Astronomy & Advanced Units
Convert astronomical distances (AU, light-years, parsecs), solar mass and radius, atomic mass units, electronvolts, Planck units, Mach numbers, and the speed of light. Uses IAU and 2019 SI definitions.
All Astronomy Converters
- Astronomical Unit Converterau ↔ m ↔ km
- Light-Year Converterly ↔ m ↔ km ↔ au
- Parsec Converterpc ↔ ly ↔ au
- Earth Distance Converterkm ↔ mi ↔ nmi
- Solar Mass ConverterM☉ ↔ kg
- Solar Radius ConverterR☉ ↔ km
- Atomic Mass Unit Converteru ↔ kg
- Electronvolt ConvertereV ↔ J
- Angstrom ConverterÅ ↔ nm ↔ m
- Planck Length ConverterℓP ↔ m
- Planck Time ConvertertP ↔ s
- Gravitational Accelerationm/s² ↔ g₀
- Speed of Light Converterc ↔ m/s ↔ km/h
- Mach Number ConverterMa ↔ m/s
- Speed of Sound Converterm/s ↔ km/h
About Astronomical Units
Astronomy deals with distances and masses that dwarf everyday experience. The Sun is about 1.5 × 10¹¹ meters from Earth. The nearest star system is about 4.2 light-years away, or roughly 4 × 10¹⁶ meters. The Milky Way is about 100,000 light-years across. Specialized units make these figures manageable.
Key exact relationships
- 1 astronomical unit (au) = 149,597,870,700 m exactly (IAU 2012)
- 1 light-year = 9,460,730,472,580,800 m exactly (c × Julian year)
- 1 parsec ≈ 3.0857 × 10¹⁶ m (derived: au / tan(1″))
- 1 solar mass = 1.98892 × 10³⁰ kg (approximate, solar mass changes over time)
- 1 atomic mass unit (u) = 1.66053906660 × 10⁻²⁷ kg (CODATA 2018)
- 1 electronvolt = 1.602176634 × 10⁻¹⁹ J exactly (2019 SI)
- 1 angstrom = 10⁻¹⁰ m exactly
- Speed of light in vacuum (c) = 299,792,458 m/s exactly
Planck units
Planck units are a natural system of units derived from fundamental physical constants: the speed of light (c), the gravitational constant (G), the reduced Planck constant (ħ), the Coulomb constant (kₑ), and the Boltzmann constant (kB). The Planck length is about 1.6 × 10⁻³⁵ m — the scale at which quantum gravity is expected to become relevant.
Speed of sound and Mach
Unlike the speed of light, the speed of sound is not a fixed constant — it depends on the medium, temperature, and pressure. In dry air at 20 °C and standard pressure, the speed of sound is about 343 m/s. Mach 1 is defined as the local speed of sound, so "Mach 2" is twice the local speed of sound and can correspond to different absolute speeds at different altitudes.