May 20, 2025: The Last Quarter moon appears above Fomalhaut as it makes its first morning appearance, known as the heliacal rising.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 5:26 a.m. CDT; Sunset, 8:09 p.m. CDT. Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.
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Fomalhaut, Heliacal Rising
Fomalhaut is making its first morning appearance or heliacal rising at the mid-northern latitudes. For sky watchers farther southward, the star is past that initial observation and higher in the sky.
Meaning “the mouth of the Southern Fish, Fomalhaut is the 13th brightest star seen at the mid-northern latitudes. Rising about four minutes earlier each night, the star is in the southern sky around midnight at the time of the September equinox. It rises at sunset around the same date. It disappears into evening twilight around the end of January.
The theoretical date of the heliacal rising for any star can be calculated, but the actual observation is more important. Local weather conditions and obstructions in the direction of the star can affect that actual date. Heliacal rising means the star was seen – the “first appearance.”
These dates can serve as calendars because of the reliability of their annual appearances. The planets do not appear in the eastern sky before sunrise on the same date each year.
Like Fomalhaut, Capella is making its first appearance in the north-northeast. This star is far enough north that it shines in the northwestern sky after sunset and rises before sunrise.
Friendly Stars
In their book, The Friendly Stars, Martha Martin and Donald Menzel, describe the star’s appearance in the evening sky: “Fomalhaut is distinctly a star of the autumn. When it first appears in [the evening sky] in August the nights have already begun to grow longer, the birds have ceased to sing and are seeking the deeper shadows of the woods in which to shed their summer suits, and the quiet of autumn is everywhere stealthily creeping upon us” (pp. 46-47).
Moon, Fomalhaut this Morning
This morning about 45 minutes before sunrise, the morning half-full moon, 51% illuminated, (Last Quarter occurs at 6:59 a.m. Central Time) is about 25° up in the southeast, less than 20° to Fomalhaut’s upper right. The star is over 5° above the horizon. Initially, use a binocular to see the star. On the first date you see it without optical aid is the heliacal rising for your location.
Look for the slightly gibbous moon this morning and attempt to look for Fomalhaut each clear morning to mark its heliacal rising for you.
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