Picture of the Week

4 November 2008

Gone with the Wind

M1-67 is the youngest wind-nebula around a Wolf-Rayet star, called WR124, in our Galaxy. These Wolf-Rayet stars start their lives with dozens of times the mass of our Sun, but loose most of it through a powerful wind, which is ultimately responsible for the formation of the nebula.

Ten years ago, Hubble Space Telescope observations revealed a wealth of small knots and substructures inside the nebula. The same team, led by Cédric Foellmi (ESO), has now used ESO's Very Large Telescope (VLT) to watch how these structures have evolved and what they can teach us about stellar winds, their chemistry, and how they mix with the surrounding interstellar medium, before the star will eventually blow everything away in a fiery supernova explosion.

The image is based on FORS1 data obtained by the Paranal Science team with the VLT through 2 wide (B and V) and 3 narrow-band filters.

30 September 2008

Milky Way above Paranal

A night of work for the Paranal Observatory, in the Chilean Atacama Desert. This picture, taken on 20 September, shows the incredible beauty of the night sky above the most advanced telescope in the world, ESO's Very Large Telescope. The Milky Way is clearly seen in this superb image. 

22 September 2008

Magnificent Spiral Galaxy NGC 7424

Composite colour-coded image of another magnificent spiral galaxy, NGC 7424, at a distance of 40 million light-years. It is based on images obtained with the multi-mode VIMOS instrument on the ESO Very Large Telescope (VLT) in three different wavelength bands. The image covers 6.5 x 7.2 square arcminutes on the sky. North is up and East is to the right.

Read more about this superb object in the ESO Press Release eso0436.

21 August 2008

The Globular Cluster NGC 3201

Colour-composite image of the globular cluster NGC 3201, obtained with the WFI instrument on the ESO/MPG 2.2-m telescope at La Silla. Globular clusters are large aggregates of stars, that can contain up to millions of stars. They are among the oldest objects observed in the Universe and were presumably formed at about the same time as the Milky Way Galaxy, in the early phase after the Big Bang. This particular globular cluster is located about 16 000 light-years away towards the Southern Vela constellation. The data were obtained as part of the ESO Imaging Survey (EIS), a public survey being carried out by ESO and member states, in preparation for the VLT First Light.

The original image and astronomical data can be retrieved from the EIS Pre-Flames Survey Data Release pages, where many other nice images are also available. 

14 August 2008

The centre of the Milky Way

The centre of our Milky Way galaxy is located in the southern constellation Sagittarius (The Archer) and is "only" 26,000 light-years away. On high-resolution images, it is possible to discern thousands of individual stars within the central, one light-year wide region.

Using the motions of these stars to probe the gravitational field, observations over the last decade have shown that a mass of about 3 million times that of the Sun is concentrated within a radius of only 10 light-days of the compact radio and X-ray source SgrA* (Sagittarius A) at the centre of the star cluster. This means that SgrA* is the most likely counterpart of the black hole believed to exist at the centre of our Galaxy.

This image was obtained in mid-2002 with the NACO instrument at the 8.2-m VLT Yepun telescope. It combines frames in three infrared wavebands between 1.6 and 3.5 µm. The compact objects are stars and their colours indicate their temperature (blue ="hot", red ="cool"). There is also diffuse infrared emission from interstellar dust between the stars. 

A newer image of that region has been published in 2008; see image eso0846a.

7 August 2008

Paranal in Atacama desert

Paranal, the site of the VLT, was chosen for its unique characteristics: extreme dryness, very low cloud coverage, high altitude, and distant from any source of pollution. This wide-angle shot of the Atacama desert around Paranal, which shows the VLT and, in foreground, VISTA, summarizes it all. Photo taken in November 2007.

30 July 2008

VLT Video Compilation 2008

The "Very Large Telescope Video Collection 2008" features High Definition video material which was obtained in June 2008. For the first time, ESO distributes HD-footage of the world's most advanced ground-based observing facility and provides free access to video sequences of outstanding technical quality and beauty.

The material has been edited especially for broadcast use, without commentary or music.

17 July 2008

Moving an ALMA Antenna

The first successful movement of an ALMA antenna took place at the Operations Support Facility (OSF) on 8 July 2008. The antenna transporter "Lore", one of the two units manufactured by Scheuerle under contract by ESO and delivered recently at the OSF, has been used to move one 12-m antenna from their site erection facility to an external antenna pad for sky testing.

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.

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