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The Kemetic calendar was originally based on twelve lunar months, grouped into three seasons of four months each. This was not ideal as the lunar month is only twenty-nine and a half days long, and so some years would actually contain thirteen new moons. Wep Ronpet (Kemetic New Years) was timed to coincide with the annual rising of the waters of the Nile. However, the actual date of the inundation could vary by as much as eighty days making it a very inaccurate marker for the beginning of the year. Luckily the Ancient Kemetics had noticed that the star Sirius (which was the brightest star in the sky), reappeared in the sky after an absence of seventy days and heralded the rising of the Nile. So they adopted this far more reliable date as the marker of their new year. It is interesting to note the connection between the seventy day absence of Sirius before the inundation and New Year and the seventy day mumification ritual which ended with the rebirth of the decesaed in the afterworld.

The calendar was not very accurate, but could be set back into alignment every Wep Ronpet. However, while this was sufficient to manage the planting of crops and time the preparations for the inundation, it was not accurate enough to support a complex administration and easy calculation and collection of taxation. As a result, a new civic calendar was developed during the Early Dynastic Period based around three seasons of four thirty day months each divided into three "decades" (sets of ten days). The two calendars ran concurrently and were used for different functions.

Yet, this only amounted to a three hundred and sixty day year, so five epagomenal days (known as "heriu renpet") were added to the end of each year and dedicated to the five children of Nut (Asar, Heru Ur, Set, Aset and Nebet Het). Yet this system still missed a quarter of a day each year, causing the calendar to slip slowly out of position. Ptolemy III tried to introduce an extra day every four years to correct this, but the Egyptians were resistant to this idea and it was not fully implemented until Augustus introduced the "leap year" in 30BC.

The Seasons and Months

Akhet
~Tekh (Thoth, Thuti, Thout, Djwhty)
~Menhet (Phaophi, Baba)
~Hwt-Hrw (hathor, Athyr)
~Ka-Hr-Ka (Nehebkau, Khoiak)

Peret
~Sf-bdt (Ta-aabet, Tybi, Tobi)
~rh-wr (Mekhir, Meshir, Amshir)
~rh- nds (Paremhat, Baramhat, Paenamenhotep, Phamenoth)
~rnwt (Pharmuthi, Paremoude, Barmouda)

Shemu
~hnsw (Pa-khonsu, Pakhon)
~hnty-hty (Paeninet, Paoni, Payni)
~iput-hmt (Epip Epiph)
~Wpt-rnpt (Mesut-Ra, Mesori)

Some people will refer to the different months depending on the season. For instance, one festival I have found called Ceremony of Djehuty takes place Ka-Hr-Ka 7th but some people will refer to it as IV Akhet 7th.

Dates of the festivals will vary depending on where you live. For instance, Wep Ronpet for my area in 2011 was August 10th. But if I was living in Lawton, OK, Wep Ronpet would be August 3rd. If you are interested in finding out when Wep Ronpet would be for your area this site was very helpful in finding out when Sirius would rise right before Civil Twilight. The first section is for people living inside the USA. The second section is for those outside of the USA.

Sources: Ancient Egypt Online - Calendar
Philae.nu - The Horizon

Crap. The Navy changed their site since I posted that. And I checked to make sure that page still worked before I posted this in here.

The link's fixed. Sorry about that.

Should have mentioned that since this year's a leap year its a little funky. So I'm gonna use the times from last year when I calculated Wep Ronpet. Modern day Kemetics may add an extra epagomenal day after Nebet Het's birthday during leap years so the calendar doesn't shift.

Screen shot The Sun data is the window behind the window for Sirius.

All you need from the data the site gives is the rise time from Sirius(in the red box), the time when civil twilight begins(the purple box), and the dates.
Sirius would "disappear" from the night sky because it was rising after the sun came up. So we need to find the first day it rises right before civil twilight. Which in the screen shot is August 10th(underlined to help see it better).

Was that what you had a question about?

I wondered what location exactly was used for the KO. Thank you for the information. I know there was somewhere on some forum someone was trying to standardize that the location was Cairo.

Oh wow, that sounds really cool actually. To know what's going on around you like that is awesome. (I do love being organised even though I somewhat lack organisation at the moment.)