Saturday, June 28, 2008

1500th SOHO comet found - satellite most prolific comet hunter ever

The ESA/NASA SOHO spacecraft has just - on June 25 - discovered its 1500th comet with its LASCO coronagraph, making it more successful than all other comet discoverers throughout history put together. Not bad for a spacecraft that was designed as a solar physics mission. Of course, LASCO itself does not make the detections; that task falls to an open group of highly-skilled volunteers who scan the data as soon as it is downloaded to Earth. Once SOHO transmits to Earth, the data can be on the Internet and ready for analysis within 15 minutes; enthusiasts from all over the world then look at each individual image for a tiny moving speck that could be a comet. For direct viewing, meanwhile, Boattini is returning to Northern skies.

In other news an amateur may or may not have detected Pluto's moon Charon with an 80-cm reflector (also M. Brown on classifications and a video of the recent occultation). • Jupiter from Germany and Puerto Rico, Mars in daytime and a preview of Mars meeting Saturn. • What a low solar max would mean for space debris, how an asteroid got named John, and NLCs on June 26 - they are surging now. • Dark sky status for Cherry Springs. • Pictures of a weird rocket body. • The strange "Deep ILmpact" web tv event (about a fictional impact in Germany) is coming today. • And here's to the KBA at 5 years (with yours truly featured on page 41)!

Sunday, June 22, 2008

Aussie amateur records Pluto occult a star!

A few hours ago Dave Gault in Australia took this nice light curve of dwarf planet Pluto occulting a star of 12th magnitude in Sgr, using a 10" Newton and a WAT-120N video camera: The star was gone for 113 seconds. This occultation had been deemed very important for scientific studies of the Pluto system.

In other news Venus is the evening 'star' again, having been recovered in Munich's dusky skies yesterday. • Despite its low elevation in Germany, detail-rich Jupiter images have been obtained this morning (more, more) as well as on June 21, June 20 and June 19. • And here's a moderately entertaining/scary chart of famous NEOs and how close they came/will come to Earth ...

Saturday, June 21, 2008

Just some pretty - or unusual - pictures ...

There was no true "Breaking News" event this week, but some pretty amazing celestial pictures taken by amateur astronomers have been published in recent days, worth a post after all:Incidentally a fine Omega effect had been seen during a partially eclipsed Sunrise in 2006, also yours truly - an inferior mirage in action. (Later I also found out where this appearance of the Sun had first been compared to an Etruscan vase: It was in Jules Verne's novel Le Rayon Vert, during the final "showdown" - on page 287 of this German translation.) Atmospheric optics is cool - but beware of faulty interpretations ...

In other news it has been determined that a recently discovered comet was very close to Jupiter in 2005, while another one came too close to the Sun on June 16. • More image processing of the June 14 Jupiter shown in the last post and another one from June 19. • And this blog has learned about an unsuccessful attempt to catch the Venus occultation by the Sun in Tasmania; here is a digital version of the newspaper article announcing the plan.

Monday, June 16, 2008

Huge "harvest" of small exoplanets by HARPS detailled; includes 'super-earth' trio

Vague reports had already come out at another conference, but today the details have been released about some 45 exoplanet candidates found with the special HARPS spectrograph at the ESO 3.6-meter telescope: they all have a mass below 30 Earth masses and an orbital period shorter than 50 days. Among the discoveries with the radial velocity method is a star having three small planets with 4.2, 6.7 and 9.4 times the mass of the Earth that orbit the star HD 40307 with periods of 4.3, 9.6 and 20.4 days, respectively. "Does every single star harbour planets and, if yes, how many?" planet hunter Michel Mayor from Geneva Observatory now wonders - exactly what he already told an audience in Bonn ½ year ago. Even the most classical of exoplanet hunting techniques, it seems, is now approaching a detection limit of an Earth mass or two.

In other news shatter cones - the largest known - from an ancient impact have been found next to a busy road, though the impact crater is long gone. • A very long paper discusses the long-term light curve of comet Encke. • Io and its shadow in front of/on Jupiter's disk yesterday, also another fine color Jupiter from mid-June. • Olga is just the latest asteroid one dedicated observer saw covering a star. • The light curve of Nova Oph is pretty variable. • Many NLC observations have already been made this year, including the first bright ones and a sighting from Germany.

• Yet another Namibian astronomy report to whet one's appetite for going there once again... • With Discovery back home, the next shuttle will fly to Hubble, if repairs on Discovery's launch pad succedd in time, as is expected. One may also dream about a huge liquid mirror telescope on the Moon in the more distant future. • And finally, in case you missed the link appearing a bit later in a link from here: These are the pics of Venus 3.7' from the solar limb!

Wednesday, June 11, 2008

IAU decides to call Pluto and Eris "plutoids"

Almost two years after the new class of dwarf planets was introduced in the solar system, with Pluto, Eris and Ceres as the first members, another directive from the 2006 General Assembly in Prague has now been fulfilled: the subclass of dwarf planets residing in the Kuiper belt has been named "plutoids". Furthermore it was decided that any Solar System body having a semimajor axis greater than that of Neptune and an absolute magnitude brighter than H=+1 mag. will be considered to be a plutoid (which has implications for the formalities by which it will be given a proper name). The IAU did not announce any new entries into the dwarf planet/plutoid class or when that will happen - but it should be only a matter of time until 2003 EL61 and 2005 FY9 are accepted; see this inofficial list once compiled by this blogger.

In other news this blog has just learned about successful imaging of Venus 3.7 arc minutes(!!!) from the solar limb yesterday morning: The photographer masked part of his DSLR's chip with a metal strip, used a neutral density filter and Herschel wedge with his refractor telescope (to keep the heat away from the electronics) and made long exposures ... • Amateur astronomers played a role in triggering crucial radio observations of dwarf nova SS Cyg. • There is now a new sunspot group which has since been given the number (10)998. • Jupiter with an 8" telescope and at low elevation from Germany - still pictures like these were possible last night, or methane observations; here is a collection. • Another Namibian astronomy expedition report. • And selected sky pictures from above.

Monday, June 9, 2008

Solar minimum unusually deep/long after all?

When the question was raised in May whether the current minimum of solar activity was unusually low, the reply from NOAA was that "it isn't all that unusual. Note, the last 2-3 minima were a bit higher than typical and I believe this one slightly below average, which makes it seem that much lower." But at a solar conference in Montana a month later things were apparently seen differently, at least according to a press release the hosting university put out today: "The scientists said periods of inactivity are normal for the sun, but this period has gone on longer than usual. [...] The next cycle is just beginning and is expected to reach its peak sometime around 2012. Today's sun, however, is as inactive as it was two years ago, and scientists aren't sure why." The release stresses the lack of knowledge about the Sun's 'plans' but mentions the Maunder minimum of the 17th century ...

In other news here are some observations of the 'other' comet Boattini currently around 11th mag. Meanwhile the 'old' Boattini is near M 41, only visible deep South at around 5th mag. • The first bright NLCs of the year have been seen in Ireland - and a weird halo in Finland.

Saturday, June 7, 2008

Venus racing towards the solar limb, still caught today ...

Eight hours from now Venus will slip behind the limb of the Sun, a rare event that happens only every 8 years and only for a few decades (in the vicinity of the transit of Venus 'seasons'). As already explained here observing the "show" may or may not be possible at all, will definitely require special equipment and is very risky for both equipment and observer. Then again, Venus has been imaged again today, just 25 arc minutes from the solar limb and 13 hours before disappearing behind it! Owners of prominence coronagraphs and full-disk H-Alpha telescopes alike might give it a try, and if Venus won't show up at all in raw images which show prominences (there is a good one near the Eastern limb right now, and on June 4 a spectacular one was observed) and/or the chromosphere well, try to overexpose. Experiments with other (wider-band) filters are at your own risk, of course. Now here is the timeline, calculated with Horizons for Bonn, Germany:
  • First contact (Venus and Sun limbs touch) - 5:07½ UTC - solar elevation 14°
  • Mid-entry - 5:14 UTC - solar elevation 15°
  • Second contact (Venus gone) - 5:20½ - solar elevation 16°
The times should be approx. true everywhere. The solar diameter will be 1890.8", Venus' diameter is 9.6", and the whole disappearing act will last 13 minutes. For Europe the exit on June 10 will be at night as will be both entry and exit in 2016. In the years 2024 and 2032, however, both entry and exit will be observable from Europe each time, and especially in 2032, the Sun will be high in the sky for both events. One can only marvel at the technical possibilities in our hands then. Looking back, by the way, coronagraphs have been used during planetary transits before: Searching several data bases yours truly found a report about Mercury being seen against a solar prominence just outside the 1970 transit as is mentioned briefly in this paper on page 4. But no reports of successful or unsuccessful attempts to image Venus or Mercury in superior conjunction "anti-transits" at the solar limb with a coronagraph could be found.

In other news we have a nice video of a stellar occultation by (618) Elfriede, the young Moon on June 4 (again) and Jupiter on June 2. • A detailled - but controversial - paper on Holmes' outburst has been published in the ICQ while there are new thoughts on the origin of the Kappa Cygnid meteors and the famous fresh Carancas crater has been visited again, 8 months after the bizarre mini-impact in Peru. • A 5 gigapixel IR image mosaic of the Milky Way has been published in several ways: through a viewer and as a mega-poster at at conference. • And here is the ISS on June 3 (also reported internationally).

Tuesday, June 3, 2008

STOP PRESS: Spitzer unravels Milky Way structure - only two arms!

Here it is: This is what our Milky Way looks like when seen from above! This artist's view, based on infrared observations with the Spitzer Space Telescope, is being presented at a press conference at the AAS Meeting in St. Louis this hour, and the embargo is now lifted. The images are "revealing that [the Milky Way] has just two major arms of stars instead of the four it was previously thought to possess," says an accompanying press release: "Since the 1950s, astronomers have produced maps of the Milky Way. Those early models were based on radio observations of gas in the galaxy, and suggested a spiral structure with four major star-forming arms, called Norma, Scutum-Centaurus, Sagittarius and Perseus. In addition to arms, there are bands of gas and dust in the central part of the galaxy. Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms. [...]

Large infrared sky surveys in the 1990s led to some major revisions of these models, including the discovery of a large bar of stars in the middle of the Milky Way. Infrared light can penetrate through dust, so telescopes designed to pick up infrared light get better views of our dusty and crowded galactic center. In 2005, [Robert] Benjamin [of the University of Wisconsin] and his colleagues used Spitzer's infrared detectors to obtain detailed information about our galaxy's bar, and found that it extends farther out from the center of the galaxy than previously thought. The team of scientists now has new infrared imagery from Spitzer of an expansive swath of the Milky Way, stretching 130 degrees across the sky and one degree above and below the galaxy's mid-plane. This extensive mosaic combines 800,000 snapshots and includes over 110 million stars.

Benjamin developed software that counts the stars, measuring stellar densities. When he and his teammates counted stars in the direction of the Scutum-Centaurus Arm, they noticed an increase in their numbers, as would be expected for a spiral arm. But, when they looked in the direction where they expected to see the Sagittarius and Norma arms, there was no jump in the number of stars. The fourth arm, Perseus, wraps around the outer portion of our galaxy and cannot be seen in the new Spitzer images. The findings make the case that the Milky Way has two major spiral arms, a common structure for galaxies with bars. These major arms, the Scutum-Centaurus and Perseus arms, have the greatest densities of both young, bright stars and older, so-called red-giant stars. The two minor arms, Sagittarius and Norma, are filled with gas and pockets of young stars. Benjamin said the two major arms seem to connect up nicely with the near and far ends of the galaxy's central bar."

"Real demon star" Epsilon Aurigae: next eclipse in 2009 - and "doom" mid-century?

They happen only every 27 years, and the next one is due in 2009-11: eclipses in the strange Epsilon Aurigae system that is easily visible to the naked eye - and at the same time a topic of intense research and also of another press conference during the AAS Meeting in St. Louis in the past hour. "Observations over the coming three years, when the mysterious star undergoes a once-per-generation eclipse event, may hold the secret to the extreme changes detected during the past few decades," the summary goes, wich includes the prediction - not overly stressed in the PC - that "the bright northern star called epsilon Aurigae is headed for a 'doomsday event' within a few decades." The spectrum of epsilon Aurigae looks like a normal F supergiant star with12 to 15 times the mass of the Sun. The mass ratio in the binary is close to one, implying that the companion is about 12 to 14 solar masses as well. Epsilon Aurigae exhibits eclipses like the "demon star" Algol every 27 years, which last for nearly 2 years. The next one starts in August 2009, and should run through May 2011.

The 12 to 14 solar mass second "star" is largely invisible, however! The secondary is probably a huge dark disk, not a sphere, requiring a massive central object(s) to stabilize it. Normal eclipsing binary star analysis suggests that the secondary is about 10 AU across but does not emit anywhere near the amount of light expected from a star of its size (nor is it a collapsed object: no X-rays). Another observation: Eps Aur shows low amplitude quasi-periodic light variations, similar to Cepheid variable stars. Currently its light variations are on a 67 day cycle, but - key point - were near 96 days during the last two decades: Something is accelerating in this system! At this rate, variations will become very rapid within six decades, perhaps cataclysmically so. Observations during the last eclipse furthermore suggest that the F supergiant star may be shrinking by about 1/2% per year. The duration of total eclipse (during which the F star is partially covered by the disk shaped companion) has increased by about 25% between the 1956 and 1983 eclipses. Despite this, the overall length of the total plus partial phases of eclipse - especially the time where the F star moves out from the cover of its partner - has gotten shorter!

If these trends continue, the F star will come out of eclipse (from totality) in only 1 or 2 weeks during 2011, but will still take 140 days or so to move from the beginning of the eclipse to totality next year, autumn. A 10% change in luminosity can result from a 5% change in radius or a 2.5% change in temperature. At an estimated distance of 625 pc, and assuming the F supergiant star has a typical diameter, the implied angular diameter is 3 milli-arcseconds (mas). Modern optical interferometers are capable of measuring down to fractions of 1 mas, close to that 5% change (0.15 mas) anticipated, and these measurements are underway: They could confirm that the F star's rapid evolution is causing the accelerating light changes. It should be bifurcated by the eclipse-causing disk, if indeed it is a disk, and state-of-the-art interferometers like CHARA on Mt.Wilson and MROI at Socorro should be able to monitor that. But at the same time when this high-end astronomy will be tried, people - 2009 being the International Year of Astronomy - all over the world will also be asked to monitor the beginning eclipse in a world-wide effort of "citizen science".

In other news another Nova Ophiuchi has been discovered, rather faint. • Daring astrophotographers have caught Venus 2° from the Sun as a disk, even with hints of NIR detail on it. • Images of Jupiter with and without the red spot trio on June 3 and June 1 from Europe and April 30 from Namibia. • Comet Boattini is now at 4.9 mag. and travels amongst star clusters for Southern observers. • Today's New Moon is the closest of the year. • Nice prominences on June 2 - and (better late than never) pictures of the annular eclipse 2006 in Suriname, total eclipse 2005 in the Pacific and many earlier eclipses by K. Delcourte (accompanied by lots of travel impressions). • EPOXI imaged the Earth-Moon system on May 29 as an exoplanet detection analog experiment. • How the Discovery-ISS docking looked like yesterday from New Zealand, and the ISS passing Saturn in a little movie. • And finally a strange exhibition where (spy) satellite watching meets art ...

Monday, June 2, 2008

STOP PRESS: Smallest planet of smallest star (or sub-star) found

A press conference is still underway in St. Louis at the 212th AAS Meeting in which D. Bennett has just announced the discovery of a planet of roughly 3 Earth masses orbiting a star or brown dwarf of 6±3 percent of a solar mass; with a high probability the mass is < 8%, so it's probably a brown dwarf. The discovery was made with a new wide-field telescope by the MOA collaboration in New Zealand which images the whole galactic bulge every hour, looking for microlensing events and signatures of planets in these. The detailled paper is rather cautious, though: "the observational coverage of the planetary deviation is sparse and incomplete, and the radius of the source was estimated without the benefit of a source star color measurement. As a result, the 2-sigma limits on the mass ratio and the finite source measurements are weak. Nevertheless, the microlensing parallax signal clearly favors a sub-stellar mass planetary host, and the measurement of finite source effects in the light curve supports this conclusion." This would be the 7th exoplanet detection via microlensing, though the mass of the planet is ill-defined at 3.3 (+4.9/-1.6) Earth masses and does not necessarily set a new record.

Sunday, June 1, 2008

Venus anti-transit of the Sun invisible(?) highlight of June

We are exactly half-way between the two transits of Venus of 2004 and 2012 - which means that in June 2008 Venus will pass behind the Sun during its superior conjunction. Astrophotographers have wondered for months whether it might be possible - with highly specialized equipment (don't try it with any regular optical system!!!Such experiments are really dangerous) - to image the tiny but very bright and fully illuminated disk of the planet approaching the solar limb and perhaps even catch it while disappearing behind the chromosphere. One system that may be able to do it is the Unigraph, a new refractor design with very little internal scattering which permits prominence photography in extreme resolution - and in white(!) light. (I once saw these images at a conference but just can't find any on the web.) Still unanswered is the question whether Venus would show up in such an image, together with the chromosphere or even a conveniently placed prominence ... The highlights of June 2008:
  • June 8, about 6:15 UTC: Venus disappears behind the solar limb as calculated with Horizons for a geocentric observer - should be nearly the same everyone on the planet.

  • June 8, evening UTC: The Moon (4 days old), Regulus and Saturn "line up", with Mars nearby.

  • June 10, around 1:00 UTC: Venus emerges again behind the Sun (because Venus is much farther from the Earth, such an 'antitransit' takes two days, not a few hours like a transit).

  • June 20: Dwarf planet Pluto in opposition to the Sun, at 13.9 mag.

  • June 30: One hundred years ago the Tunguska event hit Siberia - spare a thought for all those trees felled by an astronomically speaking insignificant cosmic airburst.
In other news according to CBET #1388 there is a 14.4 mag. supernova (SN 2008cq) in a nameless galaxy at -30° declination right now which on May 6 even had 13.4 mag. but was missed. • The brightness of Nova Oph 2008 is fluctuating wildly. • Comet Boattini has a needle-sharp ion tail in a May 30 picture (tailless pics from May 31, 30 and 28). • How STEREO saw the latest kamikaze comet, how a cosmological supernova hunt bagged many Kuiperoids as a by-product and how Cassini saw the Saturn storm on April 23. • And finally after yesterday's launch of Discovery the orbiter and its tank were widely seen over Europe as a video or trails show. Plus hi-res images of May 21 and 12.