Highlights of the Season: April-June 2023

The year's first eclipse season opens on April 19 with a hybrid solar eclipse that can be seen as either an annular or a total solar eclipse, depending on where observers are located along the path of the Moon's shadow across Earth's surface. This is because Earth's curvature makes enough of a difference in the distance and apparent size of the Moon's dark silhouette to determine whether the Moon almost covers the Sun's disk as seen from the ground or completely covers it. Because the eclipse path is mostly over water, only observers aboard ships in the South Pacific Ocean will see the annular eclipse—and even then, only very, very briefly.

The more exciting total phase of the eclipse, when the Sun's outer atmosphere (corona) is visible, will be seen from the sparse bits of land that the shadow-path runs across, including Australia's North West Cape Peninsula and Barrow Island, then the tip of East Timor in Indonesia, as well as Damar Island, some of the Maluku Islands, and a narrow strip across West Papua, New Guinea. No part of this eclipse is not visible from the United States.

Following the lull in activity after January's Quadrantid meteor shower, a couple of major displays liven up spring skywatching, with rates between 10-20 meteors per hour. The first is the Lyrid shower, which is active April 19-24, with a peak on the 22nd that coincides with a waxing crescent Moon. At this phase, the Moon sets early in the evening, so its light will not interfere with viewing after midnight, which is the optimal time to observe. The oldest-known meteor shower, Chinese records dating back to 687 BC, the Lyrids are known for occasional (but not frequent) outbursts during which about 100 meteors per hour were seen. The last time this occurred was in 1982.

The second shower is the Eta Aquarid display, which is active May 1-12, peaking on May 5, when it's accompanied by a full Moon whose bright light unfortunately interferes with viewing. Produced by Earth's plowing through the trail of dust particles left along the orbit of Halley's Comet, this display averages 30 meteors per hour under ideal conditions, but the light of the full Moon will greatly reduce the number seen. Still, NASA's Meteoroid Environment Office advises that a potential exists this year for an outburst from the shower that makes it worth watching for…even in the light of a full Moon.

Due to perspective, although meteors fall in parallel paths, they seem to radiate from one spot in the distance, and the shower is named after the constellation (or as is the case with the Eta Aquarids, the star) where that spot, or radiant, is located.

There are a couple of bonuses accompanying the full Moon of May 5. One is the Eta Aquarid meteor shower (mentioned above). The second is a subtle penumbral lunar eclipse, as the Moon passes through the thin, outer portion of Earth's shadow (the umbra). This is centered over the southern Indian Ocean and so is not visible from anywhere in the United States, but for most observers on Africa's east coast, in part of the Middle East, and in Indonesia, Australia, and in most of Asia, the full Moon might briefly seem just a little fainter than usual, with a faint, subtle shading over its face.

On the morning of May 17, the thin, waning crescent Moon occults Jupiter and briefly blocks our view of the giant planet as they both rise just before dawn. But this will be a tricky event to see on two levels: The Moon itself will be a sliver-thin crescent only two days before new, easily obscured by the morning light and difficult to spot when it rises in the east at 4:43 am PT. In addition, as seen from San Francisco, Jupiter will already be hidden from view at moonrise, and catching Jupiter just as it emerges from behind the Moon's darkened limb 34 minutes later at 5:17 am will be a challenge in the growing twilight only 40 minutes before sunrise—binoculars are recommended.

A visibility map and timing tables for various locations from the International Occultation Timing Association can be found at www.lunar-occultations.com/iota/planets/0517jupiter.htm.

Image credit: Gianluca Masi, Virtual Telescope Project

• The June solstice occurs on the morning of June 21 at 7:58 am Pacific. This is when Earth's axis is oriented with its northern northern end tipped most toward the Sun. The north pole and all points north of the Arctic Circle's latitude of 66.6°N are in continuous daylight, and the northern hemisphere receives the longest period of sunlight from the highest angle, resulting in greater warming.
• As seen from Earth, the Sun rises and sets farthest north, and north of the equator, its arc across the sky is highest. This is what many mistakenly call "the longest day" for the northern hemisphere, even though the day itself is still 24 hours long—it's just the length of the daylight period that's maximized (for San Francisco, the Sun is above the horizon for 14 hours 47 minutes, and the indirect illumination provided by twilight lengthens useful daylight even more). Meanwhile, the southern hemisphere receives sunlight at the shallowest angle and for the shortest duration, making this the winter solstice, or the start of the coldest season. For this reason, many refer to this day more precisely as the June solstice for proper context on either side of the equator.
• In Europe, this is referred to as "Midsummer's Day," allowing the first half of the season to build up to the culmination of the lengthening daylight period rather than starting off already on the wane.