Sirius Rising as seen from Astroguyz HQ on August 1st, at Lat. 28 North...Radio Telescopes pending! (Created in Starry night).
August is traditionally a real roaster for the northern hemisphere. This month usually sees the onset of what’s known as the Dog Days of summer… but did you know that this term has an actual astronomical tie-in? We’re talking about the dawn appearance of the Dog Star, Sirius. The ancient Egyptians knew this star as the dog-headed god Anubis, and the first sightings of Sirius preceded that most important of calendar dates in their world; the flooding of the life-giving Nile. This generally occurred around the July time frame, as upper to lower Egypt spans between latitude 25°-30° degrees north. Our friend, the Precession of the Equinoxes has also played a role, moving this astronomical event firmly up into August in modern times. Recently, reader and calculator of all things astronomical Ed Kotapish sent us a ephemeris of dates for this simultaneous heliacal rising (see below) of the Sirius by longitude;
|
Latitude |
HR Date |
|
50 |
8/21/2010 |
|
49 |
8/20/2010 |
|
48 |
8/19/2010 |
|
47 |
8/18/2010 |
|
46 |
8/17/2010 |
|
45 |
8/16/2010 |
|
44 |
8/15/2010 |
|
43 |
8/14/2010 |
|
42 |
8/13/2010 |
|
41 |
8/12/2010 |
|
40 |
8/11/2010 |
|
39 |
8/10/2010 |
|
38 |
8/9/2010 |
|
37 |
8/8/2010 |
|
36 |
8/7/2010 |
|
35 |
8/6/2010 |
|
34 |
8/5/2010 |
|
33 |
8/4/2010 |
|
32 |
8/3/2010 |
|
31 |
8/2/2010 |
|
30 |
8/2/2010 |
|
29 |
8/1/2010 |
This covers most heavily populated blog reading northerly latitudes… if you are reading this from the Honduran jungle, drop us a line and we’ll be happy to handcraft a table, just for you. An interesting effect to note is that Sirius may appear a tiny bit before the date above because of atmospheric refraction; it may appear later, however, because of ground clutter. Elevation or an eastward facing horizon out to sea or over a large lake may help in this astronomical endeavor. This is a fun, and above all, naked eye challenge, although a good pair of binoculars might help sweeping the horizon…or do you want to keep the challenge pre-optical, just like the Egyptians? Be sure to give this ancient astronomical sighting a try; now’s a good time to set those Sothic calendars!
This weeks’ astro-term is Heliacal Rising.This is simply the date that an astronomical object rises simultaneously with the Sun from a given vantage point on the Earth’s surface. This varies dramatically with latitude, and the brighter the object, the more likely you are to spot it during heliacal rising. Fixed stars gain about one degree per day on the Sun relative to its solar longitude along the ecliptic, which traces out the plane of the Earth’s orbit about the Sun. Heliacal risings were a good way for ancient societies to pin down the start date of a solar calendar, and Sirius was the brightest star with which to do it.
“The ancient Egyptians knew this star as the dog-headed god Anubis”
Plain wrong.
Sirius was associated wit the Goddess Sopdet Sothis (Gr) and also latterly as Isis. Sopdet & Sah equated to Isis and Osiris. The linkage, such as it is, between Sopdet and Anubis is tenuous and Greek!
http://en.wikipedia.org/wiki/Sopdet
http://www.thekeep.org/~kunoichi/kunoichi/themestream/sopdet.html
Is there an online source that would tell me the date of the heliacal rising of Sirius at various locations around the world on any date in the last few hundred years?
Many Thanks,
Jeff
I’ve never seen a dedicated online resource for calculating helical risings of Sirius versus latitude, but the original resource for this is J. Meeus’ book Mathematical Morsels… perhaps this signifies an online resource awaiting construction.