Milliarcsecond (mas)

AstronomicalCurrent unit

One thousandth of an arcsecond. Used for the parallax of stars.

1 milliarcsecond = 7.716049383×10⁻¹⁰ turns (approximately).

About the milliarcsecond

A milliarcsecond, abbreviated mas, is a thousandth of an arcsecond, or 1/3,600,000 of a degree. That is about 4.85 nanoradians, small enough to span only about 4.8 millimeters at a distance of 1,000 kilometers. The SI Brochure lists mas, along with microarcseconds and picoarcseconds, as the symbols astronomers use for very small angles.

Stellar parallax is the main customer. Because distance in parsecs is the reciprocal of parallax in arcseconds, a star with a parallax of 1 mas lies 1,000 parsecs away, roughly 3,260 light-years. Precision at this level is why astrometry missions work in microarcseconds. ESA's Gaia measured positions of objects about 4,000 times fainter than the naked-eye limit to around 24 microarcseconds, which is 0.024 mas, a precision ESA compares to the width of a human hair seen from 1,000 kilometers away.

Sources: BIPM SI Brochure, 9th edition (2019); ESA Gaia: Cosmic distances; Wikipedia: Minute and second of arc

Milliarcsecond conversion chart

1 milliarcsecond expressed in every other angle unit:

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