April showers in the predawn hours
Well, maybe one April shower. Lyrid meteors are among the oldest-known meteor displays, noted in Chinese records from 687 BC. It is active from April 16-30 as Earth passes through the dusty trail of Comet C/1861 Thatcher. It has a very narrow peak on April 22, when skywatchers can ideally expect to see 10-15 meteors per hour under a dark sky. However, the light of this year's waxing gibbous Moon may interfere, reducing the number seen to about five per hour.
- Fun fact: Meteor showers are usually named after the constellation from which the meteors appear to emanate, and this shower is named after Lyra the Harp. However, its radiant (the point from which meteors appear to stream) is actually within the border of neighboring Hercules the Strongman—soooo...why aren't the meteors known as the "Herculids" instead? That's because the shower was named before the International Astronomical Union officially defined the borders of the constellations in 1922, people had already gotten used to the name.
- Meteor-watching tips: calacademy.org/explore-science/how-to-observe-a-meteor-shower
Halley's rain of fire
Although comets are not the flaming phenomena they were once thought to be, an actual display of fire in the sky produced by a comet's leftovers takes place from April 19-May 28, with a peak on May 4. That's when Earth passes through the trail of dust left behind by Halley's Comet, and as the dust particles enter the atmosphere and burn up, the annual Eta Aquarid meteor shower can be seen.
From the ground, the meteors appear to radiate from the southerly constellation Aquarius the Water-Carrier, making this shower a better spectacle for skywatchers in the southern hemisphere, where Aquarius rises higher in the sky. This year, the shower's peak occurs when the Moon is a fat waning crescent (just past last quarter) positioned against the stars of Aquarius, near the shower's radiant point. The glare of the Moon, then, may reduce the ideal rate of 10-15 meteors per hour to a weaker five or so. However observers may still want to try looking away from the shower's radiant, where the meteor streaks are severely foreshortened—looking away from the radiant, perpendicular to the meteors' paths will present longer, more prominent streaks.
Also, consider meteor-watching on the nights before and after the peak date, since the Eta Aquarids have more of a week-long plateau, centered on May 4. And don't forget about our informative meteor-watching video linked above!
Over time, as seen from Earth, the planets appear to slowly move eastward against the stars, reflecting their motion in orbit about the Sun. Every now and then, however, a planet might seem to reverse direction, moving westward, as we see Saturn do starting on May 23. This is called retrograde motion, but the planet hasn't gone rogue—it's still orbiting in the same direction it always has, although there are two situations where appearances may seem otherwise.
One applies to an inferior planet (not a value judgement, but a term referring to planets whose orbits are closer to the Sun than Earth's—namely, Mercury and Venus). When one of these worlds passes greatest eastern elongation (greatest angular separation east of the Sun) and has begun moving to the same side of the Solar System as Earth, it will seem to move from east to west in our view as it passes between us and the Sun. It resumes normal (prograde) motion when it reaches greatest western elongation.
In the other case, Earth passes a slower-moving outer planet such as Mars, Jupiter, or Saturn. Think of a fast car on the inside lane of a race track zipping past slower cars. From the viewpoint of the driver in the fast car, the slower cars seem to move backward, which is what it looks like from Earth when we lap slower-moving outer planets in our race around the Sun.
In the dark of the Moon
On the morning of May 26, the full Moon passes through the central portion of Earth's shadow (or umbra), producing a total lunar eclipse. The entire event is visible from beginning to end for observers in the Pacific Ocean and in western California and southwest Alaska. North American observers farther to the east will see only part of the eclipse (less so the farther east one is located).
During this event, the Moon slowly slides through the dark, reddish-brown umbral shadow, starting at 2:44 am PDT (first contact). Through partiality, the rounded edge of the shadow is visible encroaching across the Moon's disk—an observation made thousands of years ago by Greek scholars that proved Earth is a sphere. Totality, during which the Moon is completely immersed in the umbra, lasts from 4:11 am (second contact) to 4:26 am PDT (third contact).
The intensity of the shadow's reddish-brown color depends on the clarity of the atmosphere where sunlight is passing through as it casts the planet's shadow into space. Partiality ends at 6:01 am.PDT (last contact)—for observers on the West Coast, just as the Moon sets in the western sky.
- Stargazing tip: During the brief 25 minutes of totality, moonlight is greatly-dimmed, enabling skywatchers to see faint targets that would otherwise be obliterated by the full Moon's dazzling light. Look with binoculars for star clusters, nebulae, or maybe even the band of the Milky Way.
A rare polar solar eclipse
An annular solar eclipse takes place on June 10. Annular eclipses aren't quite as spectacular as total solar eclipses, since the Moon is a little farther away in its orbit this time around and appears a little smaller. This results in it not covering the Sun completely, leaving a ring of the solar disk visible around our satellite's dark silhouette. Although thin, this annulus is bright enough to obscure the Sun's faint outer atmosphere, or corona.
Annularity is visible along a path that extends from Hudson Bay to southern Baffin Island and northern Greenland into Siberia. Although not an easy one for eclipse chasers to follow, this event is notable for being the only one of the 21st century whose path crosses over Earth's north pole.
The longest day
June 20 is the summer solstice in the northern hemisphere, when the Sun is farthest north of the celestial equator. This makes it follow a long, high arc across the sky during the day, rising and setting at its farthest north on the horizon. Having the longest daylight period, this date is conversely marked by the shortest night, when the Sun is below the horizon for the shortest period of the year.
Commonly viewed as the first day of summer in the northern hemisphere, this is the winter solstice in the southern hemisphere—the first day of winter, with the shortest daylight period.
Download the Morrison Planetarium's 2021 Pocket Almanac to stay up-to-date on eclipses, meteor showers, satellite spottings, and more.
The Benjamin Dean lecture series brings the world's leading experts in astronomy, astrophysics, and more to the Academy's Morrison Planetarium. Stay tuned—lectures are coming back in a virtual format this June!