I have a particular association with the "Dog Days", which has to do with the game I started playing when I was 7 years old, played for many years, and still follow closely: baseball. The pro baseball season is long: 162 games over six months (and baseball has no clock...each game is played until someone wins). August, where games are played in temperatures of 90 to 100 F, are referred to as "the dog days", and this is where the good teams emerge for the final month and playoffs, which I try to track, with some difficulty here in Europe. (It's my American stuff...)

"Once in awhile we get shown the light, in the strangest of places, if we look at it right" - Hunter/Garcia

Bobby Bobby what am I gonna do with you??

The "dog days" is from Latin.  It comes from the fact that Sirius (the "dog star") is in a certain position during the hottest days of the year.

In Romanian they are called "canicula" which comes from the same root for "dog".

Pax

Night and day you can find me Flogging the Simian

We call them bloody freezing, because it's winter in Canberra... ice on the car windows in the mornings at the moment.  :-) I don't think we really use the term 'dog days' for the end of summer in February, and I wonder why.  Is it used in the UK?

PS  I assume that's one of Monet's haystacks?  Have you been to his house at Giverny?

Incidentally, in Hungarian, "dog times" describes extreme cold or severe rain...

In the Carpathian Basin, normally, there are no hot, humid, lazy days in August - instead, there are hot, dry lazy days. (Unirrigated open fields turn into semi-desert.) But the name is the same in Hungarian - except instead of translating, the Latin name of Sirius, the Dog Star (Canicula) was absorbed and became a separate word, kánikula.

Funnier is the name of the late September-early October sunny period in autumn (the equivalent of the North American "Indian Summer"): vénasszonyok nyara means "old women's summer".

Now this would be the normal local climate, and also the one I remember from my childhood. While meteorologists always remind us that there were always examples of extreme weather and thus they don't prove global warming, I have the impression that now we have very often extreme weather. Maybe more than normal!

Last year, this peaked in the fact that autumn began twice - first in the middle of August, then in September, when old women's summer was supposed to be. By that I mean that trees began to shed leaves twice. This year, we basically had no summer! June, July and August so far was all rain and clouds, except for just ten days of clear-skies sunny weather - and that was extreme kánikula. (Not that this was a problem for myself personally - I just can't stand kánikula, in fact I don't like anything above 25°C - some Nordic genes of forgotten ancestors must have came through in me!)

*Traitor*, n.
A benighted individual who perceives an illusory distinction between serving his nation and abetting the criminals who govern it.

Just the same in German. The period from July 23 to August 24 is called "Hundstage", which literally means the same.

Some old "peasant rules" ("Bauernregeln"):

Hot Dog Days predict a cold winter.
What Dog Days pour, the grape must suffer.
Dog Days hot, winter for a long time white.
Dog Days bright and clear, show a good year.
As the weather is when Dog star rises, it will remain until he sets.

Heisse Hundstage prophezeien einen kalten Winter.
Was die Hundstage giessen, muss die Traube büssen.
Hundstage heiss, Winter lange weiss.
Hundstage hell und klar, zeigen ein gute Jahr.
Wie das Wetter, wenn der Hundsstern aufgeht, so wird`s bleiben, bis er untergeht.

May Dog Star be with you!

"Dog Days" isn't very common (I don't think) in Britain, but I have heard it. The origin, as others have explained, is the Latin caniculares dies.

Wikipedia explains it here.

In French, the word "canicule" refers to a heatwave pretty much at any time of the summer. So, the people who dies of heat in 2003 were victims of the "canicule".

We call them "wet".

Billmon: Dog Day Afternoon

These are the dog days -- a name which, according to this trivia page, dates back to the ancient Mediterranean, when the hottest part of the summer was marked by counting the 20 days to and the 20 days after the conjunction of the sun and Sirius, the dog star. No, Siriusly.

It's as good an explanation as any, I guess, although to me the expression "dog days" has always called up images of rabid canines, their muzzles dripping with foam and blood from their own self-inflicted bites, writhing in crazed torment under the blazing sun while their virus-riddled brains gradually turn to mush inside their narrow, wolfish skulls.

Which, more-or-less by coincidence, appears to be the effect that Cindy Sheehan is currently having on conservatives. Except for the gradual part.

In the long run, we're all dead. John Maynard Keynes

Hot here in Tokyo too. It is always as bad as Washington, D.C. Still, this year is better than last year when we were hit by a heat wave of 40 degrees Celsius.

I will become a patissier, God willing.