Mars sketches 25 & 26/12
Posted 26 December 2009 - 07:20 AM
Since i have the 12" dob from this summer, i don't think it's been used on planets without the apodizing mask. Next time i'm gonna set the 8" up next to it to compare an unobstructed 8" with the 12" with a.m.
still, i got some nice views because it was a good side of mars facing me, but much more than the general outlines of the features wasn't visible, no real detail within. 250x is too little on a disk of 12".
the first sketch shows Syrtis Major dissapearing, and Sinus Sabaeus riding high on the disc (the the different angle tilt this year really surprises me sometimes!). Mare Erythraeum on the right, a bright Chryse between it and Niliacus Lacus & Mare Acidalicum on the bottom. Aeria, right of Syrtis Major looked brighter than it's surroundings, and i think to have seen some line, but can't find it back on any maps...
the second sketch shows the same regions, but rotated a bit more (2 hours later). The polar cap/hood appeared different, more rounded, circular. chryse still the second brightest patch.
Both views showed limb brightening.
i was a bit surprised that the #82A blue filter gave the best views, a little less contrasty than the orange, but more detailed.
Good luck with your observations, and happy holidays!
Posted 26 December 2009 - 08:31 AM
Great detail in your drawings.
Posted 26 December 2009 - 10:35 AM
Excellent sketching. Both sketches show fine details.
I might get a chance for a break in the cloud cover on Tuesday or Wednesday.
Posted 26 December 2009 - 11:37 AM
Beautiful sketches of Mars! You are seeing great detail for seeing conditions at only poor ~ average. I cannot wait to see your sketches from nights of improved seeing.
I wish I could see that detail with my old 10" f/4.5, unobstructed or with aperture mask at 4 1/2" f/13. My 20 year old Coulter Odyssey is probably a compromise at 10 " to your two scopes as I was waiting to see Mars until weather cleared now but freezing temps and wind gusts to 60 MPH now does not allow it.
I'm curious that you indicate your 12" as f/15. Am I reading that right? That is an enormous focal ratio with a 12" diameter. Or is that the figures after the aperture mask is added? If so, would you not indicate the diameter of the final masked mirror at f/15 to be less diameter?
When I mask, my 10" becomes a 4 1/2" f/13 as the new figures for actual diameter used. I have also found that the old Orion Sky Glow filters become an amazing filter for Mars. They are not like the newer Sky Glow or light-pollution blocking filters. The old model filters have a unique gradiation transmission line that also imparts a very slight blu-ish and not disturbing from natural color to planets. [The later Orion Skyglow filters are a dark green and not usuable for planetary observing.] I was able to see tremendous detail with this filter through my 10" Dob when Mars was close in 2003 ~ 2005. If anyone has one of these older Orion filters, I suggest they try it when observing Mars.
Thanks for posting; I look forward to your future observations.
10" f/4.5 Coulter Odyssey Dobsonian
5" Celestron Nexstar 5i Cassegrain
40mm Coronado h-alpha Solar Telescope
7 X 50mm Orion BAK4 Binoculars
My CN Gallery
Posted 26 December 2009 - 01:27 PM
Mark: i'm really waiting for a night of steady seeing, these sketches represent the few moments of steadiest air. youn can notice immediately from the moment you focus mars the first time when seeing is good to great, it's not happened yet, a few times in 2007, and even more in 2005! if i look back at the details i could see in 2007 and especially 2005 with my 8" and much less to no experience, i get dissapointed with the views this year so far But i know it'll be 10 long years before mars gets really good again in the northern hemisphere, so i want to make the most of this apparition!
you're a bit mistaken about the obstruction and the f-ratio i believe. it's not an aperture mask but an apodizing mask, i don't think the f-ratio changes, but i'm not sure. in the sketch i write it as 'f/5' but you read it as f15 i guess. it would sure be a looooooong scope at f/15
thanks for the heads up about the orion filter, i have one but it's a 2", can't use it on mars with my 30mm ep
i learned about the sirius optics variable filter system (vsf) through Sol Robbins (there's a filter-review from him on cn btw) and it did help in 2007, but right now seeing and the small disk haven't allowed me to use it yet!
hope you get a chance to look at mars soon!
Posted 26 December 2009 - 02:49 PM
Nice sketches! How does it feel to observe and sketch with the snow around you? I like it.
Posted 26 December 2009 - 05:51 PM
Outstanding observations of Mars showing much detail across the martian disk. Many albedo features are recorded as I have labelled. Thank you for sharing them with us all.
Happy New Year!
Posted 26 December 2009 - 11:38 PM