The Midheaven is the degree of the ecliptic on the upper meridian, and its computation is simpler than the ascendant's in a way that has a practical payoff. It depends on the sidereal time and on the obliquity of the ecliptic, and on nothing else. The geographic latitude does not enter the formula at all.
That means the Midheaven is the same for everyone born at the same moment anywhere on a given meridian, from the equator to the pole, while their ascendants differ wildly. For a chart whose birthplace is uncertain but whose time zone and clock time are known, the Midheaven is available and the ascendant is not.
Its rate is far more even than the ascendant's but not uniform. Because the ecliptic is inclined to the equator by about 23 degrees 26 minutes, a degree of right ascension corresponds to between the cosine and the secant of that angle in ecliptic longitude, so the Midheaven advances between about 0.92 and about 1.09 degrees for every four minutes of clock time. Over a day it is exactly one circuit, like everything else fixed to the sidereal rotation.
There is one caution at high latitude. Beyond the polar circles the degree on the upper meridian can be below the horizon, so the Midheaven is not necessarily the highest point of the visible ecliptic, and quadrant house systems built on the meridian together with the horizon lose their meaning there.