Annular Eclipse 2023

The annular solar eclipse on 14 Oct 2023 over the western U.S. provides an additional test for the CATE data acquisition procedures and data processing pipeline prior to the 2024 event. Annular eclipses vary from total eclipses in that the solar disk is not completely occulted by the Moon. In 2023, the ratio between the disks is ~0.94 and annularity lasts just under five minutes for a majority of the path.

While the corona is not visible at an annular eclipse, the partial phases will be visible across the entire U.S. and provide authentic eclipse conditions for practice with the CATE setup. The annular eclipse provides an important opportunity to engage in outreach, test our procedures and equipment, and potentially provide a dataset that can drive final
refinements for the acquisition software and calibration pipeline.

We are hosting a dedicated outreach campaign centered on observations made in Climax, CO, at the site of the first coronagraph operated in the U.S. (Newkirk & Chronic, 1969). Outreach activities at the annular eclipse will help draw attention to the 2024
total eclipse and its importance, both for scientific and cultural reasons. In Climax, we highlight the important history of the site to solar physics in the U.S. and the value of both eclipses and coronagraphs to make measurements of the otherwise inaccessible corona to support both scientific research and, in the case of coronagraphs, space weather forecasts.

At the Climax site, at ~11,200 feet, airmass (the amount of atmosphere along the line of sight) is reduced by about ~30% compared to sea level, and coronagraphic observations are sometimes possible in the absence of an eclipse. We leverage the partial eclipse here, with a maximum of 82% obscuration, to attempt to observe the solar corona using a CATE 2024 setup modified for coronagraphic observations.

Although the eclipse itself does not itself reveal the corona, it reduces background sky brightness significantly, and reduces the light that must be rejected by a coronagraph by a factor of >5, improving the chances of reaching the conditions at which the corona can be observed at this high altitude.

We modify the CATE setup using an existing prototype low-diffraction occulter system constructed at SwRI during development of a space-based compact coronagraph, additional baffling at the entrance aperture to reject off-axis stray light from the ambient environment, and additional stops within the optical system to further reject stray light as necessary. The polarimetric observations of the CATE imaging system permit us to separate the polarized corona from the unpolarized background sky brightness.

History of climax: