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| None | Scheme of our experiment: Using a telescope, the light from the Sun was coupled to an optical fibre that guides it to a spectrometer (prism) in order to resolve its spectral lines. The spectral lines from the Sun (Fraunhofer lines) appear as dark bands because they represent the wavelengths of light that has been absorbed by the Sun's photosphere as it emerges from deeper within the it. Superimposed are many short, bright (white) spectral lines of the laser frequency comb. | ESO |
| None | The spectrum of colours in arriving at the Earth from a quasar. The Universe the light passes through is made up of galaxies, which we see in this picture, but these galaxies are interconnected by streams and clouds of hydrogen gas which causes a "forest" of absorption lines to appear in the quasar spectrum. | Michael Murphy |
| None | Same as above but now, instead of galaxies, a simulated universe's intergalactic structure is shown. The filamentary structure is traced by hydrogen gas which causes a "forest" of absorption lines to appear in the quasar spectrum. It is these absorption lines which, over several decades, will shift very very slightly. We need to carefully measure our quasar spectra with a frequency comb if we are to pick up this tiny effect. | Michael Murphy |
| None | The frequency comb, which is the light from pulsed laser, consists of many colours which are only revealed when observed with a high-resolution spectrometer, such as typically used in astronomical telescopes. The spectral lines of the comb can be stabilized to the frequency given in the graph using an atomic clock. | Theodor Hänsch |
| None | A planet (green) orbiting around a star imposes a wobbling movement of that star which is greatly exaggerated in this sketch. This motion is synchronized with the orbit of the planet and causes a periodic variation of the spectral lines or colour of the star. This color change is greatly exaggerated. In reality one needs the precision of an atomic clock to see it when dealing with a small planet like Earth. | Thomas Udem |
| None | Tilo Steinmetz (left) and Constanza Araujo-Hauck (right) aligning the frequency comb at the VTT solar telescope at Tenerife. | Constanza Araujo-Hauck |
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MOV_720p(290M) Full_HD_MOV,_1080p(526M) Versions without inset graph: M4V,_iPod_size(56M) MOV,_720p(307M) Full_HD_MOV_1080p(560M) | Quasar light's long journey to Earth. This movie follows the light from a quasar - a supermassive black hole, gobbling up the center of a distant galaxy - as it travels through the Universe to Earth. As light emerges from a distant. It encounters an intervening galaxy and some of the quasar light is absorbed in the interstellar medium of this galaxy. The inset graph shows the spectrum of colours from the quasar. As the light travels, the overall spectrum shifts to the red side because of the expansion of the Universe. The absorption from the intervening galaxy manifests itself as sharp lines in the spectrum, indicating the colours of light absorbed by the galaxy. | Centre for Astrophysics & Supercomputing, Swinburne University of Technology |
 | None | A planet (green) orbiting around a star imposes a wobbling movement of that star which is greatly exaggerated in this sketch. This motion is synchronized with the orbit of the planet and causes a periodic variation of the spectral lines or colour of the star. This color change is greatly exaggerated. In reality one needs the precision of an atomic clock to see it when dealing with a small planet like Earth. | Thomas Udem |
 | None. See also: Similar animation at HST website | The expansion of the universe means all galaxies seem to move away from us (and from each other). This causes their spectral lines to shift towards the red end of the spectrum. On the other hand, if the universe contracted, the spectral lines of the galaxies would appear shifted towards the blue. Through a tiny change of the magnitude of the shift, as is now measurable with the frequency comb, one can decide whether the universe's expansion is actually accelerating, as several indirect observations currently suggest. | Thomas Udem |
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 | None | Figure 1: The top left shows the solar telescope (VTT) on Tenerife which has been used for this work. The light from the Sun is superimposed on the frequency comb (shown below) with the help of a beam splitter. Together they are fed to a spectrometer (right). Since the original frequency comb has spectral lines that are too close to be resolved by the spectrometer, it is first filtered using a Fabry-Perot filter cavity. |
 | None | Figure 2: A section of the measured spectrum, magnified on top. The dark lines are caused by absorption of gaseous elements in the photosphere of the Sun and by absorption in Earth's atmosphere. The spectral lines of the frequency comb appear as bright streaks that are used as precise calibration lines for the entire solar spectrum. The frequency comb is connected to a rubidium atomic clock (Rb-clock) for that purpose. |