Refracting and Reflecting Telescopes

1
Refracting and Reflecting Telescopes 
Tools of Astronomy

• Two different types of telescopes are used to
  focus visible light.

• Refracting telescopes, or refractors, are
  telescopes that use lenses to bring visible light
  to a focus.

• Reflecting telescopes, or reflectors, are
  telescopes that bring visible light to a focus
  with mirrors.

2
Satellites, Probes, and Space-Based Astronomy
Tools of Astronomy

• Spinoffs

• Spinoffs are technologies that were originally
  developed for use in space programs that have
  been passed on to commercial industries for
  common use.

• More than 1400 different NASA technologies have
  been incorporated into products ranging from
  artificial hearts to cordless tools.

3
Reaching for the Moon
The Moon

• Plans for a crewed lunar expedition began in the
  late 1950s.

• In 1957 the Soviet Union launched the first
  satellite, Sputnik I.
• In 1961, Soviet cosmonaut Yuri A. Gagarin became
  the first human in space.
• On May 5, 1961, Alan B. Shepard Jr. became the
  first American in space as part of Project
  Mercury followed by the two-person crews of
  Project Gemini.
• On July 20, 1969, the Apollo program landed Neil
  Armstrong and Buzz Aldrin on the Moon, during
  Apollo 11.

4
Reaching for the Moon
The Moon

• Lunar Properties

• Earths moon is one of the largest moons in the
  solar system, especially compared to the size of
  the planet it orbits.
• The Moon is relatively farther from Earth than
  most moons are from the planets they orbit.
• Earths moon is a solid, rocky body, in contrast
  to the icy composition of the moons of the outer
  planets.

5
Reaching for the Moon
The Moon

• Lunar Properties

6
Reaching for the Moon
The Moon

• The Lunar Surface

• The albedo of the Moon, the amount of sunlight
  that its surface reflects, is only about 0.07 (7
  percent) contrasted with Earths average of 0.31
  (31 percent).

• Because the Moon has no atmosphere, surface
  temperatures can range from 400 K (127C) in
  sunlight to 100 K (173C) where it is dark.
• There is no erosion on the Moon because it has no
  atmosphere or flowing water.
• Craters on the Moon are preserved until one
  impact covers another.

7
History of the Moon
The Moon

• Radiometric dating of lunar rocks from the
  highlands indicates an age between 3.8 and 4.6
  billion years.

8
History of the Moon
The Moon

• Formation Theories

• The capture theory proposes that as the solar
  system was forming, a large object ventured too
  near to the forming Earth, became trapped in its
  gravitational pull, and formed into what is now
  the Moon.
• The simultaneous formation theory states that the
  Moon and Earth formed at the same time and in the
  same general area, and thus the materials from
  which they formed were essentially the same.

9
History of the Moon
The Moon

• Formation Theories

• The impact theory is the most commonly accepted
  theory of how the Moon formed.

• This theory proposes that the Moon formed as the
  result of a gigantic collision between Earth and
  a Mars-sized object about 4.5 billion years ago,
  when the solar system was forming.

10
The Sun-Earth-Moon System
The Sun-Earth-Moon System

• The relationships between the Sun, Moon, and
  Earth are important to us in many ways.

• The Sun provides light and warmth, and it is the
  source of most of the energy that fuels our
  society.
• The Moon raises tides in our oceans and
  illuminates our sky with its monthly cycle of
  phases.
• Every society from ancient times to the present
  has based its calendar and its timekeeping system
  on the apparent motions of the Sun and Moon.

11
Daily Motions
The Sun-Earth-Moon System

• The Sun rises in the east and sets in the west,
  as do the Moon, planets, and stars as a result of
  Earths rotation.

• We observe the sky from a planet that rotates
  once every day, or 15 per hour.

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Daily Motions
The Sun-Earth-Moon System

• Earths Rotation

• There are two relatively simple ways to
  demonstrate that Earth is rotating.

1. A Foucault pendulum, which has a long wire, a
heavy weight, and will swing in a constant
direction, appears from our point of view to
shift its orientation. 2. Flowing air and water
on Earth are diverted from a north-south
direction to an east-west direction as a result
of Earths rotation in what is known as the
Coriolis effect.
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Daily Motions
The Sun-Earth-Moon System

• Earths Rotation

• The length of a day as we observe it is a little
  longer than the time it takes Earth to rotate
  once on its axis.

• Our timekeeping system is based on the solar day,
  which is the time period from one sunrise or
  sunset to the next.

14
Annual Motions
The Sun-Earth-Moon System

• The annual changes in length of days and
  temperature are the result of Earths orbital
  motion about the Sun.

• The ecliptic is the plane in which Earth orbits
  about the Sun.

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Annual Motions
The Sun-Earth-Moon System

• The Effects of Earths Tilt

• Earths axis is tilted relative to the ecliptic
  at approximately 23.5.
• As Earth orbits the Sun, the orientation of
  Earths axis remains fixed in space.
• At one point, the northern hemisphere of Earth is
  tilted toward the Sun, while six months later it
  is tipped away from the Sun.
• As a result of the tilt of Earths axis and
  Earths motion around the Sun, the Sun is at a
  higher altitude in the sky during summer than in
  the winter.

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Annual Motions
The Sun-Earth-Moon System

• Solstices

• The summer solstice occurs around June 21 each
  year when the Sun is directly overhead at the
  Tropic of Cancer, which is at 23.5 N.

• The summer solstice corresponds to the Suns
  maximum altitude in the sky in the northern
  hemisphere.

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Annual Motions
The Sun-Earth-Moon System

• Solstices

• The winter solstice occurs around December 21
  each year when the Sun is directly overhead at
  the Tropic of Capricorn which is at 23.5 S.

• The winter solstice corresponds to the Suns
  lowest altitude in the sky in the northern
  hemisphere.

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Annual Motions
The Sun-Earth-Moon System

• Equinoxes

• When the Sun is directly overhead at the equator,
  both hemispheres receive equal amounts of
  sunlight.
• The autumnal equinox occurs around September
  21, halfway between the summer and the winter
  solstices when the Sun is directly over the
  equator.

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Annual Motions
The Sun-Earth-Moon System

• Equinoxes

• The vernal equinox occurs around March 21,
  halfway between the winter and the summer
  solstices when the Sun is directly over the
  equator.

• For an observer at the Tropic of Cancer or Tropic
  of Capricorn, the Sun is 23.5 from the point
  directly overhead during the equinoxes.

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Annual Motions
The Sun-Earth-Moon System

• Equinoxes

For a person standing at the x at 23.5º N, the
Sun would appear in these positions on the winter
solstice, the vernal equinox, and the summer
solstice. On the autumnal equinox, the Sun would
be at the same altitude as on the vernal
equinox.
21
Phases of the Moon
The Sun-Earth-Moon System

• Synchronous Rotation

• Synchronous rotation is the state at which
  orbital and rotational periods are equal.

• As the Moon orbits Earth, the same side faces
  Earth at all times because the Moon has a
  synchronous rotation, spinning exactly once each
  time it goes around Earth.

22
Motions of the Moon
The Sun-Earth-Moon System

• The length of time it takes for the Moon to go
  through a complete cycle of phases is called a
  lunar month.

• The length of a lunar month is about 29.5 days,
  which is longer than the 27.3 days it takes for
  one revolution, or orbit, around Earth.
• The Moon also rises and sets 50 minutes later
  each day because the Moon has moved 13 in its
  orbit over a 24-hour period, and Earth has to
  turn an additional 13 for the Moon to rise.

23
Solar Eclipses
The Sun-Earth-Moon System

• A solar eclipse occurs when the Moon passes
  directly between the Sun and Earth and blocks our
  view of the Sun.

• When the Moon perfectly blocks the Suns disk, we
  see only the dim, outer gaseous layers of the Sun
  in what is called a total solar eclipse.
• A partial solar eclipse is seen when the Moon
  blocks only a portion of the Suns disk.

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Solar Eclipses
The Sun-Earth-Moon System

• The shadow that is cast on Earth consists of two
  regions.

• A total eclipse occurs in the inner portion
  called the umbra, which does not receive direct
  sunlight.
• A partial eclipse occurs in the outer portion of
  the shadow called the penumbra, where some of the
  Suns light reaches.

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Solar Eclipses
The Sun-Earth-Moon System

• The Effects of Orbits

• The Moons distance from Earth increases and
  decreases as the Moon moves in its elliptical
  orbit around Earth.

• Perigee is the closest point in the Moons orbit
  to Earth.

• Apogee is the farthest point in the Moons orbit
  from Earth.

• When the Moon is near apogee, it appears smaller,
  and thus it does not completely block the disk of
  the Sun, resulting in an annular eclipse.

26
Lunar Eclipses
The Sun-Earth-Moon System

• A lunar eclipse occurs when the full Moon passes
  through Earths shadow.

• A lunar eclipse can happen only at the time of a
  full moon, when the Moon is in the opposite
  direction from the Sun.
• A total lunar eclipse occurs when the entire Moon
  is within Earths umbra.
• Solar and lunar eclipses occur in almost equal
  numbers, with slightly more lunar eclipses.

27
Asteroids
Formation of Our Solar System

• Asteroids comprise the thousands and thousands of
  bodies that orbit the Sun within the planetary
  orbits that are leftovers from the formation of
  the solar system.

• Asteroids range from a few kilometers to about
  1000 km in diameter and have pitted, irregular
  surfaces.
• Most asteroids are located between the orbits of
  Mars and Jupiter within the asteroid belt.

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Asteroids
Formation of Our Solar System

• Pieces of Asteroids

• As the asteroids orbit, they occasionally collide
  and break into fragments.

• A meteoroid is a asteroid fragment or any other
  interplanetary material that falls toward Earth
  and enters Earths atmosphere.

• A meteor is the streak of light produced when a
  meteoroid burns up in Earths atmosphere.

• A meteorite is part of a meteoroid, that does not
  completely burn up, that collides with the
  ground.

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Various definitions from Chapters 29-30
Formation of Our Solar System

• Retrograde motion is when a planet occasionally
  will move toward the west across the sky.
• Perihelion is when a planet is at the closest
  point to the Sun in its orbit.
• Aphelion is when a planet is farthest point from
  from the Sun during its orbit.
• Comets are small, icy bodies that have highly
  eccentric orbits around the Sun and are
  remnants from solar system formation.
• The coma is an extended volume of glowing gas
  flowing from a comets head
• The nucleus of a comet is the small solid core
  that releases gases and dust particles that form
  the coma and tails when it is heated.

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The Suns Atmosphere
The Sun

• The photosphere, approximately 400 km in
  thickness, is the lowest layer of the Suns
  atmosphere, with an average temperature of about
  5800K.
• The chromosphere, which is above the photosphere
  and approximately 2500 km in thickness, has a
  temperature of nearly 30,000 K at the top.
• The corona, which is the top layer of the Suns
  atmosphere, extends several million kilometers
  southward from the top of the chromosphere and
  has a temperature range of 1 million to 2 million
  degrees K.
• Fusion of Hydrogen atoms into Helium atoms occurs
  within the core of the Sun and is how the Sun
  derives its energy.