☰ Contents · Astronomy

Height of the pole and the sky at different latitudes

Lessons 9–10 · 2 lessons · M. Mamadazimov. Astronomy Grade 11, 1st edition. DAVR NASHRIYOTI, Tashkent, 2018
9

The height of the celestial pole and the geographic latitude of a place

Textbook: p. 15
GoalShow that the height of the celestial pole equals the geographic latitude and apply this in problems.
New words
geographic latitude · geografik kenglamaheight of the pole · qutb balandligiplumb line · shovun chizig‘imeridian plane · meridian tekisligi
Explanation

The angle from the horizon up to the north celestial pole is called the height of the pole. It equals the geographic latitude φ of the place: h_P = φ. The proof comes from a diagram in the meridian plane: the plumb line makes angle φ with the plane of the Earth’s equator, the celestial equator lies φ from the zenith, and the pole is 90° from the equator, so the pole stands above the horizon at 90° – (90° – φ) = φ. It follows that the celestial equator at the south point has altitude 90° – φ. So by measuring the Pole Star’s altitude we can find the latitude in the northern hemisphere approximately; Polaris is now ≈ 0.7° from the pole, so the error is under a degree. Uzbekistan lies roughly between 37° and 45° north: Termez ≈ 37°, Samarkand ≈ 40°, Tashkent ≈ 41°, Nukus ≈ 42.5°.

Worked examples
In Samarkand (φ ≈ 40°) the Pole Star stands about 40° above the horizon, and the celestial equator rises in the south to 90° – 40° = 50°.
An observer measures the height of the pole as 37°: so φ ≈ 37° N (near Termez) and the equator in the south stands at 90° – 37° = 53°.
Class activity

With an adult in the evening find the Pole Star and estimate its altitude with your hand (a fist at arm’s length ≈ 10°, an open hand ≈ 20°); compare with the latitude of your place.

Practice
1
What is the height of the celestial pole equal to?
2
At latitude 41° how high is the celestial equator at the south point?
3
The Pole Star stands 43° above the horizon. What is the latitude?
4
Why does the Pole Star’s altitude give latitude only approximately?