Data Set Overview : This data set contains scans of Lyman-alpha emission from neutral hydrogen in the interplanetary medium obtained by the New Horizons Alice Ultraviolet Imaging Spectrograph. This dataset provides 135155 measurements of the total instrument count rate at 1 second cadence. Each measurement lists the Mission Elapsed Time (MET, in seconds of time from the New Horizons launch on January 19, 2006) and the total analog count rate observed by the Alice instrument. That count rate includes instrumental background counts, which primarily are from the radioisotope thermoelectric generator (RTG) and stimulated pixels, and have a typical level of 120 counts/s. The sky UV brightness is highly dominated by solar Lyman-alpha emission that is scattered by interstellar hydrogen atoms passing through the solar system, so the counts above the instrumental background in this dataset are assumed to be due to Lyman-alpha except for the noteable spikes of brightness whenever stars pass through the slit. The Alice sensitivity to diffuse Lyman-alpha emissions is S : 4.92+/-0.09 counts/s/R (where 1 R : 1 Rayleigh : 10^6 photons/cm^2/s/4 pi steradian), so to convert count rates to brightness, one would subtract 120 from the value and divide the remainder by 4.92 to get a brightness in units of Rayleighs. Also provided for each measurement are the 44 right ascensions and 44 declinations of the rows of the Alice slit on the sky, in units of decimal degrees, using definitions provided in the SPICE Alice instrument kernel (nh_alice_v200.ti). For each case, SPICE is used to calculate the RA/Dec for Alice row corners at 1 second cadence. For all cases, for METs where the count rate is not available or cannot be inferred, its value is set to -1. A full description of the processing and analysis of these data can be found in [GLADSTONEETAL2018]. Version : This is VERSION 1.0 of this data set. Instrument description ---------------------- Refer to the following files for a description of this instrument. CATALOG ALICE.CAT DOCUMENTS ALICE_SSR.* SOC_INST_ICD.* NH_ALICE_V###_TI.TXT (### is a version number) Other sources of information useful in interpreting these Data -------------------------------------------------------------- Refer to the following files for more information about these data NH Trajectory tables: /DOCUMENT/NH_MISSION_TRAJECTORY.* - Heliocentric ALICE Field Of View definitions: /DOCUMENT/NH_FOV.* /DOCUMENT/NH_ALICE_V###_TI.TXT Contact Information : For any questions regarding the data format of the archive, contact New Horizons ALICE Principal Investigator: S. Alan Stern Southwest Research Institute (SwRI) Department of Space Studies 1050 Walnut Street, Suite 400 Boulder, CO 80302 USA

This data set contains higher level products derived from data taken by the Alice Ultraviolet Imaging Spectrograph. For more details about how Alice data are processed and the reliability of the most recent calibration effort, see the raw and calibrated data sets from the Arrokoth Encounter: NH-A-ALICE-2-KEM1-V5.0 NH-A-ALICE-3-KEM1-V5.0 Review : This dataset was peer reviewed and certified for scientific use by the PDS.