How SDSS Talked about Light for #IYL2015

This is a re-posting of the wrap-up article which appeared on the IYL2015 main blog.


2015 has been the International Year of Light.

As astronomers, here at the Sloan Digital Sky Survey everything we do is based on collecting light from cosmic objects. So we have been pleased to celebrate the International Year of Light, and especially the Cosmic Light Theme, supported by the IAU.cosmiclight_color_whitebgAs a small contribution to this celebration, every month in 2015 SDSS had a special blog post talking about the different ways we use light. Here’s a roundup of what we talked about through out the year.

In January we talked about How SDSS Uses Light to Study the Darkest Objects in the Universe. This blog post, by Coleman Krawcyzk and Karen Masters (both from the University of Portsmouth in the UK) with help from Nic Ross (Royal Observatory, Edinburgh) was about finding black holes by looking at the light from distant galaxies. Finding objects which are famous for not emitting any light, using light seems contradictory, but this article explains how the light created by the hot material falling onto a black hole can make these objects outshine the entire galaxy they live in.


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.

In February we wrote about How SDSS Uses Light to Measure the Distances to Galaxies. This of course was about the technique of measuring galaxy redshifts (ie. the shift of their light to longer wavelengths caused by the expansion of the Universe) by looking at absorption and emission lines in galaxy spectra and comparing their wavelength to the laboratory measurement. Edwin Hubble, and others, realised over 80 years ago, that this can be used to give distances to galaxies, as the amount of redshift increases with the galaxy’s distance. The original motivation for SDSS (back in the 1990s) was to used this technique to measure distances to a million galaxies, and in SDSS-IV we are continuing to use this in the eBOSS part of the survey, to map distances to ever more distant galaxies.

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

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

In March, we came back to the most local Universe, with a post by SDSS-IV Spokesperson, Jennifer Johnson (Ohio State University) on How SDSS Uses Light to Understand Stars Inside and Out in the Kepler Field. This was about part of the APOGEE survey, which is measuring spectra from stars which have light curves measured by the Kepler Satellite. This is a valuable experiment, as the combination of spectra and light curves allows us to measure the masses, ages and compositions of these stars.

The Kepler Field. Credit: NASA

The Kepler Field. Credit: NASA

In April, we moved back outside our own Galaxy, to measuring the invisible mass in other galaxies, with a post on How SDSS Uses Light to Explore the Invisible, by the MaNGA Lead Observer, and SDSS-IV Data Release Co-ordinator, Anne-Marie Weijmans from St Andrew University. This post talked about how MaNGA is measuring spectra across the face of nearby galaxies in order to get measurements of the internal motions (again using the redshift/blueshift of the spectra). These measurements give a way to measure the total mass of galaxies, which we find in all cases is much much more than the mass in stars.


For May we went back in the history of SDSS, and talked about How SDSS Used Light to Make the Largest Ever Digital Image of the Night Sky. This post was about the the SDSS camera and the SDSS imaging survey, which ran from 2000-2008, and created a image of over 30% of the sky, containing over a trillion pixels (an image which dwarfs others that have also been claimed as the largest).

The SDSS Camera, now in storage in the Smithsonian Museum. Credit: SDSS, Xavier Poultney

The SDSS Camera, now in storage in the Smithsonian Museum. Credit: SDSS, Xavier Poultney

June also saw a post about SDSS imaging, and about an unexpected use for them, finding asteroids, in How SDSS Uses Light to Find Rocks in Space. This has been beautiful visualized in the below video, by Alex Parker.

If our posts in February, March and April confused you because you didn’t understand what astronomers mean by measuring spectra, then the July post was for you: “How SDSS Splits Light into a Rainbow for Science”.  This post explained all about what spectra are, how to create them with gratings, and contained a with bonus activity to make your own spectroscope created by the SDSS Education and Public Outreach group.

Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2). Longer wavelengths (red) are diffracted more, but refracted less than shorter wavelengths (violet).Credit: Wikimedia

Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2).Credit: Wikimedia

Our August post, by the APOGEE survey Public Engagement officer, David Whelan (from Austin College, Texas)  was about the basic physics of the most abundant element in the Universe (hydrogen): “How SDSS Uses Light to Study the Most Abundant Element in the Universe.”

For September, we visited an IYL2015 Exhibit in Dresden with Zach Pace, Graduate Student at the University of Wisconsin, Madison. Zach reported on SDSS plates on display in the exhibit, linking back to an earlier post in which we explain why we need all these big aluminium plates to do our spectroscopic survey. IYL2015 – SDSS Plates (in Retirement).


SDSS Plate on Exhibit in Dresden.

We went back to the APOGEE survey in October, with a post by Gail Zasowski (from John’s Hopkins University) on How SDSS uses mysterious “missing” light to map the interstellar medium. In this post we learned about how SDSS has helped shed light on the the mystery of missing light caused by absorption in the material which is found between stars in our own Galaxy.

Finally last month, we talked about How SDSS Uses Light to Measure the Mass of Stars in Galaxies. Looking back to the post in February, we claimed that the total mass of galaxies is always much much more than the mass we can count in their stars. But how do we know how much mass is in the stars in a galaxy? This post explains how that can be done using measurements of the light from galaxies.

So that wraps up a year of the celebration of light in the SDSS. We certainly haven’t covered all the ways in which SDSS astronomers are using light to learn about the Universe around us, from asteroids in the solar system, to stars in our own Galaxy and galaxies are the furthest edges of the Universe. But we hope it gives you a flavour for the kinds of things the light collected by SDSS (both images and spectra) can be used for.

If you’re looking for a guided entry into SDSS science (especially suitable for educational use), please visit our site to discover guided journeys through the Universe. As always all SDSS data (through our 12th public data release, DR12) is available free to download, and look out for DR13 (including the first data from SDSS-IV) coming up in mid 2016.


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.

2014-03-08 10.51.19

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’ and we will try to connect you with your nearest SDSS institution.

Tweep of the Week: Sarah Jane Schmidt

In charge of the SDSS Twitter account for this week is Dr. Sarah Jane Schmidt, the Columbus Prize Postdoctoral Fellow in the Department of Astronomy at The Ohio State University

Dr. Sarah Jane Schmidt

Dr. Sarah Jane Schmidt

Dr. Schmidt studies the lowest mass and most numerous types of stars in our Galaxy – the M and L dwarfs. These types of cool stars have strong magnetic fields on their surfaces which results in special kinds of extra light from the stars, including dramatic flare events, which Dr. Schmidt works to observe and understand.

Within the SDSS collaboration, Dr. Schmidt has worked or is working on observing cool stars using spectroscopy from several different surveys:

1. A study of ultracool dwarfs with data from a BOSS (Baryon Oscillation Spectroscopic Survey) ancillary project

2. A TDSS (Time Domain Spectroscopic Survey) project looking at long timescale magnetic field variations on late-M and early-L dwarfs

3. Studying the colors of late-K and early-M dwarfs with measurements of temperature and metallicity from spectroscopic observations taken for the APOGEE survey.

This can all be summarised as spectroscopy of the lowest mass stars there are, and Sarah is most interested in using these to constrain the stars ages and how this relates to their magnetic activity.

We hope you’ll join the conversation with Sarah and other SDSS scientists on twitter this week so we can all learn more about the magnetic fields of the smallest stars in the Universe.

SDSS Tweep of the Week: Qingqing Mao

This week’s tweeter is Qingqing Mao, a graduate student at Vanderbilt University.
Qingqing has a wide range of research interests spanning from the structure of our Milky Way to the very large-scale structure of our universe. He has used both SEGUE and BOSS data for his research. Currently his main project is looking at how to identify cosmic voids – which are large underdense regions with very few galaxies – in BOSS data and use them to study cosmology.
Qingqing Mao

Qingqing Mao

Qingqing also participates in SDSS EPO, especially including social network activities and multilingual efforts. He leads our efforts to keep the SDSS Chinese facebook page and SDSS Chinese Weibo updated.
Qingqing has also developed an astronomy iPhone ap, which allows users to explore data of the Cosmic Microwave Background: CMB Maps.
He regularly tweets as @maoqingqing and his personal website can be found at