Transcript Diapositive 1 - e

The Milky Way in Infrared
Credit:The COBE Project, DIRBE, NASA
At night, from a dark location, part of the clear sky looks milky. This unusual swath of dim light is generally visible during any
month and from any location. Until the invention of the telescope, nobody really knew what the "Milky Way" was. About 300 years
ago telescopes caused a startling revelation: the Milky Way was made of stars. Only 70 years ago, more powerful telescopes brought
the further revelation that the Milky Way is only one galaxy among many. Now telescopes in space allow yet deeper understanding.
The above picture was taken by the COBE satellite and shows the plane of our Galaxy in infrared light. The thin disk of our home
spiral galaxy is clearly apparent, with stars appearing white and interstellar dust appearing red.
Mercury as Revealed by MESSENGER
Credit: MESSENGER,NASA,JHU APL, CIW
The planet Mercury has been known since history has been recorded, but parts of the Solar System's innermost planet have never
been seen like this before. Two days ago the robotic MESSENGER spacecraft buzzed past Mercury for the second time and
imaged terrain mapped previously only by comparatively crude radar. The above image was recorded as MESSENGER looked
back 90 minutes after passing, from an altitude of about 27,000 kilometers. Visible in the above image, among many other newly
imaged features, are unusually long rays that appear to run like meridians of longitude out from a young crater near the northern
limb. MESSENGER is scheduled to fly past Mercury once more before firing its thrusters to enter orbit in 2011.
Venus Unveiled
Credit: Magellan Project, JPL, NASA
Explanation: The surface of Venus is perpetually covered by a veil of thick clouds and remains hidden from even the
powerful telescopic eyes of earth-bound astronomers. But in the early 1990s, using imaging radar, the Venus orbiting
Magellan spacecraft was able to lift the veil from the face of Venus and produced spectacular high resolution images
of the planet's surface. Colors used in this computer generated picture of Magellan radar data are based on color
images from the surface of Venus transmitted by the Soviet Venera 13 and 14 landers. The bright area running
roughly across the middle represents the largest highland region of Venus known as Aphrodite Terra.
Earthrise
Credit: Apollo8, NASA
In December of 1968, the Apollo 8 crew flew from the Earth to the Moon and back again. Frank Borman, James Lovell, and William
Anders were launched atop a Saturn V rocket on December 21, circled the Moon ten times in their command module, and returned to
Earth on December 27. The Apollo 8 mission's impressive list of firsts includes: the first humans to journey to the Earth's Moon, the
first manned flight using the Saturn V, and the first to photograph the Earth from deep space. As the Apollo 8 command module
rounded the farside of the Moon, the crew could look toward the lunar horizon and see the Earth appear to rise, due to their
spacecraft's orbital motion. The famous picture that resulted, of a distant blue Earth above the Moon's limb, was a marvelous gift to
the world.
Welcome to Planet Earth
Credit: Apollo 17 Crew, NASA
Explanation: Welcome to Planet Earth, the third planet from a star named the Sun. The Earth is shaped like a
sphere and composed mostly of rock. Over 70 percent of the Earth's surface is water. The planet has a relatively thin
atmosphere composed mostly of nitrogen and oxygen. The above picture of Earth, dubbed Blue Marble, was taken
from Apollo 17 in 1972 and features Africa and Antarctica. It is thought to be one of the most widely distributed
photographs of any kind. Earth has a single large Moon that is about 1/4 of its diameter and, from the planet's
surface, is seen to have almost exactly the same angular size as the Sun. With its abundance of liquid water, Earth
supports a large variety of life forms, including potentially intelligent species such as dolphins and humans. Please
enjoy your stay on Planet Earth.
The Far Side of the Moon
Credit: Apollo 16 Crew, NASA
Explanation: Does this moon look familiar? Possibly not, even though it is Earth's Moon. Locked in synchronous rotation,
the Moon always presents its well-known near side to Earth. But from lunar orbit, Apollo astronauts also grew to know the
Moon's far side. This sharp picture from Apollo 16's mapping camera shows the eastern edge of the familiar near side
(top) and the strange and heavily cratered far side of the Moon. Surprisingly, the rough and battered surface of the far
side looks very different from the near side which is covered with smooth dark lunar maria. The likely explanation is that
the far side crust is thicker, making it harder for molten material from the interior to flow to the surface and form the
smooth maria.
The Full Moon
Credit: Lick Observatory
Explanation: Earth has one moon. A symbol in famous love songs, movies, poems, and folklore, many myths about
the Moon date back to ancient history. In fact, the name Monday originates from Moon-day. The Moon glows by light
it reflects from the Sun and is frequently the brightest object in the night sky. The Moon orbits the Earth about once
a month (moon-th) from about 1 light second away. The above-pictured Full Moon occurs when the Moon is nearly
opposite to the Sun in its orbit. The Moon's diameter is about 1/4 that of the Earth, and from the Earth's surface
appears to have almost exactly the same angular size as the Sun. Recent evidence indicates that the Moon formed
from a colossal impact on the Earth about 4.5 billions of years ago, and therefore has a similar composition to the
Earth. Humans walked on the Moon for the first time in 1969.
Phobos: Doomed Moon of Mars
Credit: HiRISE, MRO, LPL (U. Arizona), NASA
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons,
Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be
captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant
reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this
stunning color image from the Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel.
But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our
Moon - that gravitational tidal forces are dragging it down. In 100 million years or so Phobos will likely be shattered by
stress caused by the relentless tidal forces, the debris forming a decaying ring around Mars.
Big Mars from Hubble
Credit: J. Bell (Cornell U.), M. Wolff (SSI) et al., STScI, NASA
Explanation: At about 10 am Universal Time today, Mars and Earth will pass closer than in nearly 60,000 years. Mars,
noticeably red, will be the brightest object in the eastern sky just after sunset. Tonight and through much of this week,
many communities around the world are running a public Mars Watch 2003 campaign, where local telescopes will
zoom in on the red planet. Pictured above is an image of Mars taken just last night from the Hubble Space Telescope in
orbit around the Earth. This image is the most detailed view of Mars ever taken from Earth. Visible features include the
south polar cap in white at the image bottom, circular Huygens crater just to the right of the image center, Hellas Impact
Basin - the large light circular feature at the lower right, planet-wide light highlands dominated by many smaller craters
and large sweeping dark areas dominated by relatively smooth lowlands.
Asteroids
Credit: NEAR Project, Galileo Project, NASA
Explanation: No asteroid or comet is known to be on a collision course with Earth. The asteroid designated 1997
XF11 had been predicted to come uncomfortably close, but new estimates place its passing beyond the orbit of the
Moon. This earth-approaching asteroid was discovered by SpaceWatch astronomer Jim Scotti in December of last
year. Orbital computations using new observations suggested that it would pass within 30,000 miles of the Earth's
center on October 26, 2028 - a very near miss considering that the radius of the Earth itself is about 4,000 miles.
However, more recent and further refined calculations based on both new and archival data indicate that the
closest approach will be 600,000 miles in 2028. Imaged by NASA spacecraft, the three potato-shaped objects
above are large main-belt asteroids orbiting between Mars and Jupiter. Shown to the same scale from left to right
are Mathilde, Gaspra, and Ida. Mathilde has dimensions of about 37 by 29 miles. The asteroid 1997 XF11 is much
smaller, probably a mile wide, yet the impact of an asteroid of this size could have catastrophic effects. Over the
last two decades, teams of astronomers have just begun to catalog and track near-earth objects.
Jupiter Eclipsing Ganymede
Credit: NASA, ESA, and E. Karkoschka (U. Arizona)
Explanation: How hazy is Jupiter's upper atmosphere? To help find out, astronomers deployed the Hubble
Space Telescope to watch Jupiter eclipse its moon Ganymede. Although Ganymede circles Jupiter once a week,
a particularly useful occultation occurs more rarely. Such an occultation was captured in great visual detail in
April 2007. When near Jupiter's limb, Ganymede reflects sunlight though Jupiter's upper atmosphere, allowing
astronomers to search for haze by noting a slight dimming at different colors. One result of this investigation was
the above spectacular image, where bands of clouds that circle Jupiter are clearly visible, as well as magnificent
swirling storm systems such as the Great Red Spot. Ganymede, at the image bottom, also shows noticeable
detail on its dark icy surface. Since Jupiter and Ganymede are so bright, many eclipses can be seen right here
on Earth with a small telescope.
Io's Surface: Under Construction
Credit: Galileo Project, JPL, NASA
Explanation: Like the downtown area of your favorite city, the roads you drive to work on, and any self-respecting web
site ... Io's surface is constantly under construction. This moon of Jupiter holds the distinction of being the Solar System's
most volcanically active body -- its bizarre looking surface continuously formed and reformed by lava flows. Generated
using 1996 data from NASA's Galileo spacecraft, this high resolution composite image is centered on the side of Io that
always faces away from Jupiter. It has been enhanced to emphasize Io's surface brightness and color variations,
revealing features as small as 1.5 miles across. The notable absence of impact craters suggests that the entire surface is
covered with new volcanic deposits much more rapidly than craters are created. What drives this volcanic powerhouse? A
likely energy source is the changing gravitational tides caused by Jupiter and the other Galilean moons as Io orbits the
massive gas giant planet. Heating Io's interior, the pumping tides would generate the sulfurous volcanic activity.
In the Shadow of Saturn
Credit: CICLOPS, JPL, ESA, NASA
Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn
recently drifted in giant planet's shadow for about 12 hours and looked back toward the eclipsed Sun. Cassini saw a view
unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system.
Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn
and slightly scattering sunlight, in the above exaggerated color image. Saturn's rings light up so much that new rings were
discovered, although they are hard to see in the above image. Visible in spectacular detail, however, is Saturn's E ring,
the ring created by the newly discovered ice-fountains of the moon Enceladus, and the outermost ring visible above. Far
in the distance, visible on the image left just above the bright main rings, is the almost ignorable pale blue dot of Earth.
Uranus: The Tilted Planet
Credit: Voyager 2 Team, NASA
Explanation: Uranus is the third largest planet in our Solar System after Jupiter and Saturn. Uranus is composed
mostly of rock and ices, but with a thick hydrogen and helium atmosphere. The blue hue of Uranus' atmosphere
arises from the small amount of methane which preferentially absorbs red light. This picture was snapped by the
Voyager 2 spacecraft in 1986 - the only spacecraft ever to visit Uranus. Uranus has many moons and a ring system.
Uranus, like Venus, has a rotation axis that is greatly tilted and sometimes points near the Sun. It remains an
astronomical mystery why Uranus' axis is so tilted. Uranus and Neptune are quite similar: Uranus is slightly larger but
less massive.
Neptune: Big Blue Giant
Credit: Voyager 2, NASA
Explanation: This picture was taken by the Voyager 2 spacecraft in 1989 - the only spacecraft ever to visit Neptune.
Neptune will be the farthest planet from the Sun until 1999, when the elliptical orbit of Pluto will cause it to once again
resume this status. Neptune, like Uranus, is composed mostly of liquid water, methane and ammonia, is surrounded by
a thick gas atmosphere of mostly hydrogen and helium, and has many moons and rings. Neptune's moon Triton is
unlike any other and has active volcanoes. The nature of Triton's unusual orbit around Neptune is the focus of much
discussion and speculation.
Pluto: The Frozen Planet
Credit: R. Albrecht (ESA/ESO), Hubble Space Telescope, NASA
Explanation: The Hubble Space Telescope imaged Pluto and its moon Charon in 1994. Pluto is usually the most
distant planet from the Sun but because of its elliptic orbit Pluto crossed inside of Neptune's orbit in 1979 and will
cross back out again in 1999. Compared to the other planets, very little is known about Pluto. Pluto is smaller than
any other planet and even smaller than several other planet's moons. From Pluto, the Sun is just a tiny point of
light. Pluto is probably composed of frozen rock and ice, much like Neptune's moon Triton. Pluto has not yet been
visited by a spacecraft, but a mission is being planned for the next decade.
What are Comet Tails Made Of?
Credit: Jim Martin, Huntsville AL, Courtesy "Night of the Comet" (NASA / Ames)
Explanation: The tail of comet Hyakutake, visible in this recent color image, is composed of dust and gas driven off
the icy comet nucleus by the Sun's heat and blown away by the solar wind. Bathed in solar ultraviolet light, the gas
molecules break down and are excited, producing a characteristic glow. This glow is responsible for visible light from
the tail and astronomers using spectroscopes can identify the compounds involved. The close passage of Hyakutake
presents an excellent chance to use this technique to explore the composition of its tail. Typical comet gas tail
constituents are simple combinations of hydrogen, carbon, nitrogen, and oxygen - for example, H20 (water), CO
(carbon monoxide), and CN (cyanogen) are common. In fact, the poisonous CO and CN compounds were seen in the
spectrum of Halley's comet during its 1910 apparition. This caused some public concern at the time as the Earth was
expected to pass through Halley's tail! However, stretching for millions of miles, comet tails are extremely thin and
tenuous and don't pose a danger to the Earth's atmosphere.