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Mars Angular Size: Some Plots

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#1 Tom Polakis

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Posted 29 May 2018 - 08:14 PM

I have always been interested in how short the time is when get a favorable view of Mars, and wanted to visualize it.  Using JPL's Horizons ephemeris service (https://ssd.jpl.nasa.gov/horizons.cgi), I created a table of angular size and declination of Mars for the past 15 years, with a one-day interval.

 

The first plot shows angular size, beginning before the last close opposition in 2003.  Note the sharp peaks and the large range of sizes due to Mars's eccentric orbit.  The constellations for each opposition are also shown.  Generally, northern oppositions occur with smaller angular sizes, but more about that later.  Next, I've zoomed in on the current period, in which Mars is just now passing through 15 arcseconds.

 

The distribution of angular size is shown in the third and fourth plots.  Can't decide if I like the histogram or pie chart more.  In the pie chart, the size increases clockwise from the 12 o'clock position.  The small wedge of greater than 16 arcseconds at upper left shows how rare this territory is that we are currently entering.

 

The last plot is my favorite, with declination plotted along the vertical axis.  The 2003 and 2018 oppositions both occur when Mars is well into the southern sky, where the seeing is softer for northern observers.  In the cycle, there was one good, northerly opposition, in which it reached 20 arcseconds while it was in Aries.  Those loops show the retrograde motion in declination near opposition.

 

This has been an example of what retired engineers do for fun.

 

Tom

 

yAJiQE3.jpg

 

nT5Tv0V.jpg

 

FnXJM7b.jpg

 

ssSYLU6.jpg

 

ObEtwek.jpg


Edited by Tom Polakis, 29 May 2018 - 08:14 PM.

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#2 randcpoll

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Posted 29 May 2018 - 08:24 PM

I love the plots/charts! Well done!

 

I'm having a hard time deciding if I like the bars or the pie for emphasizing the infrequency of a large Mars.

 

I also like the last chart best. It shows graphically why Mars is usually somewhat disappointing to us 40+ latitude observers. Nevertheless, we never stop trying.



#3 Special Ed

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Posted 29 May 2018 - 08:31 PM

Very interesting set of graphics, Tom.  Glad you retired engineers are staying out of trouble.  wink.gif 

 

Jeff Beish and the other veteran Mars observers at ALPO say that, even though it's not perfect, the 2018 apparition is the best since the Great Perihelic Apparition of 2003.  The funny thing is, other apparitions for northern hemisphere observers with Mars at a smaller angular diameter can actually give better views because Mars is at a much higher altitude (like the one when Mars was at an angular diameter of 20").



#4 deSitter

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Posted 29 May 2018 - 09:17 PM

Nice, but another way to think about it this year (and similar in 2 years) is that it is larger than the worst opposition from mid-May to mid-October. That's 5 straight months of oppositions.

 

-drl



#5 Illinois

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Posted 30 May 2018 - 06:14 AM

Very nice!!!!  I realize that size 20 or larger is so rare! I like to see something like that for Jupiter! Not sure when is size 50" Jupiter!



#6 Tony Flanders

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Posted 30 May 2018 - 07:48 AM

Very nice!!!!  I realize that size 20 or larger is so rare! I like to see something like that for Jupiter! Not sure when is size 50" Jupiter!

It's much less relevant for Jupiter, which varies from an equatorial diameter of 30" to 44" -- not much of a difference at all. Moreover, Jupiter is behind the Sun when it's smallest, which means that it's unobservable anyway. For most purposes, it's reasonable to assume that Jupiter is always pretty much the same apparent size.


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#7 starcanoe

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Posted 30 May 2018 - 07:54 AM

I really like the declination vs angular size plot myself....though each of those "loops" could use a label as to which year/opposition they are.

 

Which brings up another point. This time around....Mars gets pretty big....but OMG is it down low in the murk. The next go around in a couple years...yeah it doesn't get quite as big (but IMO close enough for government work)....but it is WAY higher in the sky for folks in the northern hemisphere...that is IMO the opposition to "die for".


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#8 karstenkoch

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Posted 30 May 2018 - 08:01 AM

I really like the declination vs angular size plot myself....though each of those "loops" could use a label as to which year/opposition they are.

 

Which brings up another point. This time around....Mars gets pretty big....but OMG is it down low in the murk. The next go around in a couple years...yeah it doesn't get quite as big (but IMO close enough for government work)....but it is WAY higher in the sky for folks in the northern hemisphere...that is IMO the opposition to "die for".

Yes, a few point labels on the dec vs size plot would be excellent. Even a manually added label on the right most extents would be all that is needed.

 

Also, I was just looking for a plot of size vs time for the 2018 approach. Your plot comes just in time! Many thanks!



#9 Tom Polakis

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Posted 30 May 2018 - 02:00 PM

Thanks for the replies.  Southern Hemisphere observers have the advantage for observing Mars at its largest.  I'm thinking about cooking up a way to illustrate Mercury's altitude above the horizon at various elongations.  Here again, southern observers have it much better.

 

In the meantime, here's that declination vs. size plot with year labels.

 

Tom

 

F0XHlTK.jpg


Edited by Tom Polakis, 30 May 2018 - 02:00 PM.


#10 starcanoe

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Posted 30 May 2018 - 02:36 PM

Looks nice.

 

Where is 2020 something :)



#11 Tom Polakis

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Posted 30 May 2018 - 02:45 PM

Looks nice.

 

Where is 2020 something smile.gif

I thought about going into the future, but then considered it would be best to cover just one cycle between favorable oppositions.  As has been noted, the next opposition after the very favorable one occurs at a northerly declination.  Something like the 2005 circumstance will occur again in 2020.

 

Tom



#12 starcanoe

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Posted 30 May 2018 - 03:09 PM

Thanks.

 

Good enough for me :)

 

Compare 2005 to 2018...yeah...its a bit "smaller"...but dang its give or take 40 degees higher...the next go around is so much better....

 

That IMO makes a big difference....and I say that as observer that lives further south than 90 plus percent of US population.


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#13 deSitter

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Posted 30 May 2018 - 04:25 PM

Thanks.

 

Good enough for me smile.gif

 

Compare 2005 to 2018...yeah...its a bit "smaller"...but dang its give or take 40 degees higher...the next go around is so much better....

 

That IMO makes a big difference....and I say that as observer that lives further south than 90 plus percent of US population.

It's not that bad. DEC -25 so 30 degrees horizon clearance at 35 N. 

 

-drl



#14 Starman81

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Posted 30 May 2018 - 04:26 PM

Thanks.

 

Good enough for me smile.gif

 

Compare 2005 to 2018...yeah...its a bit "smaller"...but dang its give or take 40 degees higher...the next go around is so much better....

 

That IMO makes a big difference....and I say that as observer that lives further south than 90 plus percent of US population.

 

Yes about 31° and some change is the difference and the angular size only reduced ~8%  (22.4 in 2020 vs 24.3 in 2018). I'm sure we'll all have fun this go around later this Summer with Mars but us northerners are really looking forward to October 2020!



#15 Waddensky

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Posted 30 May 2018 - 04:35 PM

Thanks for sharing this excellent plots. Very insightful. It truly is a good year for Mars, despite the low declination.



#16 starcanoe

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Posted 30 May 2018 - 07:23 PM

Yes about 31° and some change is the difference and the angular size only reduced ~8%  (22.4 in 2020 vs 24.3 in 2018). I'm sure we'll all have fun this go around later this Summer with Mars but us northerners are really looking forward to October 2020!

 

Yeah....that reminds me of the other difference between this go around and the next....

 

In our neck of the woods the height of the summer vs fallish is a big deal "seeing" wise...

 

Summer temps...even into the late nite/early morning are "nice".....the seeing kinda sucks until the temps drop....later in the fall...the seeing gets better a fair bit sooner after sun set.....

 

Now in OTHER regions in the US perhaps the seeing the summer is BETTER than the falll....but in general I suspect that is NOT the case....hence my inclination that 2020 is THE year of Mars (this go around being the warm up :)  )



#17 karstenkoch

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Posted 31 May 2018 - 07:04 AM

For observers at 40 degrees North latitude, Mars will transit at an elevation of 55 degrees on 13 Oct 2020, which is the day of it's opposition. (reference: SkySafari 6 Pro)

 

And, it will do that with an apparent diameter of 22.4", which is almost as large as the 24.2" of 2018 (reference: http://www.nakedeyep...oppositions.htm )

 

Plus, here in Virginia, we have more cloud free days in October than in July.

 

2018 is just the warm up for us Northerners!


Edited by karstenkoch, 31 May 2018 - 07:07 AM.

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#18 Special Ed

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Posted 31 May 2018 - 08:24 AM

I'm still looking forward to seeing a 24" Mars this summer even if it is low--but altitude does make a huge difference in visually observing Mars (not so much with today's imaging).

 

Here's an example with two sketches of the same CM, about the same magnification, and almost the same angular diameter.  This sketch was made a few days ago with a C14 with Mars at  a diameter of 14.2" and an altitude of 30*.  The seeing was above average.

 

Mars_2018.05.25.v1.jpg

 

This sketch was made in 2005 with a C8.  Mars is 15.4" in apparent diameter and 62* altitude.  The seeing was only average.

 

Mars_9.12.05.1.JPG


Edited by Special Ed, 31 May 2018 - 08:27 AM.



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