Transcript The Quest Ahead - Mr. Catt`s Class

Courtesy of Hubble Space Telescope Comet Team and NASA
Chapter 1
Sections 1-1 thru1-3
Courtesy of STScI/NASA
The Quest
Ahead
© 2007 Jones and Bartlett Publishers
Science and Astronomy
1. It is not easy to define what science is. However, any
effort to define it must include its methods, its
historical development, its social context, and a clear
understanding of its language.
2. Astronomy is the oldest of the sciences. Its long
history and recent advances make it a great example
of the progressive nature of science.
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1-1 The View from Earth
1. The Milky Way, a great number of stars, the Moon, and
some of the planets are some of the objects that you
could see during clear nights.
2. Nebulae, giant clouds of gas and dust, are involved in
both the birth and death of stars.
Courtesy of T.A.Rector (NRAO/AUI/NSF and
NOAO/AURA/NSF) and B.A.Wolpa
(NOAO/AURA/NSF)
Photo by Dave Palmer
© 2007 Jones and Bartlett Publishers
1-1 The View from Earth
3. Ancient observers wondered about these objects as
we do today along with a number of even more exotic
ones.
4. These are but examples through which we will study
the basic methods of inquiry of not only astronomy
but of all the natural sciences.
5. In our quest to understand the universe we will first
study our neighborhood (Earth, Moon, and the planets
in our solar system), then our Sun (the closest star to
us), then the stars and finally galaxies.
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1-2 The Celestial Sphere
1. Celestial sphere is the imaginary
sphere of heavenly objects that
seems to center on the observer.
2. Celestial pole is the point on the
celestial sphere directly above a
pole of the Earth. In the Northern
Hemisphere one can see the north
celestial pole directly above the
Earth’s North Pole. In the
Southern Hemisphere the south
celestial pole is located above the
South Pole.
Figure 1.07: Celestial sphere
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Constellations
1. A constellation (from the Latin, meaning “stars together”) is
an area of the sky containing a pattern of stars named for a
particular object, animal or person.
2. The earliest constellations were defined by the Sumerians as
early as 2000 B.C.
3. The 88 constellations used today were established by
international agreement. They cover the entire celestial
sphere and have specific boundaries.
4. Constellations are simply accidental patterns of stars. The
stars in a constellation are at different distances from us and
move relative to each other in different directions and with
different speeds.
5. Astronomers use constellations as a convenient way to
identify parts of the sky.
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Measuring the Positions of
Celestial Objects
1. The angular separation of two
objects is the angle between
two lines originating from the
eye of the observer toward the
two objects.
2. One degree is divided into 60
arcminutes. One arcminute is
divided into 60 arcseconds.
3. A fist held at arm’s length
yields an angle of about 10°. A
little finger held at arm’s
length yields an angle of
about 1°.
Figure 1.12: Two stars, when viewed from Earth,
have an angular separation as shown
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Celestial Coordinates
1. Longitude and latitude uniquely
define the position of an object
on Earth. Similarly, right
ascension and declination
uniquely define the position of
an object on the celestial
sphere.
2. The declination of an object on
the celestial sphere is its angle
north or south of the celestial
equator (a line on the celestial
sphere directly above the
Earth’s equator); the scale
ranges from 90 to +90.
Figure 1.16a: Declination measures the angle
of a star north or south of the celestial equator.
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Celestial Coordinates
3. The right ascension of an
object states its angle
around the celestial
sphere, measuring
eastward from the vernal
equinox (the location on
the celestial equator where
the Sun crosses it moving
north). It is stated in
hours, minutes, and
seconds (with 24 hours
encompassing the entire
celestial equator).
Figure 1.16b: Right ascension measures the
angle around the celestial equator eastward from
the vernal equinox.
© 2007 Jones and Bartlett Publishers
Question 1
Record all the answers on a word document and when
completed e-mail to [email protected]. Put your
name and this class period in the subject line
If we could visit the other side of the Milky Way Galaxy
would we see the same constellations as we see here
on Earth? Why or why not?
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Question 2
Why do they use angles to measure the distance
between stars? Explain.
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1-3 The Sun’s Motion Across the Sky
1. The Sun seems to rise in the east and set in the west
just like the rest of the stars. However, as time goes
on, the Sun appears to move constantly eastward
among the stars.
2. The time the Sun takes to return to the same place
among the stars is about 365.25 days.
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The Ecliptic
1. The ecliptic is the apparent path of the Sun on the celestial
sphere.
2. The zodiac is the band that lies 9° on either side of the ecliptic
on the celestial sphere and contains the constellations
through which the Sun passes.
Figure 1.17: A map of the stars within 30 degrees of the equator.
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The Sun and the Seasons
1. For an observer in the Northern Hemisphere, the Sun rises and
sets farther north in the summer than in the winter.
2. The Sun is in the sky longer each day in summer than in winter.
This is one of the reasons for seasonal differences.
3. In summer, the Sun reaches a point higher in the sky, than in
winter.
This results in each portion of the Earth’s surface receiving more energy
in a given amount of time in the summer than in winter.
Also, sunlight passes through more atmosphere in winter than in summer,
resulting in more scattering and absorption in the atmosphere.
4. For an observer in the Southern Hemisphere the above
explanation is backward.
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Figure 1.19: The Sun's apparent path across the sky of the Northern
Hemisphere in (a) December, (b) March or September, and (c) June.
© 2007 Jones and Bartlett Publishers
5. The distance of the Earth from the Sun does not vary too
much during the year and thus is not a determining factor for
the seasons.
6. The orientation of the Earth with respect to the Sun is the
main reason for the seasons.
7. Altitude is the height of a celestial object (such as the Sun)
measured as an angle above the horizon.
8. The summer and winter solstices are points on the celestial
sphere where the Sun reaches its northernmost and
southernmost positions, respectively.
9. The vernal and autumnal equinoxes are the points on the
celestial sphere where the Sun crosses the celestial equator
while moving north and south, respectively.
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Historical Note: Leap Year and the Calendar
1. The tropical year (365.242190 days) determines the
seasons and is the time the Sun takes to return to the
vernal equinox.
2. The Julian calendar was 365 days long and added one
day at the end of February every four years. Thus it had
an average of 365.25 days.
3. The difference between the tropical and Julian year
caused the calendar to get out of synchronization with
the seasons. The Gregorian calendar has an average of
365.2425 days.
4. The leap year rule: every year whose number is
divisible by four is a leap year, except century years,
unless they are divisible by 400.
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Scientific Models
1. A scientific model is a theory that accounts for a set of
observations in nature.
2. The idea that stars reside on a giant celestial sphere is a
model.
3. A scientific model is not necessarily a physical model.
4. The Sun’s motion along the ecliptic can be explained by a
geocentric model.
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Question 3
Describe what the solstices and equinoxes have to do
with the changing temperatures throughout the year.
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