How to determine your midheaven sign:
The midheaven is a part of the ecliptic. It corresponds to the highest point in a celestial object’s apparent daily traverse of the visible sky. This is midway between its ascension on the eastern horizon and the descent on the western horizon.
In order to find your midheaven sign, you need to create your natal chart. Once you have it in front of you, you should look for the vertical line on top and the little MC above it. This marks the zodiac sign that was directly overhead at the exact moment you were born. In other words, this is your midheaven.