National Geographic : 1943 Jul
Around Polaris, the North Star, Swings the Familiar Big Dipper, in Ursa Major THE DIPPER, with all the other stars and constellations, rotates once every 24 hours around Polaris, in the center of the northern sky. Now turn the chart upside down and look at the southern sky (see directions on opposite page). Near the zenith overhead you will see the bright blue star Vega, shining in the constella tion Lyra (the Lyre), a prominent object in the July heavens. Vega is used as a star sight by navigators. Time is standard, not war time. The planet Venus shines brightly in the early evening sky in July, but will have sunk below the western horizon before the times designated for this chart to be used (see table at left of chart). The hourglass charts depict the evening sky for each month, but they can also be used for the early-morning sky (after midnight). For example, the reader who desires the chart for 2:30 a. m . of July 15 will calculate as follows: Although the stars always hold the same rela tive positions as they progress around the sky in the course of a year, each day they reach their original positions four minutes earlier. Hence, every month the stars rise for us two hours earlier. The star picture at 2:30 a. m . will be the same as that at 10:30 p. m., two months later. For 2:30 a. m. of July 15, see chart for 10:30 p. m . September 15 (page 119).