News

Historical Sky: Half a century of Potsdam solar research digitally accessible

Negative of a photograph of the entire solar disk showing groups of sunspots. It was taken on 3rd February 1949 at the Einstein Tower Solar Observatory. Credit: AIP/APPLAUSE

Historical Sky: Half a century of Potsdam solar research digitally accessible

23 September 2020. As part of the large-scale digitization project APPLAUSE, digitized photographic plates have recently become available online, with images of the sun taken between 1943 and 1991 ...

At the time of its completion in 1924, the Einstein Tower on the Telegrafenberg in Potsdam was the most modern solar telescope in Europe. Between 1943 and 1991, it captured the image of the solar disk on more than 3,500 glass photographic plates, which the Leibniz Institute for Astrophysics Potsdam (AIP) is now making available to the public in digitized and processed form.

During their internship at the Leibniz Institute for Astrophysics Potsdam (AIP), school students from Potsdam and Berlin scanned these images. Afterwards, solar physicists at the AIP calibrated the images, measured the solar radius on the sky and provided the images with additional metadata such as information on the time of observation, the prevailing observation conditions, and the exposure time. They also corrected for atmospheric effects and enhanced contrast. These improved quality images are now freely available to the scientific community and the general public in a database.

In solar physics, these historical data are needed to fill gaps in time series spanning decades or even centuries and thus to better understand fluctuations in solar activity during the 11-year sunspot activity cycle and the 22-year magnetic cycle. The imaging of the entire solar disk at the Einstein Tower began in 1943 and complemented the drawings of the solar surface used until then. The aim was to obtain precise photometry of sunspots in order to track the activity cycle of the Sun.

From the mid-1950s, a spectrograph was also used to determine the strength of the magnetic field of sunspots in order to investigate details of their complexity. Magnetic fields are concentrated in sunspots and are subject to strong and often rapid changes. Images of the entire visible solar surface allow the magnetic fields studied in detail to be assigned to processes that occur outside the measurement area.

Most of the 3,500 images were taken between 1943 and the late 1960s with about 128 pictures per year. After 1970, only sporadic solar observations took place with an average of 22 images per year. The variation in the cadence of the observations across the almost 50-year period stem from a combination of various causes: At the end of the Second World War, bomb damage interrupted the observations, and the lack of photographic plates also made it difficult to take photographs in the following years. Also, as sun spots were the main focus of solar research at this time, photographs were not taken when active sunspots were not seen. Changes in the priority of scientific objectives also led to a decline of the number of taken images. Last but not least, the weather or poor observing conditions were also responsible for interruptions in the observation series.

The primary goal of the APPLAUSE project is to preserve the scientific heritage and make it usable for contemporary scientific exploitation. The now released digitized solar plates can be brought together with other recordings of solar observations, including sunspot drawings, to create a digitized archive of solar activity comprising the last 400 years. Modern computer technology and advanced image processing software have facilitated the creation of such archives over the last decade.

 

An original glass photographic plate from the Einstein Tower with an image of the Sun taken on 20th November 1967.Credit: AIP/APPLAUSE

 

An example drawing from a sun observation book. The use of photographic plates supplemented such drawings from 1943 onwards. Credit: AIP/APPLAUSE

Data coverage of photographic plates in the years 1943–1991. Only sporadic observations were carried out after 1970. Credit: AIP


The Einstein Tower shortly after the Second World War and today. Credit: AIP


Science contact

Prof. Dr. Carsten Denker, 0331 7499 297, cdenker@aip.de

Media contact

Franziska Gräfe, 0331 7499 803, presse@aip.de

Search for photographic plates

https://public.aip.de/historical-sky

Access to the archive and further information

https://www.plate-archive.org/applause/

Movie of all images

https://www.plate-archive.org/files/DR3s/soet_full_data.mp4

Publication

Pal, P., Verma, M., Rendtel, J., González Manrique, S.J., Enke, H., Denker, C. 2020:  Solar Observatory Einstein Tower — Data Release of the Digitized Solar Full-disk Photographic Plate Archive.

Astronomische Nachrichten, in press.

https://doi.org/10.1002/asna.202013791

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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Cosmic dance: A solution to the Galactic bar paradox

In this snapshots of a Milky Way galaxy simulation, the bar seen in the center and the spiral arms rotate with different rates. Every time they meet, the bar appears longer and its rotational speed lower. Credit: T. Hilmi/ University of Surrey

Cosmic dance: A solution to the Galactic bar paradox

25 August 2020. The very heart of our Milky Way harbours a large bar-like structure of stars whose size and rotational speed have been strongly contested in the last years. A new study has found an...

While studies of the motions of stars near the Sun suggest the bar is small and rapidly rotating, direct observations of the Galactic central region find it to be significantly longer and slower. An international team of scientists led by Tariq Hilmi of the University of Surrey and Ivan Minchev of the Leibniz Institute for Astrophysics Potsdam (AIP) has found a solution to this apparent discrepancy. The team looked at the most recent stages of the Milky Way evolution. Analysing state-of-the-art galaxy formation simulations of the Milky Way, the scientists now showed that both the bar’s size and its rotational speed fluctuate in time, causing the bar to appear up to twice as long and 20 percent faster at certain times.

These bar pulsations result from its regular encounters with the Galactic spiral arms, in what can be described as a “cosmic dance”. Spiral arms are density waves within our Galaxy and move at a similar velocity as the Sun. A full rotation around the center of the Milky Way takes about 220 million years, while the central bar needs only about 60 million years. As the faster rotating bar approaches a spiral arm, their mutual attraction due to gravity makes the bar slow down and the spiral arm speed up. Once connected, the two structures move as one and the bar appears much longer than it actually is. As the dancers split apart, the bar speeds up while the spiral arm slows back down.

“The controversy of the Galactic bar found in observational studies can be simply resolved if we happen to be living at a time when the bar and spiral arms are connected, giving the illusion of a large and slow bar, while the motion of stars near the Sun is governed by the bar’s true, much smaller size,” says Ivan Minchev. Indeed, recent observations have shown that the inner Milky Way spiral arm is in fact connected to the bar.

The majority of spiral galaxies like our Milky Way host a large bar in their center. The gravitational pull of this Galactic bar shapes the stellar orbits not just near it, but all the way to our Sun and beyond. Knowledge of the true bar size and rotational speed is crucial for understanding how our Galaxy formed and evolved, as well as how galaxies form bars throughout the universe. But unlike in other galaxies, the Milky Way bar is hard to observe directly, owing to our position in the galactic disk. Data from the forthcoming 3rd data release of the Gaia mission will be able to test this model further, and future missions will discover if the dance goes on in other galaxies across the Universe.

 

The rotational speed of the bar and spiral arm varies periodically with time. As the bar slows down, the spiral arm speeds up and vice versa. About every 80 million years the two structures merge and move together (dashed horizontal line). Credit: AIP/I.Minchev


Cosmic Dance: Snapshots of a Milky Way galaxy simulation. The bar seen in the center and the spiral arms rotate with different rates. If they are disconnected, the bar shows its true and smaller structure (left). Every time they meet, the bar appears longer and its rotational speed lower (right). Credit: T. Hilmi/ University of Surrey


Science contact

Dr. Ivan Minchev, 0331 7499 259, iminchev@aip.de

Media contact

Franziska Gräfe, 0331 7499 803, presse@aip.de

Publication

Tariq Hilmi, Ivan Michev et al. (2020): Fluctuations in galactic bar parameters due to bar–spiral interaction. MNRAS 497, 933–955

https://doi.org/10.1093/mnras/staa1934

Press release of the Royal Astronomical Society

https://ras.ac.uk/news-and-press/research-highlights/galactic-bar-paradox-resolved-cosmic-dance

Movies & Images

http://bit.ly/CosmicDance_Movies

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aims at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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Mysterious dimming of Betelgeuse: Dust clearing up

The artist’s impression of the darkening of the red supergiant Betelgeuse. Credit: NASA, ESA, and E. Wheatley (STScI)

Mysterious dimming of Betelgeuse: Dust clearing up

13 August 2020. Between October 2019 and February 2020 the brightness of the star Betelgeuse has dropped by more than a factor of three. New observations by the NASA/ESA Hubble Space Telescope and ...

Betelgeuse shines as a bright star in the constellation Orion. It belongs to the class of red supergiant stars and would reach beyond the orbit of Jupiter if placed in the center of our solar system. In autumn 2019, a sudden darkening of the star began, which was first visible from Earth through telescopes and later even to the naked eye - and was initially a mystery to science. At a distance of about 725 light years, the star is relatively close to our solar system. In fact, the dimming event would have happened around the year 1300, as its light is just reaching Earth now. Betelgeuse is destined to end its life in a supernova explosion. Some astronomers think the sudden dimming may be a pre-supernova event.

Thanks to new observational data obtained with the Hubble Space Telescope, an international team has now identified a dust cloud as the probable cause of the dimming: Scientists believe that the star unleashed superhot plasma from an upwelling of a large convection cell on the star's surface, similar to rising hot bubbles in boiling water, only many hundred times the size of our Sun. The material then passed through the hot atmosphere to the colder outer layers of the star. There it cooled down and the resulting huge dust cloud blocked the light from about a quarter of the star's surface, beginning in late 2019. By April 2020, the star had returned to its normal brightness.

The Hubble observations are part of a three-year Hubble study to monitor variations in the star’s outer atmosphere. The timeline that has been produced since then provided important new clues to the mechanism behind the dimming. Hubble observed the layers above the star's surface, which are so hot that they emit mostly in the ultraviolet region of the spectrum.

During the autumn months of 2019, Hubble detected dense heated material passing from the star’s surface into its outer atmosphere. “With Hubble, we see the material as it left the star’s visible surface and moved out through the atmosphere, before the dust formed that caused the star appear to dim,” said lead researcher Andrea Dupree, associate director of The Center for Astrophysics | Harvard & Smithsonian. “We could see the effect of a dense, hot region in the southeast part of the star moving outward. This material was two to four times more luminous than the star’s normal brightness. And then, about a month later, the southern hemisphere of Betelgeuse dimmed conspicuously as the star grew fainter. We think it is possible that a dark cloud resulted from the outflow that Hubble detected.”

Of particular importance during the time of the great dimming were velocity measurements of the outer layers of Betelgeuse obtained with the STELLA telescope of the AIP on Tenerife, whose observations complement those of Hubble. "STELLA was designed for observing individual objects over a very long period of time - especially magnetically active stars. It is perfectly suited for monitoring bright stars like Betelgeuse. STELLA had and is observing it basically every clear night since 2006," explains Klaus Strassmeier, co-author of the study and director at AIP.

Although the cause of the outburst is not known, the research team thinks it was aided by the star’s pulsation cycle. This continued normally throughout the event. The AIP scientists used STELLA to measure changes in the velocity of the plasma on the star's surface as it rose and fell during the pulsation cycle. The star was expanding in its cycle at the same time as the convective cell was upwelling. The pulsation rippling outward from Betelgeuse may have helped propel the outflowing plasma through the atmosphere.

"Had a large and very cool starspot caused the dimming, the velocities of the plasma would not have followed the pulsation but the rotation of the star. The latter is very slow and takes many years. It would therefore not have been able to show what STELLA observed, and certainly not a reversal of the plasma velocity when the star was faintest," Strassmeier concludes.

 

Artist’s impression of the red supergiant star Betelgeuse. The unexpected dimming of the star was most likely caused by an immense amount of hot material ejected into space, reaching millions of miles from the seething star. At that distance, the material cooled downThe resulting dust cloud blocked light from about a quarter of the star's surface.

Credit: NASA, ESA, and E. Wheatley (STScI)


Science contact AIP

Prof. Dr. Klaus Strassmeier, 0331 7499 295, kstrassmeier@aip.de

Media contact

Franziska Gräfe, 0331 7499 803, presse@aip.de

STELLA

https://www.aip.de/en/research/facilities/stella

Publication

Andrea K. Dupree, Klaus G. Strassmeier, Lynn D. Matthews, Han Uitenbroek, Thomas Calderwood, Thomas Granzer, Edward F. Guinan, Reimar Leike, Miguel Montargès, Anita M. S. Richards, Richard Wasatonic, and Michael Weber (2020): Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse. The Astrophysical Journal, 899, 68

https://doi.org/10.3847/1538-4357/aba516

 

Press releases and images

https://hubblesite.org/contents/news-releases/2020/news-2020-44

https://www.spacetelescope.org/news/heic2014/

https://www.nasa.gov/feature/goddard/2020/nasa-satellite-s-lone-view-of-betelgeuse-reveals-more-strange-behavior/

https://www.cfa.harvard.edu/news/2020-17

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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The ultimate RAVE: final data release published

RAVE observed nearly half a million stars of our Galaxy. The Sun is located at the centre of the coordinate system. Credit: AIP/K. Riebe, the RAVE Collaboration; Milky Way image (background): R. Hurt (SSC); NASA/JPL-Caltech

The ultimate RAVE: final data release published

27 July 2020. How do the stars in our Milky Way move? For more than a decade RAVE, one of the first and largest systematic spectroscopic surveys, studied the motion of Milky Way stars. The RAVE col...

The RAdial Velocity Experiment RAVE is a spectroscopic survey of stars in the southern hemisphere. RAVE was designed to get a representative census of the movements and of the atmospheric properties of stars in the wider neighbourhood of the Sun. By means of spectroscopy, the light of a star is decomposed into its rainbow colours. By analysing the spectra, the radial velocity of a star – the movement of the stars in the direction of the observer's view, can be determined. Furthermore, stellar spectra also enable scientists to determine stellar parameters like temperatures, surface gravities, and composition. In order to trace the structure and shape of our galaxy, RAVE successfully measured 518,387 spectra for 451,783 Milky Way stars.

Astronomers are not only used to think in long time scales – their projects also are often many-year endeavours. RAVE observed the sky for almost every clear night between 2003 and 2013 at the 1.2-metre UK Schmidt telescope of the Anglo-Australian Observatory in Siding Spring, Australia. RAVE utilized a dedicated fibre-optical setup to simultaneously take spectra of up to 150 stars in a single observation. Only with this massive multiplexing such a large number of targets was achievable – the largest spectroscopic survey before RAVE featured only some 14000 targets. In this way the survey obtained a representative sample of the stars around our Sun that are located roughly in a volume 15000 light years across.

Over the past 15 years, an increasing number of stars and refined data products have been released. The final RAVE data release not only provides for the first time the spectra of all stars in the RAVE sample; the stars were also matched with stars from the DR2 catalogue of the satellite mission Gaia. Thanks to the exquisite distances and proper motions measured by Gaia, considerably improved stellar temperatures, surface gravities and the chemical composition of the stellar atmospheres could be derived.

“The RAVE data releases have provided new insights into the motion of stars and chemical structure of our Milky Way,” says Matthias Steinmetz, leader of the RAVE collaboration and scientific chairman of the Leibniz Institute for Astrophysics Potsdam (AIP). “The final data release concludes one of the first systematic spectroscopic Galactic Archaeology surveys. It’s really exciting to think about finishing this 15-year project. Thanks to RAVE, we have gained new insights into the structure and composition of our Milky Way. “ ­­

Some of the key results of RAVE include the determination of the minimum speed needed for a star to escape the gravitational pull of the Milky Way. The results confirmed that dark matter, an invisible component of the Universe of yet unknown nature, dominates the mass of our Galaxy. With RAVE it could be shown that the Milky Way disk is asymmetric and wobbles owing to the interaction with spiral arms and the infall of satellite galaxies. RAVE also allowed for the identification of stellar streams in the solar environment. These streams of stars are the residues of torn apart old dwarf galaxies that have merged into our Milky Way in the past. The chemical element abundances of the observed stars hold important clues to the chemical composition and the subsequent metal enrichment of the interstellar medium traced by stars of different ages and metallicities. With RAVE, astronomers efficiently searched for the very first stars, which are very metal-poor and give clues about the earliest epochs of star formation and the chemical evolution in the Milky Way.

The RAVE collaboration consists of researchers from over 20 institutions around the world and is coordinated by the AIP. More than 100 refereed scientific articles based on RAVE data were published since the first data release.

 

RAVE observed nearly half a million stars of our Galaxy. The Sun is located at the centre of the coordinate system. The colours represent radial velocities: red are receding stars and stars depicted in blue are approaching. Credit: AIP/K. Riebe, the RAVE Collaboration; Milky Way image (background): R. Hurt (SSC); NASA/JPL-Caltech

Map of the night sky centered on the Milky Way, with stars observed by RAVE. More than 6000 observation fields mainly from the southern sky (below the celestial equator, red line) with about half a million stars have been observed. Credit: AIP/K. Riebe, the RAVE Collaboration; Milky-Way image (background): ESO/S. Brunier

The stars observed by RAVE are from the southern celestial hemisphere, since the UK-Schmidt telescope is located in Australia. There are only a few observation fields in the area of the Milky Way disk (central part), because in this crowded area it is much harder to collect and analyse individual stars. Credit: AIP/K. Riebe, the RAVE Collaboration

This movie shows the stars observed by RAVE from 2003 to 2013, first on a map of the sky and then their 3D distribution in the Milky Way. Colouring stars by metallicity reveals the trend for lower metallicities at larger distances from the Galactic plane. Credit: AIP/K. Riebe, the RAVE Collaboration; Milky-Way images (background): ESO/S. Brunier, R. Hurt (SSC), NASA/JPL-Caltech

 

Science contact
Prof. Dr. Matthias Steinmetz, 0331 7499 800, msteinmetz@aip.de

Media contact
Franziska Gräfe, 0331 7499 803, presse@aip.de

 

RAVE Website

www.rave-survey.org

Publications

The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities

arXiv: https://arxiv.org/abs/2002.04377

Astronomical Journal: https://iopscience.iop.org/article/10.3847/1538-3881/ab9ab9

The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- II: Stellar Atmospheric Parameters, Chemical Abundances and Distances

arXiv: https://arxiv.org/abs/2002.04512

Astronomical Journal: https://iopscience.iop.org/article/10.3847/1538-3881/ab9ab8

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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First images of the Sun from Solar Orbiter

The image shows the Sun’s appearance at a wavelength of 17 nanometers, which is in the extreme ultraviolet region of the electromagnetic spectrum. Credit: Solar Orbiter/EUI Team (ESA & NASA); CSL, IAS, MPS, PMOD/WRC, ROB, UCL/MSSL

First images of the Sun from Solar Orbiter

16 July 2020. Solar Orbiter, a mission of the space agencies ESA and NASA, publishes for the first time images that show our home star as close as never before. Prior to this, the test phase of all...

Five months ago Solar Orbiter started its journey to the Sun. Between mid-March and mid-June, the ten instruments on board were switched on and tested, and the spacecraft made its first approach to the Sun. Shortly afterwards, the international science teams were able to test all instruments together for the first time.

In addition to visible light, the Sun also emits X-rays, especially during solar flares. The Leibniz Institute for Astrophysics Potsdam (AIP) is mainly involved in the mission with the X-ray telescope STIX (Spectrometer/Telescope for Imaging X-Ray). With this instrument it is possible to observe particularly hot regions that are only formed during solar flares. The rest of the Sun is not visible in X-rays, so STIX needs its own system that precisely measures its orientation towards the Sun. The team at the AIP developed and built the STIX Aspect System (SAS) and now operates it during the mission. This allows the X-ray images to be correlated with the images of the other instruments.

The first images taken by Solar Orbiter from the Sun, which have now been published, reveal previously unknown details. They show numerous small solar flares, so-called "campfires". This already illustrates the enormous potential of the mission, whose scientific phase will begin in November 2021 and continue until 2029.

"All STIX instrument parts, such as the 32 X-ray detectors, worked as expected. We solar physicists at the AIP of course were very excited. To our delight we see that SAS is delivering good data as expected. During the test phase, we were able to see how the diameter of the Sun is constantly increasing as the probe approaches the Sun," explains Gottfried Mann, head of the STIX team at the AIP.

On February 10, 2020, the Solar Orbiter spacecraft was launched. The mission will orbit the Sun in the next few years and approach it to a distance of 42 million kilometres. Solar Orbiter carries six remote sensing instruments and telescopes that image the Sun and its surroundings, as well as four in-situ instruments that measure the properties in the environment of the spacecraft. By comparing the data from the two sets of instruments, science will gain insights into the origin of the solar wind - the stream of charged particles from the Sun that affects the entire solar system.

During eruptions on the Sun, an enormous amount of high-energy electrons are generated. These electrons play an important role because they carry a large part of the energy released during the eruption. The AIP is also involved in the Energetic Particle Detector (EPD). EPD can directly measure these electrons when they hit the probe. Thanks to DLR-funded participation in the STIX and EPD instruments, the AIP will be able to investigate the processes of the high-energy electrons in their entirety in the next few years. Solar activity - also known as space weather - can have a major impact on our climate and technical civilisation. Solar Orbiter aims to study the processes on the Sun and their effects on our Earth.

 

Schematic view of Solar Orbiter with all instruments on board. Credit: ESA.

 

Science contact AIP

Prof. Dr. Gottfried Mann, 0331 7499 292, gmann@aip.de

Media contact AIP

Franziska Gräfe, 0331 7499 803, presse@aip.de

ESA press release

https://bit.ly/ESA_SolarOrbiter

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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