During the peak of this weekend’s partial solar eclipse, as much as 86 percent of the Sun’s disk will be eclipsed in some of the most distant waters of the South Pacific. For viewers in the southern portion of New Zealand’s South Island, the Moon will conceal up to 73 percent of the Sun shortly after sunrise, sending a striking crescent of light across the horizon. The moment of maximum eclipse will be at 3:41 p.m. Eastern Time (17:41 UTC), as the penumbral shadow of the Moon passes over the Southern Ocean, south of New Zealand and close to Antarctica’s Balleny Islands.
The physics of the spectacle are exacting: the Moon, only 3,474 kilometers in diameter, is almost the same apparent size as the Sun in Earth’s sky because it is approximately 400 times smaller but also 400 times nearer. This almost-perfect similarity permits alignments that partially or wholly shadow the Sun’s light. The alignment in this case is skewed, creating a partial eclipse where the Moon’s outline takes a “bite” out of the Sun’s face. As opposed to a total eclipse, no part of this occurrence will be safe to witness without protection.
NASA and the American Astronomical Society emphasize that standard sunglasses are inadequate. Safe observing involves ISO 12312-2-certified solar viewing glasses or handheld solar viewers, which are approximately 100,000 times darker than the usual pair of sunglasses. For cameras, binoculars, or telescopes, a solar filter should be securely placed over the front of the optics; eclipse glasses only will not shield from the concentrated sunlight that these devices collect. For those without special equipment, indirect methods such as a pinhole projector can safely project the Sun’s altering shape. As Jason Rhodes, NASA’s Jet Propulsion Laboratory’s chief scientist for astronomy and physics, pointed out, “We live in a very unique system (Earth/Moon/Sun) so that the Moon and the Sun are very nearly the same size in our sky.”
Although the eclipse itself will be limited to the Southern Hemisphere Australia, New Zealand, Antarctica, and isolated Pacific islands northern viewers will have their own justification for gazing up. At dawn Sunday morning, Saturn comes to opposition, the position in its orbit when Earth is between the planet and the Sun. At 2:00 a.m. Eastern Time, the ringed giant will be nearest and brightest of the year, visible through the entire night as it rises in the east at sunset and sets in the west at dawn.
Opposition is more than an issue of brightness. As described in planetary orbital geometry, it is the time when an outer planet’s fully illuminated hemisphere points towards Earth, similar to a full Moon. For Saturn, currently around 1.28 billion kilometers distant, the disk measures about 19 arcseconds across, with rings extending to 45 arcseconds tip to tip. The rings this year are tilted only 2 degrees from edge-on and will be seen as thin, bright lines instead of their typical wide arcs. The tilted inclination conceals much of their delicate form, but also ushers in spectacularly uncommon events such as the recent shadow transit of Saturn’s massive moon Titan across the top of the planet’s clouds.
With a modest backyard telescope, Saturn’s pale yellow disk and slender rings will be unmistakable. 10x binoculars can even show the planet’s slightly oval shape and Titan as a faint speck of light. Greater magnifications on clear skies may reveal faint cloud bands and the Cassini Division, the dark space between the A and B rings. At opposition, the Seeliger effect a short-term brightening resulting from the removal of ring-particle shadows may cause the rings to shine more intensely for a couple of days.
For maximum view, astronomers advise viewing from a dark place, waiting 15 to 30 minutes for eyes to adjust, and not using white light. A red flashlight saves night vision while setting up equipment. Patience is the key: lapses in atmospheric stability can briefly take Saturn’s image into focus, revealing details undetectable seconds earlier.
This infrequent alignment a deep partial solar eclipse in the south and Saturn’s opposition in the north is a study in celestial mechanics on one day. One is contingent on the exact alignment of the Sun, the Moon, and the Earth; the other on the Earth’s quicker orbit catching up with a distant giant. Collectively, they present a day when the forces of the solar system are not merely abstract, but observable to anyone who cares to look up with the proper equipment and timing.
