"It was the night but one before the full of the moon, so bright that we could see to read distinctly by moonlight, and in the evening strolled over the summit without danger..."
"...It was at no time darker than twilight within the tent, and we could easily see the moon through its transparent roof as we lay; for there was the moon still above us, with Jupiter and Saturn on either hand, looking down on Wachusett, and it was a satisfaction to know that they were our fellow-travelers still, as high and out of reach as our own destiny."
In A Walk to Wachusett, Henry David Thoreau gets astronomically specific in writing about the night spent on the mountain. Since Thoreau very often puzzles events together from different trips, adds bits from his journals, and even brings in events from completely different circumstances, I thought to check this particular detail.
He made the trip in July, 1842, as reported in Richardson's Thoreau: A life of the mind. Stellarium* shows that Jupiter and Saturn were indeed both well up in the sky in July of 1842, and close together. The Mecklenberg Jeffersonian (Charlotte, NC) for July 19, 1842 reports in its almanac that the full moon that month would be at 4:02am on the 22nd. (I know Google is too powerful, but its search engine is WONDERFUL.) Putting the 21st into Stellarium, the moon lies to one side, but on the night of the 20th they made a neat triangle with the moon almost equidistant from the two planets.
So the detail checks out, if you allow Thoreau to be one day off on the phases: the scene he describes occurred two days before full moon, rather than one. I'm quite pleased by that little bit of verisimilitude; from a distance of one-hundred-seventy-one years, I can tell you Thoreau camped on Wachusett on the 20th of July, 1842.
*I highly recommend Stellarium--an open-source planetarium for the pc--to anyone who wants to know what is visible in the sky at any time from any location. It is a simple, lean program that is pretty easy to learn to use. It's light on the bells and whistles, but that's what we have the REAL SKY for! Go to: http://www.stellarium.org/