Free Astronomy Magazine March-April 2023

20 MARCH-APRIL 2023 ASTRO PUBLISHING A ndrew Saydjari, a grad- uate student at Harvard University, researcher at the Center for Astrophysics | Harvard & Smithsonian and lead author of the study. for Astrophysics | Harvard & Smithsonian and lead author of the paper. “Doing so al- lowed us to produce the largest such catalog ever from a single camera, in terms of the number of objects ob- served.” “When combined with im- ages from Pan-STARRS 1, DE- CaPS2 completes a 360-de- gree panoramic view of the Milky Way’s disk and addi- tionally reaches much fainter stars,” said Edward Schlafly, a researcher at the AURA-managed Space Telescope Science Institute and a co-author of the paper describing DECaPS2 published in The Astrophys- ical Journal Supplement . “With this new survey, we can map the three- dimensional structure of the Milky Way’s stars and dust in unprece- dented detail.” “Since my work on the Sloan Digital Sky Survey two decades ago, I have been looking for a way to make better measurements on top of complex backgrounds,” said Douglas Finkbeiner, a professor at the Center for Astrophysics, co-au- thor of the paper, and principal in- vestigator behind the project. “This work has achieved that and more!” “This is quite a technical feat. Imag- ine a group photo of over three billion people and every single in- dividual is recognizable!” says De- bra Fischer, division director of As- tronomical Sciences at NSF. “As- tronomers will be poring over this detailed portrait of more than three billion stars in the Milky Way for decades to come. This is a fantastic example of what partnerships across federal agencies can achieve.” trove of data from DECaPS was re- leased in 2017, and with the addition of the new data release, the survey now covers 6.5% of the night sky and spans a staggering 130 degrees in length. While it might sound mod- est, this equates to 13,000 times the angular area of the full Moon. The DECaPS2 dataset is available to the entire scientific community and is hosted by NOIRLab’s Astro Data Lab, which is part of the Community Science and Data Center. Interactive access to the imaging with panning/ zooming inside of a web-browser is available from the Legacy Survey Viewer, the World Wide Telescope and Aladin. Most of the stars and dust in the Milky Way are located in its disk — the bright band stretching across this image — in which the spi- ral arms lie. While this profusion of stars and dust makes for beautiful images, it also makes the Galactic plane challenging to observe. The dark tendrils of dust seen thread- ing through this image absorb star- light and blot out fainter stars entirely, and the light from diffuse nebulae interferes with any attempts to measure the brightness of individ- ual objects. Another challenge arises from the sheer number of stars, which can overlap in the image and make it difficult to disentangle indi- vidual stars from their neighbors. De- spite the challenges, astronomers delved into the Galactic plane to gain a better understanding of our Milky Way. By observing at near-in- frared wavelengths, they were able to peer past much of the light-ab- sorbing dust. The researchers also used an innovative data-processing approach, which allowed them to better predict the background be- hind each star. This helped to miti- gate the effects of nebulae and crowded star fields on such large as- tronomical images, ensuring that the final catalog of processed data is more accurate. “One of the main reasons for the success of DECaPS2 is that we simply pointed at a region with an extraordinarily high density of stars and were careful about iden- tifying sources that appear nearly on top of each other,” said Andrew Say- djari, a graduate student at Harvard University, researcher at the Center !