2020, August 15-16: Helical Rising of Sirius

The first appearance of Sirius low in the east-southeast during mid-August 2020.

2020, August 15-16: The helical rising of Sirius is the star’s first appearance in the morning sky before sunrise.

The helical rising (annual first appearance) of Sirius in the morning sky is a spectacular sight.  During 2020, this occurs in mid-August.

(Reported sighting of Sirius from 33.8° north latitude with a binocular, August 6, 2020.)

(Author saw Sirius, with a binocular through a broken deck, 29 minutes before sunrise on August 12, 2020. Should be visible without optical assistance in a few mornings as described below.) 

by Jeffrey L. Hunt

The spectacular appearance of a bright star in the morning before sunrise is an impressive sight. While very low in the sky, the star twinkles against the brightening hues of morning twilight.

The first morning appearance of a star in the eastern sky before sunrise is known as the “heliacal rising” of the star.

The first morning appearance of Sirius attracts attention. The brightest star in the sky, it can be found near the horizon before we see other bright stars.

In the lore of earlier generations, the heliacal rising of Sirius was thought to cause “dog days.” It’s coincidental that the “Dog Star” first appears in the morning sky during the hot days of the year.

Observing the first morning appearance of a bright star is a challenging feat. This requires a perfectly clear sky to the horizon and a vantage point to see the natural horizon, free from trees, buildings, houses, and other obstructions.

A Sky and Telescope magazine article described the circumstances of the date of the heliacal rising of Sirius. The author described that when the sun is about 8° below the horizon and Sirius is 3° in altitude in the east-southeast sky, the star should be first visible. For this writer’s latitude (41.7° North), no single date meets the criteria. The best pair of days is August 15, 2020, and the following morning. On the former morning, Sirius is slightly lower than 3° and on the morning of the latter it is slightly higher than the visible limit.

The chart above shows the sky 42 minutes before sunrise on August 16, 2020. Bright Venus and the crescent moon are high in the east.

Betelgeuse, Procyon, and Sirius – while they are part of their own constellations – make a large equilateral triangle, known as the Winter Triangle. The trio is prominent in the evening sky during the colder months in the Northern Hemisphere.

Procyon is sometimes translated as “before the dog.” It rises about 25 minutes before Sirius, so it rises before the Dog Star.

For beginners, start looking in the morning sky about August 12. Locate Betelgeuse and Procyon. A binocular may help you initially find the stars. Venus is nearly above Procyon, although the planet is much higher in the sky. On the diagram, 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, at about the same altitude as brilliant Venus. 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 helical rising date one or two days earlier for the southern United States and similar latitudes. Add one to two days for locations farther north.

When do you first see Sirius? Respond in the comments section of this article.

Read the Venus as a Morning Star, 2020-2021 article.

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7 thoughts on “2020, August 15-16: Helical Rising of Sirius”

  1. I have seen Sirius now at 03.47am Cambridge UK time. It is a clear night and all stars as you described are out in all their glory. Robert Bauval in his book called ‘The Secret Chamber’ had this date calculated to land on the 4/5th August 2020. I think that he was wrong in this case by about 8 days. It would then appear that the ‘Son’ has already risen? I do hope that we have clear skies closer to the 14th. Thank you.

    1. My guess is that you’ve picked up Venus. At sunrise in Cambridge this morning, Sirius was not in the sky. At the time noted, Capella is to the upper left of Venus and Aldebaran is to the upper right of the brilliant planet.

      From Giza, Egypt, Sirius was likely visible this morning, weather permitting.

      The date of the observation depends on the latitude. The author cited in the comment appears to be noting the observation for Egypt.

  2. Hi Jeffrey,

    I am curious about what date Sirius would be coming up exactly with the Sun. Would that be a week or two before the heliacal rising? Do we have an exact date?

    Also, Would the rising dates have been much earlier back in the deep past when the Egyptians were looking for it? Do you know when?

    Thanks, Parisse

    1. From my latitude 41.7N, the sun and Sirius rose at about the same time (within a minute) on August 3 this year, according to U.S. Naval Observatory data. At 1350 B.C., just before the time of King Tut, the heliacal rising date at Giza was approximately July 19, from a quick look at the computer program Starry Night. Remember that we have had corrections to the calendar; so before 1582, the dates do not match the equivalent dates with today’s sun’s position. Following updated 08/07 – from your blog post, August 3 is not the conjunction date of Sirius and the sun. Astronomer Jean Meeus named the dates when the sun and a star rise simultaneously, the “Cosmic Rising” of the star. As noted above August 3 was the Cosmic Rising of Sirius at my latitude. Conjunction is when the star and the other object, the sun in this case have the same celestial longitude. While they were in the sky at this time (daytime), Sirius had the same celestial longitude as the sun on July 5, 2020. It was hardly a “conjunction” where 2 objects are close together in the sky. The sun and Sirius were over 39 degrees apart in the sky – Sirius to the south (below) the sun. For the most part (without appropriate optical equipment)this was unobservable. For those who want to plow through the details of heliacal risings, see Jean Meeus’ book Mathematical Astronomy Morsels, pages 289 – 296.

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