Exploring Comet Tails

Image Credit & Copyright: Joe Orman

Explanation: Comets are known for their tails. In the spring of 1997 and 1996 Comet Hale-Bopp (above) and Comet Hyakutake gave us stunning examples as they passed near the Sun. These extremely active cometswere bright, naked-eye spectacles offering researchers an opportunity to telescopically explore the composition of primordial chunks of our solar system by studying their long and beautiful tails. But it has only recently been discovered that surprising readings from experiments on-board the interplanetary Ulysses probe which lasted for several hours on May 1, 1996, indicate the probe passed through comet Hyakutake’s tail! Ulysses experiments were intended to study the Sun and solar wind and the spacecraft-comet encounter was totally unanticipated. Relative positions of Ulysses and Hyakutake on that date indicate that this comet’s ion tail stretched an impressive 360 million miles or about four times the Earth-Sun distance. This makes Hyakutake’s tail the longest ever recorded and suggests that comet tails are much longer than previously believed.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Aurora in Red and Yellow

Credit & Copyright: Jan Safar (Brno Observatory)

Explanation: The past week brought some spectacular aurora to northern skies. These aurorae were caused by a large interplanetary shock wave that exploded from the Sun on April 4. When the shock wave reached the Earth on April 6, the resulting aurora could be seen in clear skies as far south as North Carolina. As the aurorae occurred high in the Earth’s atmosphere, they were accompanied by an unusual alignment of planets far in the background. Pictured above that night, an unusual multicolored auroral display graced the skies above the domes of the Brno Observatory in the Czech Republic.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

A Superwind from the Cigar Galaxy

Credit: FOCAS, Subaru 8.3-m Telescope, NAOJ

Explanation: What’s lighting up the Cigar Galaxy? M82, as this irregular galaxy is also known, was stirred up by a recent pass near large spiral galaxy M81. This doesn’t fully explain the source of the red-glowing outwardly expanding gas, however. Recent evidence indicates that this gas is being driven out by the combined emerging particle winds of many stars, together creating a galactic “superwind.” The above recently released photograph from the new Subaru Telescope highlights the specific color of red light strongly emitted by ionized hydrogen gas, showing detailed filaments of this gas. The filaments extend for over 10,000 light years. The 12-million light-year distant Cigar Galaxy is the brightest galaxy in the sky in infrared light, and can be seen in visible light with a small telescope towards the constellation of Ursa Major.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Eagle EGGs in M16

Credit: J. Hester & P. Scowen (ASU), HST, NASA

Explanation: Star forming regions known as “EGGs” are uncovered at the end of this giant pillar of gas and dust in the Eagle Nebula (M16). EGGs, short for evaporating gaseous globules, are dense regions of mostly molecular hydrogen gas that fragment and gravitationally collapse to form stars. Light from the hottest and brightest of these new stars heats the end of the pillar and causes further evaporation of gas – revealing yet more EGGs and more young stars. This picture was taken by the Wide Field and Planetary Camera on board the Hubble Space Telescope.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

 

M20: The Trifid Nebula

Credit & Copyright: Todd Boroson, AURA, NOAO, NSF

Explanation: Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

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, Mercurywill 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. Aninformed 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)

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 extending a million miles above the Sun’s surface in this composite image from the EIT and UVCS instruments onboard theSOHO spacecraft. 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)

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)

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 allType 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)

NGC 1999: Reflection Nebula in Orion

Credit: Hubble Heritage Team (STScI) and NASA

Explanation: A dusty bright nebula contrasts dramatically with a dusty dark nebula in this Hubble Space Telescope image recorded shortly after December’s orbital servicing mission. The nebula, cataloged asNGC 1999, is a reflection nebula, which shines by reflecting light from a nearby star. Unlike emission nebulae, whose reddish glow comes from excited atoms of gas, reflection nebulae have a bluish cast as their interstellar dust grains preferentially reflect blue starlight. While perhaps the most famous reflection nebulae surround the bright young stars of the Pleiades star cluster, NGC 1999’s stellar illumination is provided by the embedded variable star V380 Orionis, seen here just left of center. Extending right of center, the ominous dark nebula is actually a condensation of cold molecular gas and dust so thick and dense that it blocks light. From our perspective it lies in front of the bright nebula, silhouetted against the ghostly nebular glow. New stars will likely form within the dark cloud, called a Bok globule, as self-gravity continues to compress its dense gas and dust. Reflection nebula NGC 1999 lies about 1500 light-years away in the constellation Orion, just south of Orion’s well known emission nebula, M42.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)