Chapter 1

The Earth's Seasons
This animation shows the relationship between the fixed angular tilt of the Earth's axis and the location in its orbit around the Sun for the different seasons over the course of an entire year. The Earth and Moon are enlarged for clarity, but are shown with the correct orbital orientation, relative speed, and orbital rate with respect to each other. The different seasons are labeled according to the astronomical definitions of the beginning and end of winter, spring, summer, and autumn, respectively.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Annular and Total Solar Eclipses
This animation shows the relationship between the fixed angular tilt of the Earth's axis and the location in its orbit around the Sun for the different seasons over the course of an entire year. The Earth and Moon are enlarged for clarity, but are shown with the correct orbital orientation, relative speed, and orbital rate with respect to each other. The different seasons are labeled according to the astronomical definitions of the beginning and end of winter, spring, summer, and autumn, respectively.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Chapter 3

The Planck Spectrum
This animation shows the growth of the black-body curve and the corresponding shift of peak wavelength with temperature for the spectrum of a heated object. The visible region of the spectrum is indicated. As temperature rises, the "red end" of the spectrum fills up first, so the object would begin to glow red, then orange-red, then yellowish-red. It eventually becomes "white hot" when the entire visible portion of the spectrum is filled in a roughly uniform way. At extremely high temperatures, such as the surface temperatures of very massive young stars, the peak of the spectrum moves beyond the visible range toward higher frequencies, and the resulting tilt in the portion of the spectrum that remains in the visible range causes the object to appear slightly more blue than white.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Chapter 4

Classical Hydrogen Atom I
A classical hydrogen atom is composed of a single electron orbiting a single proton nucleus. When the atom absorbs a photon, its electron jumps to an excited state. Eventually, the electron returns to the ground state, and an ultraviolet photon is emitted.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Classical Hydrogen Atom II
Absorption of a more energetic photon can boost the hydrogen atom’s electron to the second excited state. Here, the electron cascades back to its ground state, emitting two photons, one in the ultraviolet and one in the red part of the spectrum.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 6

Astronomical Ruler
The distance between the Sun and Earth is 1 Astronomical Unit, a huge interval by everyday standards of about 1.5 x 10 8 km. The distance between the Sun and Pluto averages nearly 40 such Astronomical Units.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Terrestrial Planets I
The four interior planets have different colors, sizes, tilts, and spins. With some artistic license, here is a rendering of these various aspects of comparative planetology. Note that, for Venus, we are looking at the much faster retrograde rotation of its upper cloud decks (not the much slower spin of its hidden surface), and for Mercury its spin rate has been increased in order to display its prograde motion.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Jovian Planets Part I
The four giant gas planets are here compared, with proper size and scale, to each other, and to planet Earth. We see their rich colors, and their many varied rings --each revolving separately. Indeed Saturn’s inner ring has a period about twice as fast as its outer ring. The tilts of the planets’ spin axes are rendered here relative to the plane of the ecliptic, including that of Uranus, which is nearly pointing at us.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 7

Simulation of Jan 10-11 Magnetic Storm
This is a computer model of a plasma cloud ejected from the Sun. The cloud impacts Earth's magnetic field and deforms it. This animation is based on real data from the WIND spacecraft.

Courtesy Goddard Space Flight Center/NASA.

 

Chapter 8

Terrestrial Planets Part II
Here, the bulk interior makeups of the four Earth-like worlds are compared, side by side, showing mostly similarities rather than major differences. The presence or absence of magnetic field must result from a combination of spin rate and heated core.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

The Orbit of Mercury
Mercury's orbit and rotation combine to produce a day that is two of its years long (176 Earth days total). In this animation, we show the relationship between Mercury's rotation about its axis and its orbit around the Sun to illustrate the amount of time taken to proceed through one complete cycle of these motions.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Chapter 9

The Phases of Venus
This animation incorporates a window-within-a-window showing the change in the phase, size and brightness of Venus as seen from Earth. This telescopic view from Earth is shown alongside a main window that gives simultaneously the positions of Earth and Venus in their respective orbits around the Sun. A numerical information window gives many details of relevant quantities, such as the percent illumination of Venus as seen from Earth, the relative distance between the two bodies, and the magnitude and angular size of Venus.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

The Rotation of Venus
The animation begins by showing the orientation of a reference marker on the surface of Venus, and how this reference marker changes with the position of Venus in its orbit, illustrating retrograde rotation and the length of Venus’ day. The animation then continues by showing a close-up of this rotation at the same time as an overview of Venus’ orbital position throughout the course of an entire Venus "year." Like the other planets, Venus moves counterclockwise in its orbit around the Sun as seen from a vantage point north of the ecliptic plane, but unlike most of the other solar system objects, it rotates about its axis in the opposite sense. As a result, the Sun rises on the western horizon of Venus and sets in the east.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved..

Chapter 10

Seasonal Changes in Martian north polar ice cap
The seasonal expansion and shrinking of Mars' northern polar cap is evident in this time-lapse sequence spanning five months. These views, looking directly down on the Martian north pole, were actually created by assembling mosaics of three sets of images taken by the Hubble telescope and projecting them to appear as they would if seen from above the pole.

Courtesy Space Telescope Science Institute/NASA

Mars Global Surveyor
The Mars Global Surveyor conducts a high-resolution mapping of Mars, seeing details as small as a meter across. Located in a polar orbit around the red planet, MGS carries six instruments to study the planet’s surface, atmosphere, and gravitational and magnetic fields. During this Mars mapping phase of the mission, the spacecraft will circle the planet once every 117 minutes at an average altitude of 378 kilometers (235 miles). In addition, the mapping orbit is tilted at nearly a right angle to the Martian equator. Consequently, Surveyor will pass over both the north and south polar regions of Mars on every revolution around the planet.

Courtesy Jet Propulsion Laboratory/
NASA

Rotation of Mars
This is a photo mosaic of the planet Mars from three separate views taken with the Hubble Space Telescope (the seams among the three pictures can be seen as dark longitudinal features). When this image was assembled in early 1995, it was springtime in Mars’ northern hemisphere. The abundance of fluffy white clouds shows that the planet is cooler and drier than when last visited by spacecraft in the mid 1970’s.

Courtesy Space Telescope Science Institute/NASA

Chapter 11

Jupiter’s Moon Ganymede
This zoom into two regions on Ganymede shows comparable resolution to images taken by the Voyager and Galileo probes. Ganymede is crisscrossed by relatively younger parallel grooves that cut across a preexisting, heavily-grooved and cratered terrain. Such widespread features mark places where two separate pieces of crust moved away from one another as Ganymede’s icy surface cooled and expanded. The finest details that can be seen are about 1.6 km across.

The terrain of the Galileo Region has been reworked by multiple episodes of shearing and deep furrowing due to movement of the surface crust. Also apparent are bright hill crests and crater rims, suggesting caps of frost. Craters are generally 3 to 5 km across.

A three-dimensional view of the Galileo Region made by combining images taken on June 27 and Sept. 6, when the Galileo craft flew past the same site at different viewing angles. This 3D terrain view highlights the heights of raised rims and the depths of furrows and impact craters.

Courtesy Jet Propulsion Laboratory/
NASA

Jupiter’s Moon Europa
Europa's maze of both linear and jumbled features resembles cracked ice flows in Earth's polar regions. In the higher resolution view the color has been enhanced to highlight differences in surface composition. The red color designates areas that are probably a dust and water ice mixture that has seeped to the surface from Europa’s subterranean ocean. Relatively fresh surface ice appears blue-white. Subtle color differences on the bright plains imply that ice grains on the surface have different sizes.

This Galileo view zooms down to the surface of Europa until features no bigger than houses - just 20 meters across - can be seen amid the tangle of overlapping ridges and grooves . Europa's outer crust is thin, perhaps only a few kilometers thick in places. An ocean or rock-ice-water slush possibly lies just below the surface.

A three dimensional view of Europa's surface, made by combining images from two different viewing angles from two Galileo probe flybys of Europa. Clearly seen are the chunky ice rafts and relatively smooth, crater-free patches on the surface of Europa . The blocks may be floating on a younger and thinner icy surface than previously believed. Also unique are long "triple bands" having dark margins and bright centers. Though they are 10 to 20 km wide, they trace across the flat terrain for hundreds of kilometers.

Courtesy Jet Propulsion Laboratory/
NASA

Galileo Mission to Jupiter, Part I
On July 13, 1995, the atmospheric probe separated from the main bus, and began its own trek toward Jupiter. The probe has instruments that measure pressure, temperature, and the chemical content of the Jovian atmosphere.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Galileo Mission to Jupiter, Part II
Here, we see the "main bus" in its initial approach to Jupiter. As the vehicle begins orbiting the planet, it will monitor data from the atmosphere probe and relay the findings back to Earth.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Galileo Mission to Jupiter, Part III
As the atmospheric probe makes its way toward Jupiter, great bolts of lightening can be seen on the dark side of the planet. These bolts can be "heard" in the radio part of the spectrum.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Galileo Mission to Jupiter, Part IV
On December 7, 1995, the probe enters the upper layers of the Jovian atmosphere at a searing 170,000 km/hr, and slows down to about 50 km/hr when it deploys its parachute.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Galileo Mission to Jupiter, Part V
Under its parachute, the probe relays data back to the main bus for approximately 90 minutes before being crushed by atmospheric pressure.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Io Cutaway
Recent observations of Juptier’s moon Io by the Galileo robot spacecraft have measured a magnetic field more intense than expected -- and hence, by inference, a larger metallic core, in fact almost half the radius of this peculiar moon.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Galileo Flyby of Io
This animation shows a detailed artist’s rendering of the Galileo spaceprobe by-passing the Jovian moon Io.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 12

Saturn Storm
This is a view of the planet Saturn as seen in December 1994 when a large white storm erupted over the equatorial region.

Courtesy Space Telescope Science Institute/ NASA

Chapter 13

Historical Observations of Pluto
This series of images shows the improvement in telescopic views of the planet Pluto since its discovery in 1930. In addition to its discovery image, which shows Pluto moving against a stellar background, other milestones include the detection of Pluto’s moon Charon in 1978 and a follow-up observation with the Hubble Space Telescope in 1990 which clearly separates the planet and its satellites.

Courtesy Space Telescope Science Institute/ NASA

Jovian Planet Part II
The Jovian Planets, especially Jupiter and Saturn, emit more radiation than they absorb, suggesting great heat within them. Jupiter and Saturn have very similar interiors of mostly hydrogen, while Uranus and Neptune are also thought to have nearly identical structures and compositions.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, , all rights reserved.

Orbits of Neptune and Pluto
Animates the relative location of Neptune and Pluto versus time, beginning with the date of the announcement of Pluto's discovery, and continuing for one orbit of Pluto around the Sun (249 Earth years). The locations at which the orbits of Neptune and Pluto cross, as seen from above the plane of the ecliptic, are easily visible. Neptune and Pluto will never collide, however, due to the fixed 3:2 ratio between their oribital periods.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Mutual Eclipses of Charon and Pluto
Much information was gained regarding the orbit of the moon Charon about Pluto through observations of a series of eclipses of each of these objects by the other (or more correctly, eclipses of Charon by Pluto and transits of Charon in front of Pluto) that occurred between 1982 and 1994. This animation shows the simulated motion of Charon around Pluto as seen from the Earth during this time period. During the first portion of the movie, the orbital motion of Charon has been slowed down for clarity. The last two portions of the animation show closer views of a particular eclipse and a transit, along with a time scale to show how these events would have been seen by an Earth observer.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Chapter 14

Path of Comet Hyakutake Across Sky
This is an animated diagram of the path of comet Hyakutake as it moved across the sky and how it changed position from early April to May 1996.

Courtesy Space Telescope Science Institute/ NASA

Rotating Comet Hale- Bopp Nucleus
This animation is based on Hubble Space Telescope observations on the nucleus of Comet Hale-Bopp. Astronomers unexpectedly caught the comet going through a sudden brief outburst, where, in little more than an hour, the amount of dust being spewed from the nucleus increased at least eight fold. The surface of Hale-Bopp’s nucleus is an incredibly dynamic place, with vents being turned on and off as new patches of icy material are rotated into sunlight for the first time. Astronomers have estimated that its nucleus may be 19-25 miles (30-40 kilometers) in diameter. The average comet is thought to have a nucleus of about 3 miles (5 kilometers) in diameter, or even smaller. The comet or asteroid that struck Earth 65 million years ago, possibly causing the extinction of the dinosaurs, was probably about 6-9 miles (10-15 kilometers) across.

Courtesy Space Telescope Science Institute/ NASA

Anatomy of a Comet I
As a comet nears the Sun, its velocity increases as does the length of its tail, which always points away from the Sun. Up close, tumbling and oddly shaped, comet nuclei resemble "dirty snowballs. "

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Anatomy of a Comet II
Nearing the Sun, comets display violent activity. Gases boil off the comet nucleus, forming a coma surrounding it. Also, two tails form--an ion tail straight back and a dust tail lagging and curved. Up close, jets are seen on the sunward side of the evaporating nucleus.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Asteroid Comet Breakup
When rounding the Sun or a Jovian planet too closely, comets and asteroids can break into small fragments. If the debris intersects Earth’s orbit, it can produce either delightful meteor showers, as is often the case with comet fragments, or catastrophic impacts, as is often the case with asteroid fragments. The animation, not done to scale, depicts mostly the latter phenomenon.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 15

Formation of Warp in Beta Pictoris Disk
This animation shows how the gravitational pull of a suspected planet might warp the inner disk of the Beta Pictoris. The dust in the disk "feels" the gravitational tug of a Jupiter-sized planet, which is orbiting in a slightly different plane from that of the disk. This pulls the dust that is near the inner edge of the disk into a different plane.

Courtesy Space Telescope Science Institute/NASA

Coalescence of Objects in a Gravitational Field
This animation shows the simulated motion of a small number of bodies of various orbital eccentricities over time. It is intended to give an overview of the processes that govern collision, coalescence, and gravitational scattering between objects in the early history of formation of planets around a star. In this simulation, 25 objects are placed into randomly distributed orbits around a more massive parent body, and allowed to interact according to Newton's laws of motion and gravitation. Objects that come within their mutual radii are allowed to coalesce, and objects can also receive gravitational boosts and decelerations if they come close enough to each other but do not collide. The result, after some late collisions that resemble the behavior of eccentric objects within our own solar system, is a general clearing of the region near the star, with one object in a nearly circular orbit and several smaller ones flung into long-period, very elongated orbits.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved..

Chapter 16

May 12 1997 Solar Flare Event
This time-lapse image shows a bright flare erupting on the Sun. The green false color actually represents a view of the Sun in ultraviolet light, as seen with the SOHO spacecraft.

Goddard Space Flight Center (GSFC) — Courtesy of SOHO/ CDS Consortium

LASCO C3 Coronograph on the SOHO shows a coronal ejection and grazing Comet
In this time lapse view the Sun ejects a massive plume of gas into space. As Earth moves along its orbit, the Sun appears to drift across the star field and Milky Way. A sun-grazing comet sweeps perilously close to the Sun.

Goddard Space Flight Center (GSFC) — Courtesy of SOHO/ CDS Consortium

Chapter 17

The Inverse Square Law
When radiation moves away from a point source, it is steadily diluted in intensity as it spreads out over progressively larger surface areas. The light intensity varies inversely as the square of the distance from the source. Gravitational attraction between two astronomical bodies follows a similar "inverse square law" for the same mathematical reason. This animation shows how the area grows with the square of distance and how light is spread out over that area as it moves from a pointlike source.

Created by Alan Sill, Texas Tech University. Copyright Prentice Hall, Inc. 1999, all rights reserved.

Chapter 18

Gaseous Pillars of Star Birth
This sequence zooms into a vast pillar of cold hydrogen gas laced with dust, which is an incubator for new star formation.

Courtesy Space Telescope Science Institute/NASA

Orion Nebula Mosaic
This sequence demonstrates how successive exposures with the Hubble Space Telescope can be combined to create a photo mosaic of a large nearby nebula. The Orion Nebula is seven light-years across and so requires several separate images to cover its entire extent.

Courtesy Space Telescope Science Institute/NASA

M16 Eagle Nebula
This animation puts a recent HST image into its historical context. We start with the parent interstellar cloud some several million years ago, show the emergence of young, hot stars within it, illustrate (by the pulsing, which is a graphic only) the intense UV radiation emanating from the central stars, and end with the finger-like remnants of the original cloud that are now being evaporated by the oncoming radiation.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 19

Bi-Polar Outflow
The wind of a protostar tends to form bipolar jets perpendicular to its disk. Eventually, the area is swept clean around the newborn star.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Evolution of a 1-Solar-Mass Star
Born from an interstellar cloud, a young star gradually sweeps away surrounding dust and debris, revealing a genuine star like our Sun. Only in old age does the star change its appearance, first becoming a red giant and then leaving a white dwarf star at its core.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 20

Bipolar Planetary Nebula: A Giant Star Swallows its Companion
A dumbbell-shaped, bipolar planetary nebula forms in a double star system when one member expands and engulfs its companion. This creates a thick disk that constricts the out-flowing stellar envelope, forcing the gas to escape along narrow lobes above and below the disk. Such a dumbbell pattern is seen in many planetary nebulae.

Courtesy Space Telescope Science Institute/NASA

Formation of Knots in Helix Nebula
Standard models predict that gaseous knots seen in the Helix Nebula should expand and dissipate within a few hundred thousand years. However, dust particles within each gas ball might collide and stick together, snowballing to planet-sized bodies over time. The resulting objects would be Earth-sized copies of the frigid, icy planet Pluto. These icy worlds would escape the dead star and presumably roam interstellar space forever.

Courtesy Space Telescope Science Institute/NASA

H-R Diagram Tracks Stellar Evolution
A plot of luminosity and temperature allows us to follow the evolution of a 1-solar-mass star, from birth to death. Motion of the data point on the plot is roughly proportional to the time spent by the star at each stage.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Formation of Helix Nebula
Planetary nebulae like the Helix Nebula form when the star is in the later stages of its life, when it ejects shells of gas into space. This "planetary nebula" formation happens in stages where, toward the end of the process, a faster moving shell of gas ejected off the doomed star collides with slower-moving gas released ten thousand years before.

Courtesy Space Telescope Science Institute/NASA

Death of the Sun Part I
In nearly 5 billion years, our Sun will evolve to the red-giant phase, eventually ending its normal nuclear-burning cycle. Its core will contract, as its atmosphere and interior recede. Some of the terrestrial planets will likely be engulfed.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Death of the Sun Part II
The evolution of our main-sequence Sun to its red-giant stage would cause the daytime sky to change dramatically. Earth itself would also greatly change - the oceans would boil, the atmosphere would escape, the land would burn, and life would end.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 21

Shockwave hitting the ring around supernova 1987a
The explosion of supernova 1987A illuminated a preexisting ring of gas which encircled the doomed star. Debris hurled into space, moving at 1/10 the speed of light, created a shockwave which is now beginning to hit the ring, causing it to heat up and glow again.

Courtesy Space Telescope Science Institute/NASA

Composition and structure of the ring of supernova 1987a
This computer model shows the three-dimensional structure and orientation of the three rings of glowing gas surrounding supernova 1987A. The rings are tilted such that one ring is in front of the supernova debris and the other ring is behind it. The smaller, yellow ring is an extension of the star’s equator and so is in the same plane of sky.

Courtesy Space Telescope Science Institute/NASA

Recurrent Nova
Matter can transfer between members of binary star systems. An accretion disk forms when gas from a red dwarf star is pulled toward a companion white dwarf. When the disk overloads, matter builds up on the surface of the white dwarf and ignites, blowing off hot gas. Such nova outbursts recur periodically as the disk becomes re-established many times.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 22

Hubble As Black Hole Hunter
This animation shows a normal spiral galaxy and then zooms into the core of the galaxy, which is the site of a super massive black hole. A disk of hot gas and dust orbit the black hole, and the velocity of the disk is a direct measure of the mass of the black hole. A source of fuel is needed to create the disk , which has been assumed to be gas that has fallen into the center of the galaxy near the black hole. The gas will form into a rapidly rotating disk. Each individual gas particle will spiral slowly toward the black hole in the center.

Courtesy Space Telescope Science Institute/NASA

Black Hole Geometry
Both isolated stellar black holes as well as much larger ones at the cores of active galaxies are surrounded by rapidly swirling accretion disks and display bipolar jets of gas. Here, we travel up to and over the central black hole.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 23

Cepheid Star in Distant Galaxy
The pulsation period of a Cepheid variable star can be used to infer the absolute luminosity of that star -- and thus to determine the distance to the star. This "yardstick" then provides an estimate of the distance from Earth to the distant galaxy housing the Cepheid star.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.

Chapter 24

Collision of Two Spiral Galaxies
This computer-generated simulation shows the collision of two spiral galaxies. Tidal forces and galactic rotation cause the galaxies to cast off stars and gas in the form of long, thin "tidal tails" similar to those observed in the collision of real galaxy pairs. As the galaxies pass by one another, their disks become distorted, forming prominent bars and spiral features. The mutual gravitational attraction of the galaxies swings them around and causes them to fall back and merge into a single object.

Courtesy Chris Mihos and NCSA.

Galaxy Formation Simulation
This supercomputer simulation illustrates the growth of galaxies in the early universe through the collision and merger of smaller clusters of stars. This simulation shows a "bottom-up" theory of galaxy formation, in which large galaxies arise from the merger of smaller objects. This theory is supported by Hubble Space Telescope observations which show possible pieces of galaxies before they began to assemble into larger objects.

Courtesy Edmund Bertschinger, MIT

The Big Dipper Zoom
This sequence of still images demonstrates that a small, relatively empty-looking portion of the sky is actually filled with hundreds of galaxies when viewed at the faintest limits of current-day telescopes, about 30th magnitude. This faint threshold reveals objects which are less than a billionth the brightness of the faintest stars that can be seen by the human eye. The image was taken by the Hubble Space Telescope which focused on this region of the sky for ten consecutive days.

Courtesy Space Telescope Science Institute/NASA

Chapter 25

Proof of Black Hole In Galaxy M84
This animation shows the differential rotation of matter around a super-massive black hole in the core of a spiral galaxy. Because of the black hole's concentrated mass, gas dust and stars swirl around it in a whirlpool -- the closer to the black hole, the faster the orbit.

Courtesy Space Telescope Science Institute/NASA

Black Hole in Galaxy M32
The video illustrates the motion of stars caught in the gravitational field of a three-million solar mass black hole in the core of nearby galaxy M32. Stars swarm around the black hole like angry bees around a hive. Hubble’s Faint Object Spectrograph was able to zoom into the central light-year of M32, providing five times higher spatial resolving power than the best ground-based observations. The projected velocities of the stars in the galaxy were measured, and their three-dimensional motion was then reconstructed using state-of-the-art computer models.

M32 is a small companion galaxy of the great galaxy in the constellation of Andromeda . Because of its proximity, only 2.2 million light years away, M32 has long been intensively studied with the best ground-based telescopes. The velocities of the stars near its nucleus suggested the presence of a black hole as early as 1984. In 1992 Hubble observations measured a bright peak or "cusp" of starlight that independently suggested that the stars were concentrated around a black hole. The Hubble measurements of the stellar motions have further strengthened the evidence for this conclusion. The animation is based on computer simulations and Hubble Space Telescope Observations of M32. These were reported in the February 13, 1997 issue of Nature Magazine by Roeland van der Marel (Institute for Advanced Study, Princeton, NJ) and co-investigators Tim de Zeeuw (Leiden University, the Netherlands), Hans-Walter Rix (University of Arizona) and Gerald Quinlan (Rutgers University, NJ). The team further includes Nicolas Cretton (Leiden University), Steinn Sigurdsson (Cambridge U, UK) and Lars Hernquist (University of California at Santa Cruz). The calculations were done in part on the Cray T3D Supercomputer of the Pittsburgh Supercomputing Center.

Courtesy R. Van Der Marel, the Pittsburgh Supercomputing Center, the Space Telescope Science Institute and NASA

Quasar Animation
This animation shows the birth of a quasar in the core of a normal spiral galaxy. Quasars are among the most baffling objects in the universe because of their small size and prodigious energy output. Quasar’s are not much bigger than Earth’s solar system but pour out 100 to 1,000 times as much light as an entire galaxy containing a hundred billion stars. A super massive black hole, gobbling up stars, gas and dust is theorized to be the "engine" powering a quasar. Most astronomers agree that an active black hole is the only credible possibility to explains how quasars can be so compact, variable, and powerful. Nevertheless, conclusive evidence has been elusive because quasars are so bright they mask the environment where they live. High resolution pictures from the Hubble Space Telescope show that quasars can reside in normal galaxies. This means a quasar might be a short-lived phenomenon in a galaxy’s existence, and may have been a very common phenomenon in the early life history of a galaxy.

Courtesy Space Telescope Science Institute/NASA

Active Galaxy
Most active galaxies have two main characteristics:

  1. Bipolar jets that expel matter outward at high speeds over thousands of light- years.
  2. A central, spinning, accretion disk thought to house a super massive black hole.

Spectroscopy can be used to study the dynamics of the disk, as depicted here by spectral Doppler Shifts, based on recent Hubble observations of the M87 active galaxy in Virgo.

Created by Dana Berry and James Palmer, Tufts Science Visualization Laboratory. Copyright Prentice Hall Inc, all rights reserved.