From J. Winthrop,Jr,to E. E. Barnard: The Arduous Path to the First Sighting of Amalthea

Galilei Galileo , Sidereus nuncius or The sidereal messenger, transl. by Van Helden A. (Chicago, 1989), 64.

See, for example, Drake S. , Galileo at work: His scientific biography (Chicago and London, 1978), 146–54; idem, “Galileo's first telescopic observations”, Journal for the history of astronomy, vii (1976), 1976–68; idem, “Galileo and satellite prediction”, Journal for the history of astronomy, x (1979), 1979–95; Robison W. L. , “Galileo on the moons of Jupiter”, Annals of science, xxxi (1974), 1974–9; Reeves E. Van Helden A. , “Verifying Galileo's discoveries: Telescope-making at the Collegio Romano”, in Die Meister und die Fernrohre, Das Wechselspiel zwischen Astronomie und Optik in der Geschichte: Festschrift zum 85. Geburtstag von Rolf Riekher, ed. by Hamel J. Keil I. (Frankfurt am Main, 2007), 127–41; Biagioli M. , Galileo's instruments of credit: Telescopes, images, secrecy (Chicago and London, 2006), 77–134; Roche J. J. , “Harriot, Galileo, and Jupiter's satellites”, Archives internationales d'histoire des sciences, xxxii (1982), 1982–51; Meeus J. , “Galileo's first records of Jupiter's satellites”, Sky & telescope, xxvii (1964), 1964–6 (reprinted from Sky & telescope, xxiv (1962), 1962–9); Débarbat S. Wilson C. , “The Galilean satellites of Jupiter from Galileo to Cassini, Römer and Bradley”, in The general history of astronomy, ii: Planetary astronomy from the Renaissance to the rise of astrophysics, Part A: Tycho Brahe to Newton, ed. by Taton R. Wilson C. (Cambridge, 1989), 144–58.

On the issue of pre-telescopic and non-telescopic sightings of the satellites, see Dutton D. , “Naked-eye observations of Jupiter's moons”, Sky & telescope, lii (1976), 482–4 and references therein, and Xi Z.-Z. , “The sighting of Jupiter's satellite by Gan De 2000 years before Galileo”, Chinese astronomy and astrophysics, v (1981), 1981–3. On the issue of priority opposing Galileo and Simon Marius, see Prickard A. O. , “Note on ‘Simon Marius’ and ‘Mundus Jovialis’”, The observatory, xl (1917), 1917–22; Johnson J. H. , “The discovery of the first four satellites of Jupiter”, Journal of the British Astronomical Association, xli (1930–31), 164–71; Pagnini P. , “Galileo and Simon Mayer”, Journal of the British Astronomical Association, xli (1930–31), 415–22.

Flammarion C. , “Le nouveau satellite de Jupiter”, L'astronomie, xii (1893), 91–4; Marsden B. G. , “Satellites of Jupiter”, International Astronomical Union circular no. 2846 (1975).

Barnard E. E. , “Discovery and observations of a fifth satellite to Jupiter”, The astronomical journal, xii (1892), 81–5; idem, “Discovery and observations of a fifth satellite to Jupiter”, Publications of the Astronomical Society of the Pacific, iv (1892), 199; idem, “An account of the discovery of a fifth satellite to Jupiter”, Astronomische Nachrichten, cxxxi (1892), cols 73–6.

Van Biesbroeck G. , “Observations by E. E. Barnard of the fifth satellite and the position angle of the belts of Jupiter”, The astronomical journal, li (1945), 202–8.

Cruikshank D. P. , “Barnard's satellite of Jupiter”, Sky & telescope, lxiv (1982), 220–4; Baum R. , “A Barnard centenary — The finding of Jupiter-V”, Journal of the British Astronomical Association, cii (1992), 316, 323, 350; Cunningham C. J. , “Who discovered Jupiter's satellites?”, Mercury, xxxvi (2007), 9. Scheiner's claim appeared in the third letter of his Tres epistolae de maculis solaribus scriptae ad Marcum Velserium (Augsburg, 1612). The original text is reproduced in Le opere di Galileo Galilei, ed. by Favaro A. , v (Florence, 1932), 21–33, esp. p. 31; it is in translation in On sunspots, ed. by Reeves E. Van Helden A. (Chicago, 2010), 59–73. The claim is discussed by Hagen J. G. , “Discussion of a questionable type of temporary stars”, The astrophysical journal, xvii (1903), 1903–5. Rheita's claim appeared in Novem stellae circa Jovem, circa Saturnum sex, circa Martem nonnullae (Louvain, 1643). It is discussed by Van Helden A. , “Telescopes and authority from Galileo to Cassini”, Osiris, ix (1994), 1994–29, pp. 20–1, as well as by Johnson C. W. L. , “Pseudo-satellites of Jupiter in the seventeenth century”, Nature, li (1895), 1895–7. Fontanas's claim appeared in Novae coelestium terrestriumque rerum observationes (Naples, 1646), and is discussed by Débarbat and Wilson, op. cit. (ref. 2), 148. de Gasparis's claim is discussed by Flammarion C. , “Astronomie”, Cosmos, xxv (1864), 1864–3, p. 203, and idem, “Astronomie: Comètes et planètes”, Cosmos, 2ème série, i (1865), 1865–7, p. 177.

For background on John Winthrop, Jr, see Waters T. F. , A sketch of the life of John Winthrop, the younger, founder of Ipswich, Massachusetts, in 1633 (Ipswich, 1899); Hartley E. N. , Ironworks on the Saugus: The Lynn and Braintree ventures of the Company of Undertakers of the Ironworks of New England (Norman, 1957); Dunn R. S. , Puritans and Yankees: The Winthrop dynasty of New England, 1630–1717 (Princeton, 1962); Black R. C. , The Younger John Winthrop (New York and London, 1966); Wilkinson R. S. , The Younger John Winthrop and seventeenth-century science (Faringdon, 1975); and Woodward W. W. , Prospero's America: John Winthrop, Jr., alchemy, and the creation of New England culture, 1606–1676 (Chapel Hill, 2010).

Clutz F. H. , “Jupiter's satellites in 1664”, Johns Hopkins University circular, xiii, no. 111 (1894), 68–9; Streeter J. W. , “John Winthrop, Junior, and the fifth satellite of Jupiter”, Isis, xxxix (1948), 1948–63.

“June Meeting, 1878”, Proceedings of the Massachusetts Historical Society, 1st ser., xvi (1878), 181–251, pp. 220–2.

Waters , op. cit. (ref. 8), 57.

The evidence for this gift rests with Winthrop's comment, made in a letter to Worsley dated 27 October 1670: “I seldom looke upon the Constellations of the heavens, or the planetts, especially Jupiter, with my telescope, or the glorious Constellation of Orion, but the most grateful memory of yourselfe is fresh to my thoughts & soule” (quoted in ref. 10, p. 215). On the chronology of the introduction of the telescope in the American colonies, with a correction of Streeter's errors, see Wilkinson R. S. , “John Winthrop, Jr., and America's first telescopes”, New England quarterly, xxxv (1962), 520–3 and Yeomans D. K. , “The origin of North American astronomy — Seventeenth century”, Isis, lxviii (1977), 1977–25. For background on the figure of Worsley, see Webster C. , “Benjamin Worsley: Engineering for universal reform from the Invisible College to the Navigation Act”, in Samuel Hartlib and universal reformation: Studies in intellectual communication, ed. by Greengrass M. Leslie M. Raylor T. (Cambridge, 2002), 213–35.

“June Meeting, 1878” (ref. 10), 221.

Baxandall D. , “Replica of two Galileo telescopes”, Transactions of the Optical Society, xxv (1924), 141–4, p. 142. Drake Stillman (Galileo at work: His scientific biography (Chicago and London, 1978), 148) has argued that Galileo used the twenty-power telescope for his observations of the satellites of Jupiter, even though he had already developed a thirty-power version. Drake also emphasized that Galileo's twenty-power telescope was “modified” by masking the objective lens with a “cardboard stop of medium aperture”, which made Jupiter's satellites visible. The stopping down of the objective probably decreased the influence of the poorly-figured areas near the edge of the lens. No such contrivance was described by Winthrop, perhaps because he was unaware of its usefulness. For a thorough discussion of the performance of Galileo's telescopes, see the informative Galilean telescope site of Tom Pope and Jim Mosher [www.pacifier.com/∼tpope/Site_Map.htm; accessed 8 July 2010].

Van Helden A. , “The telescope in the seventeenth century”, Isis, lxv (1974), 38–58, pp. 45–6. See also idem, “The ‘astronomical telescope’, 1611–1650”, Annali dell'Istituto e Museo di Storia della Scienza di Firenze, i (1974), 1974–36.

Willach R. , “The development of telescope optics in the middle of the seventeenth century”, Annals of science, lviii (2001), 381–98, p. 387.

Keil I. , “Technology transfer and scientific specialization: Johann Wiesel, optician of Augsburg, and the Hartlib circle”, in Samuel Hartlib and universal reformation: Studies in intellectual communication, ed. by Greengrass M. Leslie M. Raylor T. (Cambridge, 2002), 268–78, p. 274. For additional background on Wiesel, see Van Helden A. , “The development of compound eyepieces, 1640–1670”, Journal for the history of astronomy, viii (1977), 1977–37, pp. 27–9, as well as the references cited by Willach , op. cit. (ref. 16), 390.

Morison S. E. , “The Harvard school of astronomy in the seventeenth century”, New England quarterly, vii (1934), 3–24, pp. 17–19; Wilkinson , op. cit. (ref. 12), 523; Brasch F. E. , “The Royal Society of London and its influence on scientific thought in the American colonies”, The scientific monthly, xxxiii (1931), 1931–55, p. 342.

Browne C. A. , “Scientific notes from the books and letters of John Winthrop, Jr., (1606–1676)”, Isis, xi (1928), 325–41, p. 325; Hartley , op. cit. (ref. 8), 114.

Wilkinson R. S. , “Winthrop, John”, in Dictionary of scientific biography, xiv, 451–2.

Browne , op. cit. (ref. 19), 338. Among the observations found in Winthrop's correspondence are reports on the comets of 1664, 1667/8 and 1671/2 (Black, op. cit. (ref. 8), 309–10).

Mortimer C. , “Dedication to the Honourable John Winthrop, Esq; Fellow of the Royal Society”, Philosophical transactions, xl (1741), n.p. According to Mortimer, John Winthrop, Jr “distinguish'd himself in the highest rank of learned Men by the early acquaintance he contracted with the most eminent not only at home, but in his travels all over Europe, by the strict correspondence he afterwards cultivated with them, and by the several learned pieces he composed in Natural Philosophy”. Mortimer also provided, in a footnote, a list of over eighty correspondents with whom Winthrop would have exchanged letters: “As might appear from the great treasure of curious letters on various learned subjects still in your [Winthrop's] hands, E gr. from … Gal. Galileo…. Many of which you have given me the pleasure of perusing.” See also Wilkinson , op. cit. (ref. 8), 17–18 and 20. According to his footnote 24, the letters exchanged with Galileo, Kepler, and Tycho Brahe's son “are no longer extant”.

Browne , op. cit. (ref. 19), 338.

Wilkinson , op. cit. (ref. 12), 521.

Wilkinson , op. cit. (ref. 12), 520–2; see also Van Helden A. , “The telescope in the seventeenth century”, Isis, lxv (1974), 38–58, p. 46–7 for a correction of the quoted size of Huygens's telescope.

Wilkinson , op. cit. (ref. 20). The feeling is shared by Black (op. cit. (ref. 8), 310).

Meeus , op. cit. (ref. 2). For a reconstruction of Galileo's 1613 observations of the Jovian satellites, see Graney C. , “On the accuracy of Galileo's observations”, Baltic astronomy, xvi (2007), 443–9.

Sinnott R. W. , “Jupiter ‘without a visible satellite’”, Sky & telescope, lxiv (1982), 214–15; Meeus J. , “Jupiter without satellites, 1600–1799”, Journal of the British Astronomical Association, cix (1999), 1999–2.

Galileo , op. cit. (ref. 1), 64.

Kepler J. , Conversation with Galileo's Sidereal Messenger, transl. by Rosen E. (New York and London, 1965), 48.

“June Meeting, 1878” (ref. 10), 221.

Meeus J. , “Tables of the satellites of Jupiter”, Journal of the British Astronomical Association, lxxii (1962), 80–8.

Meeus , op. cit. (ref. 2), 106.

Drake S. , Telescopes, tides, and tactics: A Galilean dialog about the Starry Messenger and Systems of the World (Chicago, 1983), 71, 219, and note 24, p. 226.

Streeter , op. cit. (ref. 9), 163. Once precessed to J2000, the 1850 equatorial coordinates given by Clutz (op. cit. (ref. 9)) for his candidate, the star B.A.C. 6448, are identical to those of HR 7128. They are one and the same object.

Graney , op. cit. (ref. 27), 444; Standish E. M. Nobili A. M. , “Galileo's observations of Neptune”, Baltic astronomy, vi (1997), 97–104, p. 102.

Barnard , op. cit. (ref. 5). See also Barnard E. E. , “Jupiter's fifth satellite”, Popular astronomy, i (1893), 76–82; Cruikshank D. P. , “Barnard's satellite of Jupiter”, Sky & telescope, lxiv (1982), 1982–4; Verschuur G. L. , Interstellar matters: Essays on curiosity and astronomical discovery (New York, 1989), 44–6; Sheehan W. , The immortal fire within: The life and work of Edward Emerson Barnard (New York, 1995), 206–22; Osterbrock D. Gustafson J. R. Unruh W. J. Shiloh , Eye on the sky: Lick observatory's first century (Berkeley, Los Angeles and London, 1998), 80–1.

“Fifth satellite to Jupiter. Remarkable discovery by Prof. Barnard of Lick Observatory”, The New York Times, 13 September 1892, 1.

Wesemael F. Racine R. , “Why was the companion of Sirius not seen prior to 1862?”, Journal for the history of astronomy, xxxix (2008), 161–79.

Hickson P. Racine R. , “Image quality of liquid-mirror telescopes”, Publications of the Astronomical Society of the Pacific, cxix (2007), 456–65; Racine R. , “The telescopic point-spread function”, Publications of the Astronomical Society of the Pacific, cviii (1996), 1996–705.

Any seeing-disc value quoted in this paper is to be understood as a full width at half maximum (FWHM) central intensity.

For a signal to background ratio of 1, the intensity of the light from Amalthea is equal to that associated with the background glare of Jupiter.

In the case of Winthrop's putative observation, Amalthea was simply too faint even in the absence of glare from Jupiter. At V = 14.1, its visual flux from the satellite is less than 2 photons/cm²/s or less than 40 photons/s over a 5-cm diameter object glass. The quantum efficiency of the dark-adapted human retina is 5% and its effective integration time is 0.1 second. During that time, the eye perceives less than one photon, i.e. the object is completely invisible even if the sky is completely dark and there is no noise from the background light. For observers looking at Jupiter at large zenith distance (∼ 65°) from near sea level with a telescope large enough to see an object at V ∼ 14, the atmosphere-limited image size must have been at least 2” because of the low altitude and thermal imbalance in their environment ( Racine R. , “Altitude, elevation, and seeing”, Publications of the Astronomical Society of the Pacific, cxvii (2005), 401–10). To this one must add the contribution of diffraction and a probably even larger amount for optical aberrations. It is thus probable that the actual size of stellar images at the focus of these telescopes was at least 5”. Figure 2 therefore conclusively shows that Amalthea would have been totally imperceptible under those conditions.

Barnard E. E. , “Discovery and observations of a fifth satellite to Jupiter”, The astronomical journal, xii (1892), 81–5.

There is no indication given of the quality of the seeing on that night. However, a much later set of observations, secured by Barnard on 10 October 1916 ( Van Biesbroeck G. , “Observations by E. E. Barnard of the fifth satellite and the position angle of the belts of Jupiter”, The astronomical journal, li (1945), 202–8, p. 203) featured measurements of apparent distances as low as 42.6” in a seeing described by Barnard as “poor”. According to Figure 2, this observation required a seeing of 0.7” for a signal-to-background ratio ∼1. To help further contextualize this measurement so close to Jupiter's limb, we note that an experienced and sharp-eyed observer like Barnard could probably sight Amalthea at a lower contrast and that, in addition, the astronomical seeing can vary by a factor of ∼2 over a time scale of ∼10 minutes. Nevertheless, Barnard's characterization of the seeing on that night may have also involved some posturing, since he was undoubtedly aware that it was impossible to sight the satellite so close to Jupiter at most sea-level observatories, where the typical seeing would have been of the order of 1” or more. Calling the (estimated) 0.7” seeing “poor” for Lick Observatory simply added insult to injury.

Wesemael Racine , op. cit. (ref. 39), 172; see also Struve G. , “On the astronomical observing conditions at Lick Observatory on Mount Hamilton”, Publications of the Astronomical Society of the Pacific, xliv (1932), 105–10.

Osterbrock Gustafson Unruh Shiloh , op. cit. (ref. 37), 45–63; Warner D. J. Ariail R. B. , Alvan Clark & Sons, artists in optics, 2nd edn (Richmond, 1995), 118–21; Wright H. , James Lick's monument: The saga of Captain Richard Floyd and the building of Lick Observatory (Cambridge, 1987), 81–2, 117–20.

Barnard E. E. , “Discovery and observations of a fifth satellite to Jupiter”, The astronomical journal, xii (1892), 81–5, p. 81.

Barnard E. E. , “Some further observations of the fifth satellite of Jupiter”, The observatory, xv (1892), 425–7.

Tisserand F. , “Sur la découverte du cinquième satellite de Jupiter par M. Barnard”, Comptes rendus hebdomadaires des séances de l'Académie des Sciences, cxv (1892), 541–3. Incidentally, Amalthea was the last of Jupiter's satellites to have been discovered visually, as photographic detection would soon take over ( Nicholson S. B. , “The satellites of Jupiter”, Journal of the Royal Astronomical Society of Canada, xxxv (1941), 1941–20).

Hough G. W. , “The planet Jupiter”, Popular astronomy, ii (1894), 145–51, p. 147.

Young C. A. , “Observations of the fifth satellite of Jupiter, at the Halsted Observatory, Princeton, NJ by Mr. T. Reed”, The astronomical journal, xii (1892), 111; idem, “The fifth satellite of Jupiter”, The observatory, xv (1892), 1892–30.

Barnard E. E. , “Jupiter's fifth satellite”, Popular astronomy, i (1893), 76–82, p. 80. See also Stone O. , “Observations of the new satellite of Jupiter”, The astronomical journal, xii (1892), 103.

Hough , op. cit. (ref. 51).

Taylor A. , “The fifth satellite of Jupiter”, The observatory, xvi (1893), 66. See also “Jupiter's fifth satellite”, Nature, xlvii (1892), 208.

Barnard , op. cit. (ref. 53), 80; “Report of the council to the seventy-third annual general meeting of the society”, Monthly notices of the Royal Astronomical Society, liii (1893), 171–297, p. 245; “Report of the council to the seventy-fifth annual general meeting of the society”, Monthly notices of the Royal Astronomical Society, lv (1895), 1895–259, p. 215.

Sheehan , op. cit. (ref. 37), 215.

Osterbrock Gustafson Unruh Shiloh , op. cit. (ref. 37), 80. See also Sheehan , op. cit. (ref. 37), 70, 80, and 135 for additional illustrations of Barnard's exceptional eyesight.

Hough G. W. , “On the forms of the disks of Jupiter's satellites”, The astronomical journal, xiv (1894), 86–7, p. 86.