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Share your random "rules of thumb" here!

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#1 butsam

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Posted 23 January 2013 - 08:25 PM

Last Friday during my viewing session, I realized something pretty interesting.

I saw the GRS on Jupiter again, almost exactly as I had seen it for the first time with my own eyes almost exactly a week before.

So, I pulled up Stellarium, and sure enough, after exactly 1 week, the GRS is in almost exactly the same position on Jupiter.

(I realize Jupiter rotates about once every 9 hours 55 minutes, but that is not as easy a "rule of thumb" to keep in your hip pocket, to get you close for short-term, first-order "mind's eye" filtering of what may be possible again when.)

Some calculations made me realize Jupiter rotates almost exactly 17 times in exactly 1 week. (It is less than 4 minutes from this, as long as my memory on Jupiter's orbit time is correct!)

Anyway, that got me thinking -- what are some of your "rules of thumb" that you use? (For example, for the planetary moon positions, etc?)

EDIT: It looks like once you take into account the Earth & Jupiter going around the Sun, the GRS is in the same spot about once every week and 40 minutes, at least based on Stellarium's depiction; since Earth's motion, and Jupiter's solar motion, wasn't taken into account in the initial calculation, there is a bit of extra error, but it is still easily close enough to make a "rule of thumb" for mental calculation if you know where the GRS was a week ago!)

#2 herrointment

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Posted 23 January 2013 - 10:38 PM

As a saw operator for some decades my rule goes something like.......anything less than two aint good.

#3 Maverick199

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Posted 24 January 2013 - 04:41 AM

My rule of thumbs is to post here on Nexstar forums. :grin:

Seriously though, I have no rule of thumb and instead just go out and enjoy myself and take in the sights what the night beholds. Or maybe with my limited city viewing, all constellations look the same. :shrug:

#4 Peter9

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Posted 24 January 2013 - 05:11 AM

+1 for Haseeb's take on things. Relaxation and enjoyment are my goals when observing.

Regards. Peter.

#5 Skip

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Posted 24 January 2013 - 10:15 AM

I too do not use rules of thumb. But regarding Jupiter, I do have a little application that will show exactly where the moons and the GRS are at any time during the night. It is called Jupiter 2 and it is freeware. However, I can no longer get to the website unless I go through the link in the app's About tab. Don't know why. :confused:

I also, of course, have Stellarium.

#6 Peter9

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Posted 24 January 2013 - 10:49 AM

Hi Skip,
If you select Jupiter in SkySafari, center it and use the + to zoom in, it will show you Jupiter's G.R.S, (if visible) and its Moons "as is".

Regards. Peter.

#7 Arthur Dent

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Posted 24 January 2013 - 11:16 AM

Here's one for you...

The Moon moves roughly a Moon's width compared to the background stars in around an hour.

(that's roughly 1/2 degree in an hour, so 12 degrees in a day and, 12 x 28 = 336 (so nearly 360 degrees - a complete circle - in 28 days)

Figures aren't spot on, but close enough.

Art Posted Image

#8 Peter9

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Posted 24 January 2013 - 11:39 AM

Here's one for you...

The Moon moves roughly a Moon's width compared to the background stars in around an hour.

(that's roughly 1/2 degree in an hour, so 12 degrees in a day and, 12 x 28 = 336 (so nearly 360 degrees - a complete circle - in 28 days)

Figures aren't spot on, but close enough.

Art Posted Image



If that ain't "Teaching your Granny to suck eggs" I don't know what is. :shrug: :lol:

Regards. Peter.

#9 Midnight Dan

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Posted 24 January 2013 - 01:52 PM

Winter observing rule of thumb: dress like it's 20°F colder than it really is.

-Dan

#10 Skip

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Posted 25 January 2013 - 10:51 AM

If you select Jupiter in SkySafari, center it and use the + to zoom in, it will show you Jupiter's G.R.S, (if visible) and its Moons "as is".


Hi Peter,

Yep and I do use SkySafari all the time in the field. I was thinking more of during the day while I'm planning my observing for the night (when I do any planning - HA!). Of course one could use Sky Safari for that as well, but I like to use the bigger screen whenever I can. The old eyeballs, ya know! :gramps: :grin:

#11 Skip

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Posted 25 January 2013 - 10:55 AM

If you select Jupiter in SkySafari, center it and use the + to zoom in, it will show you Jupiter's G.R.S, (if visible) and its Moons "as is".


Hi Peter,

Yep and I do use SkySafari all the time in the field. I was thinking more of during the day while I'm planning my observing for the night (when I do any planning - HA!). Og course one could use Sky Safari for that as well, but I like to use the bigger screen whenever I can. The old eyeballs, ya know! :gramps: :grin:

#12 Peter9

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Posted 25 January 2013 - 12:26 PM

Fully understood Skip.

I RESEMBLE your remarks. :roflmao:

Regards. Peter.

#13 sonny.barile

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Posted 27 January 2013 - 08:02 PM

I have a rule of thumb for observing sessions.

"Never put a black towel over your head to block stray light when skunks frequent your yard."
This probably isnt what you had in mind but believe me I do follow this rule religiously.

Regards
Sonny

#14 Peter9

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Posted 28 January 2013 - 06:44 AM

I have a rule of thumb for observing sessions.

"Never put a black towel over your head to block stray light when skunks frequent your yard."
This probably isnt what you had in mind but believe me I do follow this rule religiously.

Regards
Sonny



"WHY" ??? :shrug: :thinking: :rofl2:

Regards. Peter.

#15 Chris J

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Posted 28 January 2013 - 02:06 PM

Rule 1 - the better the seeing/transparency the less time you will have for observing.

Rule 2 - the usefullness of equipment is inversely proportional to its cost cf planisphere vs filar micrometer.

#16 WaterMaster

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Posted 29 January 2013 - 11:31 AM

As a saw operator for some decades my rule goes something like.......anything less than two aint good.


:rofl2:

#17 coutleef

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Posted 29 January 2013 - 11:39 AM

Winter observing rule of thumb: dress like it's 20°F colder than it really is.

-Dan


and when this means you have to dress as if it was -60F, just stay indoors to plan your next session :roflmao:

#18 Peter9

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Posted 29 January 2013 - 12:29 PM

As a saw operator for some decades my rule goes something like.......anything less than two aint good.


:rofl2:



I hear that many ex saw operators make very good "short hand" typists. :rofl5:


Regards. Peter.

#19 Skip

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Posted 29 January 2013 - 12:30 PM

when this means you have to dress as if it was -60F, just stay indoors to plan your next session



Hi François ,

You tough Canadians crack me up! :lol: I think I would have stated that as "...when this means you have to dress as if it was 20F [positive 20] just stay indoors to plan your next session ..." :grin:

But I :bow: to your toughness. :cool:

#20 sonny.barile

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Posted 29 January 2013 - 09:16 PM

Peter, One evening last fall I was using a towel to block out a light in the next yard. When I took it off of my head to take a break there was a pair of little stinky eyes looking up at me. It was right there at my feet. I stayed motionless until he left but that was as close as I ever want to get. There are plenty of them around here. Now I dont cover my head and I try not to get to engrossed in what Im doing because i am paranoid.

#21 WaterMaster

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Posted 29 January 2013 - 10:22 PM

... a pair of little stinky eyes ...


Are you sure it was his eyes that were stinky? :p

#22 coutleef

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Posted 30 January 2013 - 09:10 AM

when this means you have to dress as if it was -60F, just stay indoors to plan your next session



Hi François ,

You tough Canadians crack me up! :lol: I think I would have stated that as "...when this means you have to dress as if it was 20F [positive 20] just stay indoors to plan your next session ..." :grin:

But I :bow: to your toughness. :cool:


not that tough in reality, the last two winters were very mild as it rarely went below -15F

the first time i used my 8se at my dark site, the temperature was at -42F. i managed to set ip, align the RDF and look at Capella ( i thougth it was mars!!) and went back in!! it took me 30 minutes just to align the finder with bare hands: it took me two months before i took the scope out again, but the month of march was glorious that year. And that was the winter i discovered cloudynigths.

this year is horrible at my dark site: we swing from -35 at nigth one week to 50F the next one. that kind of weather brings a lot of clouds and unsteady air. i just want a real winter, colder but more predictable

#23 cpl43uk

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Posted 06 February 2013 - 02:58 AM

Sorry, may not be a 'rule of thumb' but i find it helps appreciate distance.... If the earth to sun distance was an inch, then an object a light year away would be a mile. I use this at public outreach sessions to help make sense of the numbers we spout about 'faint fuzzies'....

#24 Arthur Dent

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Posted 06 February 2013 - 05:06 AM

Hi cpl,

Yep, that's a good one. A discussion about this and the distances to some famous objects using this scale can be found at: http://earthsky.org/astronomy-essentials/how-far-is-a-light-year

On this scale, the Milky Way galaxy comes out to be 100,000 miles across and we're 27,000 miles from the centre (just slightly more than once around the Earth), and M31 - The Great Galaxy in Andromeda is a staggering 2,300,000 miles away (or 10x further than the Moon).

'Course the REALLY staggering thing is that in real life, they are actually 63,000x further away than this!

Space sure is big!

Art

#25 Terrance

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Posted 11 February 2013 - 01:54 PM

Whatever can be tripped over in the dark, will, given enough time, actually be tripped over in the dark.






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