What Do the Sun and Moon Have to Do with Edwards Ferry?

A good military operations plan considers the times of sunrise, sunset, and the nighttime illumination offered by the moon.   I see no reason why a historian approaching the study of an operation or action shouldn’t also consult these factors.  (Since the data is often easy to come by, I “deduct points” from any review if an author fails to address these factors!)

The following chart was derived from data from the U.S. Naval Observatory specifying the year as 1863 and the place as Leesburg, Virginia:


The day of the month of June is listed on the far left column, and data for that particular day is listed on the row to the right of the day.  For those who are not familiar with the abbreviations across the top, here the translation:

BMNT – Beginning Morning Nautical Twilight.  The sun is 12 to 6 degrees below the horizon.  Weather and other factors aside, the first traces of illumination from the sun are apparent.  One can start making out ground objects at BMNT, but stars are still visible.

BMCT – Beginning Morning Civil Twilight.  Defined as when the sun reaches 6 degrees below the horizon.    Illumination increases to allow one to fully recognize objects on the ground, but only the brightest stars are visible.

Sunrise – Defined as when the sun is visible arising over an unobstructed horizon – not over terrain such as hills.

Sunset – Similarly, when the sun disappears below an unobstructed horizon.

EECT – End of Evening Civil Twilight – The sun passes beyond 6 degrees below the horizon.  As with morning, between sunset and EECT, illumination allows one to see objects on the ground, and some stars are visible.

EENT – End of Evening Nautical Twilight – The sun passes beyond 12 degrees below the horizon.  At this point, no ground objects are made out without artificial light or moonlight.

Moonrise and moon set are defined similarly to sunrise and set.  Note the table above adjusted the times for some moon sets to correlate the span of the moon’s visibility “overnight” for a particular day.

Moon phase – Traditional terms used to define the phase of the moon.

% Illum – Is the percentage of the moon’s surface that is illuminated.  From an operational standpoint, this gives an indication, again weather aside, of how much reflected light will aid those operating at night.

Those definitions set, the table offers some indication of the working daylight hours and the impact of night operations around Edwards Ferry in June 1863.  Based on the data, the earliest that soldiers might start work was roughly 4:15 a.m. each morning.  The terrain east of Edwards Ferry features a few hills, but nothing that would greatly obstruct the horizon.   However, to the west are the Catoctin Range, just outside Leesburg.  Given that on the horizon, probably the latest soldiers might work without aid of lanterns or candles was 8:00 p.m.

The moon had risen before sunset on each day reviewed.  However, the moon offered very little illumination over the nights of June 20-24, and sat well before sunrise.  On the vital nights of the crossing, June 25 – 27, the moon sat a few hours after midnight.  Of course cloud cover from the rains likely suppressed any illumination offered by the waxing moon.  Thus the infantry who marched beyond the bridges along the tow-path and towards Poolesville, Maryland were not offered much natural lighting.

Of note, on the night of June 20-21, when the engineers placed the first pontoon bridge, the moon sat about three hours after sunset and offered only 17% illumination (assuming no cloud cover).  Recall from the timeline that the order to place the bridge was issued at 5:20 pm on June 20.  The bridge was completed at 9:45 am the next day.  And this occurred while the Potomac was rising!

Perhaps to elaborate on that point with a visual, from my files of “photos that didn’t work out too well” is one taken on June 16, 2007 at 8:47 pm of White’s Ferry:

White's Ferry at Twilight
White's Ferry at Twilight

For the record, the Naval Observatory’s data for that day provides a sunset of 8:39 pm and a EECT of 9:11 pm.  The moon was a waxing crescent with only 8% illumination, and sat at 11:15 pm that night.  The camera, my simple point and shoot, had no extra filters and the flash of course did little good.  The ferry boat is visible to the right and the ramp in the distant center.  About the only thing standing out are the headlights of vehicles and a few on the boat.

Can you imagine walking across a swaying bridge in that lighting condition?  How about building one?

Edwards Ferry – The Weather

When I started posting information about the June 1863 crossing at Edwards Ferry, I planed at least one post dealing with the weather and its effects on operations.  Logically this discussion should have occurred early in the sequence, but I was just not happy with the source material or data.  Trouble is, while there are multitudes of first hand accounts that describe the weather, none offer the meteorological data that I would prefer.  I didn’t want to simply say it rained on a given day, but rather what time of day it rained and how much.  And even more important with regard to the bridging, how high was the river cresting.

At first I figured detailed data from the Naval Observatory (Washington, D.C.) might suffice.  After all, the station is only some 25 miles, straight line, from Leesburg, Virginia.  But common sense told me to validate that as a data set.   So I started comparing both contemporary weather and historical data from other time periods.  As I figured, there is enough variance to the samplings to invalidate the assumption that D.C. weather could be a constant with regard to approximating the weather at Leesburg.  Furthermore, the river stage in D.C. is certainly not a good measure of that upstream of the Great Falls of the Potomac.  That said, until I can locate some weather station reports that provide the data I prefer, all I can really point to are the first hand accounts which mention the rains.

Colonel Moses Lakeman offered an itinerary for the movements of the 3rd Maine (Ward’s 2nd Brigade, Birney’s First Division, III Corps) over the days in involving the crossing:

June 16th. Fair. Started at 5.30 o’clock A.M., and marched about three miles to rifle pits.
June 17th. Fair. Started at 3.30 o’clock P.M., and marched about three miles in rear of Centreville.
June 18th. Rain. Remained in bivouac. Smart rain in afternoon and evening. Lt.-Col. Burt left on fifteen days’ sick leave.
June 19th. Rain. Started at 3 o’clock P.M.; marched to Gum Spring; distance marched ten miles; a very severe march on account of rain, mud and darkness; arrived at 10.30 P.M.
June 2oth. Rainy. Remained in bivouac. Lts. Day, Anderson, Gilman and Blake missing, supposed to be captured by guerillas.
June 21st. Rainy. Remained in bivouac until 3.30 o’clock P.M., when we changed position to front. Heavy firing in direction of Aldie.
June 22d. Fair. Remained in bivouac until 5 P.M. Part of regiment went on picket, rest moved to rear on reserve. Sat on court martial on case of Major D of N. Y. Vols. at Col. Berdan’s headquarters.
June 23d. Fair. Remained in bivouac.
June 24th. Fair. Remained in bivouac.
June 25th. Rainy. Regiment relieved from picket; struck bivouac at 6 o’clock A.M., and marched to Monocacy, where we arrived at 10 P.M. ; distance marched about twenty-four miles.
June 26th. Rainy. Started at 6 o’clock A.M.; marched to near Point of Rocks; distance six miles. Division officer of day.
June 27th. Rainy. Started at 10 o’clock A.M.; passed through Jefferson and bivouacked near Middletown; distance about twelve miles.
June 28th. Fair. Started at 8 o’clock A.M. ; passed through Middletown and Frederick to Walkerville, distance about sixteen miles, and bivouacked for the night.
June 29th. Rainy. Started at 6 o’clock A.M.; passed through Walkerville, Woodsborough, Middleburg and Taneytown, distance marched about eighteen miles, and bivouacked for night.
June 3oth. Rain. Started at 2.30 o’clock p. M. and marched to near Emmitsburg; distance eight miles.

Lakeman records nine days of rain of the fifteen sampled above.  In fact, after three days of fair weather, when the 3rd Maine moved on June 25 along with the rest of the III Corps, to Edwards Ferry it rained.  And the rain did not let up until the 27th.  Recall the III Corps was among the first to cross the pontoon bridges.

Another account of the weather, with a little more detail, comes from Asa W. Bartlett of the 12th New Hampshire (Carr’s First Brigade, Humphreys’ Second Division, III Corps).  Speaking of the march to Gum Springs, Virginia on June 19, he wrote in the Regimental history:

It rained hard during the night, and the next day’s march of twelve miles to Gum Springs was through mud and water instead of heat and dust.  During the day the mercury fell thirty or forty degrees, and so great and sudden a change of temperature in a few hours, followed by a cold storm that set in just as the troops had pitched their tents, caused much suffering during the night….[2]

The temperature change mentioned is worth noting.  Bartlett further describes the march along to Edwards Ferry and the “Tow-path March”:

From Gum Springs to Edward’s Ferry, a distance of fifteen miles, the troops were hurried forward, with only a few five-minute halts to take breath.  Immediately crossing the Potomac at 5 p.m. on a pontoon bridge… the division at once entered upon the famous “tow-path march,” … ten to twelve miles further to somewhere near the Mouth of the Monocacy river….  About dark it began to rain, and soon the path was but a narrow stretch of mud, trodden by many thousand feet into mortar-like consistency….[3]

Bartlett continued to describe the march in rather descriptive prose, and offering some judgment on the choice of the tow-path by General Humphreys.  Lakeman’s itinerary, written probably at the time of the campaign, is not specific as to the time of day the rains arrived on the crossing day.  Bartlett’s account is specific, but it was written decades after the campaign (although assembled from diaries and other first hand recollections).

On both marching days highlighted in the accounts, the units made good distance – 10 to 12 miles on June 19, 24 to 27 miles on the crossing day.  The evidence that the rain affected the rate of march on the crossing day lies in the time line.  Lakeman stated the June 25 march took some sixteen hours.  Bartlett did not state the time the 12th New Hampshire began the march that day, but indicated going into bivouac between midnight and 1 a.m. the next day.

While the rains certainly resulted in a muddy path for those marching, the precipitation also offered some problems for those maintaining the bridge.  For a floating pontoon bridge, as the water level rises, the anchor points had to be reinforced, and the abutments had to be raised.  As the river rose, the points joining the bridge to the shore had to be progressively moved  up and away from the bank, otherwise the bridge would not float above the rising water and become swamped.  Conversely as the waters fell, the abutments and anchor points had to be adjusted back to prevent loose swings and grounding of pontoons.[4]

Another issue presented by rising waters was drift wood.  Military manuals of the day prescribed different barriers to deflect and collect debris in the current.  Estacades, one type recommended, were barriers formed by logs across the river.   These estacades came in fixed or floating types, but required careful placement and much maintenance. [5]  However, there is no mention of any estacades or even activities to deal with drift debris from the Army’s engineers.

A personal observation I can offer is based on crossing several times at modern day White’s Ferry, north of Leesburg.  On most days, the ride across is a peaceful event, with barely a few moments to take in the river.  However in the winter of 2008, one of our crossings took some fifteen minutes, as the crew stopped repeatedly to pull debris – and in one case an entire tree – from the ferry’s cable.  The Potomac can be a messy river after heavy rains.

Potomac at Whites Ferry During High Water
Potomac at Whites Ferry During High Water

In summary, while I cannot offer specific data as to how much rain fell or how high the Potomac River rose, clearly the weather had an impact on the crossing.



  1. From Maine at Gettysburg, by the Maine Gettysburg Commission, Lakeside Press, 1898, page 135.   (The entire volume is digitized and available by way of Google books.)
  2. Asa W. Bartlett, History of the Twelfth Regiment:  New Hampshire Volunteers in the War of the Rebellion,  I. C. Evans, printer, 1897, page 115. (The entire volume is digitized and available by way of Google books.)  Bartlett was a Sergeant-Major at the time but later promoted to Captain, serving on the regimental staff and later as a company officer.
  3. Ibid. Page 116.
  4. George Washington Cullum, Systems of Military Bridging in Use by the United States Army, D. Van Nostrand, 1863, page 199.  (The entire volume is digitized and available by way of Google books.)
  5. Ibid. Pages 201-205.