Orbital Period (P𝘰𝘳𝘣) ○◂ Entries

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Orbital Period (P𝘰𝘳𝘣) ○◂｜Definition｜1st｜20251119205401-00-⌔

Orbital period - Wikipedia

Orbital period

The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars. It may also refer to the time it takes a satellite orbiting a planet or moon to complete one orbit.

For celestial objects in general, the orbital period is determined by a 360° revolution of one body around its primary, e.g. Earth around the Sun.

Periods in astronomy are expressed in units of time, usually hours, days, or years. Its reciprocal is the orbital frequency, a kind of revolution frequency, in units of hertz.

Printed 2026-06-28.

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Mass Function ○◂｜untitled_remarks｜1st｜20261011111750-00-●

Remillard & McClintock 2006 ┃ X-Ray Properties… ⚬𓂃

An observational quantity of special interest is the mass function, $f(M)\equiv P_{\mathrm{orb}}{K}_2^3/2\pi G=M_1{\sin }^{3}i/(1+q{)}^2$ (see Table 1, column 6). The observables on the left side of this equation are the orbital period $P_{\mathrm{orb}}$ and the half-amplitude of the velocity curve of the secondary $K_2$. On the right, the quantity of greatest interest is $M_1$, the mass of the BH primary (given in column 7); the other parameters are the orbital inclination angle $i$ and the mass ratio $q\equiv M_2/M_1$, where $M_2$ is the mass of the secondary. The value of $f(M)$ can be determined by simply measuring the radial velocity curve of the secondary star, and it corresponds to the absolute minimum allowable mass of the compact object.

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