2023: The night’s brightest star makes its first appearance, heliacal rising, before sunrise in the east-southeast. The dates of first appearance depend on latitude and local weather.
By Jeffrey L. Hunt
Most stars complete celestial cycles, that begin with first appearances in the eastern sky before sunrise. Depending on its brightness the star first appears very low in the bright blush of morning twilight. The first time it can be seen without optical assistance is known as the star’s heliacal rising. The precise date can be calculated, although the actual sighting depends on local weather conditions and whether the sky watcher has a clear natural horizon, free from obstacles.
For sky watchers, the actual sighting of the celestial event is important, not just predicting when the event occurs.
The date of Sirius’ first appearance depends on latitude. More southerly stars appear first at southern latitudes, while northerly stars appear first at more northern locations. Sirius first appears at in the morning sky at southerly latitudes. From south of the equator, sky watchers see it first appear around the June solstice, even while it still appears in the evening sky.
After the first appearance, the star appears higher in the sky each morning, eventually appearing in the southern sky and then farther westward at the same time interval before sunrise. As Earth revolves around the sun, the star continues to appear earlier, about four minutes each night. Then it appears in the eastern evening sky after sundown, followed by more westerly appearances at the same time interval after sunset. The star then disappears into western twilight.
Earth’s revolution places the star in the sky at the same time as the sun, and then the cycle repeats again.
Sirius’ heliacal rising gathers the most interest for the readers of these articles and its connection with Egyptian calendars. Sirius is sometimes known as the Nile Star as its first appearance occurred at the time of the annual rainy season that flooded the river to start the agricultural season.
Some writers and emailers state that the first appearance began a new year. This is oversimplified. The Egyptian calendars were complicated and changed across time. What follows here is a quick look at the calendar. I encourage those who want to learn more to dig into the experts’ studies of the ancient Egyptian calendar.
Some records (source) indicate that the new rulers started a year on the first day they came to power. A citizen might only see one or two kings during a lifetime, so the calendar would be reasonably consistent.
The calendar easily recognized for all citizens is the lunar cycle of phases. To account for the moon’s cycle that is 29.5 days long, months were 30 days, with three seasons – inundation (or rainy), winter (or growing), summer (or harvest). Five days were added to extend the year to 365 days (source). The month began on the day following the last appearance of the waning crescent. Festivals occurred at various months and the related offerings to the gods were specified. This worked for an agrarian society. The calendar was reset easily with the appearance of Sirius so that the seasons of flooding, planting, and harvesting were consistent with the weather patterns. The new year was started at the beginning of the next month after the heliacal rising.
Sky watchers recognized an annual cycle based on the sun and stars that was 365 days long. While the lunar cycle was used by the larger population, the civil calendar, based on the summer solstice and the zenith passage of the sun, was used by the civil servants, but the sun did not appear directly overhead for all of the kingdom. Another avenue was needed to begin the year.
In the same way that today’s civil calendar of 12 months and 365 days, with a leap year every four years, rules society, a lunar calendar is used for festivals across cultures and religions. Easter, Passover, Ramadan, and other ceremonies are determined by the moon’s phases and lunar cycle count.
Assuming Sirius marked the beginning of the new year, the civil servants apparently knew about the need for a leap year, but they did not apply it. Without a leap day, the rising Sirius begins to slip in the calendar one day every four years. The beginning of the new civil year soon did not coincide with the date of the first appearance. Today, if leap year is not applied, seasonal festivals do not match with the traditional months. In the northern hemisphere, the months that we know as the cold months – December, January, and February – would occur during the hot times of the year.
Without leap years the entire cycle resets Sirus heliacal rising to the date of the new year in 1460 years. The civil servants had to track this difference in their records, an odd practice, since they apparently knew that the civil calendar could be corrected by adding a day every four years.
When the Ptolemys came to power about 305 BCE, they attempted to align the culture to Greek practices and decreed a leap day that was not implemented. Sirius heliacal rising was proclaimed to occur on the 271st day of the year. So, at some point Sirius did not open new years, especially when a new ruler could declare when a new year began. It seems, though, that the calendar based on lunar phases, restarted at the next new moon following Sirius’ heliacal rising, was the consistent mode of keeping track of the years’ passings.
When writers simplify that Sirius’ first appearance started the Egyptian new year, it is a simplistic statement. Sure, maybe at times, but not always.
For 2023, the following table, based on astronomer Jean Meeus’ equations, shows the predicted heliacal rising for Sirius for selected northern hemisphere latitudes.
|41.85° (Chicago)||August 12|
The sky watcher’s interest is to look for Sirius. Begin looking for it at 50 minutes before sunrise a day or two before the predicted date. Use a binocular as necessary. The heliacal rising occurs on the first day the star can be seen without the binocular.
Despite the description by some writers, Sirius is not especially bright at the helical rising. It appears through the beautiful colors of mid-twilight in the east-southeast, slowly fading from view as twilight brightens. The following mornings, the star is higher in the sky and easier to locate at the same time interval before sunrise.
Sirius is part of an informal pattern known as the Winter Triangle, including Procyon and Betelgeuse. The shape is nearly an equilateral triangle. Finding Betelgeuse and Procyon shows the triangle’s scale and helps locate Sirius.
From Chicago, the waning crescent moon is in the morning sky, so in a few days following Sirius’ first appearance this year, the calendar would renew, if we followed the practices in ancient Egypt.
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