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% |
Tutorial Series
This post is part of the series Introduction to Astronomy. Use the links below to advance to the next tutorial in the couse, or go back and see the previous in the tutorial series.
