hour circle

American  

noun

Astronomy.

1. a great circle on the celestial sphere passing through the celestial poles and containing a point on the celestial sphere, as a star or the vernal equinox.

---

hour circle British  

noun

1. a great circle on the celestial sphere passing through the celestial poles and a specified point, such as a star

---

hour circle Scientific  

1. A great circle passing through the poles of the celestial sphere and intersecting the celestial equator at right angles. An hour circle is equivalent to a meridian on Earth and is used in describing the position of a celestial body with respect to an observer's celestial meridian.

2. See more at hour angle

---

Etymology

Origin of hour circle

First recorded in 1665–75

Example Sentences

The sidereal time at any moment is the right ascension of the hour circle which at that moment coincides with the meridian.

From A Text-Book of Astronomy by Comstock, George C.

The hour circle A is half of a similar card with the hour marks divided into 20 minutes.

From The Boy Mechanic: Volume 1 700 Things for Boys to Do by Popular Mechanics Co.

Turn the hour circle into a position where the pointer can describe a circle through "Mizar."

From The Boy Mechanic: Volume 1 700 Things for Boys to Do by Popular Mechanics Co.

The hour circle is divided into 24 parts and subdivided to every four minutes.

From The Boy Mechanic: Volume 1 700 Things for Boys to Do by Popular Mechanics Co.

The shaft which it carries is 1/4-in. steel, carrying the hour circle at one end, and at the other the frame for the declination axis which is similar to the other, but somewhat lighter.

From The Boy Mechanic: Volume 1 700 Things for Boys to Do by Popular Mechanics Co.