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Astronomy Principles and Practice Fourth Edition.pdf

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Mathematical constants, systems of units <strong>and</strong> conversion factors 455<br />

Length of the month<br />

Synodic 29·d530 59 29 d 12 h 44 m 03 s<br />

Sidereal 27·321 66 27 07 43 12<br />

Anomalistic 27·554 55 27 13 18 33<br />

Nodical 27·212 22 27 05 05 36<br />

Tropical 27·321 58 27 07 43 05<br />

Length of the year<br />

Tropical ( to ) 365·d242 20 365 d 05 h 48 m 46 s<br />

Sidereal (fixed star to fixed star) 365·256 36 365 06 09 10<br />

Anomalistic (perigee to perigee) 365·259 64 365 06 13 53<br />

Julian 365·25 365 06 00 00<br />

A.3 Mathematical constants, systems of units <strong>and</strong> conversion factors<br />

1radian= 57·◦295 78 = 3437·′747 = 206 264·′′ 8<br />

Square degrees in a steradian = 3282·806<br />

A sphere subtends 4π steradians at its centre<br />

π = 3·141 59<br />

e = 2·718 28<br />

log 10 e = 0·434 29<br />

log e 10 = 2·302 58<br />

1km= 0·621 37 miles = 0·539 96 nautical miles = 3280·8ft<br />

1 mile = 1·6093 km<br />

1 international nautical mile = 1·8250 km = 6076·11 ft<br />

1 Å= 10 −7 mm<br />

1AU= 149 600 000 km = 92 960 000 miles<br />

1parsec= 206 264·8AU<br />

1kms −1 = 2236·9 miles per hour<br />

1 foot per second = 0·304 80 metres per second<br />

1 AU per year = 2·9456 miles per second = 4·7404 km s −1<br />

1 kilogram = 2·204 622 lb<br />

1lb= 0·453 592 kg<br />

1 electron volt (eV) = 1·602 06 × 10 −19 J<br />

Basic SI units<br />

Physical quantity Name of unit Symbol<br />

length metre m<br />

mass kilogram kg<br />

time second s<br />

electric current ampere A<br />

thermodynamic temperature degree Kelvin K

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