By Daniel Fischer
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Current mission news: MGS (latest pictures!) + Cassini + Stardust
Posted in part from the Bakubung Bush Lodge, South Africa / Links completed June 30
Transit of Venus observed widely, used for science, education, funGood weather in large parts of Europe as well as in Africa, Asia, the Americas and Australia has permitted uncounted millions to glimpse the transit of Venus in front of the Sun's disk on June 8 either for the full six hours of the event or at least in parts. The scientific value of the rare sky show was much lower than in past centuries, though some clever experiments had been devised to use it for studies of Venus' atmosphere or as a kind of proxy - under controlled conditions - for extrasolar planet transits. Attempts were made at several observatories to measure the chemistry and dynamics of the planet's upper atmosphere by noting subtle changes in the spectrum of the whole solar disk while Venus was crossing it. One group even tried to do that by observing the Moon which is illuminated by the Sun, of course.
Another major use of the transit was educational: International collaborations tried to repeat the classical transit-based experiments in oder to calculate the value of the Astronomical Unit from ingress and egress timings at different latitudes; the stunning success in that by the ESO campaign (which got the AU to within 0.001% of the true value from some 3000 timings) has already raised some eyebrows. Most observers, however, just enjoyed the rare view (that was easily visible even with simple 'eclipse glasses') - or took the best-ever photographs of a transit of Venus. Some of these, taken with moderate or large instruments, clearly show the planet's atmosphere lit brightly from behind. The most stunning close-up views, though, came from the professional solar telescopes, on the ground and in space.
Several high-resolution solar telescopes on the Canary Islands obtained amazing sequences of images, and while they missed the ingress (the Sun hadn't risen yet), they could image the egress and its assorted phenomena in a quality that our 19th and 18th century forefathers could only dream of. And then there were the solar telescopes in space: SOHO saw Venus only in front of the corona, but TRACE saw it move across the disk - and made a lot of use of that. "We used the Transition Region and Coronal Explorer (TRACE) Spacecraft to image the 8 June 2004 Transit of Venus," report Schneider & Pasachoff: "Our primary programmatic objectives were: (a) to image sunlight scattered in the circum-Cytherian back-lit atmosphere, and morphologically and photometrically study its temporal (i.e., spatial) evolution."
Furthermore they wanted "(b) to confirm the conjecture that ground-based historical reports of "Black Drops" at inner planet transits arose from the convolution of the instrumental (telescopic/optical) plus atmospheric point spread function in conjunction with the limb-darkened photospheric illumination function" as the same authors had suspected after analysis of TRACE pictures of the transit of Mercury in 1999. All images for the Venus program were obtained in TRACE's "White Light" (WL) configuration, which provides spectral sensitivity in the wavelength range from 120 to 960 nm. "During the transit, Venus's angular diameter was app. 58.2 arcseconds (12,104 km at 0.289 AU), diametrically spanning 116 detector pixels," report Schneider & al. who had to clean up some ghost effects not normally important but crucial for the transit experiment. The solar photospheric radial limb darkening profile was also removed from the images.
The images then "very clearly show the emergence of sunlight scattered by the Cytherian atmosphere
as Venus approaches the line-of-sight to the solar disk. The scattering, clearly, is asymmetric, as
a small arc of atmosphere first becomes visible 'below' the disk of Venus, not on a line
perpendicular to the solar limb. By 'geometrical mid-ingress,' when the solar limb is equally
bifurcated by Venus, this arc of scattered light is readily apparent. [...] About 12 minutes before
second contact the atmospheric arc becomes 'full' and contiguous, and grows brighter with decreasing
angular distance to the solar limb. Second contact is geometrically 'sharp' (except for 'blurring'
by the 1" FWHM TRACE WL PSF) with no evidence of the classical/historical 'black drop' effect (gone,
now, the way of the Martian canals)." This is only a preliminary analysis but agrees well with what
one can see in the professional and advanced amateur sequences as well.
Dramatic Cassini close-ups of Phoebe hint at origin of exotic Saturn satellite in the Kuiper BeltImages collected during Cassini's close flyby of Saturn's moon, Phoebe, on June 11 have yielded strong evidence that the tiny object may contain ice-rich material, overlain with a thin layer of darker material perhaps 300 to 500 meters thick. The surface of Phoebe is also heavily potholed with large and small craters. Images reveal bright streaks in the ramparts of the largest craters, bright rays which emanate from smaller craters, and uninterrupted grooves across the face of the body. Some members of the imaging team are now leaning towards the view that has been promoted recently, that Phoebe is probably ice-rich and may be an object originating in the outer solar system, more related to comets and Kuiper Belt objects than to asteroids.
In ascertaining Phoebe's origin, imaging scientists are noting important differences between the surface of Phoebe and that of rocky asteroids which have been seen at comparable resolution: Asteroids seen up close, like Ida, Mathilde, and Eros, and the small martian satellites do not have the bright "speckling" associated with the small craters that are seen on Phoebe. The landforms observed in the highest resolution images also contain clues to the internal structure of Phoebe: It is a world of dramatic landforms, with craters everywhere, landslides, and linear structures such as grooves, ridges, and chains of pits. Scientists thus think that these images are showing an ancient remnant of the bodies that formed over four billion years ago in the outer reaches of the solar system.
The Phoebe fly-by was only a bonus, of course, before the 'real thing': On July 1st (UTC) Cassini will fire its main engine to enter into Saturn's orbit, for a Galileo-style mission of at least 4 years. One June 16 Cassini fired its engine for 38 seconds, putting the vehicle on course for the Saturn orbit insertion. This was the final planned course correction prior to the make-or-break 96.4-minute orbit insertion rocket firing that will cap a seven-year voyage to the ringed planet. The rocket firing, known as Trajectory Correction Maneuver 21, or TCM-21, was needed to ensure Cassini crosses the plane of Saturn's rings in the right position, in a broad gap between the F and G rings, a region thought to be empty of orbital debris. To be on the safe side, the spacecraft will make the crossing with its high-gain dish antenna facing always forward to act as a shield.
LINEAR a nice sight even well into JuneEven more than a month after perihelion, comet C/2002 T7 (LINEAR) remained a fine sight for observers in the Southern hemisphere, once more in the Moon-free evening sky, but now at a large elevation: On June 8, e.g., yours truly could spot it one last time with the naked eye as a fuzzy blob. And in binoculars LINEAR had even become more impressive than in May, with a much shorter but also much brighter tail of perhaps one degree. At the same time comet C/2001 Q4 (NEAT) had moved towards Ursa Major where it was a less impressive though still easy-to-find object. By mid-June both comets had faded to 7th magnitude, however, and the show is now really over. (Based on observations by yours truly in South Africa from June 4 to 13).
Comet duo nice for the naked eye, brilliant for electronic imagingThese comets were not made for the visual observer and certainly not for the public at large - but for modern electronic imaging devices which are in the hands of a skyrocketing number of amateur astronomers C/2001 Q4 (NEAT) and especially C/2002 T7 (LINEAR) were stunning targets throughout May. Unfortunately the latter could only be observed well from South of the equator, but the former became an easy target for Northerners as well in mid-May. As expected, both LINEAR and NEAT could be seen simultaneously with the naked eye for several evenings from May 19 to 23 - even the lunar crescent, present from May 21 onwards, would not interfere. At about that time LINEAR also reached its greatest brightness - and it really looked like a minor copy of 1996's Hyakutake (as seen through sun glasses :-) ...
While NEAT, reaching about 3.0 mag. in early May and fading since, continues to display a broad dust tail, LINEAR has a very narrow plasma tail that showed dramatic changes from day to day. On one day there could be one or more very distinct and sharply bounded rays that would be completely absent 24 hours later. The faint tails of both comets, especially LINEAR's, could at times be seen for many degrees from dark Southern sites, in binoculars and even with the (trained) naked eye. They were far more stunning, though, for sensitive video cameras like the uniquitous Mintron or digital still cameras like the Canon 10D. The latter proved especially capable in splitting the various gas and dust components of NEAT's complex tail, thanks to their different colors. (Based largely on observations by yours truly and his companions during a big comet expedition to Namibia from May 1 to 25)
2nd or 1st magnitude expected for comets NEAT and LINEARWith May on the doorstep, the hot weeks for comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) are beginning: The former will reach perigee on May 6 (0.32 AU) and perihelion on May 15 (0.96 AU), with greatest brilliance in the sky expected in the 1st week of May, while the latter has already passed perihelion on April 23 (0.62 AU) but will not reach perigee - and probably the greatest brilliance as well - until May 19 (0.27 AU). At the end of April both comets were hovering around magnitude 4.0, according to observers in the Southern hemisphere, but NEAT is expected to reach between 2.0 and 2.7 in the coming week. And LINEAR may even rise to 1.5 mag. in the next three weeks, unless it fades faster after its visit to the Sun. And there are some worries about exactly that: In this case the comet (which switched its response factor to solar heating several times while approaching the Sun) might reach only 2.0 mag. - which, however, would still be as bright as Halley's comet ever got in 1986!
As explained in an analysis last year, NEAT will become visible in the Northern hemisphere just after its greatest brightness. Starting around May 5th or 6th, scan for Comet NEAT just above the southwest horizon as evening twilight fades: You're looking for a small, fuzzy "star" with a small tail pointing to the upper left. (The much brighter star Sirius will also be low in the southwest; on May 5th the comet will be not far to its left, and on May 6th the comet will be to Sirius's upper left.) In the next two weeks Comet NEAT will get much higher in the southwest at nightfall, crossing the line between Venus/Saturn and Jupiter on May 15, though it will also fade. Binocular users may be able to follow it through the end of May. LINEAR, however, will be visible only in the deep South during the time of its expected greatest brilliance. Thus only there one can hope for a pair of naked eye comets as last seen in 1911 (according to Sky & Tel. 5/2004 p. 79).
ISS etc. UpdateThe Moon2Mars Comm. recommends grave changes in NASA's structures & procedures, but others think that would only make things worse. The M2M Report (in PDF; exec. summ. and PR), the Plan. Soc.'s response, the Congressional Research Service on what it could cost, an Update to Implementation Plan for Space Shuttle Return to Flight and Beyond, NASA Releases on JIMO and NESC, O'Keefe on the Budget Conference Agreement, Science@NASA on BCAT-3, ESA Releases on the Soyuz' return, Kuipers' experience and the Seeds experiment, a Boeing Release on a Prometheus study and coverage of June 19: HC, AFP, ST. June 18: HC, FT, SC, Welt. June 17: HC (OpEd), FT (other story), CSM, ST. June 16: SN, Wired, USA Today, CNN, Dsc., SC (other story), BBC, FT, AFP. June 15: SR. June 14: SpaceRev (other story), ST. June 11: FT, SC, ST. June 10: SC, ST. June 9: HC. June 7: ST. June 6: FT package [SC]. June 2: UPI, SR. June 1: SC, Welt.
Yang in the US in May:
The HST crisis - it's all pointing towards a (complex) robotic servicing mission now. GSFC Solicitation for an HST-suited robot arm, a NASA Press Release (earlier), a speech by O'Keefe, a petition by numerous astronauts to reinstate the SM and coverage of June 15: SC. June 13: HC. June 11: Scotsman. June 9: CSM. June 7: USA Today. June 4: Dsc. June 2: S&T, BBC, New Sci., RP, NZ. June 1: UPI, SC, ST. May 28: HC. May 23: APOD. May 15: Wired. May 12: SC. May 10: UPI. May 5: SD. May 4: SC. May 2: ST. May 1: FT. April 30: SN.
Amateur rocket reaches space - 124 km!A rocket launched from the Nevada desert has become the first amateur-built rocket to reach space - the GoFast Rocket, assembled by a team of amateur rocketeers called the Civilian Space Exploration Team (CSXT), apparently reached a peak altitude of some 124 km: CSXT Homepage, pictures, ARRL (earlier), HobbySpace. Earlier: BBC, New Sci., AP, ST, NZ. Preview: SC.
SpaceShipOne to try first space mission on June 21 when an altitude of 100 km should be reached: Homepage, Scaled Press Release and FAQ [SR], SN, BBC (earlier, still earlier), CNN (earlier), VOA, FT (earlier), CollectSpace, HC, Economist, CSM, New Sci., UPI, SC (earlier, still earlier, even earlier, still earlier, even earlier), ST (earlier, still earlier). The vehicle reached a peak altitude of 64.6 km during a flight in May: Scaled, SpaceDev PRs, Dsc., SC (earlier), BBC, AFP, ST, NZ. X Prize to be won this summer? There are other competitors, too: FT, SC (earlier), BBC. Prize renamed: X Prize PR, ST. New Mexico to host X Prize Cup: SC, ST. Licensing issues: SpaceRev. Branson space visions? Guardian.
Gravity Probe B performing well in orbitThe exotic spacecraft is already halfway through its orbital testing phase, with no problems reported: May 28, May 24, May 14, May 7 and April 28 Status Reports [SN, SD].
GOES-8 deactivated after 10 yearsNOAA will boost GOES-8 into an orbit 350 kilometers above its original geostationary position, where it will be deactivated and disposed safely in three controlled burns: NOAA Release, SC.
"Swarm" of satellites approvedESA's Earth Observation Programme Board has decided which candidate mission will be developed and launched - Swarm, an Earth Explorer Opportunity Mission, is a constellation of satellites which will study the Earth's magnetic field: ESA Press Release.
ESA's MIRI contribution to the JWST confirmed - the mid-IR instrument will considerably extend the capability of the James Webb Space Telescope: ESA Release.
Giant UK telescope gets upgradeWork has started to use optical fibres to link up the giant radio telescope at Jodrell Bank with five others that are scattered across England: Jodrell Bank PR, BBC.
Successful "First Light" for the mid-infrared VISIR instrument on the VLT, working at 10-20 µm: ESO Press Release.
Silver coating for Gemini mirror - it's the first of its kind ever to line the surface of a very large astronomical mirror: Gemini Release.
HST confirms Hipparcos Plejades distance troublewith its Fine Guidance Sensors - so what went wrong with the celebrated astrometry satellite? HST Release.
Did Hubble image a planet of another star? Astronomers are being cautious, saying they require more data to be sure it really is a planet and not a background object caught in the same field of view: NSU, BBC, SC.
Two Architectures Chosen for Terrestrial Planet Finder - NASA has chosen to fly two separate missions with distinct and complementary architectures to achieve the goal of the Terrestrial Planet Finder: PlanetQuest.
The heaviest double starwith the masses of both partners measured directly (to about 80 solar masses each) is WR 20a: a paper by Bonanos & al., a CfA Press Release and New Sci. and BdW stories.
X-ray evidence for a solar-like activity cycle in another star, but a full one hasn't been observed yet: ESA Press Release, BdW. Maunder-style minima are rare in other stars: Ast. Fastest flashing star: NOSR PR.
Quasars sit in "humble" galaxiesQuasars appear to blaze forth from humdrum galaxies in the early universe, and surprisingly, not from the giant or disrupted ones astronomers expected, Gemini observations show: Gemini Press Release, New Sci., SC, ST, BdW.
Searching for the earliest galaxy clusters - two new projects will give astronomers an unprecedented census of the early days of galaxy formation: Ast.
Stardust Science papers outSeveral papers in the June 18 issue of Science detail the discoveries Stardust made during its flight through the coma of Wild 2 in January: JPL, U. Chicago and MPG Press Releases, NSU, SciAm, AFP, Guard., FT, WP, Telegr., Chig. Trib., P*N, SC, ST, MW, NZ, BdW.
Hayabusa flies by Earth, takes picturesOn May 19 the Japanese Hayabusa spacecraft successfully made a close Earth approach (altitude = 3725 km), thereby gaining the velocity it needs to reach the near-Earth asteroid Itokawa - and just before the fly-by, the spacecraft acquired images of the Earth and the Moon on the 16th and 17: JAXA and ISAS Releases and a Plan. Soc. story.
Genesis on final lap home - it flew past Earth on May 1 in a loop that puts it on track for home and a dramatic mid-air recovery Sept. 8: JPL Release.
SMART-1 views Europe on May 21 from 70,000 km: ESA Sensation. The s/c is already 100,000+ km from Earth: Status. And a self-portrait of Rosetta, thanks to the CIVA camera: ESA Release. The missions's 1st cruise phase has begun: Status.
Asteroid with smallest orbit discoveredThe orbit of 2004 JG6 lies entirely within the Earth's, coming within 5.6 million kilometers from the orbit of the Earth at aphelion and just 3.2 million kilometers from the orbit of Mercury at perihelion: Lowell Press Release, New Sci., SC, ST, BdW.
A crater linked to end-Permian mass extinction? An impact crater believed to be associated with the "Great Dying," the largest extinction event in the history of life on Earth, could be buried off the coast of Australia: NASA, UCSB and Univ. of Rochester Releases, S&T, Ast., Plan. Soc., BBC, SC, CNN, ST. Mass extinction details from 65 Myr ago: U Colorado PR, BBC, Wired, SC.
Chandra galaxy cluster data support Dark EnergyThe X-ray satellite studied 26 clusters of galaxies at distances corresponding to light travel times of between one and eight billion years - the data span the time when the Universe slowed from its original expansion, before speeding up again because of the repulsive effect of dark energy: Chandra Release, S&T, BBC, New Sci., AFP, SC, ST.
Cosmic Ray origin modelledwith vast magnetic reconnections: LLNL Press Release. Pulsar pair probed: JPL Release, SC, BdW. New techniques to hunt for SNRs: Ast.
Compiled and written by Daniel Fischer