Signs of Spring: May Flowers, Horseshoe Crabs and Astronomy Charts

May flowers, the season of the horseshoe crab and summer astronomical occurrences for 1993.


Breeding season for horseshoe crabs is a sign of spring.


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With all the rapid changes in nature throughout springtime, I wonder if four seasons are enough. After all, seasons are time periods characterized by a set of events or states in nature that are distinctly different from those of the previous time period. Considering the many changes between March and April alone, shouldn't we add in an extra season during this time? It might be nice to have something like the six seasons of the Elves, which appear in stories written by fantasy writer J.R.R. Tolkien. Between winter and spring comes "stirring"; between autumn and winter comes "fading." After all, in much of the United States, March (and at least some of April) are still extremely cold, the trees are not fully leaved, and the time of maximum blooming is still to come—conditions we hardly associate with spring.

On the other hand, we must be careful not to distort reality by forcing it into too many organizational schemes. Many events in the natural world are not sudden. Like the cold spells which persist in March and April, these events just grow fewer and less severe. There's also a positive side to having four seasons; it makes the details of each particular one more extreme. So as the cycle of seasons rolls around again, the nature watcher can search for the familiar details—patterns in nature and life—and then delight in the recognition of seeing them.

Bringing May Flowers  

Over 600 years ago, Chaucer opened his Canterbury Tales "Whan that Aprille with his shoures sote [sweet]/The droghte [drought] of Marche hath perced [pierced] to the rote [root]..." Everyone knows about the infamous April Showers, but does the saying actually hold up to meteorological scrutiny?

Yes. Of course the amount of rain you see depends on what part of the country you live in, and showers seem to be a phenomenon mainly of Eastern states. Keep in mind that I'm not talking about the amount of precipitation—March would probably win hands down—but the frequency of come-and-go sprinkles and downpours. Through winter and March, low-pressure systems tend to produce widespread, not localized areas of precipitation. But in April, the higher sun of longer days starts heating the ground significantly, causing warm air near the surface to expand and rise up into still-cold air aloft: this "convection" makes cumulus clouds puff up and grow enough to produce showers and thundershowers. As the year progresses, convective activity by no means stops, but a variety of factors usually prevents it from giving rise to showers on as many days as in April.

The Living World  

In addition to blooming flowers, May brings us the Season of the Horseshoe Crab, when the crabs make their big coming out. This "living fossil," which looks just like a walking helmet, has virtually no living relatives in the animal kingdom. From Maine to Mexico, you can see them traveling the Atlantic beaches. (The only other place the horseshoe crab exists in the entire world is Southeast Asia.) Perhaps it's strangest characteristic—aside from its blood, which is a rich copper blue—is its extra set of eyes, which can see in ultraviolet light. As for its most useful characteristic, it would have to be the strange chemical, limulus lysate, which is found in the horseshoe crab's blood. This life-saving chemical is used to test whether or not medicines have become contaminated with bacterial toxins.

This strange animal also provides an essential feast to several species of migrating birds in May. The primary location of this event is in New Jersey and the Delaware shores of Delaware Bay for a brief period in late May. Horseshoe crabs are then seen in enormous numbers on the beaches, because this is when the females males lay eggs for the males to fertilize. Enter hundreds of thousands of birds, most in the midst of immensely long migrations, all looking for horseshoe crab eggs and overturned horseshoe crabs. One type of sanderling (a small type of shore bird), called the Red Knot, travels 9,000 miles, from as far south as Tierra Del Fuego in Argentina on its way up to northern Canada.

Scientists believe that a significant part of the world's total population of bird species may show up in this one place for overturned horseshoe crabs. If for some reason, the horseshoe crab did not keep his appointment one year, most of these birds would perish, and entire species could actually be threatened. Only recently has the magnitude of this migration feast and its significance been recognized.



Morning Venus and Solar Eclipse . On April 1, Venus rises in the East/Northeast only 35 minutes before the Sun, but by the 10th it will rise an hour before the Sun, and by the 30th, over an hour and a half. Always the brightest point of light in the heavens, Venus gets even brighter than usual this spring. It reaches "greatest brilliancy" on May 7, but before then, we might see the finest astronomical event of the spring: its close encounter with the Moon on the morning of April 19 (see "Sky Calendar"). If you can still locate the lunar crescent towards midday, a small telescope or binoculars may show the Moon approaching Venus until it moves right in front of the planet. In Hawaii, the hiding before sunrise is spectacular.

The partial eclipse of the Sun on May 21 is an early morning event, visible from the northwestern two-thirds of the United States. On the Pacific Coast, people can see the Sun rise with a "bite" taken out of it. (Caution: Don't try to observe this eclipse without the proper filter.)

What else is in the heavens this April and May? The finest constellation sight right now is the Big Dipper, upside down and at its biggest in the north sky at night.

Special Days  

Almost every American knows of Easter, Passover, and Memorial Day, but there are plenty of springtime holidays and traditions which have only had prominence across the Atlantic, and which may seem odd to Americans.

Oak Apple Day (Restoration Day), May 29, is a commemoration of the battle of Wooster in 1651. An oak apple (or oat gall) is a swelling on a branch caused by larval infection. The tradition was to carry oak branches with galls in order to symbolize loyalty to King Charles II (who hid in an oak tree for 24 hours after being defeated by Cromwell in this battle. Village children would gather nettles and playfully whip other children who weren't carrying oak branches.

Then there are the days of "The Three Ice Saints of May" on May 11, 12, and 13. The saints are Mamertus, Pancras, and Servatius, respectively. Europeans considered these days to mark the end of the time when killing frosts were likely to occur. Not many Americans are aware of this tradition, but it holds true for northern United States too.

Almanac for April and May 1993  



1 April Fool's Day. Venus nearest Earth, at inferior conjunction—may be visible both before sunrise and after sunset.

4 Palm Sunday. Daylight savings Time begins—set clocks 1 hour forward.

5 Mercury at greatest morning elongation—but a poor one for U.S. (Moon near star Jupiter at dusk—see Sky Calendar.)

6 Passover. Full Moon (known as Grass Moon and Egg Moon). (Moon near star Spica at dusk—see Sky Calendar.)

9 Good Friday

11 Easter

13 Last Quarter Moon

18 The Sun enters the constellation (not the astrological sign). Aries; tomorrow it enters the astrological sign Taurus.

19 Superb Moon-Venus conjunction at dawn, occultation in day (see Sky Calender).

21 New Moon. Lyrid meteors from high overhead in after-midnight hours today and tomorrow.

22 Earth Day

25 Mars at aphelion (farthest from Sun in space)—something that happens about once every two years. Sky Awareness Week begins.

1 May Day (Originally Beltane). National Astronomy Day (for 1993).

2 A few Aquarid meteors might be seen from southeast just before dawn today and tomorrow.

5 Full Moon

6 Halfway point of spring.

7 Venus at greatest brilliancy in dawn sky.

11 Mars goes through north edge of Beehive star cluster this evening and tomorrow evening. St. Mamertus' Day.

13 Last Quarter Moon. Sun enters the constellation taurus.

18 Great eruption of Mount St. Helens, 1980.

19 Dark day in New England, 1780.

21 New Moon. Partial eclipse of the Sun.

29 Oak Apple Day (or Restoration

31 Memorial Day