Why Was the Companion of Sirius Not Seen Prior to 1862?

The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry∗

“…SiriusB is thus one of the most massive known WDs, particularly among the nearby sample. Historical details of these discoveries and subsequent developments have been recounted by several authors, especially thoroughly by van de Kamp (1971), GG78, Hetherington (1980), Holberg & Wesemael (2007), Holberg (2007Holberg ( , 2009Holberg ( , 2010, Brosch (2008), and Wesemael & Racine (2008).…”

Two Centuries of Image Quality Estimates from Double-Star Data

“…The history of the discovery of Sirius B by A. G. Clark in 1862 and of early observations of the companion from America and Europe has recently been recounted by Holberg & Wesemael (2007). Wesemael & Racine (2008) review and discuss prior surveys for double stars that failed to reveal the companion and surmise that inadequate DIQ was an important reason why Sirius B was not discovered earlier. The fact that, in the case of a given system, the magnitude and magnitude difference of the components are constant frees the analysis from random errors introduced by the unavoidable imperfection of the interpretative model.…”

“…William Herschel used speculum reflectors of 4 1 2 -inch and 6 1 4 -inch aperture (Wesemael & Racine 2008) for his pioneering study of double stars. The best fits to the data are obtained for quite a large contrast (c ∼ 1:8), a natural precaution for the very first double-star survey.…”

“…This provides interesting quantitative information on the historical improvements of telescope optics, on the thermal management of observatories, and on the prevailing sky brightness. It can also help answer questions such as why the faint companion of Sirius, whose existence was predicted by Bessel as early as 1844, was not seen prior to 1862 (Wesemael & Racine 2008). Finally, the examination of statistics of multiple star discoveries offers insights into some of the systematic errors, biases, and selection effects that affected searches for these objects.…”

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

“…37 Sherburne W. Burnham, the noted observer of double stars and Barnard's former colleague at Lick Observatory, called the feat "the greatest astronomical achievement of the century". 38 Just as in the case of Sirius and its companion, 39 the brightness difference between Amalthea (V = 14.1) and Jupiter (average brightness at opposition, V = -2.7) and the limited apparent distance of the satellite from the planet's centre, which hardly exceeds ~1′, made the discovery critically dependent on the factors that influence image quality at the telescope. Lower quality, more diffuse images contribute to making the faint satellite less visible by reducing the contrast between the central intensity of its image and the local brightness of the glare of Jupiter.…”