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Heliacal Rising
&
Setting of Sirius:
800 B.C. - 2000 A.D.
by
Peter J. Clark
[Translated
portions in Italic font]:
Sirius is a first magnitude star (HR 2491 HD 48915 Flamsteed Number: 9 Bayer Letter:
Alpha) in the Constellation of Canis Major, with a visual Magnitude
of -1.46. Sirius is also known as Canicula; the Dog Star and
Aschere. Sirius is 2.01 times the size of
the Sun and the brightest star in our heavens. The heliacal rising of
the dog star signalled the most
searing heat of the Summer, hence the term 'dog days.'. The star is most
easily found by tracing the belt of Orion downwards. Sirius is a binary star with a white dwarf companion, Sirius B.
This "pup" is an eight-magnitude star, separated from Sirius by a
couple of arc seconds. This makes it exceedingly difficult to see in a telescope
because of the great brilliance of Sirius.
Manilus
writes of Sirius (the Dog) as one who "will fashion unbridled
spirits and impetuous hearts; it will bestow on its sons billows of
anger, and draw upon them the hatred and fear of the whole populace.
(The impetuosity of the speaker causes him to utter words before he has
time to adapt them to grammar or logic). Their hearts start throbbing at
the slightest cause, and when speech comes their tongues rave and bark,
and constant gnashing imparts the sound of teeth to their utterance.
Their failings are intensified by alcohol, which gives them strength and
fans their savage wrath to flame. No fear have they of woods or
mountains, or monstrous lions, the tusks of the foaming boar, or the
weapons which nature has given wild beasts; they vent their burning fury
upon all legitimate prey. Lest you wonder at these tendencies under such
a constellation, you see how even the constellation itself hunts among
the stars, for in its course it seeks to catch the Hare in front."
( Liber V Astronomica, lines 206-233). See original
Latin text.
Sirius
has always been considered a very important star, and it was watched diligently. It is also one of the primary stars of navigation. The importance
of calculating the heliacal rising and setting of Sirius was recognized in
Ancient times and is still relevant today . The table below shows the
anticipated times of the heliacal rise and set dates in three locations over a
span of 2800 years.
-
|
Babylon (+32°33 ')
Invisibility 65-66 days
|
Athens (+37°58 ')
invisibility: 76-78 days
|
Rome (+41°54 ')
invisibility: 84-86 days
|
- Year
|
- Rise
|
- Set
|
- Rise
|
- Set
|
- Rise
|
- Set
|
- 2000
|
- 2-August
|
- 28-May
|
- 8-August
|
- 22-May
|
- 11-August
|
- 18-May
|
- 1800
|
- 31-July
|
- 26-May
|
- 6-August
|
- 20-May
|
- 9-August
|
- 16-May
|
- 1600
|
- 29-July
|
- 24-May
|
- 4-August
|
- 19-May
|
- 8-August
|
- 15-May
|
- 1400
|
- 27-July
|
- 23-May
|
- 2-August
|
- 17-May
|
- 6-August
|
- 13-May
|
- 1200
|
- 25-July
|
- 21-May
|
- 31-July
|
- 15-May
|
- 4-August
|
- 11-May
|
- 1000
|
- 24-July
|
- 19-May
|
- 29-July
|
- 14-May
|
- 2-August
|
- 10-May
|
- 800
|
- 22-July
|
- 17-May
|
- 27-July
|
- 12-May
|
- 31-July
|
- 8-May
|
- 600
|
- 20-July
|
- 15-May
|
- 26-July
|
- 10-May
|
- 30-July
|
- 6-May
|
- 400
|
- 18-July
|
- 14-May
|
- 24-July
|
- 8-May
|
- 28-July
|
- 5-May
|
- 200
|
- 16-July
|
- 12-May
|
- 22-July
|
- 7-May
|
- 27-July
|
- 3-May
|
- 0
|
- 14-July
|
- 10-May
|
- 20-July
|
- 5-May
|
- 25-July
|
- 1-May
|
- -200
|
- 12-July
|
- 8-May
|
- 19-July
|
- 3-May
|
- 23-July
|
- 29-April
|
- -400
|
- 11-July
|
- 6-May
|
- 17-July
|
- 1-May
|
- 22-July
|
- 27-April
|
- -600
|
- 9-July
|
- 4-May
|
- 16-July
|
- 29-April
|
- 20-July
|
- 25-April
|
- -800
|
- 7-July
|
- 2-May
|
- 14-July
|
- 27-April
|
- 18-July
|
- 24-April
|
The original table in Italian
is @ 
| As is true of any star, Sirius is
only visible between the time of its
helical rising and setting. Conversely, it is invisible from the time of
heliacal setting until its heliacal rising. The "heliacal
rising" is the first day when the star rises and the Sun is far
enough below the eastern horizon to make it visible in the morning
twilight. In the same way, the "heliacal setting" is the last
day when the star sets and the Sun is far enough below the western
horizon to make the star visible in the evening twilight. This in not to
be confused with what is called “cosmic rising". In the latter case,
it is not possible to see the star, due to the light of the Sun.
Because the magnitude and
brilliance of stars differ considerably, their heliacal risings
and settings occur with different altitudes of the Sun below the horizon
(this is called in Latin "arcus visionis" of the star). For
example, the Sun's altitude which makes Sirius visible (-7°) is quite
smaller than the altitude (-11°) that allows Antares to be visible in
the early dawn or twilight sky. This is because Sirius is brighter than
Antares and can therefore be seen in a lighter sky.
The
approximation in calculations of these heliacal rising and setting times over the centuries is unavoidable .(see J.
Meeus, Mathematical Astronomy Morsels, Richmond, Virginia 1997, pp.
289-2960.) However, this table
serves as a very close approximation of the
periods of the first and last dates of the visibility of Sirius in
relation to the horizon. It is oriented from the horizon (height 0°), with the Suns place to a negative
height of 7°.
It may be difficult for many
contemporary astrologers to understand the phenomena of first and
last visibility of a celestial body. This is due to the unfortunate
modern divorce of astrology from her sister science, astronomy. In
ancient and Classical astrology, no such divorce had occurred and the
heavens were watched very closely. The sky maps below are designed to
help illustrate the concept of heliacal rising more clearly.
This sky map was generated using SkyChart software,
set for sunrise in
Rome, 08 August 2000. 6:19 am. The red line is the local horizon. The
Sun is seen at the far left. Sirius is the bright star in the
constellation Canis Major. Note that the Sun is on
the eastern horizon, but Sirius is still not visible in the
morning twilight.
The
sky map above is for the same date and location, at 05:38:01 am, which
is the precise time of the rising of Sirius. Sirius is seen
ascending on the eastern horizon, but is still not visible due to the
morning twilight.
Picture
courtesy of Marco Fumagalli, using Starry Night Pro, with
labels added in Adobe Photoshop.
This
sky map is set for one day after the anticipated date of the
heliacal rising of Sirius in Rome according to the table, on 12 August
2000 at 3h34m UT --- 4:31am LMT. This is the precise time of the
heliacal rising of Sirius, seen rising on the eastern horizon. The star
is visible because it has cleared the necessary -7 negative height
of the Sun, for the first time after
approximately 3 months of invisibility This is the true heliacal
rising of Sirius for the date given. On the anticipated date of 11
August, the Sun's altitude is only -6°52’, and we cannot be
sure of the visibility of Sirius.
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