Why does most F1 seasons nowadays start in Australia?

May be...

cause they summer is when it is are winter in the us

Partly because of the weather, partly because the F1 season tends to start and finish away from the European heartland for logistical reasons. The "fly-away" parts of the season have book-ended the championship since the 1950s, when travel was a lot more complicated than it is today. The Australian GP is so far away from anywhere else that it logically has to be the first or last race of the season to avoid unnecessary long journeys between races during the season.

As a previous poster said, the Australian GP was the season-ender when it was held in Adelaide from 1985-1995, and it was a great place to wrap up the year. The South African GP had earlier undergone the same conversion; it was the end-of-year world championship event held in December, and was followed by the non-Championship Rand GP after New Year. Those two races switched places, making the Rand GP a season-ending money-spinner and the South African GP the first race of the next World Championship season...that was also for logistical reasons.

I've never taken to the season starting in Australia and Brazil being near the end of the year...it seems the wrong way around to me!

They used to finish the season in Australia when the race was held in Adelaide. Then, in 1996, when Melbourne outbid Adelaide to host the race, the Australian GP was moved to the start of the season to avoid a clash with the Melbourne Spring Racing Carnival (major horse racing event held between October/November).spousal trust