[...]... move towards adopting a single set of units for the benefit of all I hope it succeeds! 1 Introduction 1.1 Using SI units in astronomy The target audience for a book on using SI units in astronomy has to be astronomers who teach and/or carry out astronomical research at universities and government observatories (national or local) or privately run observatories If this group would willingly accept the... the advantages to be gained by all astronomers using the same set of units and proceed to lead by example, then it should follow that the next generation of astronomers would be taught using the one set of units Since many of the writers of popular articles in astronomy have received training in the science, non-technical reviews might then also be written using the one set of units Given the commitment... seconds So in each of these cases we could use SI units, though quite obviously many are unwieldy and a good scientific argument for using special astronomical units may readily be made In many areas of astronomy, the combination of research workers trained initially at different times, in different places and in different disciplines (physics, chemistry, electrical engineering, mathematics, astronomy. .. base SI names occurring Table 2.3 gives some examples of such special names, with the derived unit expressed in terms of both other SI units and of base SI units only Note that the radian and steradian were originally termed supplementary SI derived units Table 2.4 lists some examples of SI derived units whose names and symbols include SI derived units with special names and symbols 12 2.3 Non -SI units. .. phenomena concerned.’ In addition to the non -SI units listed in Table 2.5 and Table 2.6, the non -SI units given in Table 2.13 are recognized for use in astronomy: The IAU recommendations for prefixes are in line with those of BIPM and are as given in Table 2.10 Non -SI units such as British Imperial, American or other national systems of units should not be used The cgs and obsolete units given in Table 2.14... chapters in this book 2.2 The set of SI derived units Derived SI units are those that may be expressed directly by multiplying or dividing base units, e.g., density (kg m−3 ) or acceleration (m s−2 ) or electric charge (A s) Table 2.2 lists examples of SI derived units obtained from base units Special names have been assigned to selected derived units that are used to prevent unwieldy combinations... reasons cited in Cardarelli (2003) for using SI units are: 1 It is both metric (based on the metre) and decimal (base 10 numbering system) 2 Prefixes are used for sub-multiples and multiples of the units and fractions eliminated, which simplifies calculations 3 Each physical quantity has a unique unit 4 Derived SI units, some of which have their own name, are defined by simple expressions relating two or... used the compact shorthand M8 instead of 108 M with Mn representing a mass of 10n solar masses 2.6 IAU recommendations regarding SI units The International Astronomical Union in its style manual (Wilkins, 1989)8 states that: ‘The international system (SI) of units, prefixes and symbols should be used for all physical quantities except that certain special units, may be used in astronomy, 7 remember that... given in both forms This would lead to SI units becoming familiar, acceptable and, hopefully, the universal system of choice 2 An introduction to SI units The name Système International d’Unités (International System of Units) , with the abbreviation SI, was adopted by the 11th Conférence Générale des Poids et Mesures (CGPM) in 1960 This system includes two classes of units: - base units - derived units, ... s−3 Table 2.5 Non -SI units accepted for use with the International System (BIPM, 2006) Name Symbol Value in SI units minute hour day degree minute second litre tonne neper bel min h d 60 s 3600 s 86 400 s (π/180) rad (π/10 800) rad (π/648 000) rad 10−3 m3 103 kg 1 Np = 1 1 B = (1/2) ln 10 (Np) ◦ l, L t Np B 16 An introduction to SI units Table 2.6 Non -SI units accepted for use with the International System . h0" alt="" USING SI UNITS IN ASTRONOMY A multitude of measurement units exist within astronomy, some of which are unique to the subject, causing discrepancies. it to move towards adopting a single set of units for the benefit of all. I hope it succeeds! 1 Introduction 1.1 Using SI units in astronomy The target audience