Mercury on the Horizon Credit: Juan Carlos Casado Explanation: Have you ever seen the planet Mercury? Because Mercury orbits so close to the Sun, it is never seen far from the Sun, and so is only visible near sunrise or sunset. If trailing the Sun, Mercury will be visible for several minutes before it follows the Sun behind the Earth. If leading the Sun, Mercury will be visible for only several minutes before the Sun rises and hides it with increasing glare. An informed skygazer can usually pick Mercury out of a dark horizon glow with little more than determination. Above, a lot of determination has been combined with a little digital trickery to show Mercury's successive positions during the middle of last month. Each picture was taken from the same location in Spain when the Sun was 10 degrees below the horizon and superposed on the single most photogenic sunset. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Apollo 16: Exploring Plum Crater Credit: John W. Young, Apollo 16 Crew, NASA Explanation: Apollo 16 spent three days on Earth's Moon in April 1972. The fifth lunar landing mission out of six, Apollo 16 was famous for deploying and using an ultraviolet telescope as the first lunar observatory, and for collecting rocks and data on the mysterious lunar highlands. In the above picture, astronaut John W. Young photographs Charles M. Duke, Jr. collecting rock samples at the Descartes landing site. Duke stands by Plum Crater while the Lunar Roving Vehicle waits parked in the background. The Lunar Roving Vehicle allowed the astronauts to travel great distances to investigate surface features and collect rocks. High above, Thomas K. Mattingly orbits in the Command Module. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
A Wind From The Sun Credit: SOHO Consortium, UVCS, EIT, ESA, NASA
Explanation: A wind from the Sun blows through our Solar System. The behaviour of comet tails as they flapped and waved in this interplanetary breeze gave astronomers the first hint of its existence. Streaming outward at 250-400 miles/second, electrons and ions boiling off the Sun's incredibly hot but tenuous corona account for the Solar Wind - now known to affect the Earth and other planets along with voyaging spacecraft. Rooted in the Solar Magnetic Field, the structure of the corona is visible in this composite image from the EIT and UVCS instruments onboard the SOHO spacecraft, extending a million miles above the Sun's surface. The dark areas, known as coronal holes, represent the regions where the highest speed Solar Wind originates. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Martian Dust Devil Trails Credit: Malin Space Science Systems, MGS, JPL, NASA Explanation: Who's been marking up Mars? This portion of a recent high-resolution picture from the orbiting Mars Global Surveyor spacecraft shows twisting dark trails criss-crossing a relatively flat rippled region about 3 kilometers wide on the martian surface. Newly formed trails like these presented researchers with a tantalizing martian mystery but have now been identified as likely the work of miniature wind vortices known to occur on the red planet - martian dust devils. Another example of wind processes on an active Mars, dust devils had been detected passing near the Viking and Mars Pathfinder landers. Such spinning columns of rising air heated by the warm surface are common in dry and desert areas on planet Earth. Typically lasting only a few minutes, they becoming visible as they pick up loose dust. On Mars, dust devils can be up to 8 kilometers high and leave dark trails as they disturb the bright, reflective surface dust. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
A Panorama of Oddities in Orion A Credit: T. A. Rector, B. Wolpa, G. Jacoby, AURA, NOAO, NSF Explanation: New stars, fast jets, and shocked gas clouds all occupy Orion A, a giant molecular cloud just south of the Orion Nebula. The bright object visible below and slightly left of center of this recently released picture is the reflection nebula NGC 1999. Wind from NGC 1999's central star, V380 Orionis, appears to have created the surrounding billows of red and brown gas. Several bright young stars illuminate reflecting dust at the top right of the image. Jets shoot from dozens of young stars creating glowing compressed shocked waves known Herbig-Haro objects. One such shock is the unusual Waterfall, the bright streak on the upper right, which is a source of unusual radio waves. The cone-shaped shock to the Waterfall's lower right may result from a jet emitted HH1 and HH2, located 10 light-years away below NGC 1999. The unusual and energetic oddities that occur and interact in star forming regions are often as complex as they are beautiful. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Crown Point - This classic view of the Columbia River Gorge is very popular with photographers. The ever-changing light makes every shot an original. PhotoTripUSA: In and Around Portland - The Photography of Ken Dietz
Supernova 1994D and the Unexpected Universe Credit: High-Z Supernova Search Team, HST, NASA Explanation: Far away, long ago, a star exploded. Supernova 1994D, visible as the bright spot on the lower left, occurred in the outskirts of disk galaxy NGC 4526. Supernova 1994D was not of interest for how different it was, but rather for how similar it was to other supernovae. In fact, the light emitted during the weeks after its explosion caused it to be given the familiar designation of a Type Ia supernova. If all Type 1a supernovae have the same intrinsic brightness, then the dimmer a supernova appears, the farther away it must be. By calibrating a precise brightness-distance relation, astronomers are able to estimate not only the expansion rate of the universe (parameterized by the Hubble Constant), but also the geometry of the universe we live in (parameterized by Omega and Lambda). The large number and great distances to supernovae measured over the past few years have been interpreted as indicating that we live in a previously unexpected universe. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Sun Storm: A Coronal Mass Ejection (Smaller)Credit: SOHO Consortium, ESA, NASA Explanation: Late last month another erupting filament lifted off the active solar surface and blasted this enormous bubble of magnetic plasma into space. Direct light from the sun is blocked in this picture of the event with the sun's relative position and size indicated by a white half circle at bottom center. The field of view extends 2 million kilometers or more from the solar surface. While hints of these explosive events, called coronal mass ejections or CMEs, were discovered by spacecraft in the early 70s this dramatic image is part of a detailed record of this CME's development from the presently operating SOlar and Heliospheric Observatory (SOHO) spacecraft. Near the minimum of the solar activity cycle CMEs occur about once a week, but as we approach solar maximum rates of two or more per day are anticipated. Though this CME was clearly not headed for Earth, strong CMEs are seen to profoundly influence space weather, and those directed toward our planet and can have serious effects. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Saturn At Night Credit: Voyager Project, JPL, NASA Explanation: From a spectacular vantage point over 1.4 billion kilometers from the sun, the Voyager 1 spacecraft looked back toward the inner solar system to record this startling view of Saturn's nightside. The picture was taken on November 16, 1980, some four days after the robot spacecraft's closest approach to the gorgeous gas giant. The crescent planet casts a broad shadow across its bright rings while the translucent rings themselves can be seen to cast a shadow on Saturn's cloud tops. Since Earth is closer to the sun than Saturn, only Saturn's dayside is visible to Earth-bound telescopes which could never take a picture like this one. After this successful flyby two decades ago, Voyager 1 has continued outward bound and is presently humanity's most distant spacecraft. The next spacecraft to approach Saturn will be Cassini, on course to arrive in 2004. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
The Pipe Dark Nebula Credit & Copyright: Jerry Lodriguss Explanation: The dark nebula predominant at the lower left of the above photograph is known as the Pipe Nebula. The dark clouds, suggestively shaped like smoke rising from a pipe, are caused by absorption of background starlight by dust. These dust clouds can be traced all the way to the Rho Ophiuchi nebular clouds on the right. The brightest star in the field is Antares. Many types of nebula are highlighted here: the red are emission nebula, the blue are reflection nebula, and the dark are absorption nebula. This picture has been digitally enhanced. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. LHEA at NASA/ GSFC & Michigan Tech. U.
Zal Patera on Jupiter's Moon Io Credit: Galileo Project, SSI, University of Arizona, JPL, NASA Explanation: The Galileo orbiter's flyby of Io last November captured an unusual part of Jupiter's volcanic moon. From 26,000 kilometers away, Zal Patera was found to be a cauldron of flowing lava, gaseous vents, and tremendous peaks. Red lava can be seen in the above picture erupting along the base of the volcanic caldera, while cooling black lava lines the edge of a volcanic plateau. Shadow lengths indicate that the top of Zal Patera towers nearly 5 kilometers over Io's molten surface. Galileo zoomed past Io again last month, and has begun beaming back images taken only 200 kilometers over Io's surface. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Nearer To Asteroid ErosCredit: NEAR Project, JHU APL, NASA Explanation: As the robot spacecraft NEAR lowers itself toward asteroid 433 Eros, more surface details are becoming visible. Last week's maneuvers brought NEAR to within 204 kilometers of the floating mountain's surface. With increased resolution, NEAR's camera then documented Eros' unusual shape, craters large and small, boulders, and mysterious grooves similar to asteroid Gaspra and Martian moon Phobos. If you could stand on Eros, you would still be too small to be visible on this recent image, which shows features as small as 20 meters across. However, you would feel gravity only 1/1000 that on Earth, so that you could easily jump over even this large 5 kilometer wide crater. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. LHEA at NASA/ GSFC & Michigan Tech. U.
M13: The Great Globular Cluster in Hercules (Small Version) Credit & Copyright: Yuugi Kitahara - Explanation: M13 is one of the most prominent and best known globular clusters. Visible with binoculars in the constellation of Hercules, M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision. M13 is a colossal home to over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old. At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13. The reason for the low abundance of unusual blue straggler stars in M13 is currently unknown. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Julius Caesar and Leap Days Photo Credit & Copyright: Rune Rysstad - Explanation: Even as leap days go, today is a remarkable one. In 46 BC, Julius Caesar, pictured above in a self-decreed minted coin, created a calendar system that added one leap day every four years. Acting on advice by Alexandrian astronomer Sosigenes, Caesar did this to make up for the fact that the Earth's year is slightly more than 365 days. In other words, the time it takes for the Earth to circle the Sun is slightly more than the time it takes for the Earth to rotate 365 times (we now know it takes about 365.24219 rotations). So, if calendar years contained 365 days they would drift from the actual year by about 1 day every 4 years. Eventually July (named posthumously for Julius Caesar himself) would occur during the northern hemisphere winter! By adopting a leap year with an extra day every four years, the calendar year would drift much less. This Julian Calendar system was used until the year 1582 when Pope Gregory XIII added that leap days should not occur in years ending in "00" except if divisible by 400, providing further fine-tuning. This Gregorian Calendar system is the one in common use today. Therefore, even though this year 2000 ends in "00", it remains a leap year, and today is the added leap day. That makes today the first leap day for a centurial year since year 1600 and the second such leap day of the Gregorian Calendar. Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. LHEA at NASA/ GSFC & Michigan Tech. U.
The Sombrero Galaxy from VLT Credit: Peter Barthel (Kapteyn Inst.) et al., FORS1, VLT ANTU, ESO Explanation: Why does the Sombrero Galaxy look like a hat? Reasons include the Sombrero's unusually large and extended central bulge of stars, and dark prominent dust lanes that appear in a disk that we see nearly edge-on. Billions of old stars cause the diffuse glow of the extended central bulge. Close inspection of the bulge in the above photograph shows many points of light that are actually globular clusters. M104's spectacular dust rings harbor many younger and brighter stars, and show intricate details astronomers don't yet fully understand. The very center of the Sombrero glows across the electromagnetic spectrum, and is thought to house a large black hole. Fifty million-year-old light from the Sombrero Galaxy can be seen with a small telescope towards the constellation of Virgo. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Impact: 65 Million Years Ago Credit: courtesy V.L. Sharpton, LPI -Explanation: What killed the dinosaurs? Their sudden disappearance 65 million years ago, along with about 70 percent of all species then living on Earth, is known as the K-T event (Cretaceous-Tertiary Mass Extinction event). Geologists and paleontologists often entertain the idea that a large asteroid or comet impacting the Earth was the culprit. In such a cosmic catastrophe, the good(!) news would be that the impact would generate firestorms, tidal waves, earthquakes, and hurricane winds. As for the bad news ... debris thrown into the atmosphere would have a serious global environmental consequences, creating extended periods of darkness, low temperatures, and acid rains - resulting in a planet-wide extinction event. In 1990, dramatic support for this theory came from cosmochemist Alan Hildebrand's revelation of a 65 million year old, 112 mile wide ring structure still detectable under layers of sediment in the Yucatan Peninsula region of Mexico. The outlines of the structure, called the Chicxulub crater (named for a local village), are visible in the above representation of gravity and magnetic field data from the region. In addition to having the right age, the crater is consistent with the impact of an asteroid of sufficient size (6 to 12 miles wide) to cause the global disruptions. Regardless of the true cause of the K-T event, it is fortunate that such impacts are presently believed to happen only about once every 100 million years!Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. A service of: LHEA at NASA/ GSFC & Michigan Tech. U