December 18, 2017

Astro-Event: The Dog Days of Summer 2012.

Can you feel the heat? The first half of 2012 was a hot one for the record books. And the bad news is, we haven’t even reached the month of August! Here at Astroguyz HQ in central Florida, having any chance of clear skies in the summertime means rising early in the 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 Earthly vantage point of 8.6 light years distant. In fact, Sirius is bright enough to see in the daytime under pristine sky conditions, if you know exactly where to look for it. The first dawn sightings of the star were crucial to the Egyptians as it coincided with the annual flooding of the Nile and the start of their solar-based calendar.

Venus, Jupiter, & Aldebaran low in the dawn this past July… can Sirius be far behind?

(Photo by Author).

The term “The Dog Days of Summer”¯ has come to refer to the hottest time of the year in the northern hemisphere, the lag after the summer solstice in late July through early August when solar isolation has built up making for hot, stagnant weather. During Roman times, the heliacal rising of Sirius fell around mid-July. However, due to the intervening effects of precession and the adoption of the modern Gregorian calendar in the 16th century, the simultaneous rising and sighting of Sirius and the Sun now falls in early August.

Sirius rising to the SE at sunrise as seen from latitude ~28 north (i.e. Astroguyz HQ) on August 1st.

(Created by the author using Starry Night).

Keep in mind, the effects of atmospheric extinction will knock down a rising Sirius to about magnitude +2.4. And although the ancient Egyptians accomplished this sighting with the naked eye, don’t be afraid to use binoculars for a modern day “assist.”¯ On what date can you first spy Sirius with binocs? With the naked eye? Can you track it up into daylight with the same or using a polar-aligned telescope? Dates for the theoretical sighting by northern latitude are as follows;

Date

8/1

8/2

8/2

8/3

8/4

8/5

8/6

8/7

8/8

8/9

8/10

Latitude

29

30

31

32

33

34

35

36

37

38

39

Date

8/11

8/12

8/13

8/14

8/15

8/16

8/17

8/18

8/19

8/20

8/21

Latitude

40

41

42

43

44

45

46

47

48

49

50

This table is pretty much perpetual for the first half of this century. Also, remember that while your latitude determines the first date that Sirius should be visible low in the dawn, your longitude east to west within your time zone determines when Sirius actually rises locally. The USNO has an excellent calculator to determine this. Remember, that this will be against a brightening dawn sky!

How the “Dog Days”¯ became known as such through history is a matter of some conjecture, though of course in modern times, Sirius is known as the “Dog Star”¯ in the constellation Canis Major or “The Great Dog,”¯ So there’s that obvious leap (bad pun)… Sirius also has some interesting mythology surrounding it that we looked at recently in our post on the Curious Case of the Dogon people of Mali.

Also this week, The Full Surgeon Moon occurs on August 1st at 11:27PM EDT/3:27 GMT (on the 2nd). Known variously as the Red, Green Corn, Grain, Lightning, or Dog Moon, this is also the first of two Full Moons in August, setting us up for that greatest of non-events for 2012, a Blue Moon on August 31st.

Also coming to a sky above you, The planet Neptune nears 38 Aquarii on August 2nd around 5AM EDT/9UTC. 8th magnitude Neptune will be 1′ arc minute from 9th the magnitude star, looking like a wide double. It’ll be fun to watch the planet approach the star on successive mornings. Both transit to the south for northern hemisphere observers around 3AM local time.

The coordinates for the 38 Aquarii are as follows;

Right ascension: 22H 18′

Declination: 11° 12′

Next up this week, asteroid 185 Eunike occults a +5.9 magnitude star in the constellation Eridanus on August 3rd ~12:01 UTC for northern Mexico and the tip of southern Texas. This is one of the brightest stars occulted by an asteroid this year; don’t miss it if you’re in its path!

Finally, asteroid 4 Vesta sits just 0.3° degrees from the +0.8 magnitude star Aldebaran on the morning of August 5th. Vesta has been lurking in the direction of the Hyades and has been under scrutiny by the Dawn spacecraft for the past year, which will depart Vesta late this month. Dawn is headed to Ceres for an arrival around February 2015. Can you spot the motion of Vesta on successive mornings while on vigil for the heliacal rising of Sirius? And of course, don’t forget to check out the ever-changing celestial dance of those two bright nearby show-stealing planets low in the August dawn sky, Jupiter and Venus…all worthy reasons to set your alarm!

Comments

  1. Ed Kotapish says:

    Dave,

    I goofed on the Sirius magnitude. A mag 4 extinction from -1.6 is 2.4 not 3.4.

    Ed

  2. David Dickinson says:

    Thanks; is fix’ed. Saw Sirius this AM via binocs… helps to know where to look!

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  1. [...] to take the heat off this summer? We certainly did, as the sultry Dog Days of 2012 seem to march endlessly on. Fortunately, we found a “cool read” (last bad pun, I swear) in [...]

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