Astronomy Briefs
Saturn's Family of Moons counts 60 (2007/08/03)
On May 30, 2007, the Cassini orbiter cruising the Saturnian system has discovered a small moon which could be confirmed on images taken back in 2004. Tentatively designated S/2007 S4, the moon is approximately 2 kilometers across. It's orbit with a period of 1.04 days lies between those of Methone (XXXII) and Pallene (XXXIII), 3400 km away from Methone, 197,700 kilometers from Saturn's core.

This discovery screws Saturn's moon count up to 60, while Jupiter is still with 63 known moons, obviously because Jupiter currently lacks orbiters. 		   
Click for a larger image
Credit: NASA/JPL/Space Science Institute
Released: July 19, 2007
Summer Solstice 2007 (2007/06/21)
This year's summer solstice occurred on June 21th 18:06 UT. At summer solstice the sun is farthest north bringing the longest daytime hours to the northern hemisphere thus marking the beginning of summer and the midnight sun above 66.6° northern latitudes.

The name "solstice" is Latin for sol (sun) and sistere (to stand still), because the Sun stands still in declination for a very short moment when the sun is directly over the Tropic of Cancer.

Many believe that the summer warmth is because the sun is closer to Earth than in winter. Actually it's vice-versa. As the sun apparently moves north, its rays pass through less atmosphere for which reason the impact is stronger. For instance, here on Okinawa, the maximum noon altitude of the sun at summer solstice is over 87°, which is almost overhead in the zenith.

The image shows the position of the sun at summer solstice 2007 in the constellation of Gemini right next to M35. 		   
Click for a larger image
Created with StellaNavigator 8.0
Eris and its Moon Dysnomia (2007/06/16)
Eris, originally nicknamed Xena and cataloged as 2003 UB313, has been detected in 2005 followed by the discovery of its Moon designated Dysnomia. Eris is located far out in the Kuiper Belt (a region in the Solar System beyond the orbit of Neptune) in a current distance of 96.82AUs from the Sun. Its highly eccentric orbit (0.441) takes the object to a maximum distance of 97.6 AUs in aphelion while the closest approach at perihelion occurs at 37.85AUs during a period of 556.98 years! Eris' orbit inclination to the ecliptic measures 44.178°. If placed in 1AU, Eris would shine bright at -1.2 magnitudes.

On August 30th., 2006, astronomers joined the forces of the Hubble Space Telescope and the W.M. Keck Observatory to precisely measure the mass of Eris by observing the orbital motion of its moon. Based upon the known orbital radius of 37,350 ±140 kilometers in a 15.774 days period, Eris has 1.27 times the mass of Pluto while its density amounts to 2.3 grams per cubic centimeter giving reason to assume that its composition is not overall icy but also quite rocky. Mass and density values for Eris are similar to other large Kuiper Belt objects and Neptune's moon Triton.

The results ranks Eris as both the largest Kuiper Belt object (KBO) and the most massive dwarf planet known so far.

Further reading... 		   
Eris and the superimposed orbit of its moon Dysnomia.
Credit: NASA, ESA, and M. Brown (California Institute of Technology)


Credit: NASA
Actual Image of Altair (2007/06/15)
For the first time astronomers succeeded in creating a real image of a sun-like star, Altair. Thanks to technical enhancements in fiber-communications and data analyses of the CHARA interferometer on Mt Wilson, California, a two-dimensional image of the surface of a star could be generated.

The light of four widely separated CHARA telescopes was so combined as to obtain a 265 x 195 meters large virtual telescope with sub-milliarcsecond resolution. The shape of the star's photosphere was computed upon knowledge of its fast rotation speed by which Altair assumed the shape of an ellipsoide clearly showing the effect of "gravitational darkening". As a result of the flattening the effective temperature around the equator is 60 to 70% lower than on the poles because the equator is farther away from the star's nuclear core.

The same phenomona has been found earlier with interferometry on other rapid spinners, such as Vega, however, this time, CHARA's image reconstruction enabled the creation of a photosphere temperature map.

Altair, one of the three Summer Triangle stars, is the brightest star in the constellation Aquila, the Eagle. Shining at 0.76 magnitudes, the 16.8 light-years remote star is hotter and younger than the Sun, nearly twice its size and rotates approximately 60 times faster.

Further reading... 		   
The power of interferometry: A stellar picture of Altair. Soon, it might be possible to isolate exoplanets from their home stars.
Credit: John Monnier (University of Michigan)
Ishigaki Dome Repaired (2007/05/13)
The Ishigaki observatory dome has been repaired after a typhoon damage in September last year. The reopening ceremony took place on April 1st. (sorry for the late notice). As a result of the repair it is believed that the dome will now withstand a 100m-class typhoon.
The First Map of an Exoplanet (2007/05/12)
Out there in the constellation Vulpecula is a faint 8th magnitude star with 0.8 Sun masses in a distance of some 63 light-years. The star, designated HD 189733, is known to be orbited by one planet slightly more massive than Jupiter. For the first time ever, astronomers using the Spitzer infrared space telescope succeeded in taking a surface temperature map of an extra-solar planet.

With an average distance of 0.0312AU in a mere 2.2 days orbit period, the surface of the planet is heated up to 930 °C (1,700°F). Owing to the extreme proximity to its Sun, 12 times closer than Mercury is to our Sun, the planet is tidally locked with one hemisphere always lit by star light, while the other lies in eternal darkeness.

Nevertheless, the Spitzer data (bighter color = higher temperature) depicts a temperature variation of 650 to 930°C (1,200 to 1,700°F), which is a relatively narrow window for a tidally locked planet. Interestingly, the sun-facing point of the planet (the center of the map) is offset by 30° to the right. This gives reason to conclude that ferocious winds 9,700 kmh (6,000 mph) fast are forcing the 'hot spot' to an easterly location. The same winds carry the heat from the sunlit side over to the night side, explaining the 'mild' temperature difference.

Further reading:
The Spitzer Space Telescope Newsroom. 		   
The first-ever map of an alien world
Credit: NASA/JPL-Caltech/H. Knutson (Harvard-Smithsonian CfA)


A DSS image of HD189733
Asteroid Vesta in Sight (2007/05/05)
It was 18 years ago when Vesta was last at its brightest. This month, the asteroid is back within reach of the naked eye and will be a little brighter than last time. Because of it's high albedo (surface brightness), Vesta is the only asteroid located in the asteroid belt between Mars and Jupiter that can be observed with the naked eye as it approaches Earth on its orbit.

This month, Vesta, shining 5.1 magnitudes bright late this month, can be found above Jupiter in Ophiuchus and Antares in Scorpius. Vesta is an ellipsoid about 530km (330 miles) wide and the second most massive asteroid, actually accounting for 9% of the mass of the asteroid belt. It spins around its axis in 5.34 days and orbits the sun in 3.63 years. The largest body in the belt, Ceres, has been classified a dwarf planet in 2006.

A pair of binoculars will help find Vesta easily, but challenge with your unaided eye as well in absence of the moon during May 7 to 20. Vesta will be less than 1.2 AUs close.

What you won't be able to see, Vesta, 330 miles in diameter is marked by a giant crater 285 miles across. If Earth had a crater of proportional size, it would fill the Pacific Ocean basin. 		   
A Hubble snapshot of Vesta released in 1997.
Credit: Ben Zellner (Georgia Southern University), Peter Thomas (Cornell University) and NASA

Finder chart for Vesta (S & T).
The Smallest Planet To Date (2007/04/28)
Using its most precise spectrograph, HARPS, installed in La Sillia, Chile an ESO team of European astronomers announced discovery of an exoplanet which to date resembles Earth closest. It is the third planet discovered around the red dwarf star Gliese 581, a faint 20.4 light-years remote 10.6 magnitude star in the constellation of Libra, no larger than 0.38 sun radii, weighing a mere 0.31 sun masses.

The planet, designated Gliese 581c, orbits the star in a distance of 0.073AU (14 times closer than our Earth is to its sun) with a period of 12.932 days. In spite of its close proximity, the planet is well situated within the habitable zone of the star which is smaller, colder and far less intrinsically luminous than our sun.

The planet's surface temperature is estimated to span over 0 and 40°C (30 to 100°F), a window within which water exists in liquid form. Gliese 581c is 50% larger than Earth in diameter and could be rocky as well as be covered with an ocean. In its close orbit 10 times as eccentric as Earth's, Gliese 581c may be subjected to strong seasonal variations and tidal forces, while the planet may be tidally locked, with one hemisphere always lit and the other always dark.

The 3 known planets are:
PlanetMass (E)PeriodDistance
Gliese 581b15.65.37d0.041AU
Gliese 581c5.0612.93d0.073AU
Gliese 581d8.383.6d0.243AU
    

Gliese 581c with another, but Neptune-like planet (artist's impression).
Credit: ESO (PR Photo 22a/07)


The star Gliese 581 centered in a 6 arcminute wide section of the sky.
Credit: Digitized Sky Survey

Another system known to have three low mass planets is HD 69830 also discovered by HARPS which is capable of detecting velocity variations between 2 and 3 meters per second, corresponding to about 9 km/h, in other words, near walking speed! Gliese 581c is a milestone. We may look forward to further discoveries of Earth-like planets and eventually find a sister world, hopefully not too far away. 20 light-years is astronomical neighborhood, however, mankind cannot (yet) travel over such huge distances (probably fortunate for possibly existing nature).

Partial Eclipse Made Total (2007/03/31)
Launched in September 2006, Hinode (Solar-B) is a spacecraft jointly developed by JAXA (JPN), NASA (US) and PPARC (UK) for the purpose of investigating the interaction between the Sun's magnetic fied and corona. This is the official mission description, but Hinode (Japanese for sunrise) can do much more.

It lies in the nature of unmanned spacecrafts to be remoted controlled from Earth. Not only can onboard instruments be aligned to observation targets but also the orbital position of the craft can be changed within tolerance limits. Hinode is in a polar orbit from which it always has the Sun in its view. A relatively slight excursion into the Moon's shadow enables Hinode to observe solar eclipses in total while on Earth the eclipse is partial.

March 19 2007, saw only a partial solar eclipse in most parts of Asia. Hinode's X-ray telescope, far better positioned above ground, spotted the Moon as it transited the Sun towards a total eclipse. As a matter of fact, Hinode's vantage 600 kilometers above in space allows observation of eclipses which are not on our eclipse calendar on Earth.

September 11, 2007 schedules the next partial solar eclipse visible only from Antarctica and parts of South America. Another opportunity for Hinode!

Tracking the path of Hinode. 		   


Image credit: SAO, NOAJ, JAXA, and NASA-MSFC
Hubble's ACS Camera Shut Down (2007/02/04)
On January 29, a power failure forced the Hubble operators to shut down the Advanced Camera for Surveys (ACS), which was installed on the Hubble Space Telescope in March 2002. The ACS is the finest camera in space which has delivered numerous ultra-high resolution images. Among the cameras on Hubble, the ACS has the widest field, provides the sharpest images and is the most sensitive element onboard. Moreover, it sees in wavelengths ranging from far ultraviolet to infrared. A repair is unlikely before the next scheduled mission in September 2008. Until then, the job of the ACS will be transferred to the Wide Field Planetary Camera (WFPC2). One of the purposes of the coming service mission is for installation of a new camera, the WFPC3, which is said to outperform the ACS. Nevertheless, the loss of the ACS is sad and painful for the NASA and ESA engineers who invested a tremendous amount of work for the camera.    
The ACS before installation in 2002.
Credit: NASA/STScI
C/2006 P1 McNaught Brightens Up! (2007/01/11)
That bright thing shining in close vicinity of the sun is comet McNaught (C/2006 P1) which has meanwhile reached negative visual magnitude. The comet can be seen extremely low in the western sky immediately after sunset from the 10th to the 13th. This is a rare chance to witness a comet that rivals Hale-Bopp in brightness. A comet appearing bright in its perhelion (closest approach to the sun) is not unusual at all. However, its minute elongation from the sun renders observation either difficult or next to impossible. As McNaught emerges from perihelion it won't be observable from the northern hemisphere any longer. In the southern hemisphere, it will rise up high in the sky and eventually become a Great Comet. Don't miss this....
Here is more:
Space Weather
Cortina Stelle (in Italian).

The image was taken in the early morning glow of January 8 at 06:21 JST is a composite of eight 1/8th seconds exposures captured in Saitama, Japan with a 10 inch F5 reflector and a Fujifilm FinePix S2 Pro camera. 		   
Image credit: Ken-ichi Kadota, AstroArts Inc., used with permission.
Click to enlarge.
Hubble Imaged NGC 602 in N90 (2007/01/11)
NGC 602 is a young star cluster within a star-forming region cataloged as N90 in the Small Magellanic Cloud (SMC), approximately 196,000 light-years out there in the constellation of Tucana at 73.5° southern celestial declination. The abundant presence of hot, bright blue young stars allow astronomers to examine star forming processes in a region being different from that in larger galaxies, such as our Milky Way. The image shows a number of galaxies in the background owing to the fact that N90 is located at the less dense edge of the SMC. Note the razor-sharp gas filaments and dust pillars at the upper left and lower right in the image pointing at the blue star cluster -- a strong evidence for ongoing star formation.

Images captured by the Hubble Space Telescope and produced by its science teams, continue being irreplacable for cosmic discoveries. The first machine that has qualified itself already long ago for registration as World Heritage. 		   
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) - ESA/Hubble Collaboration
Further reading...
Ishigaki Observatory Damaged (2007/01/10)
The last typhoon in 2006 has worn heavily on the dome of the Ishigaki Observatory. Repair works have begun on January 6, however, the observatory will be not be reopened until sometime in April. A damage that requires 3-4 months repair is everything else but trivial. Ishigaki is a preferrable observation site, but, as all Okinawa Islands, torn by typhoons and other severe weather conditions. Information and photo kindly provided by Yasuo Touji, President of the Yaeyama Astronomy Club, Ishigaki City. Yasuo is an avid astrovideo specialist always waiting for a clear sky to move up to the Banna hills on Ishigaki where he captures the Milky Way and meteors with his CCD camera and wide angle lenses. The Banna hills are undisturbed by skyglow casted from Ishigaki City.    
Credit: Yasuo Touji, Yaeyama Astronomy Club
Debris Disk around AU Microscopii (2007/01/08)
The Hubble Space Telescope (HST) has confirmed existence of seed for planet formation in the disk around the star AU Microscopii which lies 32 light-years out in the southern constellation of Microscopium. About 3.7 billion and 4.6 billion miles from the star, the particles from which solid bodies appear to form are larger than interstellar dust grains - comparable with snowflakes. AU Mic, also cataloged as HIP 102409 and SAO 212402, is a class M1 red flare star 8.61 magnitudes faint. Since its distance is about 10 parsecs (32.6 light-years) the absolute magnitude is approximately the same as its visual.    
Credit: NASA, ESA, J. R. Graham and P. Kalas (University of California, Berkeley), and B. Matthews (Hertzberg Institute of Astrophysics)
Further reading...
HINODE (2007/01/07)
Hinode (Solar-B) was launched on September 22 (UT) from the Uchinoura Space Center in Kyushu, Japan with the mission to observe the Sun's corona and magnetic field. Among other instrumentation equipped with three solar telescopes, Hinode captured the 8 November 2006 transit of Mercury. Positioned in a sun-synchronous orbit around the Earth, the satellite does not suffer from atmospheric turbulences while it passes over the same part of Earth at approximately the same local time each day. Hinode will be well positioned for imaging solar eclipses between May and July 2007, however, strenuous thermal changes in vacuum space may affect the sensitive instruments, for which reason Hinode might need to be shut down.    
Image credit: NAOJ, JAXA, NASA. (composite of two images)
Further reading...
C/2006 P1 McNaught (2007/01/06)
Detected on August 7, 2006, comet McNaught sticks closely to the sun and is therefore a challenge to observe. (be wary of observing comets near the sun!). These days, about 0.3AU from Earth, the comet shines at 2 magnitudes or brighter. It will reach perihelion on Jan 12th., assuming a distance to the sun of 0.17AU, which is within the orbit of Mercury, very unfortunately with a mere elongation of 6.3° from the sun. As emerging later this month, the comet will probably brighten up to negative magnitudes. With a measured orbit eccentricity of 1.000014, McNaught is a non-periodic comet which will not return after this visit to our solar system.    
Comet C/2006 P1 McNaught on 5.1.2007 5h50m UT. Courtesy Michael Jager and Gerald Rhemann. Used with permission.