"It is written, that the collision of iron and stone will release sudden sparks; and thus there is the golden body, shining white, and the half moon positioned in the west."
Okay, so you've split your first arrow with your second arrow while shooting at a candle flame at night in the azuchi and now you're ready to run out to the edge of the dojo and see Venus in the east and the half moon in the west!
Just one problem...exactly what night should you schedule your practice to allow for this ultimate feat of shooting enlightenment?
Well thanks to the wonderful volunteers at the British Astronomical Association you can schedule all your satori practices just by visiting their web page! Here's the link:
Is this totally cool or what! Here is a screen shot for Sept 21, 2015 at 6 AM. Type in that date and time and you'll see this:
This really is an awesome sky chart. It looks strange at first because the sun is sitting at both ends of the chart but it makes sense when you realize what this sky chart is designed for. It is designed for backyard astronomers who need to plan their night viewing and they want to know if moonlight is going to mess up their night session so they need to plan ahead to see if the moon is going to be so bright that they can't see the star or planet they want to observe.
So planet watchers (like us) need to know if Venus is going to be so close to the sun that it can't be seen at all or perhaps it can only be seen at twilight or, even worse, Venus is on the "wrong" side of the sun and is actually an evening star for that month. That's where this sky chart is just brilliant. It shows the phase of the moon on the date and hour you want in relationship to all the planets. So what you want is to find a time when Venus is far enough away from the Sun in the morning to be seen and the moon is in half phase in the western part of the sky. All of that is quickly seen in this one chart. Looking at the picture above you can see that the half moon is on the far right while Venus is on the far left. That means Venus is going to be a morning star and, importantly, Venus is still on the right side of the twilight line (that second straight line on the left). That means you'll be able to see Venus at night, not in twilight.
Also, I cheated a little and looked at another star chart to see when Venus was going to be at it's brightest in 2015 as a morning star i.e. just before sunrise:
"Sep 1, 2015 - Venus is the brightest planet and third-brightest sky object overall, after the sun and moon. When it's visible, it's very, very prominent in our sky. This month, Venus will exhibit its greatest brilliancy as the morning “star” for approximately one week, centered on September 21, 2015."
That's how I knew to start with the month of September. Now you just click the various days of the month and you'll see the moon moving steadily through the sky and changing phase. When you get the moon in half phase and as far away from Venus as you can get (which puts it in the west) then bingo, you know when to schedule that night dojo satori practice you've been looking forward too. :)
Now the usual observing warnings apply. You need to find the latitude and longitude for your city and put that in the application. Armed with this knowledge then you should go to a more detailed sky chart or table that shows the night sky as it will appear at your location and get the exact time twilight ends and the moon sets and so on to make sure you schedule your practice accurately.
But this wonderful sky chart is absolutely the starting point.
Once you have your date go here and select sky charts to see when you have to get up in the morning to see all this for your location: