Why is seeing so bad lately?

[tomski]

Hi team,

Could someone explain to me why is seeing so bad last couple of months in Melbourne?

Ok, so June, July most clear nights in my backyard showed a nice sky full of stars with milky way just visible to the naked eye. But lately, August September and this month the occasional clear night and there are hardly any stars visible. Is it the season, moisture in the atmosphere, winds, air temp... Even SkippySky shows cloudless sky but seeing is average or below.

Do i have to wait till next winter for a decent sky or am i missing something??? Looking forward to being educated :) Thanks.

[cometcatcher]

It's the same here up north. Sep / Oct are bad due to smoke and haze. At least that's what's going on here.

[glend]

Get out of the city/suburbs to a dark sight, that should be your benchmark. If he seeing is great at a dark sight then you've answered your question.

[CJ]

Pollen perhaps?

[tomski]

Glen, i understand what you are saying, I've been to Grampians in Sep for 3 nights and the skies were amazing - no need for telescope :)

My question is about Melbourne suburbs, why in winter the seeing was so much better than last 2 months?

My theory and it's only a guess is that, lately we have been getting lots of rain, and when you have a clear day it's obviously much warmer and that would cause evaporation, resulting in hazy atmosphere.

[Allan]

Have a look at how the Jetstreams change throughout the year. During winter they are at their most northerly position, and generally run across Australia well north of Melbourne. During Summer they are farther South, around Tasmania or below that.

So twice a year if you live in Melbourne, you are going to get periods where the Jetstream is overhead a lot of the time. Coincidently, around this time of the year, and you are complaining of bad seeing. A chart I saw for last weekend had the Jet right overhead Melbourne at 140 knots. When you observe through a river of turbulent air moving that fast, everything will look like it is boiling. Not much you can do, except use lower magnification.

Moving to a dark site won't make any difference if the Jet is still overhead. You will see more stars than in the city, but the seeing will still be terrible.

[pgc hunter]

Check the jetstream and pressure charts on Skippysky.

The last couple of months have also been very windy and unsettled with low pressure systems frequently passing near Tassie. The pattern is basically a quick succession of high pressure systems over us, followed by cold fronts and low pressure cells resulting in strong unstable interaction of the different airmasses, with the result of strong winds and storms.

check out the BOM observations for Wilsons Prom and Hogan Island for the last 2-3 months. Cat 1 and 2 hurricane force winds almost every week, with many instances of multiple consecutive days of such weather.

This time of year is also when the temperature contrast between the warm continent and cold oceans is greatest which results in a greater frequency of unsettled weather.

[mulberry]

Agreed, the winter nights are much better - I can observe this with the naked eye but have not had an explanation until now. I live at a relatively dark sky site but I really notice that the winter months are much better for seeing.

[Logieberra]

High smoke in NSW/ACT ain't helping... but astro ain't a priority in these circumstances.

[glend]

Here is a SMH feature on the smoke pollution blanketing the Sydney basin and spreading from the fires:

http://www.smh.com.au/environment/weather/nsw-bushfires-pollution-levels-soar-50fold-20131021-2vvyw.html

While a wind is a serious problem for the fire affected it is the only thing that's going to clear it away.

[PSALM19.1]

Hi..have heard that skies in Spring are traditionally the worst for astronomy...I believe it's due to wind and dust being more prominant this time of year: if it's any consolation, Sydney/Wollongong is not too good either - I got a more satisfying view of Jupiter last February with a 60mm refractor than a few weeks back through an 8" Dob! :shrug: