2019, August: Mercury and Heliacal Rising of Sirius


The heliacal rising is the first appearance of a bright star in the morning sky before sunrise.

During August, as Mercury makes a morning appearance, brilliant Sirius, the sky’s brightest star, makes its first morning (heliacal) rising just before sunrise.  For the latitude on the diagram, about 41.7 degrees, this is August 14, 2019.  For locations farther south, this occurs days earlier and later for latitudes farther north.

August 29:  Now appearing in the darker morning sky, Sirius is visible with Betelgeuse and Procyon.

Sirius, the Dog Star, is sometimes called the Nile Star as its heliacal rising historically coincided with the flooding of the Nile River.  The Dog Days of Summer (in the northern hemisphere) occur, coincidentally, during August when Sirius and Procyon, the Little Dog Star, appear in the eastern sky before sunrise.

Update:  August 9, Mercury is low in the northeast.  First located with a binocular then observed without its assistance.

Mercury is at greatest elongation on August 9.  Because Mercury is closer to the sun than Earth, we see Mercury appear in either the morning or evening sky around the time the sun rises or sets.  It appears in the sky earlier each morning or stays there later each night.  It reaches its greatest separation from the sun and then seems to reverse its direction, moving back into sunlight, only to repeat the process a few months later at the other horizon and sky setting.

As Mercury moves back toward the sun in August, it is lower in the sky each morning at about the same time.  Sirius appears higher in the sky each morning at the same time.  And Mercury gets brighter as it appears nearer to the sun.  As Sirius appears higher, it seems to brighten because it gets above the thicker atmosphere that tends to diminish the brightness of celestial objects.  They are not quite the same brightness, but appear at the same altitude around August 19.

To locate the planet and the star, find a clear horizon in the east-northeast and east-southeast.  Start looking for Mercury and Sirius about 30 minutes before sunrise.  A binocular may help in viewing them.  Mercury is low in the east-northeast, about 10 degrees up.  Sirius is very low, in the east-southeast about 3 degrees up when first visible.  Sirius may twinkle wildly this low in the sky.  To be sure you have Sirius, don’t confuse it with Procyon in the east and a little higher.  Orion is higher in the sky and its three belt stars make an imaginary pointer that take us to the area to find Sirius.  Reddish Betelgeuse is higher in the sky,  Sirius, Procyon, and Betelgeuse make nearly an equilateral triangle known as the Winter Triangle.

Sirius’ heliacal rising occurs every year about this time.  This year the event is a little more interesting because a bright planet is in the sky.

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8 thoughts on “2019, August: Mercury and Heliacal Rising of Sirius”

    1. My estimate is August 11 to make your first attempt. Locate a clear horizon as it’ll be low. Take a binocular. Start about 45 minutes before sunrise. Many local factors, such as fog, may present a challenge. Look then each morning for it. When can you first see it without a binocular?

    1. Start looking on August 15, about 45 minutes (5:37 a.m. EDT) before sunrise; that’s 6:22 a.m. EDT. by my estimate. My estimate is that you’ll start seeing Sirius with a binocular on August 17, 5:39 a.m. It’ll be very low in the east-southeast near the horizon. Continue to look for Sirius for about 10-15 minutes as the sky brightens and the star appears higher in the sky. Use Orion’s belt stars as a pointer to get an approximate location for Sirius. As you look through a binocular, gently move it along the horizon point around the spot that you estimate from the belt stars. Do not confuse Sirius with Procyon. This star is above the east direction point. The next day or two you should see Sirius without a binocular, depending on the weather, sky clarity, and such; and the how well you can see the natural horizon without trees or other obstacles. Sunrise changes (later) about one minute each day, so figure that into your viewing time. A viewing spot at the lakefront looking across Lake Ontario give you a great natural horizon, but you could suffer from fog or other effects. Let us know when you first see Sirius!

  1. Hi Jeffrey,

    I understand that the ancient Egyptians focused on the Sirius season and celebrated its heliacal rise, the date of which changed as time went on. I know that the founders of America timed the signing of the Declaration of Independence to coincide with the beginning of that season because of its spiritual import.

    Nowadays, we have a lot of new-agers shouting about something they seem to have invented called “****’* ****, */*”, which they think was an authentic Egyptian holiday, and they insist that there is special cosmic energy entering our plane that day every year, because they are confused about when the heliacal rising of Sirius is, not understanding that that is what the Egyptians were focusing on.

    Do you know if the Egyptians celebrated a “****’* ****” and if so, when? And can you comment on any of the rest of this?

    Thanks.

    1. Thanks for your question. As you likely know from reading the posts here, my interests are in observational astronomy, especially what I can see from my backyard with and without a telescope or binocular. Numerology and other such thinking are outside my area of interest.

      I edited your original question on the page to remove the specific reference as I don’t want this idea to show my post in an internet search. I gladly decline being part of this conversation.

      I will write here that August became in the 8th month in 1752 when the beginning of the new year was moved to January 1. The calendar lost 11 days that year. Additionally, the names of some of the months indicate their order in the original calendar: September (Sept = 7, 7th month), October (Oct = 8, 8th month), November (Nov = 9, 9th month), December (Dec = 10, 10th month). So, if the date is important it’s celebrated in the wrong month and it’s been a “mystical date” for less than 300 years.

      A celestial lion is a concept throughout the Middle East, North Africa, and southern Europe.

      The sun does not move into Leo until August 11 and leaves on September 17. Regulus, the constellation’s brightest star, is in solar conjunction on August 23.

      Here are my notes for the date:

      August 8: Thirty minutes before sunrise, Mercury (m =0.2) is over 9° up in the east-northeast and 9.1° to the lower right of Pollux. In the evening, one hour after sunset, the moon (8.0d, 64%), over 28° up in the south-southwest, is 1.9° to the upper right of Graffias (β Sco, m = 2.5). At the same time the moon is over 10° to the upper right of Antares (α Sco, m = 1.0) and nearly 12° to the right of Jupiter.

      1. Start looking in the morning (August 9) about 5 a.m. MST. You’ll need a clear horizon. You may need a binocular to see it first. Then try to locate it without optical help. My estimate is August 11 you should be able to see it without optical help and haze at the horizon. Let us know when you see it! (Also look for Mercury in the Northeast. Still not blazingly bright; you make need a binocular to see it.)

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