Introduction to Astronomy Series
- Introduction to Astronomy
- The Celestial Sphere - Right Ascension and Declination
- What is Angular Size?
- What is the Milky Way Galaxy?
- The Astronomical Magnitude Scale
- Sidereal Time, Civil Time and Solar Time
- Equinoxes and Solstices
- Parallax, Distance and Parsecs
- Luminosity and Flux of Stars
- Kepler's Laws of Planetary Motion
- What Are Lagrange Points?
- Glossary of Astronomy & Photographic Terms
- Astronomical Constants - Some Useful Constants for Astronomy
Defining constants
| Quantity | Symbol | Value | Relative uncertainty |
|---|---|---|---|
| Gaussian gravitational constant | k | 0.017,202,098,95 A3/2,S-1/2,D-1 | defined |
| Speed of light | c | 299,792,458 ms-1 | defined |
| Mean ratio of the TT second to the TCG second | 1 - LG | 1 - 6.969,290,134×10-10 | defined |
| Mean ratio of the TCB second to the TDB second | 1 - LB | 1 - 1.550,519,767,72×10-8 | defined |
Primary constants
| Quantity | Symbol | Value | Relative uncertainty |
|---|---|---|---|
| Mean ratio of the TCB second to the TCG second | 1 - LC | 1 - 1.480,826,867,41×10-8 | 1.4×10-9 |
| Light-time for unit distance | ?A | 499.004,786,3852 s | 4.0×10-11 |
| Equatorial radius for Earth | ae | 6.378,1366×106m | 1.6×10-8 |
| Potential of the geoid | W0 | 6.263,685,60×107m2,s-2 | 8.0×10-9 |
| Dynamical form-factor for Earth | J2 | 0.001,082,6359 | 9.2×10-8 |
| Flattening factor for Earth | 1/ƒ | 0.003,352,8197 = 1/298.256,42 | 3.4×10-8 |
| Geocentric gravitational constant | GE | 3.986,004,391×1014m3,s-2 | 2.0×10-9 |
| Constant of gravitation | G | 6.673,84×10-11 m3,kg-1,s-2 | 1.2×10-4 |
| Ratio of mass of Moon to mass of Earth | µ | 0.012,300,0383 = 1/81.300,56 | 4.0×10-8 |
| General precession in longitude, per Julian century, at standard epoch 2000 | Ρ | 5029.796,195? | * |
| Obliquity of the ecliptic, at standard epoch 2000 | ε | 23ε 26' 21.406? | * |
Derived constants
| Quantity | Symbol | Value | Relative uncertainty |
|---|---|---|---|
| Constant of nutation, at standard epoch 2000 | N | 9.205,2331? | * |
| Unit distance = c?A | A | 149,597,870,691 m | 4.0×10-11 |
| Solar parallax = arcsin(ae/A) | p? | 8.794,1433? | 1.6×10-8 |
| Constant of aberration, at standard epoch 2000 | κ | 20.495,52? | |
| Heliocentric gravitational constant = A3k2/D2 | GS | 1.327,2440×1020m3,s-2 | 3.8×10-10 |
| Ratio of mass of Sun to mass of Earth = (GS)/(GE) | S/E | 332,946.050,895 | |
| Ratio of mass of Sun to mass of (Earth + Moon) | (S/E) (1 + μ) | 328,900.561,400 | |
| Mass of Sun = (GS)/G | S | 1.9818×1030kg | 1.0×10-4 |
System of planetary masses & Ratios of mass of Sun to mass of planet
| Planet | Ratios of mass | ||
|---|---|---|---|
| Mercury | 6,023,600 | ||
| Venus | 408,523.71 | ||
| Earth + Moon | 328,900.561,400 | ||
| Mars | 3,098,708 | ||
| Jupiter | 1047.3486 | ||
| Saturn | 3497.898 | ||
| Uranus | 22,902.98 | ||
| Neptune | 19,412.24 | ||
| Pluto | 135,200,000 |
Other constants (outside the formal IAU System)
| Quantity | Symbol | Value | Relative uncertainty |
|---|---|---|---|
| Parsec = A/tan(1") | pc | 3.085,677,581,28×1016 m | 4.0×10-11 |
| Light-year = 365.25cD | ly | 9.460,730,472,5808×1015m | defined |
| Hubble constant | H0 | 70.1 km,s-1,Mpc-1 | 0.019 |
| Solar luminosity | L? | 3.939×1026 W = 2.107×10-15S,D-1 | variable, ±0.1% |
