We present New Horizons Alice spectral observations of interstellar hydrogen Ly alpha emissions at a vantage point of 57 au from the Sun. The observations were conducted as a pair of orthogonal scans to produce high spatial angular resolution measurements of a dark patch of sky located at high Galactic latitudes. We find that the brightness of the UV background remains relatively constant over the selected sky region, with the exception of areas near a few bright stars and galaxies. Most stars do not affect the brightness of Ly alpha in this region; however, we detect a 25 Rayleigh Ly alpha enhancement near the location of hot subdwarf CD-38 222. This enhancement is consistent with nebular emission produced by ionizing photons from a bow shock as the object interacts with a high-latitude interstellar gas cloud. We do not find correlations of Ly alpha or background UV brightness with dust structures seen by the Planck space observatory. Our analysis at higher angular resolution and with the full Alice bandpass of 520-1870 & Aring; confirms the results of the global Ly alpha maps produced by G. R. Gladstone et al. at lower spatial resolution. The near-constant Ly alpha is consistent with their interpretation that scattering of H within our Local Bubble produces a nearly isotropic Ly alpha distribution. Future Alice global scans in photometer mode can be used to assess changes in the Ly alpha sky as a function of solar distance. High-resolution FUV Ly alpha scans with the full spatial and spectral information should be repeated over the entire sky to resolve additional small-scale structures.

We present observations of the cosmic ultraviolet background (CUVB) from 912 - 1600 A using the Stem aperture of the Alice spectrograph on the New Horizons spacecraft at 56 AU from the Sun, providing a spectral resolution of 9 A for diffuse sources. We detect emission lines of CIII (977 A) and CIV (1548/1551 A) at the 3 sigma level with strengths of 4200 +/- 1500 and 4100 +/- 1200 ph cm(-2) s(-1) sr(-1), respectively, and a marginal detection of OVI (1032/1038 A) at 1400 +/- 1300 ph cm(-2) s(-1) sr(-1). We report a 3 sigma detection of an emission line at 1135 A, which we have identified with the N I resonance triplet. Although this line had earlier been observed in FUSE and SPEAR data, it had been attributed to airglow or instrumental effects. We confirm, for the first time, that it must originate in the Galaxy. The dust-scattered continuum is dominated by a small number (N < 100) of O9 - B2 stars and shows the deep absorption feature near 1000 A seen in the stellar spectrum. Our models suggest an albedo of a < 0.5 over most of the spectrum (950 – 1550 A) for the dust grains with the phase function asymmetry of g < 0.6. We find an offset, comprising the extragalactic background light and halo contributors, consistent with our earlier results from the Box, including the decline in the offset near the Lyman limit. We confirm that much of the emission must be from an unidentified component of the CUVB.

We have used archival GALEX data to separate the cosmic ultraviolet background at the Galactic Poles into two components: the dust scattered light and an offset. We have modeled the dust-scattered light using a single- scattering model finding 1 sigma limits of 0.54 – 0.71 for the albedo (a) and 0.74 – 0.83 for the phase function asymmetry factor (g) at 1530 Å and 0.66 – 0.73 for a and 0.71 – 0.77 for g at 2360 Å, that is, the grains are moderately reflective and highly forward-scattering. The offsets are 277 – 284 photon units at 1530 Å and 513 – 520 photon units at 2360 Å. We have estimated other Galactic and extragalactic contributors to the offset finding that 161 +- 18 photon units is unaccounted for at 1530 Å and 335 +- 38 at 2360 Å. The offsets are constant over these regions with variances of 20 – 30 photon units.

The Earth possesses many environmental extremes that mimic conditions on extraterrestrial worlds. The stratosphere at 30-40 km altitude closely resembles the surface of Mars in terms of pressure, temperature, and radiation levels (UV, proton, and Galactic cosmic rays). While microbial life in the troposphere is well documented, the true upper limit of Earth's biosphere remains unclear. The stratosphere offers a promising environment to explore microbial survival in such extreme conditions. Despite its significance to astrobiology, this region remains largely unexplored due to difficulties in access and avoiding contamination. To address this, we have developed SAMPLE (Stratospheric Altitude Microbiology Probe for Life Existence), a balloon-borne payload designed to collect dust samples from the stratosphere and return them in conditions suitable for lab analysis. The entire system is novel and designed in-house, with weight- and stress-optimized components. The main payload includes three pre-sterilized sampling trays and a controller that determines altitude and governs tray operation. One tray will remain closed during flight (airborne control) and another on the ground (cleanroom control) to monitor contamination. Additional systems include environmental sensors, GPS trackers, cameras, and a Flight Termination Unit (FTU) to end the mission once sampling is complete. A parachute ensures the safe recovery of the payload. Upon retrieving the payload, the sampling trays (including controls) will be sent to a suitable laboratory where the samples will be examined for the presence and nature of collected material.

During 2023 September the Alice ultraviolet spectrograph on the New Horizons (NH) spacecraft was used to map diffuse Lyα emission over most of the sky, at a range of ∼56.9 au from the Sun. At that distance, models predict that the interplanetary medium Ly α emissions result from comparable amounts of resonant backscattering of the solar Ly α line by interstellar hydrogen atoms (H i ) passing through the solar system, in addition to an approximately isotropic background of ∼50 ± 20 R from the local interstellar medium (LISM). The NH observations show no strong correlations with nearby cloud structures of the LISM or with expected structures of the heliosphere, such as a hydrogen wall associated with the heliopause. To explain the relatively bright and uniform Ly α of the LISM, we propose that hot, young stars within the Local Hot Bubble shine on its interior walls, photoionizing H i atoms there. Recombination of these ions can account for the observed ∼50 R Ly α background, after amplification of the diffuse Ly α by resonant scattering, although sophisticated (i.e., 3D) radiative transfer models should be used to confirm this conjecture. Future observations of the diffuse Ly α , with instruments capable of resolving the line profile, could provide a new window on H i populations in the LISM and heliosphere. The NH Alice all-sky Ly α observations presented here may be repeated at some point in the future, if resources allow, and the two maps could be combined to provide a significant increase in angular resolution.

Murthy et al. (2025) (hereafter Paper I) have recently reported the discovery of unexpectedly bright diffuse extreme-ultraviolet radiation at high latitudes in both the Northern and Southern Galactic Hemispheres. After correction for extinction by the total interstellar dust in the direction of each observation, the spectra are nearly identical, suggesting that the radiation has a unique source and likely originates in the halo of our galaxy. The observed spectrum extends down to 912 Å, the interstellar hydrogen absorption edge. Radiation even slightly short of that edge would, if ubiquitous, be sufficient to explain the high degree of ionization in our galaxy and throughout the universe. We hypothesize that this newly discovered radiation originates in the slow decay of dark matter. The intensity of the radiation implies that the decay cannot be via the weak interaction, suggesting the existence of a new, even weaker fundamental interaction, consistent with the exceedingly long decay lifetime required.

I explore models of the dust-scattered component of the cosmic ultraviolet background (CUVB) at the north galactic pole (NGP) to develop a framework for calculating the dust-scattered light as a function of the optical depths. As expected, I find that the dust-scattered emission scales linearly, with reddening up to E(B-V) ≈ 0.1 mag and derive a parametric model for this dependence. I have applied these models to fit the far-ultraviolet (1350–1800 Å) observations from the galaxy evolution explorer (GALEX) finding that the optical constants of the interstellar dust grains—albedo (a) and phase function asymmetry factor (g)—are consistent with predictions from the Astrodust model ( a = 0.33 , g = 0.68 ). I detect an isotropic offset of 267 ± 7 ph cm ^-2 s ^-1 sr ^-1 Å ^-1 , half of which remains unaccounted for, by known Galactic or extragalactic sources. I will now extend my analysis to wider sky regions with the goal of generating high-resolution extinction maps.

The Near Ultraviolet Transient Explorer (NUTEx) is a CubeSat-based near-ultraviolet (NUV) imaging payload designed for transient sky surveys and is currently under development. CubeSats are compact and cost-effective satellite platforms that have emerged as versatile tools for scientific exploration and technology demonstrations in space. NUTEx is an imaging telescope operating in the 200–300 nm wavelength range, intended for deployment on a micro-satellite bus. The optical system is based on a Ritchey–Chrétien (RC) telescope configuration, featuring a 146-mm primary mirror. The detector is a photon-counting microchannel plate (MCP) device with a solar-blind photocathode, paired with an in-house-developed readout unit. The instrument has a wide field of view (FoV) of 4°, a peak effective area of approximately 18 cm2 at 260 nm, and can reach a sensitivity of 21 AB magnitude (SNR = 5) in a 1200-s exposure. The primary scientific objective of NUTEx is to monitor the night sky for transient phenomena, such as supernova remnants, flaring M-dwarf stars, and other short-timescale events. The payload is currently scheduled for launch in Q2-2026. This paper presents the NUTEx instrument design, outlines its scientific goals and capabilities, and provides an overview of the electronics and mechanical subsystems, including structural analysis.

We present new observations of the cosmic ultraviolet background (CUVB) at high Galactic latitudes (∣ b ∣ > 40 ∘ ), made using the Alice UV spectrograph on board the New Horizons spacecraft. These observations were taken at about 57 au from the Sun, outside much of the foreground emission affecting previous missions, and allowed a new determination of the spectrum of the CUVB between 912–1100 Å and 1400–1800 Å. We found a linear correlation between the CUVB and the Planck E ( B − V ) with offsets at zero-reddening of 221 ± 11 photon units at 1000 Å and 264 ± 24 photon units at 1500 Å (4.4 ± 0.2 nW m −2 sr −1 at 1000 Å and 5.3 ± 0.5 nW m −2 sr −1 at 1500 Å). The former is the first firm detection of the offset in the range 912–1100 Å while the latter result confirms previous results from the Galaxy Evolution Explorer, showing that there is little emission from the solar system from 1400 to 1800 Å. About half of the offset may be explained by known sources (the integrated light of unresolved galaxies, unresolved stars, emission from ionized gas, and two-photon emission from warm hydrogen in the halo) with the source of the remaining emission as yet unidentified. There is no detectable emission below the Lyman limit with an upper limit of 3.2 ± 3.0 photon units.

We report results of intensive time-resolved imaging photometry and synoptic deep imaging of the comet C/2012 S1 (ISON) performed in February 2013. The data were obtained at the Wise Observatory in Israel (WO), at the Himalayan Chandra Telescope (HCT) in India, and at the Polaris Observatory Association in California, USA. During this period, the comet's heliocentric distance changed from 4.9 to 4.6 AU, just within the orbit of Jupiter. We analyze these early images in an attempt to determine the nuclear rotation period, assuming that at these relatively large heliocentric distances it would be possible to detect the photometric modulation of a rotating nucleus against an underdeveloped coma. Since this is not evident in our February 2013 data, with more than 400 independent photometric measurements analyzed, we can only set upper limits of 0.05 mag for periodic brightness modulations. We discuss (and discount) a possible brightening event (minor outburst) that occurred on 15-16 February 2013. We also present deep synoptic images of the comet, obtained by combining our exposures for each night, and analyze them. We find that during the period of our observations the comet exhibited a ∼30^''≃ 60000-km tail with no substructures visible and that this appearance did not change throughout our campaign. The comet, as indicated by a single spectroscopic measurement obtained during this observation period, showed a dust coma reflecting the solar light. Our observations indicate that during February 2013, comet ISON was relatively quiet, with the dust coma presumably hiding any light modulation by a spinning nucleus.

We present here an STM32 microcontroller based on-board computer designed for use in small satellites and CubeSat missions that was developed using commercial-off-the-shelf (COTS) electronics components. An on-board computer (OBC) is one of the important subsystems of any CubeSat mission. An on-board computer is the central brain of a CubeSat or small satellite, responsible for coordinating and controlling various subsystems to achieve mission objectives efficiently and autonomously. It performs crucial tasks such as power management, communication, command and data handling, on-board data processing and on-board software execution. This paper discusses the development of one such OBC designed for a spectroscopic mission called Spectroscopic Investigator of Nebular Gas (SING).

. Star sensors are an essential instrument used to determine the attitude of satellites by identifying the stars in the field of view. The high cost and large sizes of commercially available star sensors pose challenges for small satellite missions. We at the Indian Institute of Astrophysics have developed a low-cost star sensor, StarberrySense, based on the Raspberry Pi as the main controller and built from commercial off-the-shelf components. The StarberrySense was flown on the PS4 experimental orbital platform module of the Polar Satellite Launch Vehicle C-55 by the Indian Space Research Organization. This work describes the flight hardware, environmental tests in preparation for the flight, and in-orbit performance of our StarberrySense.

In ultraviolet (UV) astronomical observations, photons from the sources are very few compared to the visible or infrared (IR) wavelength ranges. Detectors operating in the UV usually employ a photon-counting mode of operation. These detectors usually have an image intensifier sensitive to UV photons and a readout mechanism that employs photon counting. The development of readouts for these detectors is resource-intensive and expensive. In this paper, we describe the development of a low-cost UV photon-counting detector processing unit that employs a Raspberry Pi with its in built readout to perform the photon-counting operation. Our system can operate in both 3x3 and 5x5 window modes at 30 frames per sec (fps), where 5x5 window mode also enables the provision of detection of double events. The system can be built quickly from readily available custom-off-the-shelf (COTS) components and is thus used in inexpensive CubeSats or small satellite missions. This low-cost solution promises to broaden access to UV observations, advancing research possibilities in space-based astronomy.

The 2175 angstrom bump shows considerable variations in its strength, width, and central wavelength when observed along different sightlines in the Milky Way and other galaxies. These variations offer valuable insights into the composition, size distribution, and processing of interstellar dust grains along different sightlines. This paper introduces a mission concept called UVESS (Ultra Violet Extinction Sky Survey) aimed at exploring the composition of the interstellar medium (ISM) within both the Milky Way and nearby Local Group Galaxies by mapping the variation of UV extinction curve slopes and the 2175 angstrom feature across a majority of the sky to gain insights into the makeup of the ISM. Recent advancements in UV instrumentation and technologies pave the way for the development of high-throughput instruments in compact form factors. In this paper, we outline mission science goals and instrument concept tailored for a small satellite-based platform dedicated to the study of UV extinction.

This article describes the development of a space-based near-Ultraviolet (NUV) spectrograph, focusing on the intricate fabrication and meticulous evaluation of an optical slit employing advanced techniques such as optical lithography and deep reactive ion etching (DRIE). The fabrication process entails a precise definition of the slit pattern on silicon wafer substrates through optical lithography, followed by the transfer of the pattern into the substrate material using DRIE. The resultant optical slit boasts sub-angstrom surface roughness and nanometerscale slit width uniformity, essential for achieving superior spectrographic performance. Through comprehensive evaluation methodologies, including interferometry and spectrophotometry, the optical slit's spectral resolution, throughput, and stray light rejection are rigorously examined. These breakthroughs promise to elevate the sensitivity, resolution, and dependability of space-based NUV spectrographic instruments, enabling deeper exploration of celestial phenomena and cosmic evolution.

The Ultra Violet Imaging Telescope (UVIT) onboard India's first dedicated multiwavelength satellite AstroSat observed a significant fraction of the sky in the ultraviolet with a spatial resolution of 1.4''. We present a catalogue of the point sources observed by UVIT in the far ultraviolet (FUV; 1 300-1 800 angstrom) and near ultraviolet (NUV; 2 000-3 000 angstrom). We carried out astrometry and photometry of 428 field pointings in the FUV and 54 field pointings in the NUV band, observed in 5 filter bands in each channel, respectively, covering an area of about 63 square degrees. The final catalogue contains about 102 773 sources. The limiting magnitude(AB) of the F148W band filter, that has the largest number of detections is similar to 21.3. For the NUV channel, we find the limiting magnitude at around similar to 23. We describe the final catalogue and present the results of the statistical analysis.

The Spectroscopic Investigation of Nebular Gas (SING) is a near-ultraviolet (NUV) low-resolution spectrograph payload designed to operate in the NUV range, 1400 $\unicode{x212B}$ -- 2700 $\unicode{x212B}$, from a stable space platform. SING telescope has a primary aperture of 298 mm, feeding the light to the long-slit UV spectrograph. SING has a field of view (FOV) of 1$^{\circ}$, achieving a spatial resolution of 1.33 arc minute and spectral resolution of 3.7 $\unicode{x212B}$ ($R\sim600$) at the central wavelength. SING employs a micro-channel plate (MCP) with a CMOS readout-based photon-counting detector. The instrument is designed to observe diffuse sources such as nebulae, supernova remnants, and the interstellar medium (ISM) to understand their chemistry. SING was selected by the United Nations Office for Outer Space Affairs to be hosted on the Chinese Space Station. The instrument will undergo qualification tests as per the launch requirements. In this paper, we describe the hardware design, optomechanical assembly, and calibration of the instrument.

We have modeled the diffuse background at the Galactic Poles in the far-ultraviolet (FUV: 1536 Å) and the near-ultraviolet (NUV: 2316 Å). The background is well-fit using a single-scattering dust model with an offset representing the extragalactic light plus any other contribution to the diffuse background. We have found a dust albedo of 0.35–0.40 (FUV) and 0.11–0.19 in the NGP ( b > 70^∘ ) and 0.46–0.56 (FUV) and 0.31–0.33 (NUV) in the SGP ( b < 70^∘) . The differences in the albedo may reflect changes in the dust-to-gas ratio over the sky or in the dust distribution. We find offsets at zero-reddening of 273–286 and 553–581 photons cm^-2 s^-1 sr^-1 Å ^-1 in the FUV and NUV, respectively, in the NGP with similar values in the SGP.