SDSS Plates as Art in Nashville, Tennessee

Check out these cool art pieces made from SDSS spectroscopic plates!  Nashville based artist, Adrienne Outlaw, designed and built them and they will be exhibited in various locations at Vanderbilt University over the next year. The pictures show their first installation, just in time for the Inclusive Astronomy meeting that started yesterday. The concept design was done by Adrienne Outlaw in collaboration with Vanderbilt astronomers David Weintraub and Billy Teets, and the project was funded by Vanderbilt University’s Curb Creative Campus program.

If you want to learn more about what these plates are, and see them in other art installations please see this previous post on SDSS plates.

We love seeing images of SDSS plates around the world. Please send any you find to us via social media (you can find us on Facebook, Twitter and Google+), or email to outreach ‘at’ sdss.org.

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SDSS at the New York Hall of Science

A few months ago (at the end of March), SDSS Members spent a Saturday taking part in the Big Data Fest at the New York Hall of Science, in Queens, NY.

This event was aimed at helping people find out how data is relevant to their lives and featured interactive experiences focused on data literacy and data gathering and visualization.

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Chang Hahn and Yuqian Liu from NYU ready to go with the SDSS booth

Seven SDSS members in total helped out – six from NYU (Chang Hahn, Yuqian Liu, Nitya Mandyam Doddamane, Kilian Walsh, Ben Weaver, and Mike Blanton), along with Guang Yang who travelled up from Penn State University (PSU). This group ran one of about a dozen booths spread throughout the Hall of Science buildings in between the regular exhibits.

The SDSS booth contained an SDSS plate, along with a large-scale printout of the imaging for the part of the sky it was designed for. There was also a set of flash cards with images of galaxies on them, next to an invitation to try classifying them. Visitors were invited to take a card home with them if they wished. There were laptops running both Galaxy Zoo and the SDSS SkyServer. The SkyServer demo was set up to allow visitors to explore the data taken with the plate on display. Finally a monitor displayed a loop of videos about SDSS from the SDSS YouTube Channel.

Galaxy flashcards ready for classifying.

Galaxy flashcards ready for classifying.

The audience were made up of a mixture of children, teenagers and adults (including some who were very scientifically literate). The location in Queens meant that it was mostly NY area residents – with fewer tourists than Manhatten based museums attract.

Nitya Mandyam Doddamane and Yuqian Liu talks about SDSS with some visitors, while Chang Hahn is running a demo of Skyserver.

Nitya Mandyam Doddamane and Yuqian Liu talks about SDSS with some visitors, while Chang Hahn is running a demo of Skyserver.

This event at the NY Hall of Science is just one example of SDSS scientists around the world working to engage members of the public with our data. If you are running a similar event and might be interested in seeing if SDSS would be able to participate, please contact outreach ‘at’ sdss.org and we will try to connect you with your nearest SDSS institution.

How SDSS Used Light to Make the Largest Ever Image of the Night Sky

The Sloan Digital Sky Survey imaged over 30% of the sky between the years of 1998-2008, creating the largest digital colour image of the sky ever taken. To view all of the SDSS imaging at once, would require 500,000 HD televisions (so it can be displayed at full resolution), and with more than a trillion pixels, this image dwarfs the 1.5 billion pixel image that NASA recently claimed was the biggest ever taken.

The SDSS Camera which took all of this imaging is now retired, and was collected by the Smithsonian Institution, to be packed away in a basement as an “artifact of scientific significance”.

The SDSS Camera in its current home - a basement of the Smithsonian Museum in Washington, D.C. Image Credit: Xavier Poultney, SDSS.

The SDSS Camera in its current home – a basement of the Smithsonian Museum in Washington, D.C. Image Credit: Xavier Poultney, SDSS.

The SDSS camera was made by arranging together an array of thirty, 2048×2048 pixel CCD chips. In the 1990s this was state-of-the-art, and even today a 126 Megapixel camera is nothing to sniff at (e.g the current state-of-the-art is DECam which has 62 CCDs and a total of 520 Megapixels).

The CCD chips in the SDSS camera were aligned in five columns, each covered by one of the five filters used to make the colour imaging (the u-, g-, r-, i- and z-bands, roughly corresponding to collecting light in the near-ultraviolet, green, red, near-infrared and a bit less near-infrared respectively).

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An illustration of the arrangement of the CCDs and filters on the camera. The filters from top to bottom are r, i, u, z and g-band. Image credit: SDSS.

This arrangement meant that the camera could take images continuously as the Earth rotated and moved it with respect to the sky overhead. SDSS images are therefore arranged in long stripes of constant Declination across the sky (the most famous being “Stripe 82” which was imaged many times). You can make out some of these stripes around the edges of the stitched together image (the “legs of the orange spider” below).

Orange Spider! This illustration shows the SDSS imaging on many scales. The picture in the top left shows the SDSS view of a small part of the sky, centered on the galaxy Messier 33 (M33). The middle and right top pictures are further zoom-ins on M33. The figure at the bottom is a map of the whole sky derived from the SDSS image. Visible in the map are the clusters and walls of galaxies that are the largest structures in the entire universe. Figure credit: M. Blanton and SDSS

All SDSS imaging is publicly available and can be explored online via the SDSS Skyserver. The Navigate Tool is especially fun as you can scroll around the entire image.

A much more technical description of the camera can be found in Gunn et al. (1998) and in the SDSS-I project book.


This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe. 

SDSS Plates for Education

Here at SDSS we’re working on a new educational initiative, where teachers and informal educators will be able to take back to their classroom their very own piece of SDSS history – an actual SDSS plate which was used to map a small patch of the night sky.

We have been developing a “Plate packet” to distribute to teachers and educators. This packet contains an SDSS plate, along with a custom made poster showing the SDSS image of the region of sky the plate was designed for, as well as some selected educational materials, and links to specially designed activities on SDSS Voyages.

Certificate handed out with each plate.

Certificate handed out with each plate.

On Saturday 30th May 2015, SDSS Members from the University of Washington handed out the first plates to a group of  teachers representing high schools from around the western Washington, USA. These teachers spent the day at the in Seattle discussing ideas for using the plates in their classrooms, as well as getting a tour of the machine shop, where all the SDSS plates are manufactured.

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“Hard at Work”: SDSS Member Oliver Fraser (pink shirt) shows some educators how to find the data from their plates and use it for classroom investigations. A plate poster can be seen on the board in back. Credit: Danielle Skinner

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“Yay Plates!”: some happy educators (and SDSS Member, Danielle Skinner in black) excited to be taking their very own SDSS plates back to their schools. Credit: Oliver Fraser.

The University of Washington is already planning more such workshops, and we look forward to expanding this program to other SDSS Member Institutions.


If you’re a teacher or educator reading this and interested to know how you can get your own SDSS plate, please contact the outreach representative at your nearest SDSS Institution, or email outreach ‘at’ sdss.org for assistance doing that. SDSS members interested in getting involved in this programme should join the EPO mailing list (details on the password protected collaboration wiki). 

How SDSS uses light to see dark matter in galaxies

Some of the most beautiful pictures taken by telescopes are those of galaxies. Containing billions of stars, they come in many shapes and sizes. We can study the stellar structures in galaxies from telescope images to learn more about the ways that galaxies form and evolve. We also can look at gas and dust features in galaxies, and the role that these play in the formation of new stars.

Elliptical galaxy NGC 4636 (left) and spiral galaxy M81 (right), as seen by the Sloan Telescope. The telescope captures the light of the stars, and in M81 we can also see some dust in the spiral arms. Both galaxies reside in large, invisible, dark matter haloes.

Elliptical galaxy NGC 4636 (left) and spiral galaxy M81 (right), as seen by the Sloan Telescope. The telescope captures the light of the stars, and in M81 we can also see some dust in the spiral arms. Both galaxies reside in large, invisible, dark matter haloes.

Yet, the largest and most massive component of a galaxy, the dark matter halo, is truly invisible. Dark matter is not made out of ‘normal material’ or baryons, which are the building blocks of stars, planets and all other matter surrounding us. Instead, dark matter is thought to be an exotic particle that does not emit or absorb any light: it does not interact with the electromagnetic force like normal matter. So how do we then know that the dark matter is there?

The answer lies in the light that we observe from the stars and the gas in galaxies. With images we capture the presence of light, but with spectrographs we unravel the light into different colours or wavelengths. The resulting galaxy spectra show us how the stars are moving around in the galaxy. In most galaxies, the stars will rotate around the centre of the galaxy, and this rotational velocity can be seen in the spectrum by a shift in the stellar absorption lines. This shift results from the Doppler Effect, which causes the lines of stars that move away from us to shift towards the red part of the spectrum, while the lines of stars that are moving towards us shift to the blue part of the spectrum. This way, we can find out how fast the stars in a galaxy are rotating around the galaxy centre. But there is more information in the spectrum: the lines are not infinitely thin, but are slightly broadened. This broadening is called ‘velocity dispersion’ and is caused by the additional random motions of the stars. With the new Sloan Survey, MaNGA, we are measuring the rotational and random motions of the stars in 10,000 galaxies. And because MaNGA is an integral-field spectrograph, we can map these motions not only in the very centre of the galaxies, but also in their outskirts, as shown below.

MaNGA is an integral-field spectrograph, capturing spectra at multiple points in the same galaxy with a fiber bundle. The bottom right illustrates how each fiber will observe a different section of the galaxy. The top right shows data gathered by two fibers observing two different part of the galaxy, showing how the spectrum of the central regions differs dramatically from outer regions. From these spectra, we measure the rotational and random motions of stars, to deduce how much dark matter is present in the galaxy. Image Credit: Dana Berry / SkyWorks Digital Inc., David Law, and the SDSS collaboration

How do these velocity and dispersion maps help us to find the dark matter? The answer is gravity. The stars are moving around in a galaxy under the influence of gravity: the more matter (mass) there is in the galaxy, the faster the stars are moving. Now that we have measured the movements of the stars in the galaxies, we can deduce how much matter is needed to have the stars move around with those measured velocities. And we can compare that gravitational mass with the luminous mass in the galaxy (the stars, gas and dust). For all galaxies studied so far, the gravitational mass is much larger than the luminous mass: hence the need for dark matter.

Example of a galaxy observed with MaNGA. Left is the image of the galaxy, showing the stellar light. The middle image is the rotational velocity field of the galaxy: the red part of the galaxy is moving away from us with 254 km/s, and the blue part of the galaxy is moving towards us with the same velocity. The green axis down the middle is the rotation axis. The right image shows the random motions of the stars: these are higher in the centre (red: 257 km/s) than in the outskirts of the galaxy (blue: 94 km/s). Figure taken from Bundy et al. 2015.

Example of a galaxy observed with MaNGA. Left is the image of the galaxy, showing the stellar light. The middle image is the rotational velocity field of the galaxy: the red part of the galaxy is moving away from us with 254 km/s, and the blue part of the galaxy is moving towards us with the same velocity. The green axis down the middle is the rotation axis. The right image shows the random motions of the stars: these are higher in the centre (red: 257 km/s) than in the outskirts of the galaxy (blue: 94 km/s). Figure taken from Bundy et al. 2015.

Sophisticated mass or dynamical models of the galaxies, based on the observed velocity and dispersion maps, tell us how the luminous and dark matter are distributed in the galaxy, and what the properties (mass, size, concentration) of the dark haloes are. Comparing these mass models with predictions from galaxy formation theories will help us forward in our quest to understand galaxies, and the dark haloes that surround them. But it all starts with capturing the stellar light of galaxies in spectrographs, to map the invisible.


This post was written by Dr. Anne-Marie Weijmans (St Andrews) and is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe.

How SDSS Uses Light to Understand Stars Inside and Out in the Kepler Field

Stars are not only fascinating objects in their own right — they also help us understand the history of our Milky Way galaxy. Our galaxy was created as dark matter’s pull brought gas together, and the gas formed stars and planets. As part of the APOGEE survey, we wish to map the Milky Way’s star formation throughout cosmic time. As stars died, many of the elements they fused in their interiors during their lives or death throes are mixed back into the remaining gas, changing its composition and the composition of subsequent generations of stars and providing the raw materials for planets (and humans!) and we are exploring this chemical history as well.

A small part of the spectra of a few of the stars observed by APOGEE. The dark lines are caused by absorption of atoms in the star's atmosphere (or sometimes the Earth's). A few of them are highlighted. The bright lines are caused by emission in the Earth's atmosphere ("night sky lines") These particular stars have also been observed by the Kepler satellite.

A small part of the spectra of a few of the stars observed by APOGEE. The dark lines are caused by absorption of atoms in the star’s atmosphere (or sometimes the Earth’s). A few of them are highlighted. The bright lines are caused by emission in the Earth’s atmosphere (“night sky lines”) These particular stars have also been observed by the Kepler satellite.

APOGEE studies stars by passing their infrared light through gratings that spread the light out in wavelength (think infrared rainbows). We do this for > 250 stars at once (one of the reasons why the APOGEE instrument is fantastic). We can tell a lot about stars from studying these spectra. For example, in an earlier blog post, we discussed how we can tell the surface temperature of stars from such data. Another very important property is the composition of the star, for example, how many atoms of iron, calcium, or oxygen it has relative to hydrogen. The image to the left shows a small part of the spectra we gathered for stars that were also observed by the Kepler satellite. The stars do not give off the same amount of light at each wavelength (=color) of light. Instead, there are many dark lines, which are created when atoms in a star’s atmosphere absorb light at very particular wavelengths. Each element has a different pattern of these absorption lines, and by measuring the depth of these lines (+ additional information and math), we can determine the composition of the gas out of which the star formed.

But this doesn’t tell us everything about the star! In particular, we can’t see inside the star where the original composition of the gas is being transformed from hydrogen into helium as the star ages. We have a good idea of how long it takes for a star with a certain mass and original chemical composition to run out of fuse-able hydrogen in its center (about 10 billion years in the case of a star with the mass and composition of the Sun). When that happens, the star undergoes a dramatic change, turning into a red giant or supergiant. So if we can determine the mass to go with the spectral  composition information for red giants that we observe, we can determine the age of those particular stars.

Measuring the mass of a star is hard work, but one possible technique is to use asteroseismology, which is the study of the waves that move through stars. In the outer parts of stars, these waves are actually sound waves that can evocatively be described as ringing the star like a bell (For more information see The Song of the Stars). The motions of these waves cause a star’s brightness to change by small amounts, and thus the frequency of these waves can be measured by studying the lightcurves of red giant stars. The Kepler satellite, in addition to studying many Sun-like stars looking for transiting planets, also measured the brightnesses over many years of thousands of red giants. The favorite frequencies of waves in different stars have been measured by members of the Kepler Asteroseismic Science Consortium. While much can be learned about the insides of stars from these data, we are particularly intrigued by the fact that how long and at what speed waves can move through the star depends on the star’s density and therefore (with some more math) its mass!

Combining together spectra from APOGEE and lightcurves from Kepler therefore gives us a way to figure out the ages of red giant stars in our Galaxy by measuring the masses and composition of stars that have just exhausted their hydrogen. In conclusion, songs and rainbows are good things.

This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe. 

SDSS Scientists in Europe Enjoy #eclipse2015

SDSS collaboration members in Europe have enjoyed a partial solar eclipse today (20th March 2015).

At least two groups planned to project the eclipse through SDSS plates (as have been done previously for the October 2014 eclipse). Sadly Portsmouth was clouded out, but in St. Andrews the experiment was a success.

The European #eclipse2015 viewed through an SDSS plate. Credit: Rita Tojeiro.

The European #eclipse2015 viewed through an SDSS plate. Credit: Rita Tojeiro (St Andrews).

How SDSS Uses Light to Measure the Distances to Galaxies

Here at the Sloan Digital Sky Surveys our mission is to explore and map the Universe, from planets to the edges of the observable Universe. The way we do this is to collect light from specially selected objects we see in the night sky – but we can’t visit them in order to measure how far away they are. So how do we actually know how far away they are in order to make a map of the Universe?

Measuring the distance to objects in the Universe has always been one of the biggest challenges for astronomers. Until we know the distance to something we cannot really understand its physical properties, and the history of astronomy is full of examples where new techniques for measuring distances opened up entirely new areas of study. For example when the “spiral nebulae” were first discovered there was a long debate over if they were small clouds of gas in our own Galaxy, or external galaxies in their own right each made up of millions or billions of stars. Only by measuring their distances was this finally settled, and our understanding of the size of the Universe suddenly jumped many orders of magnitude.

A collection of "spiral nebulae". But how can we tell that they are distant galaxies rather than nearby gas clouds? Credit: SDSS

A collection of “spiral nebulae”. But how can we tell that they are distant galaxies rather than nearby gas clouds? Credit: SDSS

There’s some really useful bits of physics we can use to help measure distances to the galaxies from their light. To do this we need to understand spectroscopy. Once SDSS had finished imaging more than a quarter of the sky with its camera, it became entirely focused on “spectroscopic” surveys. Our telescope in New Mexico collects the light from stars and galaxies and uses instruments called spectroscopes to split it up into its different colours (we actually have two different spectroscopes working right now – the APOGEE spectroscope and the BOSS spectroscope). These measurements split the light into a rainbow (or a spectrum), and we look for the precise colours of series of emission and/or absorption lines to tell us all sorts of things about the light source we’re looking at.

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A hot bright light source (like a star) will have a “continuous spectrum” (with the peak colour depending on its temperature – hot things glow red, even hotter things glow white or blue hot). If the light from that passes through a cool cloud of gas before we measure it, that will create “absorption lines” where very specific colours (or “wavelengths” in proper scientific terms) are absorbed by atoms in the gas cloud. The exact pattern of colours/wavelengths which are absorbed tell you which atoms are in the gas cloud. If the gas cloud gets heated up enough we might instead see emission lines – at the same specific colours, where the atoms are now re-emitting these very specific colours/wavelengths. Each atom has a very distinctive pattern of lines it emits – for example hydrogen (the most abundant element in the Universe) has a very distinctive and bright emission/absorption line in the red part of the spectrum (at a wavelength of 656.3nm).

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Emission spectrum of hydrogen in visible light (wikimedia commons)

Astronomers have been using this technique to work out the materials which make up the Sun and other stars for decades. It’s not always easy (it has been compared to trying to reconstruct a piano from the noise it makes falling down the stairs), but it works. When astronomers first used the technique to look at galaxies however they were very surprised by what they found. The patterns of lines seemed to be in completely the wrong places – for example the famous hydrogen lines weren’t even visible in some cases – they had moved right into the infra-red part of the spectrum.

In order to understand why this could happen we need to learn about another part of physics – the Doppler effect. First proposed in 1842, by a Physicist named Christian Doppler this is the observation that when a source emitting a wave is moving, the waves are shortened if the source is moving towards the observer, and lengthened if it is moving away. Most people are familiar with this effect when they have listened to ambulance sirens passing them on the street; the siren is higher in pitch when the ambulance is moving towards you and lower when it’s moving away (when sound waves are lengthened the pitch drops, and when they are shortened the pitch rises).

Wikimedia commons illustration of the Doppler effect.

Since light is a wave, the same effect happens when light is emitted from a moving source. When the waves of light are shortened the light becomes bluer, and when they are lengthened the light becomes redder.

An astronomer named Vesto Slipher, was the first person to try this out on galaxies, and he found that almost all galaxies he looked at showed enormous “redshifts”, implying that almost all the galaxies were moving away from the Earth at very high speeds.

Edwin Hubble is given the credit for explaining this observation by realising that we live in a Universe which is constantly expanding. In such a Universe any observer will observe almost all other galaxies moving away from them. Hubble published the first description of a relationship between how fast galaxies appear to be moving away from us (their “redshifts”) and their distances – this relationship is now called Hubble’s Law.

It is this relationship that we use to measure the distances to the galaxies from detailed observations of the light they emit, and astronomers are now used to describing the distances to galaxies as simply their “redshift”.

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A map of the Universe from SDSS where the distance to galaxies is given in terms of their redshift. Credit: SDSS


This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe.


How SDSS uses light to study the darkest objects in the Universe

Black holes are intriguing objects. A black hole is a phenomenon whose gravity is so strong that not even light, the fastest traveller in the Universe, can escape from its influence. Once thought mere oddities due to their extreme properties, today, black holes are found to be vital in the formation and lives of galaxies, including our own Milky Way.

But how do we know black holes exist if we can’t see them? Well, even if we can’t see a black hole directly we can observe their influence and indeed the energy and light emitted as gas, dust and stars fall into a black hole; that is, we can see black holes when they are actively “eating” material.  When the supermassive black hole, which can be up to a billion times more massive than our Sun, at the center of a galaxy starts to eat new material the resulting process is so bright it can be seen out to ~200 billion lightyears away.  Astronomers call the observational result of this process either an active galactic nuclei, or in the most extreme examples a “quasar”. So you might be surprised to find that an object that emits no light can cause the brightest known phenomenon in the Universe!

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An artist’s rendition of a quasar created by Coleman Krawczyk (ICG Portsmouth).  The image is drawn on a radial log scale with the central black hole 1 AU in size.

The light of quasars is not produced by the black hole itself, but instead it comes from the material, mostly gas, that is falling into the black hole.  Different types of light are produced by this material at different distances outward from the black hole.  Near the surface (or horizon) of the black hole (about the distance of the Earth’s orbit away for supermassive black holes in galaxies) this gas becomes extremely hot and produces X-rays. Stretching out from this to fill a region about the size of our Solar System, a disk of gas shaped like a frisbee is formed.  The inside of this disk is closer to the black hole than the outside, so it rotates faster causing friction within the disk.  This friction causes the gas to heat up and glow, producing light in the optical to ultraviolet part of the spectrum.

From the edge of the gas disk to a distance of about 3 light years (similar to the distance from the Sun to the next closest star), the temperature becomes low enough that particles of “interstellar dust”, made of carbon and silicon, form.  These dust clouds form what is know as the “dusty torus,” a donut shaped ring round the gas disk. Some of the light coming from the gas disk is absorbed by the dust and re-emitted at longer wavelength infrared light. At very large distances from the black hole, some quasars have radio jets coming out along the poles.  As the name suggests, this jets produce light at radio wavelengths cased by electrons being accelerated along a strong magnetic field.  When these jets are present they can be up to ~300 thousand lightyears (~3 times the diameter of our entire galaxy!) in size.

Not only can a black hole produce light, it can create light at all wavelengths from the radio up to the X-ray, and across an area stretching from the size of the Earth’s orbit out to distances larger than the Milky Way.  Therefore, growing black holes, and the regions around them are anything but “black.”

With discoveries from its earliest imaging campaigns, the SDSS extended the study of quasars back to the first billion years after the Big Bang, showing the rapid early growth of black holes and mapping the end stages of the epoch of reionization.

Stacked spectra of more than 46,000 quasars from the SDSS; each spectrum has been converted to a single horizontal line, and they are stacked one above the other with the closest quasars at the bottom and the most distant quasars at the top. Credit: X. Fan and the Sloan Digital Sky Survey.

Stacked spectra of more than 46,000 quasars from the SDSS; each spectrum has been converted to a single horizontal line, and they are stacked one above the other with the closest quasars at the bottom and the most distant quasars at the top.
Credit: X. Fan and the Sloan Digital Sky Survey.

With full quasar samples hundreds of times larger than those that existed before, the SDSS has given us the most accurate descriptions of the growth of black holes over cosmic history.  SDSS spectra show that the properties of quasars have changed remarkably little from the early universe to the present day.

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Growth in the number of known quasars in the largest homogeneous (solid) and heterogeneous (dashed) quasar catalogs as a function of time. The Sloan Digital Sky Survey catalogues started being produced in 2000. Fig. 1 from Richards et al. (2009).

SDSS studies have probed the dark matter environments of quasars through clustering measurements, revealed populations of quasars whose central engines are hidden by obscuring dust, captured changes in quasar spectra that show clouds moving in the gravitational grip of the central black hole, and allowed a comprehensive census of the much fainter accreting black holes (active galactic nuclei, or AGN) in present-day galaxies.
This, our first post for the IYL2015 is a collaboration between Coleman Krawcyzk (ICG Portsmouth); Nic Ross (ROE) with help from Karen Masters (ICG Portsmouth).

This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe. 

SDSS Celebrates the International Year of Light 2015

As astronomers, at the Sloan Digital Sky Survey everything we do is based on collecting light from cosmic objects. SDSS is therefore pleased that in 2015 we are celebrating the International Year of Light, and we especially would like to point out the Cosmic Light Theme, supported by the IAU.cosmiclight_color_whitebg

As a small contribution to this celebration, every month in 2015 SDSS will have a special post on here talking about the different ways we use light. Our first post, which will appear before the end of January will be about how we use light to study black holes, something which seems like a contradiction, but has taught us a lot!

This post will be updated to collect all the links as the year progresses:

SDSS Plates

The SDSS has used thousands of plug plates in its fourteen year history. These are large aluminium plates into which tiny holes are drilled. Each hole has an optical fibre plugged into it (by hand by our plate pluggers). Each hole corresponds to the sky location where there is an object (a star or a galaxy) which SDSS wants to measure a spectrum for.

During SDSS spectroscopic observations, between six and nine of these are used every night. Each plate is custom drilled for a special part of the sky (about the size of your palm stretched out at arms length), and once all the data is collected for the astronomical objects in that plate, it becomes surplus to requirements.

All SDSS Collaboration members can request that used plates be sent to them (contact your Collaboration Council Representative for assistance with this). This has resulted in some interesting uses for the leftover plates across our diverse collaboration.

You might like to mount your plates on the wall for display.

A wall mounted plate at the Institute of Cosmology and Gravitation, Portsmouth, UK.

A wall mounted plate at the Institute of Cosmology and Gravitation, Portsmouth, UK. Image credit: Karen Masters

SDSS plates on display at CCAPP (Center for Cosmology and Astrophysics), Ohio State University. Image credit: Qingqing Mao.

SDSS plates on display at CCAPP (Center for Cosmology and Astrophysics), Ohio State University. Image credit: Qingqing Mao.

If doing this, it is helpful to have a good description as a guide. This is especially helpful if you are donating a plate to a local science museum or other location away from SDSS collaboration members who know what it is. The example below was made for a display of plate 825 by Jordan Raddick from Johns Hopkins University in Baltimore.

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To make a version of Jordan’s information sheet tailored for your own plate you can find the sky co-ordinates of your plate in this List of plate observation dates and centres. Then visit the Skyserver Navigate Tool to find an image at this location. You will likely want to invert the images, zoom out to the second largest scale, and overlay the plate location (all under “Drawing Options” to the right of the screen). You can then use Google sky to work out roughly which constellation this plate is in (unless you happen to know!), and the constellation maps are available from the IAU. To convert the MJD of observation to something understandable you might like this MJD converter.

We have a second example of plate display information from David Kirkby at UC Irvine. Here David has made an overlay of the SDSS imaging and coloured marks corresponding to the holes in BOSS plate 6640 (green for galaxies and purple for quasars), as well as an 3D representation of the distances to these objects (based on their SDSS measured redshifts).

An overlay for Plate 6640 showing both SDSS imaging and the location of drilled holes (green = galaxies; purple = quasars). Image credit: David Kirkby.

An overlay for Plate 6640 showing both SDSS imaging and the location of drilled holes (green = galaxies; purple = quasars). Image credit: David Kirkby.

A visualisation of the 3D structure behind BOSS plate 6640 based on redshifts measured by SDSS. Image credit: David Kirkby.

A visualisation of the 3D structure behind BOSS plate 6640 based on redshifts measured by SDSS. Image credit: David Kirkby.

It’s possible to back light wall mounted plates in some circumstances, to really nice effect. The below example was made by Mark Klaene at Apache Point Observatory.

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Mounted in the corner of Mark Klaene’s office at APO. It is spray painted black with a fluorescent desk lamp back light.

If you’re lucky you might find a natural source of light for this effect, as in this example where Stephen Bailey from LBL has mounted a plate in the window in his office door.

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SDSS Plate in an Office Door (the hole was there already).

Several collaboration members have used plates to make special coffee tables, or coffee table covers.

The most basic version of this is just placing a plate on top of a round coffee table of similar diameter.

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Coffee table topper by Bob Nichol, ICG Portsmouth.

This second one uses a 36″ round glass top table topped with a plate. Bumpers have been added to the plate and the normal glass top placed on top of it. The lighting shown below is from a single puck from a modular LED lighting system.

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Coffee table with under lighting by Brian Lee from SDSS-II.

At JHU they have made two coffee tables with the SDSS plates. The base is a hollow box made from scratch of four wood pieces and there is a lamp inside so at night you can see the light shining through the slits.

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Custom coffee table at JHU. Credit: Ting-Wen Lan, Murdock Hart, Guangtun Zhu and Brice Ménard. Photo courtesy of Zheng (Jared) Zheng.

SDSS Plug Plate Coffee Tables in use at JHU. Image credit: Gail Zasowski

SDSS Plug Plate Coffee Tables in use at JHU. Image credit: Gail Zasowski

Plates have also been used to make lab demos. The below is an example set up which LBL has to give quick demos.

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SDSS Plate Demo at LBL.

SDSS plates have also been used to make works of art. The most well know is work by Josiah McElheny in collaboration with David Weinberg (also described here and in this NYTimes Article).

Sculpture by Josiah McElheny using SDSS plug plate. Image provided by David Weinberg.

Sculpture by Josiah McElheny using SDSS plug plate. Image provided by David Weinberg.sdss

 

Sarah Ruether, an artist from Seattle and London based artist Xavier Poultney have also made artwork using plates.

Public art by Sarah Ruether made from SDSS-II plug plates

Public art by Sarah Ruether made from SDSS-II plug plates

Plate Artwork by Xavier Poultney as part of his Transient Objects exhibit.

Plate Artwork by Xavier Poultney as part of his Transient Objects exhibit.

If you have other examples of interesting uses of SDSS plates please let us know about them by commenting below, or emailing outreach@sdss.org.

See how the plates are drilled at the SDSS Plate Drilling Labs at the University of Washington in Seattle:

See how the optical fibres are plugged into a BOSS plate by our awesome SDSS plate pluggers (at Apache Point Observatory):

An Artistic Exploration of SDSS

Last summer, London based conceptual artist, Xavier Poultney, made a tour of various SDSS sites in the US. He visited Apache Point Observatory to see the SDSS telescope, the plate drilling labs at the University of Washington in Seattle, and he even went to see the now retired SDSS imaging camera in storage at the Smithsonian Museum in Washington DC. Several of the photographs taken on that visit can been seen on Xavier’s website, and also the website of Adam Laycock (Xavier’s photographic assistant). Xavier has also made several trips to SDSS Institutional Member, The University of Portsmouth to talk to scientists at the Institute of Cosmology and Gravitation about the astronomical significance of SDSS.

Out of his various visits, Xavier has developed an exhibit called “Transient Objects” which he describes as: “an artistic investigation into the evolution of knowledge and the cultural ramifications of technological and scientific progress.”

Xavier explains his exhibit further:

The SDSS hardware sits in a region of the New Mexico Desert that has been inhabited by various civilisations of North American Indian for thousands of years. The high-tech, cutting edge equipment of the SDSS observatories are surrounded by the ruins of ancient equivalents. My work explores both the disconnect and the parallels between these two paradigms of human understanding.

This summer I made a photographic research trip across America, visiting working SDSS sites and also archeological sites on Indian
Reservation land. The body of photographs focus on the progress of ideas; on supersession and outmoded thought. The relics of human
progress layer up and fall away, we glimpse the stratification of human knowledge, sitting awkwardly within the deep time of the silent desert landscape.

These photgraphs are to be exhibited alongside a number of large sculptures. The sculptures are made from modern materials (similar
to those used in the technical facilities of the SDSS), machined and designed with computers. However, in form the objects reference naive
religious artifacts, perhaps from a tribal society of some kind, making the sculptures look more like cross between ritualistic object
and defunct scientific instrument.

Some of the photos have already been exhibited in at The Space Inbetween Gallery in London as part of a group show, and the full show (including a sculpture featuring an SDSS plate) is about to open at a the Meet Factory Gallery in Prague, where it will run from March 6-30th.

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Xavier Poulney’s SDSS inspired artwork on show at The Space Inbetween Gallery in London, Jan 2014.

Astronomers attending the UK National Astronomy Meeting in Portsmouth in June will also have a chance to view some of Xavier’s work, which is being shown as part of the public programme linked to the conference.