July 24, 2014

AstroEvent(s): Of Heliacal Risings and Slender Moons.

Can you see the ultra-thin crescent? (Photo by Author).

Dust off those Sothic cycle calendars again; the Dog Days of summer are upon us; yes, it’s time this first week of August to try that feat that the Ancient Egyptians depended on, with a sighting of the dawn heliacal rising of the bright star, Sirius. The first sighting of Sirius in the dawn sky marked an all-important date to the ancient Egyptians, as it coincided with the flooding of the Nile river, upon which their agricultural livelihood depended. The following times this feat can be repeated this year by are listed by northern latitude as follows;

Latitude

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

Date

8/01

8/02

8/02

8/03

8/04

8/05

8/06

8/07

8/08

8/09

8/10

8/11

8/12

8/13

8/14

8/15

8/16

8/17

8/18

8/19

8/20

50

8/21

 

Thanks to our human astronomical computer Edward Kotapish for bringing this fun to try astronomical feat to our attention. Ed also notes that due to atmospheric extinction, Sirius will shine at a murky +3.4 in low dawn skies rather than its usual luster of    -1.46. Add that to a low contrast, brightening dawn sky, and you’ve got the makings of a naked eye astro-challenge!

Speaking of which, another astronomical notable occurs this weekend with calendar-spanning connotations; the sighting of the waxing crescent Moon marks the start of Ramadan for Muslims worldwide. The Jewish and Buddhist calendars are pegged to a luni-solar cycle as well, but the start of Ramadan is perhaps the most well known. Odds are that the slim moon will be spotted by dusk on August 1st, but there is a possibility that an early sighting can occur on July 31st. New Moon occurs on July 30th at 4:40EDT/18:40UT, and as the photo above demonstrates, it is just possible to spot a slender crescent moon within 24 hours of New…traditionally, this sighting was conducted on a village-by-village basis, and in modern times, this is often still the case. For those who cannot site the Moon due to weather, the start of Ramadan is set by convention by a sighting from Mecca. This also holds true in extreme circumstances, such as living in areas with seasons of perpetual daylight (such as near the poles)… and did you know that there are protocols for practicing Muslims in space? In this circumstance, times and dates are set to follow the launch site of the astronauts’ terrestrial origin. (Thanks to @spicyskies & @ramizq1 on Twitter for an enlightening discussion on the topic!) On what date can you catch the Ramadan Moon? Happy Sirius and Crescent Moon hunting!

The Astro-Word/term for this Week is The Dog Days of Summer. The link between the 1st sighting of Sirius (the dog star) and the onset of the hottest days of summer in the northern hemisphere is an obvious one; what isn’t so clear is how green-skinned Osiris (re: Sirius) comes into the picture. In his outstanding work Star Names, Their Lore and Meaning, author Richard Hinckley Allen makes mention of research by linguist John Minsheu, who cites;

“Some thinke that (at the) time the Dog-starre reigneth, the Nile also overfloweth as through the water where led by that Starre…”

Clearly, the Egyptian priests where making a causal, though erroneous connection that the combined strength of the Sun and Sirius were somehow leading or bringing on the flooding and the oppressive heat of summer; you can sorta see how they went there. In any case, the connection was cemented by Roman times, leaving the reference to the “Dog Days of Summer” that we have today. Its interesting to note that this occurred much closer to the Summer Solstice in ancient times than it does today; blame a host of celestial mechanical gremlins, but mainly our friend the Precession of the Equinoxes is to blame. Stay cool on the upcoming sultry days of August!

Comments

  1. Ed Kotapish says:

    Hi Dave,

    Sirius was easy, easy, easy to spot from my location (33N) on Aug 08. So Aug 05 seems possible above the horizon muck.

    Any luck?

    Ed

  2. David Dickinson says:

    Yeah, I caught Sirius rising last weekend from 28N on my morning dog jog… hey, (Dog star, Dog jog) that’s a dual meaning thing…

Trackbacks

  1. [...] AM. And the first week of August sees an ancient observation that is fun to try and replicate; the heliacal rising of the star Sirius. At magnitude -1.46, Sirius is the brightest star in the sky as seen from our [...]

  2. [...] tangible dates for a Dog Days of Summer change depending on a source, though are customarily quoted as regulating from mid-July to [...]

  3. [...] actual dates for the Dog Days of Summer vary depending on the source, but are usually quoted as running from mid-July to mid-August. The [...]

  4. [...] actual dates for the Dog Days of Summer vary depending on the source, but are usually quoted as running from mid-July to mid-August. The [...]

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