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About 26,000 light-years. Measured by tracking the orbits of stars near the galactic center.

The radius of a black hole's event horizon. For non-rotating black holes, it's calculated by $R_S = \frac{2GM}{c^2}$, where $G$ is the gravitational constant, $M$ is the mass, and $c$ is the speed of light.

Roughly 384,400 km. It's commonly measured by laser ranging experiments.

Around 2.537 million light-years from Earth. Measured using variable stars and other standard candles.

About 1.39 million km. Determined by observations and calculations from Earth.

Approximately 3.262 light-years or 30.857 trillion km. It's the distance at which one astronomical unit subtends an angle of one arcsecond.

Change in the wavelength of light due to the expansion of the universe. Quantified by the redshift parameter $z$.

Estimated at 100,000 to 200,000 light-years. Measured by observing the distribution of stars in the galaxy.

The rate of expansion of the universe. Currently estimated to be about 70 kilometers per second per megaparsec ($\text{km/s/Mpc}$).

About $1.989 \times 10^{30}$ kg. Measured through gravitational effects on nearby objects and orbital mechanics.

Roughly 149.6 million km. Defined as the mean distance between the Earth and the Sun.

It's the afterglow of the Big Bang, detected as a temperature of about 2.7 Kelvin throughout the universe.

Approximately 12,742 km. It's measured using geodesy and satellites.

Approximately 9.461 trillion km. The distance light travels in a vacuum in one Julian year.