by Robert Sheaffer
Because Mercury and Venus have been so close to each other this past week, I made several attempts to observe them both together. However, since I didn't want to get up and go outside before dawn, that means observing during the daytime.
Last weekend it was clear, so I got out my Baby Celestron 114 GOTO mount, currently with a Meade ETX-90 mounted on it. (I'm sure some people would be very amused by this Meade Celestron scope!) Since I have a solar filter for it, the approach I took was this: turn on the scope, level it, enter the information. It asks you for two star alignments, which of course you cannot see. So you pretend like you do, then clikc "align". It thinks it's aligned, but it's actually several degrees off. You "goto" the Sun, solar filter in place. You're still a bit off, but you get the sun in by moving the scope and mount MANUALLY, not electronically, so that the virtual position and the actual position pretty much agree. After I was done looking at the nice sunspots, I did a "goto Venus", and removed the solar filter. I found Venus without too much trouble, but I simply could not see Mercury. Using Venus as a reference, I moved over the appropriate offset in altitude and azimuth. A lot of hunting, but no success. I just don't think Mercury is visible in the daytime in the ETX-90.
This weekend it's clear again, so this time I try using my Celestron GPS-11. What a difference! On Saturday I tried essentially the same trick. Not having a solar filter for it, I kept the front cover on. Two bogus star alignments, then a "goto sun." Guess what: the "Sun" is not one of the choices in the menu! But being resourceful, I looked up its RA and DEC, the went there. It was a few degrees off. I loosened the clutches, then manually moved the scope until the image of the sun from the finder was seen, using eyepiece projection, directly centered. Then I did "goto Venus," but was unable to find it. I didn't want to scan the skies that close to the sun, so I gave up. I later found out that the finder alignment was 'way off. This trick might work if the finder alignment is good.
However, Saturday evening I got a proper Goto alignment using the stars, then kept the scope turned on all night, covered up, plugged into the 110v adapter. I turned off tracking, but the processor was still running. This morning, hiding the optics with the front cover, I did "goto Venus." Perfect! A beautiful, bright little ball shone brilliantly in the middle of the field, almost full phase. Now the big test - can I "goto Mercury"? YES! Another beautiful, bright little round ball, not quite as brilliant but still quite easily seen. Using a 35mm 2" erfle, I was able to "just barely" get both planets in view at the same time. A very memorable sight!
OK, I'm on a roll - what else can I see? Jupiter is still up, although low in the sky. It was also seen easily, although its surface brightness is less. It's an "extended object" in the daytime, its brightness per square arcsecond is less than Venus or even Mercury. I could see some faint details in its clouds, but no satellites.
Can I see any stars? "Goto Arcturus." YES! An easy target! Very easily seen, twinkling in the blue. I could even make out its orange color. But what about fainter targets? "Goto Mizar." No, I don't see it. Wait - what is that - there it is!! Not only did I see Mizar, but, amazingly, **its companion was visible**! (I'm not talking about Alcor, but about Mizar's companion, which is only 14" from it.) Am I saying that I saw a 4th magnitude star in the daytime? I guess I am. It would fade in and out of visibility with the air currents. In fact, Mizar itself would sometimes virtually disappear for seconds at a time, with waves of poor seeing.
So, while the daytime is probably not a good time to continue your Messier marathon, with proper GOTO alignment you can observe the bright planets in the daytime, as well as the brightest stars. It's probably the best time to see Mercury. The next time that planet is closer to earth and in a more interesting phase, I'll have to try this again.