Astronomical Data

• Mass = 1.9891 * 10³⁰ kg.
• Radius = 696,265 km.
• Surface temperature = 5,780 K.
• Inclination of the solar equator on the ecliptic of date = 7°.25
• Longitude of the ascending node of the solar equator on the ecliptic of date = 76°
• Period of rotation at equator:
  • Sidereal = 25.38 d
  • Mean synodic = 27.275 d
• Solar wind speed near Earth » 450 km/s (travel time, Sun to Earth » 4 d).
• Solar velocity = 19.75 km/s toward a = 18.07 h, d = +30° (solar apex).

• Mass = 10¹² solar masses.
• Center: a = 17 h 45.7 min, d = -29°00¢ (2000).
• Distance to center » 9 kpc
• Diameter » 100 kpc
• North pole: a = 12h 51 min, d = 27°08¢ (2000).
• Rotational speed (at Sun) » 250 km/s
• Rotational period (at Sun) » 220 Ma
• Velocity relative to the 3 K background » 600 km/s toward a » 10 h, d » -20°

• D: The diameter of the objective in mm.
• LG (Light Grasp): The ratio of the light flux intercepted by a telescope's objective lens or mirror to that intercepted by a human eye having a 7 mm diameter entrance pupil.
• Lm: Limiting visual magnitude, where Lm » 2.7 + 5 log D, assuming transparent, dark-sky conditions and magnification M ³ 1D.
• a: The smallest resolvable angle, where a » 120/D seconds of arc. However, atmospheric conditions seldom permit values less than 0.5².
• Useful magnification range » 0.2D to 2D. The lower limit may be a little less, but depends upon the maximum diameter of the entrance pupil of the individual observer's eye. The upper limit is determined by the wave nature of the light and the optical limitations of the eye, although atmospheric turbulence usually limits the maximum magnification to 400x or less. For examination of double stars, detection of faint stars, and studying structure in bright nebulae, magnification of up to 4D are sometimes useful. Note that the reciprocal of the coefficient to D is the diameter (in mm) of the telescope's exit pupil.

The following table (based upon work by E.A. Whitaker) gives the approximate diameters of the smallest crater half-filled with shadow, and of the narrowest black line certainly distinguishable. Perfect seeing conditions and optical equipment are assumed. Observationally, different observers will have different limits.

• Speed of light, c º 299,792,458. m/s
• p = 3.14 15 92 65 35 89 79
• Number of square degrees on a sphere = 41,253
• For 360° = 24 h, 15° = 1 h, 15¢ = 1 min, 15² = 1 s

1. Observer's HandBook, of the Royal Astronomical Society of Canada (RASC), edited by Mr. Roy Bishop, after taking his kind permission.
2. Sky Catalogue 2000.0, by Hirshfeld, Sinnott, and Ochsenbein. After taking permission from Mr. Sinnott of the Sky Publishing Corp.
3. The Amateur Astronomer, by Patrick Moore.
4. StarList 2000, by Richard Dibon-Smith.

Note: Many of the numbers listed above are determined by measurement. Exceptions include defined quantities (indicated by three lines in the equal sign º), quantities calculated from defined quantities (e.g. m/ly, AU/pc), and numbers of mathematical origin such as p and conversion factors in angular measure. Of the measured quantities, some are known to only approximate precision. For these the equal sign is reduced to ».