
(Click on the image above for a larger view.)
I was fascinated to read the letter from Oleksiy V. Arkhypov (Kharkiv, Ukraine) in the February 2025 issue of Sky & Telescope, p. 6, where he describes a 5th-magnitude star in the constellation Hercules that has apparently disappeared. John Flamsteed (1646-1719) had recorded the star at the end of the 17th century. Flamsteed listed the brighter stars in each constellation in order of right ascension at the time, but did not number them. That task fell to Joseph Jérôme de Lalande (1732–1807) who assigned what we now know as the “Flamsteed numbers” to each of the stars in Flamsteed’s catalogue. Two adjacent stars in Hercules in Flamsteed’s catalogue were given the designations 54 Her and 55 Her.
William Herschel (1738-1822) observed both stars on October 10, 1781 (and had noted that they were both red in color) and again on April 11, 1782, but on May 24, 1791 (and afterwards), only 54 Her was visible. Apparently, 55 Her disappeared from sight between 1782 and 1791, and it hasn’t been seen since.
In Herschel’s own words:
On the Disappearance of the 55th Herculis.
Among the changes that happen in the sidereal heavens we enumerate the loss of stars; but, notwithstanding the real destruction of an heavenly body may not be impossible, we have some reasons to think that the disappearance of a star is probably owing to causes which are of the same nature with those that act upon periodical stars, when they occasion their temporary occultations. This subject, however, being of great extent and consequence, we shall not enter into it at present, but only relate a recent instance of the kind.
Two stars of the 5th magnitude, whose places we find inserted in all our best catalogues, were to be seen in the neck of Hercules. They are the 54th and 55th of Flamsteed’s, in that constellation. In the year 1781, the 10th of October, I examined them both, and marked down their colour, red. The 11th of April, 1782, I looked at them again, and noted my having seen them distinctly, with a power of 460; and that they were single stars.
The 24th of last May, I missed one of the two, and examining the spot again the 25th, and many times afterwards, found that one of them was not to be seen. The situation of the stars is such that, not having fixed instruments, I could not well determine which of the two was the lost one. I therefore requested the favour of my much esteemed friend, the astronomer royal, to ascertain the remaining star ; and it appears from Dr. Maskelyne’s answer to my letter, that the 55th Herculis is the one which we have lost.
The coordinates for 54 Her are:
α2000 = 16h 55m 22s, δ2000 = +18° 26′ 00″