October 20, 2026: Find Arcturus and the Big Dipper in the western sky after sunset. Discover the star’s seasonal transition and its role in Chicago’s 1933 World’s Fair.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 7:09 a.m. CDT; Sunset, 6:01 p.m. CDT. Times are calculated by the US Naval Observatory’s MICA computer program. Check local sources for sunrise and sunset times.
Arcturus, Big Dipper in Western Sky
The seasonal stars are making their transitions. Arcturus, the brightest star in the northern half of the sky, is low in the western sky after sunset, not to be confused with Sirius, the brightest star for all sky watchers
The sky has hemispheres like Earth, separated by the celestial equator – an extension of Earth’s equator into the sky. Sirius is the brightest star in the sky, while it is in the southern celestial hemisphere. Arcturus is the brightest star in the northern celestial hemisphere.
The topaz star is 37 light years away and shines with the intensity of about 100 suns. Its color suggests that it is near the end of its stellar cycle. With its outer layers expanded and cooled, the interior rages with temperatures of millions of degrees from nuclear fusion.
Arcturus’ name means the Guardian of the Bear, part of Boötes. The celestial figure follows the Great Bear, Ursa Major, around the northern sky. The constellation’s brightest seven stars are known as the Big Dipper. The dipper’s bowl outlines most of the bear’s body, while the handle outlines a long celestial tail. It is to Arcturus’ right at this season, with the curved handle generally pointing toward the star. By finding the dipper and following the handle’s curve, Arcturus is located.
Stellar Double Play
Along with Vega, Capella, and Deneb, Arcturus can appear in the west after sunset and in the eastern sky before sunrise. In about a week, look for that double view of the star. This occurs because the star is farther north than the sun. It rises before sunrise and sets after sunset.
Arcturus makes its first evening appearance in the eastern sky during March each year. It appears farther westward after sunset during the spring and summer seasons. As mid-autumn approaches it begins the night in the western sky.
1933 World’s Fair Connection
In Chicago, Arcturus has connections to great events in the city. The 1933 World’s Fair used Arcturus’ light to energize photoelectric cells attached at the eyepieces of four telescopes in the eastern U.S. – Yerkes Observatory, University of Illinois, Allegheny Observatory, and Harvard Observatory – to switch on a searchlight that signaled the beginning of the fair.
Arcturus was thought to be 40 light years away. The 1933 fair was 40 years after the 1893 Columbian Exposition that also occurred in Chicago.
Look for Arcturus and the Big Dipper in the western sky after sunset.
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