Photo of the Week - Archive
4 May 2008: Uranus and satellites
An image of the planet Uranus (located 20 Astronomical units from Earth) obtained at the Very Large Telescope Observatory using the Adaptive Optics system NAOS and the near-infrared imager CONICA to capture high-contrast images of the giant planet and its system of satellites and rings during its 2008 equinox. Every 42 years, the ring (and satellites) plane of Uranus crosses the Sun, providing us with a unique opportunity to observe the rings while they present their edge to us. Ring plane crossing also allow us to observe the rings form their dark side (i.e. while the Sun is illuminating them from the opposite side), so one can search for faint satellites, faint rings, or faint ring structures, which could not be seen otherwise. Ring Plane Crossings are also an excellent opportunity to observe mutual events between satellites such as eclipse or occultation phenomena.
The image above corresponds to a one minute exposure (maximum permitted time to prevent trailing of the moving satellites) obtained at 2.2 micron with a K band filter. The bandpass of this filter matches the absorption bands of methane, which is present in the atmosphere of Uranus, and has the effect of making the bright planet (almost) completely disappear from our images. Thanks to this observing trick, we can observe the faint rings and small satellites of Uranus, which would become invisible otherwise, lost in the glare of the planet. The bright spots on each side of Uranus are Miranda (~470km diam.) and Ariel (~1100km diam.), respectively to the right and left of the image. Two much smaller satellites can be seen just above the ring plane, to the left of the planet, the closer to Uranus being Puck (~150km diam.) and the other Portia (~100km), near the ring tip in this image.
A movie of these observations is also
available. The movie shows an animation of this system of satellites over a two hour period. You can easily see the impact of fluctuating seeing conditions on the image quality. Under good seeing, both small satellites Puck and Portia becomes clearly visible when they move along their orbital path, while the images start to blur when the seeing conditions degrade.
Credit: C. Dumas, B. Sicardy, and J.-E. Arlot
This is one of the
ESO Chile Image of the Month.
27 April 2008: Distant Galaxy Cluster
A composite infrared image of the X-ray luminous galaxy cluster XMMU J2235.3-2557 at redshift 1.4, one of the most distant galaxy clusters known.
The composite is made of 4 HAWK-I pointings in both J and Ks and covers 13.5 arc minutes on a side. The cluster is right in the middle of the frame and is difficult to see, given the large field of view, so a blow-up centred on the cluster is shown in the inset. As can be seen by eye, the core of the cluster is dominated by red galaxies with very similar colours. The stars in these galaxies are already very old. On average they formed when the Universe was only one billion years old. As one moves away from the center of the cluster, cluster galaxies become slightly bluer, suggesting that galaxies in the outskirts are either younger or have recently experienced a small amount of star formation (commonly called "frosting"). As one moves even further out, the authors hope to find small groups of galaxies that will, one day, merge with the core.
In the standard flat, lambda-dominated cosmology, the universe is 4.6 billion years old at redshift 1.4 and 1.1 billion years old at redshift 5. The universe at redshift 0 (today) is 13.7 billion years old.
At a redshift of 1.4, 10 arc minutes on the sky corresponds to a linear distance of 5 Mpc (15,000,000,000,000,000,000 km).
Authors: Chris Lidman, Piero Rosati, Masyuki Tanaka and the HAWK-I science verification team.
This is one of the
ESO Chile Image of the Month.
18 April 2008: The ALMA OSF
A dramatic picture of the ALMA Operations Support Facility (OSF), located 2900m high in the Chilean Atacama Desert, close to the town of San Perdo de Atacama. Visible from left to right are the OSF Building, still in construction, the ALMA Antenna Transporter carrying a dummy antenna, and four antennas, that are being prepared. In the background, lenticular clouds are seen over the Lascar Volcano.
Credit: Jean-Michel Moresmau (ESO)
Weeks from 27 March to 18 April were dedicated to the
Catch a Star! competition and the
James Bond at Paranal web site.
20 March 2008: Recoating Yepun's mirror
The 8.2-m primary mirror of Yepun, Unit Telescope 4 of ESO's Very Large Telescope, after its recoating in early March. Credit: Gerhard Huedepohl.
11 March 2008: The Orion Nebula
The central region of the Orion Nebula (M42, NGC 1976) as seen in the near-infrared by the HAWK-I instrument on the VLT.
25 February 2008: ALMA Transporters Arrive in Chile
Arrival of the ALMA Antenna Transporters at the Operations Support Facility (OSF) in Chile as the convoy passed through the Valle de Luna.
11 February 2008: Light echoes whisper the distance to a star
Taking advantage of the presence of light echoes, a team of astronomers have used an ESO telescope to measure, at the 1% precision level, the distance of a Cepheid - a class of variable stars that constitutes one of the first steps in the cosmic distance ladder. Credit: ESO.
29 January 2008: The Growing-up of a Star
Using ESO's Very Large Telescope Interferometer, astronomers have probed the inner parts of the disc of material surrounding a young stellar object, witnessing how it gains its mass before becoming an adult. Credit: ESO.
21 January 2008: Cosmic Interactions
Colour-composite image of the triplet of galaxies, catalogued as NGC 7173 (top), 7174 (bottom right) and 7176 (bottom left), and located 106 million light-years away towards the constellation of Piscis Austrinus (the 'Southern Fish'). The image is based on data obtained with the FORS1 instrument on ESO's Very Large Telescope through three different filters, B, V, and R. NGC 7173 and 7176 are elliptical galaxies, while NGC 7174 is a spiral galaxy with quite disturbed dust lanes and a long, twisted tail. This seems to indicate that the two lower galaxies - whose combined shape bears some resemblance to that of a sleeping baby - are currently interacting. Astronomers have suggested that the three galaxies will finally merge. The data were extracted from the ESO Science Archive and fully processed by Henri Boffin (ESO).
14 January 2008: Robert's Quartet
Robert's Quartet is a family of four very different galaxies, located at a distance of about 160 million light-years, close to the centre of the southern constellation of the Phoenix. Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel in the 1830s. Credit: ESO.
7 January 2008: The White Penitents
Field of 'white penitents' at 5000m altitude on the Chajnantor plain, close to where the ALMA array will be located. These are ice blades produced by the competition between sublimation and melting of the snow. At Chajnantor at the summer solstice, the Sun is close to the zenith at noon, and penitents are vertical.
This is one of the images of the beautiful ESO Calendar 2008. Credit: ESO.
24 December 2007: The Tinker Bell Triplet
Using ESO's Very Large Telescope, an international team of astronomers has discovered a stunning rare case of a triple merger of galaxies. This system, which astronomers have dubbed 'The Bird' - albeit it also bears resemblance with a cosmic Tinker Bell - is composed of two massive spiral galaxies and a third irregular galaxy.
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17 December 2007: ALMA Transporters
On 3 and 4 December 2007, the two ALMA antenna transporters, Otto and Lore, were being loaded onto a barge on the Neckar at Heilbronn harbour (Germany) to start their long journey to Chile. From there, they will travel to Antwerpen (Belgium) and then put onto a ship towards the port of Mejillones, in the north of Chile, to finally reach the ALMA base, close to San Pedro de Atacama. Credit: ESO.
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10 December 2007: Antennas at Sunset
The first three Japanese ALMA antennas of the Atacama Compact Array (ACA) at the ALMA Operation Support Facility, located close to the town of San Pedro de Atacama in the Chilean Atacama Desert, at an altitude of 2900m. At the time of the picture, in November 2007, the antennas were undergoing final tests before being handed over to the ALMA Observatory. The 12-m antennas were built by MELCO for the National Astronomical Observatory of Japan, one of the partners in the ALMA partnership. Credit: H. Boffin/ESO/ALMA
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1 December 2007: Minister Marie-Dominique Simonet at Paranal
On 17 and 18 November 2007, the Regional Minister for Research of the Belgian French-speaking Community, Marie-Dominique Simonet, visited Paranal. This was part of a week-long visit to Brazil and Chile, in which the Minister promoted the 'Competitivity Poles' as well as Research and Education in this part of the world. Credit: ESO
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23 November 2007: Sunset over Paranal
Twice per year, the sunset passes exactly behind Paranal for somebody located on the summit of Armazones mountain, 20km away. Credit: Use of this image is only permitted with express permission from the author, Stephane Guisard. More...