2025: Sirius makes its first morning appearance or heliacal rising during the summertime, depending on latitude.
by Jeffrey L. Hunt
Sirius was the revered Nile Star or Star of Isis to ancient Egyptians.
Its annual appearance just before dawn at the summer solstice heralded the rise of the Nile,
upon which Egyptian agriculture – and in fact all of life in Egypt – depended.
Robert Burnham
Sirius’ Heliacal Rising
Stories about Sirius appearance are the most-read articles written here. Whether the reader’s interest is in astronomy or some other worldly topic, the star’s first appearance occurs each summer in the northern hemisphere.
Of all the pronouncements that are made in readers’ comments, private emails, and articles written elsewhere, those statements about Sirius’ heliacal rising are made with precision and absolutism. I encourage readers and researchers not to analyze ancient cultural events with the precision of modern technology that is available on computers and smartphones. Later in this article, the mathematics is explained for the heliacal rising predictions table below. The actual date of the first appearance is affected by weather and obstructions at the horizon and the key factor is observing the star – the date of the first morning appearance, not the theoretical date.
At the mid-northern latitudes, Sirius disappears into bright western evening twilight during mid-May each year. The star is not visible again until it appears in the east-southeast during morning twilight later in the summer. Several web sites (source) state that the star was in the sun’s light for 70 days at Egypt’s latitude
For southern hemisphere sky watchers, Sirius does not go through a similar period of disappearance. Sirius is still in the evening sky during late fall (northern hemisphere spring) and early winter (northern hemisphere summer). Like the familiar Arcturus, Vega, and Capella in the northern hemisphere, Sirius stays in the sky for long periods when viewed south of the equator. Sirius is still in the western evening sky when it makes its first morning appearance.
From 30° south latitude, Sirius first appears on June 22nd, while it continues as an evening body until July 11 when it is lost in evening twilight. Then the star is higher in the eastern sky each morning. Until the cycle repeats again.
Calendars
Some writers and emailers state that for ancestral Egyptians, Sirius’ first appearance began a new year and they make absolute statements on the date. 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 might be reasonably consistent.
During Egyptian dynasties, Sirius’ heliacal rising occurred during the rainy season in the Lower Nile River. (Remember that the river flows from south to north.) It helped signal the beginning of an agricultural cycle.
Two calendars were in effect. One was 365 days long, without a leap year. The year consisted of 12 months of 30 days, with each month broken into 10-day segments. Five days were added to complete a 365-day year.
Civil Calendar
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, important civil dates began to slip in the calendar one day every four years. The beginning of the new civil year soon did not coincide with the date Sirius’ first appeared. 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 1,460 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 writers simplify that Sirius’ first appearance started the Egyptian new year, it is a simplistic statement. Sure, maybe at times, but not always. In about 3000 B.C. the morning rising occurred near the time of the summer solstice. Because Earth slightly wobbles, known as precession, the star’s rising date has slipped to later in the summer.
Lunar Calendar
The second calendar used is the moon’s lunation, that is easily recognized by everybody. 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 new month began on the day following the last appearance of the waning crescent moon. 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 started at the beginning of the next month after the heliacal rising.
Looking for Sirius
For 2025 at Chicago’s latitude, Sirius first appears on August 11th. The next waning moon occurs ten days later, beginning a new month and a new year similar to the ancestral Egyptian lunar calendar.
Again, I encourage readers to skeptically look at the view of modern precision applied to ancient practices, especially with those that depended on life and survival. The imprecise date of the beginning of the flood, and the need to prepare for the inundation and following growing season were very important.
Sky watchers recognized an annual cycle based on the sun and stars that was 365 days long. While the lunar cycle was likely used by the larger population, the civil calendar, was used by the civil servants.
Calendar Resets
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 and accomplishing survival.
This year, attempt to view Sirius at its heliacal rising. During morning twilight, venture to a spot with a clear horizon to search for the star’s first morning appearance at your home latitude.
Despite the description by some writers, Sirius is not especially bright at the heliacal 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.
2025 Dates
For 2025, the following table, based on astronomer Jean Meeus’ equations, shows the predicted heliacal rising for Sirius for selected northern hemisphere latitudes.
| Latitude (North) | Date |
| 20° | July 24 |
| 25° | July 28 |
| 30° | August 1 |
| 35° | August 5 |
| 40° | August 10 |
| 41.85° (Chicago) | August 11 |
| 45° | August 15 |
| 50° | August 20 |
| 55° | August 27 |
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.
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. This year a Venus-Jupiter conjunction occurs on August 12th. At the various latitudes, the two planets are near each at the time of Sirius’ heliacal rising
Mathematical Note
In his book Mathematical Astronomical Morsels, Jean Meeus derives a formula for predicting the first date of the appearance for any star. When the astronomical coordinates of the star and the observer’s latitude are entered, the formula calculates the sun’s longitude along the ecliptic when the star is about 2° above the horizon, Meeus’ estimate for Sirius’ first appearance.
Then it is necessary to generate a list of the sun’s celestial longitude for summer dates, using the computer program MICA from the US Naval Observatory. Applying some tiny, but important factors that account for the radius of our planet, the dates above were determined by aligning the Meeus equation output with the MICA computations.
For certainty, the dates reflect the day following when the sun appeared at the Meeus coordinates.
Look for Sirius at its first appearance or heliacal rising. This year, brilliant Venus and bright Jupiter are in the eastern sky near their conjunction.