Spaceflight Now +
Premium video content for our Spaceflight Now Plus subscribers.
STS-31: Opening window to the Universe
The Hubble Space Telescope has become astronomy's crown jewel for knowledge and discovery. The great observatory was placed high above Earth following its launch aboard space shuttle Discovery on April 24, 1990. The astronauts of STS-31 recount their mission in this post-flight film presentation.
Small | Medium | Large
Atlantis on the pad
Space shuttle Atlantis is delivered to Kennedy Space Center's launch pad 39B on August 2 to begin final preparations for blastoff on the STS-115 mission to resume construction of the International Space Station.
Atlantis rollout begins
Just after 1 a.m. local time August 2, the crawler-transporter began the slow move out of the Vehicle Assembly Building carrying space shuttle Atlantis toward the launch pad.
ISS EVA preview
Astronauts Jeff Williams and Thomas Reiter will conduct a U.S.-based spacewalk outside the International Space Station on August 3. To preview the EVA and the tasks to be accomplished during the excursion, station managers held this press conference from Johnson Space Center in Houston.
Dial-up | Broadband
STS-34: Galileo launch
The long voyage of exploration to Jupiter and its many moons by the Galileo spacecraft began on October 18, 1989 with launch from Kennedy Space Center aboard the space shuttle Atlantis. The crew of mission STS-34 tell the story of their flight to dispatch the probe -- fitted with an Inertial Upper Stage rocket motor -- during this post-flight presentation film.
Small | Medium | Large
Atlantis on the move
Space shuttle Atlantis is transported to the cavernous Vehicle Assembly Building where the ship will be mated to the external fuel tank and twin solid rocket boosters for a late-August liftoff.
PLAY | TIME-LAPSE
Discovery ride along!
A camera was mounted in the front of space shuttle Discovery's flight deck looking back at the astronauts during launch. This video shows the final minutes of the countdown and the ride to space with the live launch audio included. The movie shows what it would be like to launch on the shuttle with the STS-121 crew.
Shuttle from the air
A high-altitude WB-57 aircraft flying north of Discovery's launch trajectory captures this incredible aerial footage of the space shuttle's ascent from liftoff through solid rocket booster separation.
This is the full launch experience! The movie begins with the final readiness polls of the launch team. Countdown clocks then resume ticking from the T-minus 9 minute mark, smoothly proceeding to ignition at 2:38 p.m. Discovery rockets into orbit, as seen by ground tracker and a video camera mounted on the external tank. About 9 minutes after liftoff, the engines shut down and the tank is jettisoned as the shuttle arrives in space.
Delta 2 launches MiTEx
MiTEx -- an experimental U.S. military project to test whether the advanced technologies embedded in two miniature satellites and a new upper stage kick motor can operate through the rigors of spaceflight -- is launched from Cape Canaveral aboard a Boeing Delta 2 rocket.
Become a subscriber
New definition would add 3 "planets" to Solar System
ASTRONOMICAL UNION NEWS RELEASE
Posted: August 16, 2006
The world's astronomers, under the auspices of the International Astronomical Union (IAU), have concluded two years of work defining the difference between "planets" and the smaller "solar system bodies" such as comets and asteroids. If the definition is approved by the astronomers gathered 14-25 August 2006 at the IAU General Assembly in Prague, our Solar System will include 12 planets, with more to come: eight classical planets that dominate the system, three planets in a new and growing category of "plutons" - Pluto-like objects - and Ceres. Pluto remains a planet and is the prototype for the new category of "plutons."
With the advent of powerful new telescopes on the ground and in space,
planetary astronomy has gone though an exciting development over the past
decade. For thousands of years very little was known about the planets
other than they were objects that moved in the sky with respect to the
background of fixed stars. In fact the word "planet" comes from the
Greek word for "wanderer". But today hosts of newly discovered large
objects in the outer regions of our Solar System present a challenge to
our historically based definition of a "planet".
If the definition is approved by the astronomers gathered at the IAU General Assembly in Prague, our Solar System will consist of 12 planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. The three new proposed planets are Ceres, Charon (Pluto's companion) and 2003 UB313. Credit: The International Astronomical Union/Martin Kornmesser
Download larger image version here
At first glance one should think that it is easy to define what a planet
is - a large and round body. On second thought difficulties arise, as one
could ask "where is the lower limit?" - how large, and how round should an
asteroid be before it becomes a planet - as well as "where is the upper
limit?" - how large can a planet be before it becomes a brown dwarf or
IAU President Ron Ekers explains the rational behind a planet definition:
"Modern science provides much more knowledge than the simple fact that
objects orbiting the Sun appear to move with respect to the background of
fixed stars. For example, recent new discoveries have been made of objects
in the outer regions of our Solar System that have sizes comparable to and
larger than Pluto. These discoveries have rightfully called into question
whether or not they should be considered as new ‘planets.' "
The International Astronomical Union has been the arbiter of planetary and
satellite nomenclature since its inception in 1919. The world's
astronomers, under the auspices of the IAU, have had official
deliberations on a new definition for the word "planet" for nearly two
years. IAU's top, the so-called Executive Committee, led by Ekers, formed
a Planet Definition Committee (PDC) comprised by seven persons who were
astronomers, writers, and historians with broad international
representation. This group of seven convened in Paris in late June and
early July 2006. They culminated the two year process by reaching
a unanimous consensus for a proposed new definition of the word "planet."
Owen Gingerich, the Chair of the Planet Definition Committee says: "In
July we had vigorous discussions of both the scientific and the
cultural/historical issues, and on the second morning several members
admitted that they had not slept well, worrying that we would not be
able to reach a consensus. But by the end of a long day, the miracle had
happened: we had reached a unanimous agreement."
The three new planets. Credit: The International Astronomical Union/Martin Kornmesser
Download larger image version here
The part of "IAU Resolution 5 for GA-XXVI" that describes the planet
definition, states "A planet is a celestial body that (a) has sufficient
mass for its self-gravity to overcome rigid body forces so that it assumes
a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around
a star, and is neither a star nor a satellite of a planet." Member of the
Planet Definition Committee, Richard Binzel says: "Our goal was to find a
scientific basis for a new definition of planet and we chose gravity as
the determining factor. Nature decides whether or not an object is a
According to the new draft definition, two conditions must be satisfied
for an object to be called a "planet." First, the object must be in orbit
around a star, while not being itself a star. Second, the object must be
large enough (or more technically correct, massive enough) for its
own gravity to pull it into a nearly spherical shape. The shape of objects
with mass above 5 x 1020 kg and diameter greater than 800 km would
normally be determined by self-gravity, but all borderline cases would
have to be established by observation.
If the proposed Resolution is passed, the 12 planets in our Solar System
will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus,
Neptune, Pluto, Charon and 2003 UB313. The name 2003 UB313 is provisional,
as a "real" name has not yet been assigned to this object. A decision and
announcement of a new name are likely not to be made during the IAU
General Assembly in Prague, but at a later time. The naming procedures
depend on the outcome of the Resolution vote. There will most likely be
more planets announced by the IAU in the future. Currently a dozen
"candidate planets" are listed on IAU's "watchlist" which keeps changing
as new objects are found and the physics of the existing
candidates becomes better known.
The IAU draft Resolution also defines a new category of planet for
official use: "pluton". Plutons are distinguished from classical planets
in that they reside in orbits around the Sun that take longer than 200
years to complete (i.e. they orbit beyond Neptune). Plutons typically
have orbits that are highly tilted with respect to the classical planets
(technically referred to as a large orbital inclination). Plutons also
typically have orbits that are far from being perfectly circular
(technically referred to as having a large orbital eccentricity). All
of these distinguishing characteristics for plutons are scientifically
interesting in that they suggest a different origin from the classical
There will most likely be more planets announced by the IAU in the future. Currently a dozen "candidate planets" are listed on IAU's "watchlist" which keeps changing as new objects are found and the physics of the existing candidates becomes better known. A number of these planet candidates are shown here. Credit: The International Astronomical Union/Martin Kornmesser
Download larger image version here
The draft "Planet Definition" Resolution will be discussed and refined
during the General Assembly and then it (plus four other Resolutions) will
be presented for voting at the 2nd session of the GA 24 August between
14:00 and 17:30 CEST.
The IAU is the international astronomical organisation that brings
together distinguished astronomers from all nations of the world. IAU's
mission is to promote and safeguard the science of astronomy in all its
aspects through international cooperation. Founded in 1919, the IAU is the
world's largest professional body for astronomers. The IAU General
Assembly is held every three years and is one of the largest and most
diverse meetings in the astronomical community's calendar.