - groupings of stars named after mythical heroes, gods, and
mystical beasts
- made up over at least the last 6000 years - maybe more
- used to identify seasons:
- farmers know that for most crops, you plant in the spring and
harvest in the fall.
- in some regions, not much differentiation between the seasons.
- different constellations visible at different times of the year - can
use them to tell what month it is. For example, Scorpius is only
visible in the northern hemisphere's evening sky in the summer.
- many of the myths associated with the constellations thought to
have been invented to help the farmers remember them - made
up stories about them
NATS 1311 - From the Cosmos to Earth
Picture at right shows a start chart of the region around the constellation
Orion. Picture at the left is an ornate star chart printed in 1835 - shows the
great hunter Orion. He is holding a lion's head instead of his traditional bow
or shield. He is stalking Taurus, the Bull in the upper right hand corner.
Behind him, his faithful dog, Canis Major, is chasing Lepus, the Hare.
NATS 1311 - From the Cosmos to Earth
Constellations
Western culture constellations originated in Mesopotamia over 5000 years
ago - added to by Babylonian, Egyptian, and Greek astronomers - current list
based charts of Roman astronomer, Claudius Ptolemy (~140 AD)
In modern world - constellations
redefined so now every star in the sky
is in exactly one constellation.
In 1929, the International
Astronomical Union (IAU) adopted
official constellation boundaries that
defined the 88 official constellations
that exist today.
NATS 1311 - From the Cosmos to Earth
Star Names
Brightest stars named thousands of
years ago - most come from ancient
Arabic
Astronomers now use Bayer
designations for the brighter stars introduced by Johann Bayer in his star
atlas Uranometria in 1603 - consists of a
Greek letter followed by the genitive (in
Latin) of the name of the constellation in
which the star lies:
Aries → Arietis; Taurus → Tauri; Gemini
→ Geminorum; Virgo → Virginis; Libra →
Librae; Pisces → Piscium; Lepus →
Leporis.
- brightest star of the constellation given the designation Alpha, the next brightest
Beta, and so on.
Flamsteed designations (introduced by John Flamsteed in 1712) - used when no
Bayer designation exists - use numbers instead of Greek letters. Numbers were
originally assigned in order of increasing right ascension within each constellation due to the effects of precession they are now slightly out of order in some places.
NATS 1311 - From the Cosmos to Earth
A model of the celestial
sphere shows the
patterns of the stars, the
borders of the 88 official
constellations, the
ecliptic, and the celestial
equator and poles.
NATS 1311 - From the Cosmos to Earth
Latitude and Longitude
Latitude - lines of latitude parallel
to Earth’s equator - labeled north
or south relative to equator - from
90º N to 90º S
Longitude - lines of longitude
extend from North Pole to South
Pole - by international treaty,
longitude 0 (the prime meridian)
runs through Greenwich,
England
Dallas:
latitude = 32.78º N
longitude = 96.78º W
NATS 1311 - From the Cosmos to Earth
A circumpolar constellation never rises or sets - they are always visible.
Your latitude determines the portion of the celestial sphere visible in your
sky.
(a) A Northern Hemisphere sky.
(b) A Southern Hemisphere sky.
At what latitude would you see the entire sky?
NATS 1311 - From the Cosmos to Earth
Star Trails
The Southern Hemisphere
The Northern Hemisphere
The Earth's rotation causes stars to trace daily circles around the sky. The north
celestial pole lies at the center of the circles. Over the course of a full day,
circumpolar stars trace complete circles, and stars that rise in the east and set
in the west trace partial circles. Here, the time exposure lasted about 6 hours we see only about one-quarter of each portion of the full daily path.
NATS 1311 - From the Cosmos to Earth
Finding the Celestial Poles
You can always find north using the North Star. Polaris can be found
using the big dipper. Draw a line through the two “pointer” stars at the
end of the big dipper and follow it upwards from the dipper about four
outstretched hand’s width. The big dipper is circumpolar in the US so is
always above the horizon. The south celestial pole can be found using
the Southern Cross. There is no “South Star”
NATS 1311 - From the Cosmos to Earth
The Big and Little Dippers
NATS 1311 - From the Cosmos to Earth
Motion of the Night Sky Animation
NATS 1311 - From the Cosmos to Earth
The height in degrees of the north star above the horizon is the same as
your latitude.
NATS 1311 - From the Cosmos to Earth

The angle  between the horizon and Polaris is the latitude of the observer.
If Dallas is at 33º latitude, where is Polaris in the sky? Where is it at the
Equator?
NATS 1311 - From the Cosmos to Earth
Angular Size
Distances in the sky
measured by angular
distance:
Minute of arc = 1/60th of
a degree
Second of arc = 1/3600th
of a degree
Angular diameter angular distance from
one side of an object to
the other
NATS 1311 - From the Cosmos to Earth
Revolution
Earth travels around the sun (orbits) once per year in the same direction it
rotates. It’s orbit is not quite a perfect circle - it is elliptical. The location in
the orbit of the minimum and maximum distances from the Sun are called
perihelion and aphelion. The plane of the orbit is called the ecliptic.
NATS 1311 - From the Cosmos to Earth
Earth’s Axial Tilt
Ecliptic
Plane
The Earth’s axis is currently tilted 23.5º to the ecliptic. It varies over time
between 22º and 25º due the the gravitational forces from Jupiter and the
other planets.
NATS 1311 - From the Cosmos to Earth
The axis remains at the same tilt angle - pointed at Polaris - throughout the
orbit because of conservation of angular momentum. The ecliptic plane is the
plane of the Earth’s orbit. Looking from the Earth, it is the apparent path of
the Sun (and planets) in the sky.
NATS 1311 - From the Cosmos to Earth
The Relationship of the Celestial Equator and the
Ecliptic Plane
NATS 1311 - From the Cosmos to Earth
The Zodiac
The Sun appears to move steadily eastward along the ecliptic, through the
constellations of the zodiac. As Earth orbits the Sun, we see the Sun
against the background of different zodiac constellations at different times
of year. For example, on August 21 the Sun appears to be in the
constellation Leo. Defines astral calendar.
NATS 1311 - From the Cosmos to Earth
Sun’s Path Through the Zodiac
NATS 1311 - From the Cosmos to Earth
Celestial
Sphere
The apparent
Sphere of the
sky
Celestial
Poles
The points
about which
the celestial
sphere
appears to
rotate
Celestial
Equator
Projection of
the Earth’s
equator on the
celestial
sphere
Ecliptic
Apparent
annual path of
the sun on the
celestial
sphere