This list was originally compiled by Dale Greer. Additions would be

    Numbers in parentheses are approximations that will serve for most
    blue-skying purposes.

    Unix systems provide the 'units' program, useful in converting
    between different systems (metric/English, etc.)


        7726 m/s         (8000)  -- Earth orbital velocity at 300 km altitude
        3075 m/s         (3000)  -- Earth orbital velocity at 35786 km (geosync)
        6371 km          (6400)  -- Mean radius of Earth
        6378 km          (6400)  -- Equatorial radius of Earth
        1738 km          (1700)  -- Mean radius of Moon
        5.974e24 kg      (6e24)  -- Mass of Earth
        7.348e22 kg      (7e22)  -- Mass of Moon
        1.989e30 kg      (2e30)  -- Mass of Sun
        3.986e14 m^3/s^2 (4e14)  -- Gravitational constant times mass of Earth
        4.903e12 m^3/s^2 (5e12)  -- Gravitational constant times mass of Moon
        1.327e20 m^3/s^2 (13e19) -- Gravitational constant times mass of Sun
        384401 km        ( 4e5)  -- Mean Earth-Moon distance
        1.496e11 m       (15e10) -- Mean Earth-Sun distance (Astronomical Unit)

        1 megaton (MT) TNT = about 4.2e15 J or the energy equivalent of
        about .05 kg (50 gm) of matter. Ref: J.R Williams, "The Energy Level
        of Things", Air Force Special Weapons Center (ARDC), Kirtland Air
        Force Base, New Mexico, 1963. Also see "The Effects of Nuclear
        Weapons", compiled by S. Glasstone and P.J. Dolan, published by the
        US Department of Defense (obtain from the GPO).


        Where d is distance, v is velocity, a is acceleration, t is time.
        Additional more specialized equations are available from:


        For constant acceleration
            d = d0 + vt + .5at^2
            v = v0 + at
          v^2 = 2ad

        Acceleration on a cylinder (space colony, etc.) of radius r and
            rotation period t:

            a = 4 pi**2 r / t^2

        For circular Keplerian orbits where:
            Vc   = velocity of a circular orbit
            Vesc = escape velocity
            M    = Total mass of orbiting and orbited bodies
            G    = Gravitational constant (defined below)
            u    = G * M (can be measured much more accurately than G or M)
            K    = -G * M / 2 / a
            r    = radius of orbit (measured from center of mass of system)
            V    = orbital velocity
            P    = orbital period
            a    = semimajor axis of orbit

            Vc   = sqrt(M * G / r)
            Vesc = sqrt(2 * M * G / r) = sqrt(2) * Vc
            V^2  = u/a
            P    = 2 pi/(Sqrt(u/a^3))
            K    = 1/2 V**2 - G * M / r (conservation of energy)

            The period of an eccentric orbit is the same as the period
               of a circular orbit with the same semi-major axis.

        Change in velocity required for a plane change of angle phi in a
        circular orbit:

            delta V = 2 sqrt(GM/r) sin (phi/2)

        Energy to put mass m into a circular orbit (ignores rotational
        velocity, which reduces the energy a bit).

            GMm (1/Re - 1/2Rcirc)
            Re = radius of the earth
            Rcirc = radius of the circular orbit.

        Classical rocket equation, where
            dv  = change in velocity
            Isp = specific impulse of engine
            Ve  = exhaust velocity
            x   = reaction mass
            m1  = rocket mass excluding reaction mass
            g   = 9.80665 m / s^2

            Ve  = Isp * g
            dv  = Ve * ln((m1 + x) / m1)
                = Ve * ln((final mass) / (initial mass))

        Relativistic rocket equation (constant acceleration)

            t (unaccelerated) = c/a * sinh(a*t/c)
            d = c**2/a * (cosh(a*t/c) - 1)
            v = c * tanh(a*t/c)

        Relativistic rocket with exhaust velocity Ve and mass ratio MR:

            at/c = Ve/c * ln(MR), or

            t (unaccelerated) = c/a * sinh(Ve/c * ln(MR))
            d = c**2/a * (cosh(Ve/C * ln(MR)) - 1)
            v = c * tanh(Ve/C * ln(MR))

        Converting from parallax to distance:

            d (in parsecs) = 1 / p (in arc seconds)
            d (in astronomical units) = 206265 / p

            f=ma    -- Force is mass times acceleration
            w=fd    -- Work (energy) is force times distance

        Atmospheric density varies as exp(-mgz/kT) where z is altitude, m is
        molecular weight in kg of air, g is local acceleration of gravity, T
        is temperature, k is Bolztmann's constant. On Earth up to 100 km,

            d = d0*exp(-z*1.42e-4)

        where d is density, d0 is density at 0km, is approximately true, so

            d@12km (40000 ft) = d0*.18
            d@9 km (30000 ft) = d0*.27
            d@6 km (20000 ft) = d0*.43
            d@3 km (10000 ft) = d0*.65

                    Atmospheric scale height    Dry lapse rate
                    (in km at emission level)    (K/km)
                    -------------------------   --------------
            Earth           7.5                     9.8
            Mars            11                      4.4
            Venus           4.9                     10.5
            Titan           18                      1.3
            Jupiter         19                      2.0
            Saturn          37                      0.7
            Uranus          24                      0.7
            Neptune         21                      0.8
            Triton          8                       1

        Titius-Bode Law for approximating planetary distances:

            R(n) = 0.4 + 0.3 * 2^N Astronomical Units (N = -infinity for
            Mercury, 0 for Venus, 1 for Earth, etc.)

            This fits fairly well except for Neptune.


        6.62618e-34 J-s  (7e-34) -- Planck's Constant "h"
        1.054589e-34 J-s (1e-34) -- Planck's Constant / (2 * PI), "h bar"
        1.3807e-23 J/K  (1.4e-23) - Boltzmann's Constant "k"
        5.6697e-8 W/m^2/K (6e-8) -- Stephan-Boltzmann Constant "sigma"
    6.673e-11 N m^2/kg^2 (7e-11) -- Newton's Gravitational Constant "G"
        0.0029 m K       (3e-3)  -- Wien's Constant "sigma(W)"
        3.827e26 W       (4e26)  -- Luminosity of Sun
        1370 W / m^2     (1400)  -- Solar Constant (intensity at 1 AU)
        6.96e8 m         (7e8)   -- radius of Sun
        1738 km          (2e3)   -- radius of Moon
        299792458 m/s     (3e8)  -- speed of light in vacuum "c"
        9.46053e15 m      (1e16) -- light year
        206264.806 AU     (2e5)  -- \
        3.2616 light years (3)   --  --> parsec
        3.0856e16 m      (3e16)  -- /

    Black Hole radius (also called Schwarzschild Radius):

        2GM/c^2, where G is Newton's Grav Constant, M is mass of BH,
                c is speed of light

    Things to add (somebody look them up!)
        Basic rocketry numbers & equations
        Aerodynamical stuff
        Energy to put a pound into orbit or accelerate to interstellar
        Non-circular cases?



    References that have been frequently recommended on the net are:

    "Fundamentals of Astrodynamics" Roger Bate, Donald Mueller, Jerry White
    1971, Dover Press, 455pp $8.95 (US) (paperback). ISBN 0-486-60061-0

    NASA Spaceflight handbooks (dating from the 1960s)
        SP-33 Orbital Flight Handbook (3 parts)
        SP-34 Lunar Flight Handbook   (3 parts)
        SP-35 Planetary Flight Handbook (9 parts)

        These might be found in university aeronautics libraries or ordered
        through the US Govt. Printing Office (GPO), although more
        information would probably be needed to order them.

    M. A. Minovitch, _The Determination and Characteristics of Ballistic
    Interplanetary Trajectories Under the Influence of Multiple Planetary
    Attractions_, Technical Report 32-464, Jet Propulsion Laboratory,
    Pasadena, Calif., Oct, 1963.

        The title says all. Starts of with the basics and works its way up.
        Very good. It has a companion article:

    M. Minovitch, _Utilizing Large Planetary Perubations for the Design of
    Deep-Space Solar-Probe and Out of Ecliptic Trajectories_, Technical
    Report 32-849, JPL, Pasadena, Calif., 1965.

        You need to read the first one first to realy understand this one.
        It does include a _short_ summary if you can only find the second.

        Contact JPL for availability of these reports.

    "Spacecraft Attitude Dynamics", Peter C. Hughes 1986, John Wiley and

    "Celestial Mechanics: a computational guide for the practitioner",
    Lawrence G. Taff, (Wiley-Interscience, New York, 1985).

        Starts with the basics (2-body problem, coordinates) and works up to
        orbit determinations, perturbations, and differential corrections.
        Taff also briefly discusses stellar dynamics including a short
        discussion of n-body problems.


    More net references:

    "Explanatory Supplement to the Astronomical Almanac" (revised edition),
    Kenneth Seidelmann, University Science Books, 1992. ISBN 0-935702-68-7.
    $65 in hardcover.

        Deep math for all the algorthms and tables in the AA.

    Van Flandern & Pullinen, _Low-Precision Formulae for Planetary
    Positions_, Astrophysical J. Supp Series, 41:391-411, 1979. Look in an
    astronomy or physics library for this; also said to be available from

        Gives series to compute positions accurate to 1 arc minute for a
        period + or - 300 years from now. Pluto is included but stated to
        have an accuracy of only about 15 arc minutes.

    _Multiyear Interactive Computer Almanac_ (MICA), produced by the US
    Naval Observatory. Valid for years 1990-1999. $55 ($80 outside US).
    Available for IBM (order #PB93-500163HDV) or Macintosh (order
    #PB93-500155HDV). From the NTIS sales desk, (703)-487-4650. I believe
    this is intended to replace the USNO's Interactive Computer Ephemeris.

    _Interactive Computer Ephemeris_ (from the US Naval Observatory)
    distributed on IBM-PC floppy disks, $35 (Willmann-Bell). Covers dates

    "Planetary Programs and Tables from -4000 to +2800", Bretagnon & Simon
    1986, Willmann-Bell.

        Floppy disks available separately.

    "Fundamentals of Celestial Mechanics" (2nd ed), J.M.A. Danby 1988,

        A good fundamental text. Includes BASIC programs; a companion set of
        floppy disks is available separately.

    "Astronomical Formulae for Calculators" (4th ed.), J. Meeus 1988,

    "Astronomical Algorithms", J. Meeus 1991, Willmann-Bell.

        If you actively use one of the editions of "Astronomical Formulae
        for Calculators", you will want to replace it with "Astronomical
        Algorithms". This new book is more oriented towards computers than
        calculators and contains formulae for planetary motion based on
        modern work by the Jet Propulsion Laboratory, the U.S. Naval
        Observatory, and the Bureau des Longitudes. The previous books were
        all based on formulae mostly developed in the last century.

        Algorithms available separately on diskette.

    "Practical Astronomy with your Calculator" (3rd ed.), P. Duffett-Smith
    1988, Cambridge University Press.

    "Orbits for Amateurs with a Microcomputer", D. Tattersfield 1984,
    Stanley Thornes, Ltd.

        Includes example programs in BASIC.

    "Orbits for Amateurs II", D. Tattersfield 1987, John Wiley & Sons.

    "Astronomy / Scientific Software" - catalog of shareware, public domain,
    and commercial software for IBM and other PCs. Astronomy software
    includes planetarium simulations, ephemeris generators, astronomical
    databases, solar system simulations, satellite tracking programs,
    celestial mechanics simulators, and more.

        Andromeda Software, Inc.
        P.O. Box 605
        Amherst, NY 14226-0605


    Astrogeologist Gene Shoemaker proposes the following formula, based on
    studies of cratering caused by nuclear tests.

    D = S  S  c  K  W       : crater diameter in km
         g  p  f  n

    S = (g /g )             : gravity correction factor for bodies other than
     g    e  t                Earth, where g = 9.8 m/s^2 and g  is the surface
                                            e                 t
                              gravity of the target body. This scaling is
                              cited for lunar craters and may hold true for
                              other bodies.

    S = (p / p )            : correction factor for target density p  ,
     p    a   t                                                     t
                              p  = 1.8 g/cm^3 for alluvium at the Jangle U
                              crater site, p = 2.6 g/cm^3 for average
                              rock on the continental shields.

    C                       : crater collapse factor, 1 for craters <= 3 km
                              in diameter, 1.3 for larger craters (on Earth).

    K                       : .074 km / (kT TNT equivalent)
     n                        empirically determined from the Jangle U
                              nuclear test crater.

              3            2                   19
    W = pi * d  * delta * V  / (12 * 4.185 * 10  )
                            : projectile kinetic energy in kT TNT equivalent
                              given diameter d, velocity v, and projectile
                              density delta in CGS units. delta of around 3
                              g/cm^3 is fairly good for an asteroid.

    An RMS velocity of V = 20 km/sec may be used for Earth-crossing

    Under these assumptions, the body which created the Barringer Meteor
    Crater in Arizona (1.13 km diameter) would have been about 40 meters in

    More generally, one can use (after Gehrels, 1985):

    Asteroid        Number of objects  Impact probability  Impact energy
    diameter (km)                      (impacts/year)      (* 5*10^20 ergs)

     10                     10               10^-8              10^9
      1                  1 000               10^-6              10^6
      0.1              100 000               10^-4              10^3

    assuming simple scaling laws. Note that 5*10^20 ergs = 13 000 tons TNT
    equivalent, or the energy released by the Hiroshima A-bomb.


    Gehrels, T. 1985 Asteroids and comets. _Physics Today_ 38, 32-41. [an
        excellent general overview of the subject for the layman]

    Shoemaker, E.M. 1983 Asteroid and comet bombardment of the earth. _Ann.
        Rev. Earth Planet. Sci._ 11, 461-494. [very long and fairly
        technical but a comprehensive examination of the

    Shoemaker, E.M., J.G. Williams, E.F. Helin & R.F. Wolfe 1979
        Earth-crossing asteroids: Orbital classes, collision rates with
        Earth, and origin. In _Asteroids_, T. Gehrels, ed., pp. 253-282,
        University of Arizona Press, Tucson.

    Cunningham, C.J. 1988 _Introduction to Asteroids: The Next Frontier_
        (Richmond: Willman-Bell, Inc.) [covers all aspects of asteroid
        studies and is an excellent introduction to the subject for people
        of all experience levels. It also has a very extensive reference
        list covering essentially all of the reference material in the


    Two easy-to-find sources of map projections are the "Encyclopaedia
    Brittanica", (particularly the older volumes) and a tutorial appearing
    in _Graphics Gems_ (Academic Press, 1990). The latter was written with
    simplicity of exposition and suitability of digital computation in mind
    (spherical trig formulae also appear, as do digitally-plotted examples).

    More than you ever cared to know about map projections is in John
    Snyder's USGS publication "Map Projections--A Working Manual", USGS
    Professional Paper 1395. This contains detailed descriptions of 32
    projections, with history, features, projection formulas (for both
    spherical earth and ellipsoidal earth), and numerical test cases. It's a
    neat book, all 382 pages worth. This one's $20.

    You might also want the companion volume, by Snyder and Philip Voxland,
    "An Album of Map Projections", USGS Professional Paper 1453. This
    contains less detail on about 130 projections and variants. Formulas are
    in the back, example plots in the front. $14, 250 pages.

    You can order these 2 ways. The cheap, slow way is direct from USGS:
    Earth Science Information Center, US Geological Survey, 507 National
    Center, Reston, VA 22092. (800)-USA-MAPS. They can quote you a price and
    tell you where to send your money. Expect a 6-8 week turnaround time.

    A much faster way (about 1 week) is through Timely Discount Topos,
    (303)-469-5022, 9769 W. 119th Drive, Suite 9, Broomfield, CO 80021. Call
    them and tell them what you want. They'll quote a price, you send a
    check, and then they go to USGS Customer Service Counter and pick it up
    for you. Add about a $3-4 service charge, plus shipping.

    A (perhaps more accessible) mapping article is:

        R. Miller and F. Reddy, "Mapping the World in Pascal",
        Byte V12 #14, December 1987

        Contains Turbo Pascal procedures for five common map projections. A
        demo program, CARTOG.PAS, and a small (6,000 point) coastline data
        is available on CompuServe, GEnie, and many BBSs.

    Some references for spherical trignometry are:

        _Spherical Astronomy_, W.M. Smart, Cambridge U. Press, 1931.

        _A Compendium of Spherical Astronomy_, S. Newcomb, Dover, 1960.

        _Spherical Astronomy_, R.M. Green, Cambridge U. Press., 1985 (update
        of Smart).

        _Spherical Astronomy_, E Woolard and G.Clemence, Academic
        Press, 1966.


        "Computer Simulation Using Particles"
        R. W. Hockney and J. W. Eastwood
        (Adam Hilger; Bristol and Philadelphia; 1988)

        "The rapid evaluation of potential fields in particle systems",
        L. Greengard
        MIT Press, 1988.

            A breakthrough O(N) simulation method. Has been parallelized.

        L. Greengard and V. Rokhlin, "A fast algorithm for particle
        simulations," Journal of Computational Physics, 73:325-348, 1987.

        "An O(N) Algorithm for Three-dimensional N-body Simulations", MSEE
        thesis, Feng Zhao, MIT AILab Technical Report 995, 1987

        "Galactic Dynamics"
        J. Binney & S. Tremaine
        (Princeton U. Press; Princeton; 1987)

            Includes an O(N^2) FORTRAN code written by Aarseth, a pioneer in
            the field.

        Hierarchical (N log N) tree methods are described in these papers:

        A. W. Appel, "An Efficient Program for Many-body Simulation", SIAM
        Journal of Scientific and Statistical Computing, Vol. 6, p. 85,

        Barnes & Hut, "A Hierarchical O(N log N) Force-Calculation
        Algorithm", Nature, V324 # 6096, 4-10 Dec 1986.

        L. Hernquist, "Hierarchical N-body Methods", Computer Physics
        Communications, Vol. 48, p. 107, 1988.


    If you just need to examine FITS images, use the ppm package (see the FAQ) to convert them to your preferred format. For more
    information on the format and other software to read and write it, see
    the sci.astro.fits FAQ.


    The 6th Edition of the Unix operating system came with several software
    systems not distributed because of older media capacity limitations.
    Included were an ephmeris, a satellite track, and speech synthesis
    software. The ephmeris, sky(6), is available within AT&T and to sites
    possessing a Unix source code license. The program is regarded as Unix
    source code. Sky is <0.5MB. Send proof of source code license to

        E. Miya
        MS 258-5
        NASA Ames Research Center
        Moffett Field, CA 94035-1000


    To generate 3D coordinates of astronomical objects, first obtain an
    astronomical database which specifies right ascension, declination, and
    parallax for the objects. Convert parallax into distance using the
    formula in part 6 of the FAQ, convert RA and declination to coordinates
    on a unit sphere (see some of the references on planetary positions and
    spherical trignometry earlier in this section for details on this), and
    scale this by the distance.

    Two databases useful for this purpose are the Yale Bright Star catalog
    (sources listed in FAQ section 3) or "The Catalogue of Stars within 25
    parsecs of the Sun" (in pub/SPACE/FAQ/ and stars.doc on

NEXT: FAQ #5/13 - References on specific areas