Picture of the Week

7 July 2008

APEX at Chajnantor*

While ALMA is currently under construction, astronomers are already doing millimetre and submillimetre astronomy at Chajnantor, with the Atacama Pathfinder Experiment (APEX). This is a new-technology 12-m telescope, based on an ALMA prototype antenna, and operating at the ALMA site. It has modified optics and an improved antenna surface accuracy, and is designed to take advantage of the excellent sky transparency working with wavelengths in the 0.2 to 1.4 mm range.

This image is available as a mounted image in the ESOshop

1 July 2008


The image shows X-shooter, the first of the second generation VLT instruments, under test in the integration lab at ESO, Garching. The instrument has been built by a Consortium including ESO and institutes from Denmark, Italy, The Netherlands and France, and will start operation at the telescope in 2009.

X-shooter is a single target, wide band, intermediate spectral resolution spectrograph, designed to get the full spectrum of the faintest cosmic sources from the atmospheric cutoff in the near-ultraviolet to the infrared K-band in a single exposure.

In this image the instrument is shown as mounted on a telescope Cassegrain focus simulator, pointing at a large zenith distance. At the centre is the cryostat with the near-infrared arm of the spectrograph and at the left is the lower side of the visual spectrograph with its CCD detector. The two large boxes on the sides host the control electronics of the instrument.

23 June 2008

Echinopsis Atacamensis and the Milky Way

The winding road connecting the ALMA Operation Support Facility at 3,000m altitude to the Array Operation Site (5,000m high) passes an area between 3500m and 3800m dominated by large cacti (Echinopsis Atacamensis). These cacti grow on average 1cm per year, and reach heights of up to 9m.

Stephane Guisard recently captured the beautiful sky above this unique location in the Chilean Atacama Desert. The Milky Way is seen in all its glory, as well as, in the lower right, the Large Magellanic Cloud. 

10 June 2008

Paranal summit ready for the VLT - 1994

This aerial view of Cerro Paranal, the site of ESO's Very Large Telescope, was obtained in 1994. It shows the construction of the concrete base for the four telescope enclosures. To the left and a little lower than the rest of the platform is the excavation for the control building.

The platform altitude is about 2640 metres above sea level and it measures about 150 metres across. The width of the access road is no less than 12 metres, i.e. nearly equal to that of a three-lane highway; this is necessary to ensure the safe transport of all telescope parts, especially the four 8.2-metre fragile mirrors, to the top. 

The summit of Paranal has been blasted away so to create the flat platform that supports the 4 Unit Telescopes, as well as the network of tunnels that transport the light from the telescopes to the interferometric laboratory. On this 1994 aerial view, the summit is ready: the platform is flattened, and the volume of the foundations is excavated. Note the white marks indicating the location of the interferometric tunnels.

26 May 2008

Trailing stars above Paranal

The rotating sky above ESO's Very Large Telescope at Paranal. This long exposure shows the stars rotating around the southern (left) and northern (right) celestial poles, the celestial equator being in the middle of the photo — where the stars seem to move in a straight line. The motion of the VLT's enclosures are also visible.

13 May 2008

Transporters at Chajnantor

Heavyweights at 4,000 metre altitude: this photo shows the two ALMA antenna transporters during the final phase of the acceptance testing in April on the road between the ALMA OSF at 2,900 metre altitude and the AOS at 5,000 metres. The first transporter ("Otto") is travelling unloaded, while the second one ("Lore") is carrying the 115-tonne antenna dummy.

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.

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

11 March 2008

The Orion Nebula Spied by Hawk-I

The central region of the Orion Nebula (M42, NGC 1976) as seen in the near-infrared by the High Acuity Wide field K-band Imager (HAWK-I) instrument at ESO's Very Large Telescope at Paranal.

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 (Artist's impression)

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. 

The determination of the distance to RS Pup, following the method of the American astronomer Robert Havlen, is based on the measurement of the phase difference between the variation of the star and the variation of isolated nebular features. Because the luminosity of the star changes in a very distinctive pattern, the presence of the nebula allows the astronomers to see light echoes and use them to measure the distance of the star. The light that travelled from the star to a dust grain and then to the telescope arrives a bit later than the light that comes directly from the star to the telescope. As a consequence, if we measure the brightness of a particular, isolated dust blob in the nebula, we will obtain a brightness curve that has the same shape as the variation of the Cepheid, but shifted in time. This delay is called a 'light echo', by analogy with the more traditional echo, the reflection of sound by, for example, the bottom of a well.

By monitoring the evolution of the brightness of the blobs in the nebula, the astronomers can derive their distance from the star: it is simply the measured delay in time, multiplied by the velocity of light (300,000 km/s). Knowing this distance and the apparent separation on the sky between the star and the blob, one can compute the distance of RS Pup.

This artist's illustration is not to scale.

29 January 2008

The Growing-up of a Star: the disc around MWC 147

Artist's impression of the disc of matter surrounding the young stellar object MWC 147 as inferred from observations made with ESO's Very Large Telescope Interferometer. Thanks to these observations, astronomers have probed the inner parts of the disc of material surrounding the MWC 147, witnessing how it gains its mass before becoming an adult.

A slice has been cut to show the inner structure better. The disc extends out to 100 times the distance between the Earth and the Sun (100 Astronomical Units — 100 AU). It is inclined by about 50 degrees as seen from Earth. The dust in the outer disc emits mainly at mid-infrared wavelengths, while close to the star there is also strong near-infrared emission from very hot gas. This gas is transported towards the forming star, increasing its mass at a rate of 7 millionths of the mass of the Sun — or about 2 times the mass of the Earth — per year.

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'). This triplet of galaxies makes up part of the Hickson Compact Group HCG 90. 

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 size of the image is about 5.3 arcminutes. The image is based on data obtained with the VLT FORS1 instrument on ESO's Very Large Telescope through three different filters, B, V, and R. 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.

NGC 87 (upper right) is an irregular galaxy similar to the satellites of our Milky Way, the Magellanic Clouds. NGC 88 (centre) is a spiral galaxy with an external diffuse envelope, most probably composed of gas. NGC 89 (lower middle) is another spiral galaxy with two large spiral arms. The largest member of the system, NGC 92 (left), is a spiral Sa galaxy with an unusual appearance. One of its arms, about 100,000 light-years long, has been distorted by interactions and contains a large quantity of dust.

7 January 2008

The White Penitents*

These bizarre snow and ice formations, called "penitentes", form in high-altitude regions such as 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 image was taken in December 2005.

This image is available as a mounted image in the ESOshop

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' - although it also bears resemblance with a cosmic Tinker Bell - is composed of two massive spiral galaxies and a third irregular galaxy.

In this image, a 30-min VLT/NACO K-band exposure has been combined with archive HST/ACS B and I-band images to produce a three-colour image of the 'Bird' interacting galaxy system. The NACO image has allowed astronomers to not only see the two previously known galaxies, but to identify a third, clearly separate component, an irregular, yet fairly massive galaxy that seems to form stars at a frantic rate.

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.

The ALMA antenna transporters are each 20 metre long, 10 metre wide and 6 metre high, and weigh 130 tonnes. They will be able to transport a 115-tonne antenna and set it down on a concrete pad within millimetres of a prescribed position. Image taken in December 2007.

10 December 2007

ALMA 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.

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.

The Minister was accompanied by a delegation comprising Claude Gonfroy and Jean-Luc Horward, members of her Cabinet, Jean-Pierre Swings, former member of the ESO Council, Claude Jamar from the Centre Spatial de Liėge, and Bill Collins, from the AMOS company which built the four Auxiliary Telescopes. Ten French-speaking Belgian journalists, including two TV crews, also joined the Minister for a day at Paranal.

Felix Mirabel, ESO's Representative in Chile, Olivier Hainaut, Head of Science Operations at Paranal, and Ueli Weilenmann, were the hosts of the Minister. The Minister visited the telescopes and facilities on site and showed a clear interest for these most advanced pieces of technology. Her visit coincided with her birthday and, at the dinner, she was offered a cake and flowers, as well as gifts from members of her delegation.

23 November 2007

Sunset at Paranal

Twice per year, the sunset passes exactly behind Paranal for somebody located on the summit of Armazones mountain, 20 kilometres away. The dates and time when this happens were calculated using coordinates of both sites found on Google Earth and taking into account atmospheric effects.

The picture clearly shows 3 of the 4 big 8.2-m Unit Telescope (UT) domes (the 4th one is behind the others) of ESO's Very Large Telescope, the VST enclosure on their right and the high meteorological post with the DIMM tower on the extreme right. On the left of the picture, the partially opened domes of the smaller 1.8-m Auxiliary Telescopes (AT) are also visible.

The image was taken with a Takahashi FS128 refractor telescope, a Canon20Da camera and special Solar filters, by Stéphane Guisard (ESO).

Please remember that looking at the Sun through an optical device (Camera, Telescope, Binoculars etc.) is VERY dangerous, and could cause immediate blindness!

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