Sky and Telescope - August 2017 - 71

occurred sometime between June and November 1817.
In the ﬁrst edition of the poem, published by Murray, a
note by Byron appears to provide a precise date of August
18th for the spectacular twilight:
A single star is at her side, and reigns
With her o'er half the lovely heaven.
The above description may seem fantastical or exaggerated to
those who have never seen an Oriental or an Italian sky, yet it
is but a literal and hardly sufﬁcient delineation of an August
evening (the eighteenth) as contemplated in one of many
rides along the banks of the Brenta near La Mira.

However, this date may not be exactly correct. Byron
scholars have published reproductions of the poet's manuscripts that show he ﬁrst wrote the date as August 19, then
crossed it out and changed his recollection by writing "18th."
The exact date matters, as we shall see.
Remarkably, an even better source for the correct date
exists. Byron and Hobhouse frequently made trips on horseback from La Mira to the town of Dolo and back. A biography
of Byron noted, regarding the fourth canto, that "Stimulated
by his rides at sunset along the Brenta, Byron added more
stanzas." Hobhouse himself later recalled that "part of it was
begot as it were under my own eyes . . . some of the stanzas
owe their birth to our morning walk or evening ride at La
Mira." Hobhouse kept a diary in the summer of 1817, and the
relevant entry shows that the memorable twilight occurred
on August 20th:

have been genuinely abnormal, stemming from the greatest
volcanic eruption in recorded history.
In a previous Sky & Telescope article, our Texas State University group identiﬁed the blood-red sky in Edvard Munch's
most famous painting, The Scream, as likely a depiction of a
"Krakatoa twilight" (S&T: Feb. 2004, p. 28). For several years
after the 1883 eruption of Krakatoa, in what's now Indonesia,
dust and sulfate aerosols in the upper atmosphere produced
remarkable red hues in twilight skies worldwide.
But much more powerful than the Krakatoa event was the
April 1815 eruption of Mount Tambora (also in Indonesia).
In 1984 Richard Stothers wrote in Science that the Tambora
"eruption stands out as being an order of magnitude bigger in
volume of discharged pyroclastics than the Krakatau eruption
in 1883. . . . In fact, it exceeds any other known eruption,
historical or otherwise, during the past 10,000 years." Stothers noted that in 1815, "prolonged and brilliantly colored
sunsets and twilights were frequently seen . . . the twilight

Wednesday August 20th 1817: Ride with Byron. Return over
the other side of the river from Dolo . . . . Riding home,
remarked the moon reigning on the right of us and the Alps
still blushing with the gaze of the sunset. The Brenta came
down upon us all purple - a delightful scene, which Byron
has put in three stanzas of his "Childe Harold."

TOP: N ASA L A NDSAT 7, BOT TO M: N ASA / PD -USGOV

The Moon and Jupiter
For a location between Dolo and La Mira along the Brenta
Canal path, astronomical planetarium programs give the
time of sunset on August 20, 1817, as 7:00 p.m. Local Mean
Time (LMT). At sunset the Moon, a day past ﬁrst quarter,
stood 20° above the scene's southern horizon, and it was
still 18° high an hour later when deep twilight would have
matched Byron's description. And we see that Byron's "Single
Star . . . at her side" was not a star at all. The planet Jupiter
shone brilliantly 10° to the right of the Moon in the twilight
- close enough that the pair would be memorable.
Antares was closer to the Moon, only 5° to its lower right,
but Antares was only a twentieth as bright as Jupiter was that
night and not nearly as eye-catching.

Volcanic Twilights
Byron's twilight rhapsodizing has another aspect of scientiﬁc
interest. The spectacular colors he observed were likely to

p SKY PAINTER The 1815 explosion of Mount Tambora on Sumbawa
Island, Indonesia, blew away an estimated 160 cubic kilometers (38 cubic
miles) of rock, wiped out the area's population, and left a summit caldera
about 6 km (4 miles) wide, seen in these USGS Landsat images. The
eruption was heard more than 2,000 km (1,200 mi) away, and its global
atmospheric aftermath lasted for several years.
s k y a n d t e l e s c o p e .c o m

* AUGUST 2017

http://www.skyandtelescope.com

Sky and Telescope - August 2017

Table of Contents for the Digital Edition of Sky and Telescope - August 2017