your horizon
The zenith.
The correct term is "zenith angle." It is the angle measured from the vertical direction (zenith) to the point directly above an observer. It is used to determine the position of an object in the sky relative to the observer's horizon.
Everywhere. The zenith at a given point is the local vertical direction pointing away from the direction of the force of gravity at that location. In other words it is the point that is exactly straight up, no matter where you are on earth's surface.
The zenith is the point directly overhead in the sky, while the horizon is the line where the sky appears to meet the Earth. The zenith is the highest point above an observer, while the horizon represents the farthest visible point on the Earth's surface.
straight up or pointing to the zenith or in a direction at right angles to the surface of the earth
The zenith is the direction directly above the observer. The astronomical horizon is the plane that is perpendicular to that direction, i.e. horizontal. The "true horizon", however, is the cone from the observer to the point on the earth, below which you can not "see over", so it is a small amount lower in angle. In practice, the two horizons can be considered to be the same, because the height of the observer is often small in comparision to the diameter of the earth, unless the observer is standing on a tall point, such as a mountain.
zenith
During the equinoxes, when the Sun is at its highest, it will be at a distance from the zenith which is the same as your geographical latitude, but in the opposite direction. For example, if you live 50 degrees north of the equator, the Sun will be 50 degrees south of the zenith at noon.
Yes, the zenith distance at upper culmination is less than the zenith distance at lower culmination. The zenith distance is the angle between the zenith (straight overhead point) and a celestial body. At upper culmination, the body is closest to the zenith, resulting in a smaller zenith distance. At lower culmination, the body is furthest from the zenith, leading to a greater zenith distance.
It appears Zenith gas refers to gas obtained from the Zenith Oil and Gas company.
Hey Zenith! Awesome! LOLZ
If you are at a location with a latitude of 10 degrees north, a star with a declination of 10 degrees would be located directly overhead, at your zenith. This means the star is in the same plane as your latitude, making it the highest point in the sky relative to your position.