# Astronomical Term *Mezzocielo*

What is the name of the point of intersection of the great circle passing through the celestial north pole P and the Zenith Z, with the celestial equator? (Point T in the figure)

In Italian this point is called "Mezzocielo", which translates into mid-sky, since it is located halfway between the Zenith and the horizon for an observer in Italy ($$\phi \approx 40^{\circ}$$).

• I don't believe that that point has a specific name in English. – James K Mar 30 at 20:59
• It actually is quite an important point, since the Hour Angle (HA) is measured from it. Shouldn't we give it a name :)? – Flaffo Mar 31 at 15:29
• "Should" is a different question. – James K Mar 31 at 15:39
• The hour angle is really a measure of the angle between the plane of the meridian and the plane passing through the object, so it does not need to be measured along the equator. Like James K, I do not know of a single work to describe point T. The closest would be "equator culmination". – JohnHoltz Mar 31 at 16:06
• @JohnHoltz sometimes, however, HA is defined as an arc width, rather than an angle. In this case it is important to measure it along the celestial equator. For instance the above image is incorrect, because it shows HA measured as an arc width on the wrong parallel of declination, leading to a measurement of HA/cos(delta). – Flaffo Mar 31 at 16:54