  Astronomical precision spectroscopy underpins searches for life beyond Earth,
direct observation of the expanding Universe and constraining the potential
variability of physical constants across cosmological scales. Laser frequency
combs can provide the critically required accurate and precise calibration to
the astronomical spectrographs. For cosmological studies, extending the
calibration with such astrocombs to the ultraviolet spectral range is highly
desirable, however, strong material dispersion and large spectral separation
from the established infrared laser oscillators have made this exceedingly
challenging. Here, we demonstrate for the first time astronomical spectrograph
calibrations with an astrocomb in the ultraviolet spectral range below 400 nm.
This is accomplished via chip-integrated highly nonlinear photonics in
periodically-poled, nano-fabricated lithium niobate waveguides in conjunction
with a robust infrared electro-optic comb generator, as well as a
chip-integrated microresonator comb. These results demonstrate a viable route
towards astronomical precision spectroscopy in the ultraviolet and may
contribute to unlocking the full potential of next generation ground- and
future space-based astronomical instruments.
