The first morning appearance of a star before sunrise is known as the heliacal rising of the star. Sirius, the brightest star, makes its first appearance each year during mid-August from mid-northern latitudes. For 2021, under the best conditions, the star is first visible without optical help on August 11 for latitude 41.7 ° North.
Sirius gallery of images from its 2020 heliacal rising.
Notes from the 2020 appearance of Sirius: Sirius was visible for several mornings through a binocular. On the images above, Sirius was shows on short time exposure photographs made on August 14. The sky was cloudy on August 15, the first predicted date when it was visible without optical assistance. On August 16, the star was easily visible without a binocular.
by Jeffrey L. Hunt
The first morning appearance of a bright star is an impressive sight, a star near the horizon that is shining during twilight.
The first morning appearance of a star or planet is known as the “heliacal rising.”
The dates can be predicted. Locally the first appearance is affected by weather, clarity of the sky and having an unobstructed, cloud-free horizon. Additionally, one must consider the sharpness of their eyesight.
For 2021, under the best conditions, the star is first visible without optical help on August 11 for latitude 41.7 ° North.
The first appearance of the star depends on the factors of the predictions. Astronomer Jean Meeus predicts that Sirius can be seen when the sun is 5 ° below the horizon and Sirius is only 2° up in the sky.
A Sky and Telescope magazine article explains that Sirius’ heliacal rising occurs when the sun is about 8° below the horizon and Sirius is 3° in altitude in the east-southeast sky, For this writer’s latitude (41.7° North), this occurs on August 16.
During 2020, the star was easily visible through a binocular on August 13 and August 14, but not visible to the unaided eye for this writer. The sky was cloudy on August 15, but the star was easily visible without a binocular on August 16.
For beginners, start looking in the morning sky about August 8. Locate Betelgeuse and Procyon. A binocular may help you initially find the stars. On the chart, Procyon is only 8° in altitude; that’s about one-tenth of the way up in the sky from the horizon to overhead (zenith). Betelgeuse is higher, about one-third of the way up in the sky. Once you see the two stars, you can visualize the scale of this large celestial triangle.
After you recognize Procyon and Betelgeuse, look each clear morning to continue to find the visible pair. Then scale the other two sides of the Winter Triangle, Betelgeuse – Sirius and Procyon – Sirius, and attempt to look for the nighttime’s brightest star very low in the east-southeast sky.
For observers north or south of this writer’s location, shift the heliacal rising date one or two days earlier for the southern United States and similar latitudes. Add one to two days for locations farther north.
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