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This report first describes the status quo regarding the emerging deployment of very large groups of low-Earth-orbit satellites in the late 2010s, the concerns raised by the international astronomy community, and steps the community took to address the issue. We then describe the results of a series of four conferences held in 2020-21 that considered the impacts of large satellite constellations as it impacted a number of stakeholders, and how those outcomes resulted in the establishment of both the IAU Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS) and its Community Engagement (CE) Hub. We finish with a brief description of CE Hub's initial plans and activities, flowing from the recommendations of those conferences., Comment: 18 pages

Fifty years after the first mention of light pollution in Science, the journal recently elevated this topic to the cover of its 16 June 2023 issue, highlighting the large impact on human and ecological health, circadian rhythms, migratory patterns, and more. We offer here the term noctalgia to express "sky grief" for the accelerating loss of the home environment of our shared skies - representing loss of science, heritage, millennia-old sky traditions, place-based language, and more - and summarize next steps to address the protection of our nighttime and daytime skies., Comment: 2 pages; published as a Science e-Letter in response to the Introduction of the Special Section on light pollution in the June 16, 2023 issue of Science. E-letter available only online (hyperlink in PDF)

The rising population of artificial satellites and associated debris in low-altitude orbits is increasing the overall brightness of the night sky, threatening ground-based astronomy as well as a diversity of stakeholders and ecosystems reliant on dark skies. We present calculations of the potentially large rise in global sky brightness from space objects, including qualitative and quantitative assessments of how professional astronomy may be affected. Debris proliferation is of special concern: since all log-decades in debris size contribute approximately the same amount of night sky radiance, debris-generating events are expected to lead to a rapid rise in night sky brightness along with serious collision risks for satellites from centimetre-sized objects. This will lead to loss of astronomical data and diminish opportunities for ground-based discoveries as faint astrophysical signals become increasingly lost in the noise. Lastly, we discuss the broader consequences of brighter skies for a range of sky constituencies, equity/inclusion and accessibility for Earth- and space-based science, and cultural sky traditions. Space and dark skies represent an intangible heritage that deserves intentional preservation and safeguarding for future generations., Comment: 22 pages, 2 figures, 1 table; accepted for publication by Nature Astronomy

Our planet and our species are at an existential crossroads. In the long term, climate change threatens to upend life as we know it, while the ongoing COVID-19 pandemic revealed that the world is unprepared and ill-equipped to handle acute shocks to its many systems. These shocks exacerbate the inequities and challenges already present prior to COVID in ways that are still evolving in unpredictable directions. As weary nations look toward a post-COVID world, we draw attention to both the injustice and many impacts of the quiet occupation of near-Earth space, which has rapidly escalated during this time of global crisis. The communities most impacted by climate change, the ongoing pandemic, and systemic racism are those whose voices are missing as stakeholders both on the ground and in space. We argue that significant domestic and international changes to the use of near-Earth space are urgently needed to preserve access to - and the future utility of - the valuable natural resources of space and our shared skies. After examining the failure of the U.S. and international space policy status quo to address these issues, we make specific recommendations in support of safer and more equitable uses of near-Earth space., Comment: 18 pages; published in Virginia Policy Review, Vol. XV, Issue 1 (Spring 2022), pp. 58-86

Ground-based optical astronomy necessarily involves sensing the light of astronomical objects along with the contributions of many natural sources ranging from the Earth's atmosphere to cosmological light. In addition, astronomers have long contended with artificial light pollution that further adds to the 'background' against which astronomical objects are seen. Understanding the brightness of the night sky is therefore fundamental to astronomy. The last comprehensive review of this subject was nearly a half-century ago, and we have learned much about both the natural and artificial night sky since. This Review considers which influences determine the total optical brightness of the night sky; the means by which that brightness is measured; and how night sky quality is assessed and monitored in the long term., Comment: 39 pages, 6 figures; accepted for publication by Nature Astronomy

The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite `mega-constellations' in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached $\sim$20 $\mu$cd m$^{-2}$, which amounts to an approximately 10 percent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories., Comment: Accepted for publication in MNRAS-L, with minor corrections. 6 pages, 4 figures

Anthropogenic skyglow dominates views of the natural night sky in most urban settings, and the associated emission of artificial light at night (ALAN) into the environment of cities involves a number of known and suspected negative externalities. One approach to lowering consumption of ALAN in cities is dimming or extinguishing publicly owned outdoor lighting during overnight hours; however, there are few reports in the literature about the efficacy of these programs. Here we report the results of one of the largest municipal lighting dimming experiments to date, involving $\sim$20,000 roadway luminaires owned and operated by the City of Tucson, Arizona, U.S. We analyzed both single-channel and spatially resolved ground-based measurements of broadband night sky radiance obtained during the tests, determining that the zenith sky brightness during the tests decreased by ($-5.4\pm0.9$)% near the city center and ($-3.6\pm0.9$)% at an adjacent suburban location on nights when the output of the street lighting system was dimmed from 90% of its full power draw to 30% after local midnight. Modeling these changes with a radiative transfer code yields results suggesting that street lights account for about ($14\pm1$)% of light emissions resulting in skyglow seen over the city. A separate derivation from first principles implies that street lighting contributes only 2-3% of light seen at the zenith over Tucson. We discuss this inconsistency and suggest routes for future work., Comment: 44 pages, 9 figures; accepted by Journal of Quantitative Spectroscopy and Radiative Transfer

The transition from earlier lighting technologies to white light-emitting diodes (LEDs) is a significant change in the use of artificial light at night. LEDs emit considerably more short-wavelength light into the environment than earlier technologies on a per-lumen basis. Radiative transfer models predict increased skyglow over cities transitioning to LED unless the total lumen output of new lighting systems is reduced. The City of Tucson, Arizona (U.S.), recently converted its municipal street lighting system from a mixture of fully shielded high- and low-pressure sodium (HPS/LPS) luminaires to fully shielded 3000 K white LED luminaires. The lighting design intended to minimize increases to skyglow in order to protect the sites of nearby astronomical observatories without compromising public safety. This involved the migration of over 445 million fully shielded HPS/LPS lumens to roughly 142 million fully shielded 3000 K white LED lumens and an expected concomitant reduction in the amount of visual skyglow over Tucson. SkyGlow Simulator models predict skyglow decreases on the order of 10-20% depending on whether fully shielded or partly shielded lights are in use. We tested this prediction using visual night sky brightness estimates and luminance-calibrated, panchromatic all-sky imagery at 15 locations in and near the city. Data were obtained in 2014, before the LED conversion began, and in mid-2017 after approximately 95% of $\sim$18,000 luminaires was converted. Skyglow differed marginally, and in all cases with valid data changed by $<{\pm}$20%. Over the same period, the city's upward-directed optical radiance detected from Earth orbit decreased by approximately 7%. While these results are not conclusive, they suggest that LED conversions paired with dimming can reduce skyglow over cities., Comment: 34 pages, 16 figures, presented at "Light Pollution: Theory, Modelling and Measurements" (Cellers, Spain, 27-30 June 2017); accepted by Journal of Quantitative Spectroscopy and Radiative Transfer (9 February 2018, manuscript JQSRT_2017_636_R1)

We present new constraints on the density profiles of dark matter (DM) halos in seven nearby dwarf galaxies from measurements of their integrated stellar light and gas kinematics. The gas kinematics of low mass galaxies frequently suggest that they contain constant density DM cores, while N-body simulations instead predict a cuspy profile. We present a data set of high resolution integral field spectroscopy on seven galaxies and measure the stellar and gas kinematics simultaneously. Using Jeans modeling on our full sample, we examine whether gas kinematics in general produce shallower density profiles than are derived from the stars. Although 2/7 galaxies show some localized differences in their rotation curves between the two tracers, estimates of the central logarithmic slope of the DM density profile, gamma, are generally robust. The mean and standard deviation of the logarithmic slope for the population are gamma=0.67+/-0.10 when measured in the stars and gamma=0.58+/-0.24 when measured in the gas. We also find that the halos are not under concentrated at the radii of half their maximum velocities. Finally, we search for correlations of the DM density profile with stellar velocity anisotropy and other baryonic properties. Two popular mechanisms to explain cored DM halos are an exotic DM component or feedback models that strongly couple the energy of supernovae into repeatedly driving out gas and dynamically heating the DM halos. We investigate correlations that may eventually be used to test models. We do not find a secondary parameter that strongly correlates with the central DM density slope, but we do find some weak correlations. Determining the importance of these correlations will require further model developments and larger observational samples. (Abridged), Comment: 29 pages, 18 figures, 10 tables, accepted for publication in ApJ

We report the results of a spectroscopic study of the high-mass protostellar object NGC 7538 IRS 9 and compare our observations to published data on the nearby object NGC 7538 IRS 1. Both objects originated in the same molecular cloud and appear to be at different points in their evolutionary histo- ries, offering an unusual opportunity to study the temporal evolution of envelope chemistry in objects sharing a presumably identical starting composition. Observations were made with the Texas Echelon Cross Echelle Spectrograph (TEXES), a sensitive, high spectral resolution (R = {\lambda}/{\Delta}{\lambda} \simeq 100,000) mid-infrared grating spectrometer. Forty-six individual lines in vibrational modes of the molecules C2H2, CH4, HCN, NH3 and CO were detected, including two isotopologues (13CO, 12C18O) and one combination mode ({\nu}4 + {\nu}5 C2H2). Fitting synthetic spectra to the data yielded the Doppler shift, excitation temperature, Doppler b parameter, column density and covering factor for each molecule observed; we also computed column density upper limits for lines and species not detected, such as HNCO and OCS. We find differences among spectra of the two objects likely attributable to their differing radiation and thermal environments. Temperatures and column densities for the two objects are generally consistent, while the larger line widths toward IRS 9 result in less saturated lines than those toward IRS 1. Finally, we compute an upper limit on the size of the continuum-emitting region (\sim2000 AU) and use this constraint and our spectroscopy results to construct a schematic model of IRS 9., Comment: 23 pages, 15 figures, 6 tables; accepted for publication in ApJ

Galaxy formation and growth under the {\Lambda}CDM paradigm is expected to proceed in a hierarchical, bottom-up fashion by which small galaxies grow into large galaxies; this mechanism leaves behind large "classical bulges" kinematically distinct from "pseudobulges" grown by internal, secular processes. We use archival data (Spitzer 3.6 \mum wavelength, Hubble Space Telescope H-band, Two Micron All Sky Survey Ks-band, and Sloan Digital Sky Survey gri-band) to measure composite minor- and major-axis surface brightness profiles of the almost-edgeon spiral galaxy NGC 5746. These light profiles span a large range of radii and surface brightnesses to reveal an inner, high surface brightness stellar component that is distinct from the well-known boxy bulge. It is well fitted by S\'ersic functions with indices n = 0.99 \pm 0.08 and 1.17 \pm 0.24 along the minor and major axes, respectively. Since n < 2, we conclude that this innermost component is a secularly-evolved pseudobulge that is distinct from the boxy pseudobulge. This inner pseduobulge makes up 0.136 \pm 0.019 of the total light of the galaxy. It is therefore considerably less luminous than the boxy structure, which is now understood to be a bar seen nearly end-on. The infrared imagery shows further evidence for secular evolution in the form of a bright inner ring of inner radius 9.1 kpc and width 1.6 kpc. NGC 5746 is therefore a giant, pure-disk SB(r)bc galaxy with no sign of a merger-built bulge. We do not understand how such galaxies form in a {\Lambda}CDM universe., Comment: 23 pages, 7 figures, 2 tables; accepted for publication in ApJ

Numerical simulations show that box-shaped bulges of edge-on galaxies are not bulges: they are bars seen side-on. Therefore the two components that are seen in edge-on Sb galaxies such as NGC 4565 are a disk and a bar. But face-on SBb galaxies always show a disk, a bar, and a (pseudo)bulge. Where is the (pseudo)bulge in NGC 4565? We use archival Hubble Space Telescope H-band images and Spitzer Space Telescope 3.6 micron wavelength images, both calibrated to 2MASS K_s band, to penetrate the prominent dust lane in NGC 4565. We find a high surface brightness, central stellar component that is clearly distinct from the boxy bar and from the disk. Its brightness profile is a Sersic function with index n = 1.55 +- 0.07 along the major axis and 1.33 +- 0.12 along the minor axis. Therefore it is a pseudobulge. It is much less luminous than the boxy bar, so the true pseudobulge-to-total luminosity ratio of the galaxy is PB/T = 0.06 +- 0.01, much less than the previously believed value of B/T = 0.4 for the boxy bulge. We infer that published B/T luminosity ratios of edge-on galaxies with boxy bulges have been overestimated. Therefore, more galaxies than we thought contain little or no evidence of a merger-built classical bulge. From a formation point of view, NGC 4565 is a giant, pure-disk galaxy. This presents a challenge to our picture of galaxy formation by hierarchical clustering: it is difficult to grow galaxies as big as NGC 4565 without also making big classical bulges., Comment: Four pages, 3 figures; requires emulateapj.sty, psfig.tex; accepted for publication in ApJ (Letters); for a version with full resolution figures, see http://chandra.as.utexas.edu/~kormendy/NGC4565.pdf

N-body simulations show that "box-shaped bulges" of edge-on galaxies are not bulges at all: they are bars seen side-on. The two components that we readily see in edge-on Sb galaxies like NGC 4565 are a disk and a bar, but face-on SBb galaxies always show a disk, a bar, and a (pseudo)bulge. Where is the (pseudo)bulge in NGC 4565? We use archival Hubble Space Telescope K-band and Spitzer Space Telescope 3.6 um images to penetrate the dust in NGC 4565. We find a high surface brightness, central stellar component, distinct from the boxy bar and from the galaxy's disk. Its minor-axis profile has a Sersic index of 1.33+/-0.12, so it is a pseudobulge. The pseudobulge has the smallest scale height (~90 pc) of any component in the galaxy, in contrast to ~740 pc for the boxy bar plus thin disk. The disky pseudobulge is also much less luminous than the boxy bar, so the true (pseudo)bulge-to-total luminosity ratio of the galaxy is much less than previously thought. We infer that the pseudobulge-to-total luminosity ratios of edge-on galaxies with box-shaped bulges have generally been overestimated. Therefore more galaxies than we have recognized contain little or no evidence of a merger-built classical bulge. This challenges our picture of galaxy formation by hierarchical clustering, because it is difficult to grow big galaxies without also making a big classical bulge. Solving the puzzle of the "missing pseudobulge" in NGC 4565 further increases our confidence that we understand box-shaped bulges correctly as edge-on bars. This supports our developing picture of the formation of pseudobulges -- both edge-on bars and disky central components -- by secular evolution in isolated galaxies., Comment: 5 pages, 3 figures, requires asp2006.sty, to be published in Galaxy Evolution: Emerging Insights and Future Challenges, ed. S. Jogee et al., Astron. Soc. Pacific, 2009

We present a catalogue of morphologically classified bright galaxies in the north equatorial stripe (230 deg$^2$) derived from the Third Data Release of the Sloan Digital Sky Survey (SDSS). Morphological classification is performed by visual inspection of images in the $g$ band. The catalogue contains 2253 galaxies complete to a magnitude limit of $r=16$ after Galactic extinction correction, selected from 2658 objects that are judged as extended in the photometric catalogue in the same magnitude limit. 1866 galaxies in our catalogue have spectroscopic information. A brief statistical analysis is presented for the frequency of morphological types and mean colours in the catalogue. A visual inspection of the images reveals that the rate of interacting galaxies in the local Universe is approximately 1.5% in the $r\le16$ sample. A verification is made for the photometric catalogue generated by the SDSS, especially as to its bright end completeness., Comment: Accepted for publication in Astronomical Journal. Table 2 available at http://www.icrr.u-tokyo.ac.jp/~fukugita/MCGpaper/table2.txt