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Chapter 1

Chapter One Review: Charting the Heavens


Department
Astronomy
Course Code
ASTA01H3
Professor
Brian Wilson
Chapter
1

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September 14th, 2010
ASTA01H
Intro to Astronomy and Astro Part I
Chapter One: Charting the Heavens
Our Place in Space (pg.4)
Universe: The totality of space, time, matter, and energy
Astronomy: The study of the universe
Light-year: A unit for measuring distance, the distanced traveled by light in a year
(about 300,000 kilometers per second, typically 10 trillion kilometers a year)
A typical galaxy is a collection of a hundred billion stars, about 100,000 light-years
in diameter
Distances in space are truly astronomical and often hard to wrap your head around
such vast distances and sizes
Scientific Theory and the Scientific Method (pg.6)
The earliest descriptions of the universe were based largely on mythology and
imagination
The power of logical and reasoned arguments grew and the power of myths weakened
They realized that thinking about nature was no longer sufficient looking at it was
also necessary
Theory: The framework of ideas and assumptions used to explain some set of
observations and make predictions about the real world these theories must be
continually tested
A theory to construct a theoretical model of a physical object (planet/star) or a
phenomenon (gravity) that accounts for its known properties
If experiments and observations favour this proposed models, the theory can be
developed and refined. If not, the theory must be reformulated or rejected , this
approach to investigation, combining thinking and doing is called scientific
method
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Scientific Method evolves through a combination of observation, theoretical
reasoning and prediction, which in turn suggests new observations
Several characteristics define a modern scientific theory, they are as follows:
oThey must be testable they must be able to be exposed to experimental
verification
oThey must be continually tested, and their consequences tested, too.
oThey should be simple. The most successful theories tend to be the simple
ones that fit the facts
oMost scientists have the additional bias that a theory should in some sense be
elegant. When a clearly stated principle naturally ties together and explains
several phenomena previously thought up
Hypothesis: a proposed explanation for an observable event or phenomenon. Not
proven, meaning to put under or to suppose
Scientific method observation, theory, and testing
Scientific method is designed to produce an objective view of the universe we inhabit,
presenting no bias
The Obvious View (pg. 8)
The night sky we see today is not so different from that seen by our ancestors
hundreds or even thousands of years ago
However, our interpretation of that night sky has changed dramatically
Constellations in the Sky (pg.8)
About 3000 stars are visible at any given time on either side of the world (about 6000
in total)
A natural human tendency is to see patterns and relationships among objects even
when no true connection exists, and people long ago connected the brightest stars
into formations called constellations
The stars in constellations are not actually close together, even by astronomical
standards, but merely are bright enough to be observe with the naked eye and
happen to lie in roughly the same direction in the sky as seen from Earth
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The Celestial Sphere (pg.10)
Ancient astronomers naturally assumed that the stars surrounding earth were
attached to a celestial sphere a canopy of stars resembling an astronomical
painting on a sort of heavenly ceiling
Believed this canopy of stars to be moving around a stationary earth
Time-lapsed photos of the stars will reveal how all the stars appear to be moving in
circles around a point very close to the star Polaris (North Star)
oTo the ancients this point represented the axis for which the entire celestial
sphere turned on
Today, we recognize that the apparent motion of these stars is a result of the spin or
rotation, not of the celestial sphere but of the Earth itself
The celestial sphere is an incorrect description of the heavens, however we still use it
as a generally true portrayal of the positions of stars in the night sky
The points were Earths axis intersects the celestial sphere are called the celestial
poles
The celestial equator is midway between the north and south celestial poles,
representing the intersection of Earths equatorial plane with the celestial sphere
More Precisely 1-1 (pg.11)
Angular Measure
Full circle = 360 degrees, thus the half circle that stretches from horizon to horizon,
spanning the portion of the sky visible to one person at any one time, 180 degrees
Each 1 degree increment can be further divided into fractions of a degree, called arc
minutes. There are 60 arm minutes (written as 60) in 1 degree (The term arc is
used to distinguish this angular unit from the unit of time). Both the Sun and the
Moon project an angular size of 30 arc minutes (half a degree) on the sky. Your little
finger, held at arms length, has a similar angular size, covering about a 40 slice of
the 180 degree horizon-to-horizon arc
An arc minute can be divided into 60 arc seconds (60). An arc second is roughly
equivalent to the angular size of a dime at a distance of about 2 kilometers
Earths Orbital Motion (pg.12)
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