Stars & Sun constants

20 values, each with its units, its uncertainty, and where it came from.

Chandrasekhar Limit measured

M_{\mathrm{Ch}} = 2.86 \times 10^{30}\ \text{kg}

kgMaximum mass a white dwarf can support by electron degeneracy pressure, about 1.44 solar masses or 2.86 × 10³⁰ kg.

d_{\alpha\,\mathrm{Cen}} = 4.13 \times 10^{16}\ \text{m}

mDistance to Alpha Centauri A, 4.13 × 10¹⁶ m or 4.365 light-years — the nearest Sun-like star, and the nearest whole stellar system.

d_{\mathrm{Barnard}} = 5.6413 \times 10^{16}\ \text{m}

mDistance to Barnard's Star, 5.64 × 10¹⁶ m or 5.96 light-years — the fastest-moving star in the sky, crossing a Moon-width per lifetime.

d_{\mathrm{Bet}} = 5.184 \times 10^{18}\ \text{m}

mDistance to Betelgeuse, about 168 parsecs or 548 light-years — uncertain by ten per cent, because the star is bigger than its own parallax.

d_{\mathrm{Prox}} = 4.0175 \times 10^{16}\ \text{m}

mDistance to the nearest star beyond the Sun, 4.017 × 10¹⁶ m — 4.246 light-years or 1.302 pc, from a Gaia parallax of 768.07 mas.

d_{\mathrm{Sirius}} = 8.137 \times 10^{16}\ \text{m}

mDistance to Sirius, 8.14 × 10¹⁶ m or 8.60 light-years — the brightest star in the night sky owes half its rank to simple nearness.

L_{\alpha\,\mathrm{Cen\,A}} = 5.815 \times 10^{26}\ \text{W}

WPower output of Alpha Centauri A, 1.52 times the Sun's — a slightly older, slightly brighter solar twin, our best preview of the Sun's future.

L_{\mathrm{Sir\,A}} = 9.72 \times 10^{27}\ \text{W}

WPower output of Sirius A, 25.4 times the Sun's — the true wattage behind the night sky's brightest star, mostly poured out in the ultraviolet.

L_{\mathrm{Vega}} = 1.536 \times 10^{28}\ \text{W}

WApparent luminosity of Vega, about 40 Suns — the star that defined magnitude zero, later caught cheating by spinning nearly apart.

M_{\mathrm{Prox}} = 2.428 \times 10^{29}\ \text{kg}

kgMass of Proxima Centauri, 0.1221 solar masses — an eighth of a Sun, just clear of the hydrogen-burning limit, with a trillion-year future.

M_{\mathrm{Sir\,A}} = 4.102 \times 10^{30}\ \text{kg}

kgMass of Sirius A, 2.063 solar masses — weighed by watching its 50-year waltz with the white dwarf companion Bessel predicted unseen.

M_{\mathrm{Sir\,B}} = 2.024 \times 10^{30}\ \text{kg}

kgMass of the white dwarf Sirius B — 1.018 Suns packed into an Earth-sized sphere, the heaviest white dwarf with a precision mass.

\mathcal{L}^{\mathrm{N}}_\odot = 3.828 \times 10^{26}\ \text{W}

WIAU nominal solar luminosity, exactly 3.828 × 10²⁶ W — the conventional unit in which every other star's power output is quoted.

\mathcal{R}^{\mathrm{N}}_\odot = 695,700,000\ \text{m}

mIAU nominal solar radius, exactly 6.957 × 10⁸ m — a fixed convention, since a gaseous Sun has no true surface to measure.

R_{\mathrm{Bet}} = 5.315 \times 10^{11}\ \text{m}

mRadius of Betelgeuse, about 764 solar radii or 3.6 au — placed at the Sun it would swallow Mars, with honest error bars nearly a full au wide.

R_{\mathrm{Prox}} = 107,280,000\ \text{m}

mRadius of Proxima Centauri, 0.154 solar radii — the nearest star is only half again the size of Jupiter, glowing at 3000 K.

R_{\mathrm{Sir\,B}} = 5,634,000\ \text{m}

mRadius of Sirius B, 5634 km — a star smaller than the Earth, whose surface gravity compresses a sugar-cube's volume to a tonne of matter.

r_{s,\odot} = 2,953.25\ \text{m}

mRadius to which the Sun would have to be crushed to become a black hole, 2GM⊙/c² — a shade under three kilometres.

\mathcal{T}^{\mathrm{N}}_{\mathrm{eff}\odot} = 5,772\ \text{K}

KIAU nominal effective temperature of the Sun, 5772 K — the blackbody temperature that radiates the solar luminosity from the solar radius.

M_\odot = 1.98841 \times 10^{30}\ \text{kg}

kgMass of the Sun, about 333 000 Earths and 99.86 per cent of all matter in the solar system — the yardstick for every stellar mass.