Finding your way around the sky “I don’t pretend to understand the Universe. It’s a great deal bigger than I am” - Thomas Carlyle

Angular measures used to describe positions & apparent size Ex: The angular diameter (or angular size) of the Moon is ½°.

Recall that - Full circle = 360º 1º = 60 (arcminutes) 1 = 60 (arcseconds) Use this slide if you want to review the definitions of arc minutes and arc seconds.

Pretend there are lines from your eye to each of two stars, the angle between the lines is the angular distance between the two stars.

The adult human hand held at arm’s length provides a means of estimating angles

Angular Size An object’s angular size appears smaller if it is farther away Use this slide if you want to review the definitions of arc minutes and arc seconds.

Altitude of the celestial pole = your latitude Show students how to locate the NCP and SCP, and how the sky moves around them. (You might wish to repeat the time exposure photo of the sky at this point to re-emphasize what we see.) Can also ask students where they’d find the north celestial pole in their sky tonight…

Prominent constellations can be used to find your way around the sky.

Figure 2-6 The Big Dipper as a Guide The North Star can be seen from anywhere in the northern hemisphere on any night of the year. This star chart shows how the Big Dipper can be used to point out the North Star as well as the brightest stars in two other constellations. The chart shows the sky at around 11 P.M. (daylight savings time) on August 1. Due to the Earth’s orbital motion around the Sun, you will see this same view at 1 A.M. on July 1 and at 9 P.M. on September 1. The angular distance from Polaris to Spica is 102°.

Figure 2-7 The “Winter Triangle” This star chart shows the view toward the southwest on a winter evening in the northern hemisphere (around midnight on January 1, 10 P.M. on February 1, or 8 P.M. on March 1). Three of the brightest stars in the sky make up the “winter triangle,” which is about 26° on a side. In addition to the constellations involved in the triangle, the chart shows the prominent constellations Gemini (the Twins), Auriga (the Charioteer), and Taurus (the Bull).

Figure 2-8 The “Summer Triangle” This star chart shows the eastern sky as it appears in the evening during spring and summer in the northern hemisphere (around 1 A.M. daylight savings time on June 1, around 11 P.M. on July 1, and around 9 P.M. on August 1). The angular distance from Deneb to Altair is about 38°. The constellations Sagitta (the Arrow) and Delphinus (the Dolphin) are much fainter than the three constellations that make up the triangle.