Mars aurora
(http://blogs.nationalgeographic.com/blogs/news/breakingorbit/breakingorbitimages/mars-aurora-map.jpg)
An artist's impression of auroras on Mars's night side
—Image courtesy M. Holmström (IRF)/ESA
On Mars the geomagnetic field is very low (uncapable of shielding any lifeforms on its sulrface).
This is a serious problem for it's colonization but.....without the geomagnetic field the thick martian atmosphere is simply GLOWING from aurora.
It's not only becous of the weak magnetic field. It's also becous of the thin atmosphere - the ionized gases are even 10x closer to mars surface then those on earth!
What that all also means is that a martian aurora DOES APPEAR EVERY NIGHT!
There is a minus of course. Due the lack of geomagnetic field solar particles are scatered around all the atmosphere, and the lack of oxygen in air (main glowing gas on Earth) the auroras are dimmer.
So every night the aurora glows, but it doesnt glow brightly.
There is an exception of course - some regions of Mars have a magnetic field due to isc magnetic ground. There the auroras are the brightes becous they steal from the nearby regions solar particles.
On what hours does the aurora appear?
Well thats a shame but....without the geomagnetic field protecting the planet it can only apear for a shor time when solar wind is having a direct - straight-forward contact with its atmosphere. That means that on Mars it can only appear durring the day, when it's not goying to be noticed due to the bright light of the sun and.......moments befor sundown and after sunrise.
Imagine.....you are waiting on Mars for sunrise....you can still see the stars, and sudenly....you see a dim light on the sky on the east side of the horizon, that goes brighter and brighter every minute until the sun goes-up....and it vanishes as even brighter sun starts to shine :)
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If something I said is untrue please correct me. No one has been to Mars to see them on his own eyes, so it's only natural that aurorar can be brighter or dimmer than we expect.
You can get some infor on Martian Auroras here:
http://www.esa.int/esaCP/SEMLQ71DU8E_index_1.html (http://www.esa.int/esaCP/SEMLQ71DU8E_index_1.html)
http://www.irf.se/Topical/Press/?dbfile=Swedish%20instrument%20studies%20auroras%20on%20Mars&dbsec=P3 (http://www.irf.se/Topical/Press/?dbfile=Swedish%20instrument%20studies%20auroras%20on%20Mars&dbsec=P3) (for instance: here they say they appear at midnight - not after sunset and befor sunrise as I said)
http://blogs.nationalgeographic.com/blogs/news/breakingorbit/2008/11/ (http://blogs.nationalgeographic.com/blogs/news/breakingorbit/2008/11/)
(keep in mind that the mapped auroras on Mars that had been analysed are in the invisible spectrum for a human eye due to the instruments of Mars Express which were constructed for other purposes)