Astronomy and the Start of Autumn

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PHOTO: STEVE DALTON/PHOTO RESEARCHERS INC.
As fall comes, the monarch butterflies begin their annual migration.

Once the Dog Days are over, the rest of August and
September offers us the year’s finest days to be outdoors
and alive. This is particularly enhanced by the beautiful,
somewhat bittersweet feeling that summer is gradually being
lost. Once I feel the first late-August cold front truly
break the siege of summer, see the swallows begin to gather
for departure, and notice the sunsets get rapidly earlier,
I know that summer’s golden days are numbered and that
autumn’s pageant of beauty and change is near at hand.

Seasons and Calendar: Equinox and Blue
Moon
 

It’s during the autumn equinox that the Sun crosses the
equator, making day and night everywhere of equal length.
Some cultures viewed this time period as so important that
they actually began and based their calendar year at or
during the equinox. Such was the case of both the ancient
Spartans and Macedonians–the latter’s calendar
becoming of widespread importance when Alexander the Great
whirled out of Macedonia and conquered the “known world.”
The Jewish New Year, Rosh Hashanah (“head of the year”),
begins with the sunset nearest the new moon t hat falls
closest to the autumn equinox. As most farmers can tell
you, the harvest moon is said to be the full moon closest
to the autumn equinox. However, this year the full moon of
August 31 will hold its own special distinction: it will be
a spectacular “blue moon:”

SKY CALENDAR OF SPECIAL EVENTS FOR 1993
 

AUGUST

These days a blue moon is somewhat of a calendrical
curiosity since the definition alters with time. Presently
the blue moon is said to be the second full moon when there
are two full moons in a calendar month. But there is also a
phenomenon by which the Moon (or Sun) can actually appear
distinctly blue in color (or sometimes green or
“brass-colored”). This occurs when particles in clouds are
all about the same (unusually small) size–often due
to the effects of major forest fires or dusty volcanic
eruptions. These particles scatter out the longer
wavelengths of light, leaving alone the shorter
wavelengths, which are bluer–or blue and
green–in color. It was the pall of particles from
Canadian forest fires, for example, that produced the
amazing blue moon and Sun seen in New England and parts of
the mid-Atlantic states on September 24, 1950. (I’ll
discuss this remarkable event in greater detail in future
issues.)

Americans will be able to seek out the blue moon of August,
as the Moon will be full on both August 2 and 31. Note:
The eastern hemisphere will experience our August 31 moon
on September 1 (their time) and their blue moon (the second
of their month) on September 30.
We can just fit two
full moons into a 30-day-long month because the Moon’s
“synodic period” (the time from one phase to the next
recurrence of that phase) is approximately 29 1 / 2 days.
Of course, that explains why you’ll never see the
phenomenon in February–even on a leap year. But how
often does a year have a month with the supposedly rare
“once in a blue moon” blue moon? The interval between one
such blue moon and the next is less than three years.
Writer Guy Ottewell points out that about only one year in
19 has two months with a blue moon. The next will be 1999,
when both January and March have two full moons.

Astronomy: See Seven
Planets
 

The most exciting sky event likely to occur this season is
the Perseid meteor storm.

Besides the possible “shooting star” deluge and the
interesting full moons, there are plenty of planets visible
this August and September. Saturn, at its brightest, rises
in the east-southeast and is visible all night long. Bright
Venus and always-low Mercury are at their highest in the
east before dawn (watch 45 minutes before sunup) in early
August. Jupiter and Mars have a close conjunction (meeting)
low in the west-southwest at dusk on September 4 to 6, and
form a lovely but low grouping with the star Spica, and a
lunar crescent at dusk on September 17. Have veteran
observers help you glimpse the far and dim Uranus and
Neptune having their last conjunctions with each other
until the middle of the 22nd century.

The most cloud-free period of the year is late August
to late October.

Enjoy a Perseid Shower
 

Chances are, just a few hours before darkness begins
falling in the United States on August 11, Europe will see
what may be one of the greater meteor displays in history.
It’s also possible that the aftermath of the shower’s peak
will provide quite a view for Americans, displaying
hundreds of meteors per hour.

To refresh your memory, a meteor is the streak of light
produced when a piece of space rock or iron enters our
atmosphere at such great speed that it burns up from
friction with the air. A meteor shower is an increased
number of meteors appearing to come from a single spot
among the constellations. And the Perseid meteor shower
(from the constellation Perseus) is often the best of all
annual meteors showers, producing as many as 50, 60, or
sometimes more meteors for observers to see.

But this year the Earth is likely to see a super display of
the Perseids. The parent comet of the meteors,
Swift-Tuttle, finally returned to the inner solar system
last year and on August 11 we will be passing close a to
where it went late last December.

Many experts think the Earth will experience the Perseid
meteor storm. In 1991, the Perseids poured over Japan at
rates of 300 to 400 per hour for one hour. Last year, the
Moon was full and cloudiness prevailed over the Far East,
but again that part of the world was rained over by a
powerful Perseid burst. There were so many meteors that
bright ones were visible like flashes of lightning even
through the clouds. Rates of a few thousand might have been
visible in the hour of outburst if skies had been clear.

The world’s leading authority on comet and meteor stream
orbits, Harvard University’s Brian Marsden, thinks the great
burst will be at its best around 6:22 PM.
EDT–approximately an hour and a half before sunset on
the East Coast. Marsden also calculates that this August
11, Earth is coming closer to the orbit of the parent comet
years. Yet there are records a mere thousands years ago of
Perseid storms so strong that meteors “fell like snow!”

There is something U.S. viewers can do to increase their
chances of catching the storm outburst if it occurs over
America (or at least if a strong aftermath should occur).
First of all, try to find a site many miles away from city
light. (Be prepared to view far less if the sky is hazy
that night.) On August 11, look in the northeast sky
between 6 P .m. and 7 P.m. just to make sure that there
aren’t some day-bright Perseids zooming there. Keep your
fingers crossed as darkness falls after 8 P .m. Even then,
the constellation Perseus is still low in the northeast,
but if the spate occurs, the sight will still be
tremendous.

Weather: Clear Sides and Hurricanes
 

There comes a cold snap in late August or early September
when I always say: “Summer’s back is broken.” The period
from then until late October is the most cloud-free month
(and longer) of the year across most of the eastern half of
the United States. For much of the Southwest, June is the
most cloud-free, while July is for the Pacific Northwest
and northern Rockies. For nowhere in the 48
states–except southern Florida–is any month
from November through May most cloud-free.

But September is not all coolness and clarity, and neither
is August for that matter. These two months are the dreaded
months of hurricane season. And this isn’t only true for
prime targets, Florida and the Gulf Coast. Hurricanes need
warm water, but the oceans take longer to cool down from
summer’s maximum solar radiation than the atmosphere. Thus
it is quite possible for spots far north of the Atlantic
Coast to get hit by devastating hurricanes in September and
October, and possibly even early November.

The Living World: Monarchs
 

Fall migrations begin in August (actually a little earlier
for some species, believe it or not) and rise to a peak in
September. Everywhere, birds are on the move. But it is not
just birds that migrate or are capable of winging thousands
of miles, sometimes across hundreds of miles of water. So,
too, does one of the few members of the insect world that
is adored by just about everyone–the monarch
butterfly.

I can’t tell you exactly when to look for the most monarchs
passing by because they seem to come in different groups
from August through October, and the weather and other
complications mean that the size and time of the largest
group may vary greatly each year. If you’re lucky, you’ll
be near a bay or large lake where the butterflies pause to
refresh themselves on the nectar of plants before
attempting the perilous crossing. The most spectacular
display I’ve ever seen in New Jersey was on October 9, when
some tall cedar trees near our bay were literally covered
with the beautiful, colorful creatures.

Of course, the most amazing fact is nearly all of the
monarchs in the eastern United States and Canada winter in
a single tiny locale in the mountains of Mexico; nearly all
of those in the western United States and Canada winter in
a single tiny locale in California. You can visit the
“monarch trees” in Pacific Grove, California, where laws
against bothering these butterflies are, happily, quite
strong.

Of all the stories I’ve heard about them, the most moving
is related by naturalist Edwin Way Teale. In Autumn
Across America
, Teale tells how he and his wife were
driving across the Great Salt Lake Desert in Utah and were
depressed by the fact that no plants, birds, reptiles, or
even insects were visible–none were capable of living
in that stretch of white flatness without water. Then Teale
and his wife suddenly saw five spots of color flying
steadily onward–five monarch butterflies were on
their way home to California.

Special Day: Time for Loaf Mass
 

Cross-quarter days, those that occur halfway through the
seasons, have all been the occasion for holidays. But not
many surpass Lammas, once celebrated widely in the British
Isles on August 1st.

There are two theories regarding the origin of the
holiday’s name. One holds that it comes from “Lamb-Mass”
because the early Roman church supposedly took a lamb to
the altar when commemorating St. Peter’s miraculous freeing
from his prison chains.

The other theory holds that the name comes from the Middle
English lammasse, or”loaf mass:’ August 1 was when the
people of the British Isles consecrated the first bread
baked from the new wheat or corn of the season. The Old
English form of the holiday’s name was hlaf-mass. Our word
“lady” comes from the Old English hlafdig, which means
something similar to “loaf dispenser” or “loaf kneader.” On
Lammas it was the custom in England to give money to
servants to buy gloves (“Glove-Silver”) and for every
church to have a sheaf placed over its door.

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