My first Magazine Sky & Telescope - 02.2019 | Page 40
Variable Stars
he was observing in late November 1779. A total eclipse of
the Moon occurred on November 23, 1779. Was Goodricke
checking his homework or merely planning to observe an
astronomical event? We don’t know, but we do know that he
was interested in observing before meeting Edward Pigott.
In 1781 Goodricke completed his studies at Warrington and
rejoined his family in York.
That same year, Edward Pigott (1753–1825) also moved
to York with his parents. Edward’s father Nathaniel used
astronomical observations for determining latitude and
longitude, and Edward learned the art of observing from him.
In York, Nathaniel constructed a two-story stone observatory.
The instruments — telescopes, a quadrant, and a theodolite
— came from London’s finest instrument makers. Nathan-
iel was a member of the Royal Society of London, and both
Pigotts kept abreast of current astronomical developments
through correspondence with astronomers such as William
Herschel and Charles Messier.
Edward Pigott’s astronomical interests ranged further than
his father’s, however. He frequently compared the apparent
stellar magnitudes reported by Flamsteed with those of earlier
observers such as Tycho and Ptolemy. One of Edward’s early
journals contains a list of publications entitled “Authors on
Variable Stars.” When Goodricke joined him, Pigott suggested
that they systematically observe suspected variables.
After Goodricke first saw Algol’s “very unexampled
change,” in which the star’s brightness dropped from an
estimated third magnitude to somewhere between fourth
and fifth magnitude, both men observed the star every clear
night. Neither saw another dimming event until both wit-
nessed one on December 28, 1782. They found the brightness
remained approximately constant except for a seven-hour
dip every 2 days, 20 hours, and 45 seconds. The two realized
that the cause of such a pattern might be one body passing in
front of another, and each speculated in his observing jour-
nal. Goodricke wrote:
[Algol’s variation] can’t be accounted for in any other manner
than supposing it to have suffered an Eclipse . . . by the interposi-
tion of a Planet revolving around it. . . .
Edward Pigott elaborated, writing:
Having, on further consideration stronger reasons to believe
that what I wrote to Mr. J. Goodricke on the 29th of December
1782 may possibly happen induces me to make the following
memorandum of it — the opinion I suggested was that the altera-
tion of Algol’s brightness was maybe occasioned by a Planet of
about half his size, revolving around him, and therefore does
sometimes eclipse him partially. . . .
In May 1783, William Herschel confi rmed the discovery of
Algol’s variability, and Goodricke sent his report to the Royal
Society. In the report’s conclusion, Goodricke wrote that he
. . . should imagine [Algol’s variation] could hardly be
accounted for otherwise than either by the interposition of a large
body revolving round Algol, or some kind of motion of its own,
whereby part of its body, covered with spots or such like matter, is
periodically turned towards the earth.
Covered with Spots
The starspot hypothesis may seem strange to modern minds.
How could a large and apparently permanent spot cause the
brightness to drop for seven hours during a period of almost
three days? Yet at the time there was considerable support for
q WORKING FROM HOME In 1782, John Goodricke lived and observed near the close of York Minster. In 1949 Sidney Melmore used dates, times,
and notes written in Goodricke’s observing logs to argue that Goodri cke observed from the north window on the top fl oor of the southeast wing (at
right, behind the tree branch) of the Treasurer’s House, looking south toward the cathedral. However, records show that the Goodricke family rented
rooms from Edward Topham, who owned the northwest wing of the house (left).
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FE B RUA RY 2 019 • SK Y & TELESCOPE