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Objectives• Describe electromagnetic radiation.
Tools of Astronomy
• Explain how telescopes work.
• Describe space exploration.
– refracting telescope
– reflecting telescope
– interferometry
– spinoff
Vocabulary
• In most cases, there is no other way to study the cosmos except to analyze the light that we receive from it.
Tools of Astronomy• The light that comes to Earth from distant
objects is the best tool that astronomers can use to learn about the universe.
Tools of Astronomy
Radiation• Electromagnetic radiation consists of waves of
electrical and magnetic disturbances.
Tools of Astronomy
• It includes visible light, infrared and ultraviolet radiation, radio waves, microwaves, X rays, and gamma rays.
Radiation• Electromagnetic radiation travels at the same
speed and is classified by:
Tools of Astronomy
– Wavelengths—the distance between peaks on a wave.
– Frequency—the number of waves or oscillations occurring per second.
Telescopes• When exploring space, telescopes have
many benefits:
Tools of Astronomy
– Detectors can be attached to a telescope to observe all wavelengths, not just visible light.
– A telescope brings much more light to a focus than the human eye can, allowing the observation of faint objects.
– Specialized equipment, such as a photometer which measures the intensity of visible light, can be used with a telescope.
– With the aid of imaging devices, telescopes can be used to make time exposures to detect objects that are too faint for the human eye to see.
Telescopes
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.
– Reflectors make up the majority of telescopes that are in use today.
– Most major observatories are located in remote, high elevation locations in order to minimize light and atmospheric interference.
• Reflecting telescopes, or reflectors, are telescopes that bring visible light to a focus with mirrors.
Telescopes
Telescopes at Other Wavelengths
Tools of Astronomy
– For all telescopes, the goal is to bring as much radiation as possible to a focus.
– Interferometry is the process of linking separate telescopes together so that they act as one telescope.
– This process has been used with radio telescopes for a number of years and is now being applied to other telescopes as well.
– The detail in the images that they produce improves as the distance between the telescopes increases.
Satellites, Probes, and Space-Based Astronomy
• Instruments often must be sent into space to collect information because:
Tools of Astronomy
– Earth’s atmosphere blocks infrared radiation, ultraviolet radiation, X rays, and gamma rays.
– When Earth’s atmosphere does allow certain wavelengths to pass through, the images are blurred.
– It is the only way to make close-up observations and even obtain samples from nearby objects in the solar system.
Satellites, Probes, and Space-Based Astronomy
• The Hubble Space Telescope (HST) makes observations in visible-light, infrared, and ultraviolet wavelengths.
Tools of Astronomy
• Other space-based telescopes, such as the Far Ultraviolet Spectroscopic Explorer, the Chandra X-Ray Observatory, and the Spitzer Space Telescope, observe other wavelengths that are blocked by Earth’s atmosphere.
Satellites, Probes, and Space-Based AstronomySpacecraft
Tools of Astronomy
– Space-based exploration can be achieved by sending spacecraft directly to the bodies being observed.
– Robotic probes make close-up observations and sometimes land to collect information directly.
– More recently, the twin robots Spirit and Opportunity conducted scientific experiments on Mars in 2004.
Satellites, Probes, and Space-Based AstronomyHuman Spaceflight
Tools of Astronomy
– Exploring the short term effects of space has been accomplished with the space shuttle program, which began in 1981.
– Since habitation and research began in 2000, a multi-country space station called the International Space Station has been used to study the long-term effects of life in space.
Satellites, Probes, and Space-Based AstronomySpinoffs
Tools of Astronomy
– 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.
Section Assessment
1. What is the difference between a reflecting and a refracting telescope?
Tools of Astronomy
Section Assessment
2. What are the categories of electromagnetic radiation?
Tools of Astronomy
______ Electromagnetic radiation travels at different speeds that are determined by wavelength.
______ When applying interferometry, the detail of the images produced improves as the distance between telescopes increases.
______ The Hubble Space Telescope is able to observe X rays.
______ More than 1400 spinoffs using NASA technologies exist.
Section Assessment
3. Identify whether the following statements are true or false.
Tools of Astronomy
Objectives• Describe the development of exploration of the Moon.
• Identify features on the Moon.
• Explain the theories about how the Moon formed.
– albedo
– highland
– mare (plural, maria)
– impact crater
– ejecta
– ray
– rille
– regolith
Vocabulary
The Moon
Reaching for the Moon• Plans for a crewed lunar expedition began in
the late 1950s.
The Moon
– 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.
Reaching for the Moon
Lunar Properties
The Moon
– Earth’s moon is one of the larger 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.
– Earth’s moon is a solid, rocky body, in contrast to the icy composition of the moons of the outer planets.
– Earth’s moon is the only large moon among the inner planets.
Reaching for the Moon
The Lunar Surface
The Moon
– The albedo of the Moon, the amount of sunlight that its surface reflects, is only about 0.07 (7 percent) contrasted with Earth’s average of 0.31 (31 percent).
– Because the Moon has no atmosphere, surface temperatures can range from 400 K (127°C) in sunlight to 100 K (–173°C) where it is dark.
– There is no erosion on the Moon—except for surface creep and wear caused by recent impacts—because it has no atmosphere or flowing water.
– Craters on the Moon are preserved until one impact covers another.
Reaching for the Moon
The Lunar Surface
The Moon
– The surface of the Moon consists of several features:
• The Highlands are lunar regions that are light in color, mountainous, and heavily covered with craters.
• The Maria (singular, mare) are lunar regions that are dark, smooth plains, which on average are 3 km lower in elevation than the highlands.
Reaching for the Moon
The Lunar Surface
The Moon
– The surface of the Moon consists of several features:
• Impact craters were formed when objects from space crashed into the lunar surface.
• Ejecta is material blasted out during impacts that fell back to the surface.
• Rays are long trails of ejecta that radiate outward from some craters.
• Rilles are meandering, valleylike structures that are found in the Maria.
Reaching for the Moon
Composition
The Moon
– The Moon is made up of minerals similar to those of Earth—mostly silicates.
– The highlands are predominately lunar breccias, which are rocks formed by the fusing together of smaller pieces of rock during impacts.
– The maria are predominately basalts that contain no water.
History of the Moon• Radiometric dating of lunar rocks from the
highlands indicates an age between 3.8 and 4.6 billion years.
The Moon
Regolith is a layer of loose, ground-up rock on the surface of the Moon that formed as a result of the heavy bombardment during its first 800 million years.
• The maria which are between 3.1 and 3.8 billion years old formed when lava welled up from the Moon’s interior and filled in the large impact basins.
History of the Moon
Tectonics on the Moon?
The Moon
– The Moon, like Earth, has a layered structure, which consists of the crust, the upper mantle, the lower mantle, and the core.
– Although the Moon experiences moderate moonquakes approximately once a year, scientists theorize that the Moon is not tectonically active.
– That the Moon has no active volcanoes and no significant magnetic field supports this conclusion.
History of the Moon
Formation Theories
The Moon
– 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.
History of the Moon
Formation Theories
The Moon
– The impact 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.
Section Assessment
1. Match the following terms with their definitions.
___ maria
___ albedo
___ rille
___ regolith
The Moon
A. a layer of loose, ground-up rock on the surface of the Moon
B. the amount of light a surface reflects
C. dark, smooth plains, which are on average 3 km lower than lunar highlands
D. meandering, valleylike structures on the Moon
Section Assessment
3. Identify whether the following statements are true or false.
The Moon
______ The United States was the first country to launch a human into space.
______ There is only one other large moon among the inner planets.
______ On the Moon, craters are preserved until one impact covers another.
______ Less than 10 percent of the light striking the Moon’s surface is reflected back into space.
– ecliptic
– summer solstice
– winter solstice
– autumnal equinox
– vernal equinox
Objectives• Identify the relative positions and motions of Earth, the
Sun, and the Moon.
• Describe the phases of the Moon.
• Explain eclipses of the Sun and Moon.
Vocabulary
The Sun-Earth-Moon System
– synchronous rotation
– solar eclipse
– perigee
– apogee
– lunar eclipse
The Sun-Earth-Moon System• The relationships between the Sun, Moon, and
Earth are important to us in many ways.
The Sun-Earth-Moon System
– 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.
Daily Motions• The Sun rises in the east and sets in the west,
as do the Moon, planets, and stars as a result of Earth’s rotation.
The Sun-Earth-Moon System
• We observe the sky from a planet that rotates once every day, or 15° per hour.
Daily Motions
Earth’s Rotation
The Sun-Earth-Moon System
– 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 Earth’s rotation in what is known as the Coriolis effect.
Daily Motions
Earth’s Rotation
The Sun-Earth-Moon System
– 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.
Annual Motions• The annual changes in length of days and
temperature are the result of Earth’s orbital motion about the Sun.
The Sun-Earth-Moon System
The ecliptic is the plane in which Earth orbits about the Sun.
Annual Motions
The Effects of Earth’s Tilt
The Sun-Earth-Moon System
– Earth’s axis is tilted relative to the ecliptic at approximately 23.5°.
– As Earth orbits the Sun, the orientation of Earth’s 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 Earth’s axis and Earth’s motion around the Sun, the Sun is at a higher altitude in the sky during summer than in the winter.
Annual Motions
The Effects of Earth’s Tilt
The Sun-Earth-Moon System
Altitude is measured in degrees from the observer’s horizon to the object. There are 90 degrees from the horizon to the point directly overhead, called the zenith of the observer.
Annual Motions
Solstices
The Sun-Earth-Moon System
– As Earth moves from position 1, through position 2, to position 3, the altitude of the Sun decreases in the northern hemisphere.
– Once Earth is at position 3, the Sun’s altitude starts to increase as Earth moves through position 4 and back to position 1.
Annual Motions
Solstices
The Sun-Earth-Moon System
– 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 Sun’s maximum altitude in the sky in the northern hemisphere.
Annual Motions
Solstices
The Sun-Earth-Moon System
– 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 Sun’s lowest altitude in the sky in the northern hemisphere.
Annual Motions
Equinoxes
The Sun-Earth-Moon System
– 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.
Annual Motions
Equinoxes
The Sun-Earth-Moon System
– 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.
Annual Motions
Equinoxes
The Sun-Earth-Moon System
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.
Phases of the Moon• The sequential changes in the appearance of
the Moon are called lunar phases.
The Sun-Earth-Moon System
– A new moon occurs when the Moon is between Earth and the Sun and we cannot see the Moon because the sunlit side is facing away from us.
– As the Moon moves along in its orbit, the amount of reflected sunlight that we can see increases until we are able to see the entire sunlit side of the Moon, known as a full moon.
– Once a full moon is reached, the portion of the sunlit side that we see begins to decrease as the Moon moves back toward the new-moon position.
Phases of the Moon
Synchronous Rotation
The Sun-Earth-Moon System
– 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.
Motions of the Moon• The length of time it takes for the Moon to go
through a complete cycle of phases is called a lunar month.
The Sun-Earth-Moon System
• 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.
Motions of the Moon
Tides
The Sun-Earth-Moon System
– The Moon’s gravity pulls on Earth along an imaginary line connecting Earth and the Moon, creating bulges of ocean water on both the near and far sides of Earth.
– As Earth rotates, these bulges remain aligned with the Moon.
– When the Sun and Moon are aligned along the same direction, the result is higher-than-normal tides, called spring tides.
– When the Moon is at a right angle to the Sun-Earth line, the result is lower-than-normal tides, called neap tides.
Solar Eclipses
A solar eclipse occurs when the Moon passes directly between the Sun and Earth and blocks our view of the Sun.
The Sun-Earth-Moon System
– When the Moon perfectly blocks the Sun’s 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 Sun’s disk.
Solar Eclipses• The shadow that is cast on Earth consists of two
regions.
The Sun-Earth-Moon System
• 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 Sun’s light reaches.
Solar Eclipses
The Effects of Orbits
The Sun-Earth-Moon System
– The Moon’s orbit is tilted 5° relative to the ecliptic and usually the Moon passes north or south of the Sun as seen from Earth, during a new moon.
– A solar eclipse can occur only when the intersection of the Moon and the ecliptic is in a line with the Sun and Earth.
Solar Eclipses
The Effects of Orbits
The Sun-Earth-Moon System
– The Moon’s distance from Earth increases and decreases as the Moon moves in its elliptical orbit around Earth.
• Perigee is the closest point in the Moon’s orbit to 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.
• Apogee is the farthest point in the Moon’s orbit from Earth.
Lunar Eclipses
A lunar eclipse occurs when the full Moon passes through Earth’s shadow.
The Sun-Earth-Moon System
• 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 Earth’s umbra.
• Solar and lunar eclipses occur in almost equal numbers, with slightly more lunar eclipses.
Section Assessment
1. Match the following terms with their definitions.
___ ecliptic
___ summer solstice
___ winter solstice
___ apogee
The Sun-Earth-Moon System
A. occurs when the Sun is directly overhead at the Tropic of Cancer
B. the point in the Moon’s elliptical orbit that is the farthest from Earth
C. the plane that contains Earth’s orbit
D. occurs when the Sun is directly overhead at the Tropic of Capricorn
Section Assessment
2. Number the lunar phases in the correct order, beginning after the new moon.
___ waxing gibbous
___ full moon
___ waning crescent
___ third quarter
___ first quarter
___ waning gibbous
___ waxing crescent
The Sun-Earth-Moon System
Section Assessment
The Sun-Earth-Moon System
3. Identify whether the following statements are true or false.
______ A maximum of five eclipses, solar and lunar combined, can occur in a year.
______ The Sun will appear at the same altitude in the sky during both the autumnal and vernal equinoxes.
______ The Earth has a synchronous rotation.
______ To witness a total solar eclipse, you must be inside the umbra of the Moon’s shadow.
Section 28.1 Main Ideas• Visible light, radio waves, infrared and ultraviolet
radiation, X rays, and gamma rays are types of electromagnetic radiation.
• A telescope collects light over a large area, makes time exposures, and can use other instruments to analyze light.
• Visible-light telescopes can be made using lenses, as in refracting telescopes, or mirrors, as in reflecting telescopes.
• Space is explored by telescopes, satellites, probes, and humans.
Section 28.1 Study Guide
Section 28.2 Main Ideas• The first step toward exploration of the Moon was the
launch of the Soviet satellite Sputnik 1. The American spacecraft Apollo 11 was the first crewed exploration of the Moon.
• The Moon’s surface has many features that are not present on Earth because the Moon lacks an atmosphere and therefore its surface does not undergo erosion.
• Scientists have three theories on how the Moon formed—simultaneous formation with Earth, a passing object captured by Earth’s gravity, or as the result of an object colliding with Earth. The collision theory is the most widely accepted.
Section 28.2 Study Guide
Section 28.3 Main Ideas• The entire sky appears to rotate daily because we observe
it from a rotating Earth. Our timekeeping system is based on the solar day, the length of day as observed from Earth.
• Our view of the Sun’s position changes throughout the year as Earth moves in its orbit about the Sun. Seasons occur on Earth because Earth’s axis is tilted.
• The Moon goes through a cycle of phases each lunar month that correspond to our changing view from Earth of the sunlit side of the Moon.
Section 28.3 Study Guide
Section 28.3 Main Ideas• Tides are caused by the gravitational attraction of the
Moon, and to a lesser extent, the gravitational attraction of the Sun.
• A solar eclipse occurs when the Moon lies directly between Earth and the Sun. A lunar eclipse occurs when the Moon passes through Earth’s shadow.
Section 28.3 Study Guide
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Chapter 28 Images
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