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Astronomy and D-Day: The Solar, Moon, and Tides at Normandy

June 3, 2019 - Comment

The invasion of occupied France on D-Day, June 6, 1944, modified the course of the Second World Warfare. Astronomy performed a vital position within the timing of the occasion. This month marks the 75th anniversary of the D‑Day invasion of Normandy, France. However why was June Sixth chosen? Astronomy performed a job: The Moon and

The invasion of occupied France on D-Day, June 6, 1944, modified the course of the Second World Warfare. Astronomy performed a vital position within the timing of the occasion.

This month marks the 75th anniversary of the D‑Day invasion of Normandy, France. However why was June Sixth chosen? Astronomy performed a job: The Moon and Solar affected the planning and the collection of this date.


Coast Guard Chief Photographer’s Mate Robert F. Sargent captured this well-known D Day picture of the scene on Omaha Seashore at about 7:40 a.m.
U.S. Coast Guard, Division of Protection

Did the airborne divisions need the darkness of a brand new Moon or the brightness of a full Moon when the paratroopers started parachuting into France simply after midnight? And the way did planners coordinate that lunar part with the requirement for a low tide close to dawn, in order that engineers may destroy uncovered seashore obstacles earlier than the touchdown craft of the primary assault waves got here in?

Invasion of Europe

Within the early morning hours of June 6, 1944, the complicated operation code-named Overlord started to unfold. The Allies had assembled an armada of 5,000 ships and touchdown craft carrying 130,000 troopers throughout the English Channel to the Normandy seashores. Airborne operations carried a complete of 24,000 troops utilizing greater than a thousand transports and gliders. Close to dawn, aerial and naval bombardment shook the German coastal strongpoints, and touchdown craft began the lengthy runs in to the seashores.

Any invasion date in Might or June would go away all the summer time for the Allied drive throughout France and towards the German homeland earlier than dangerous climate in fall or winter may gradual the advance. However the invasion planners later made clear that the collection of June Sixth specifically was for astronomical causes: moonlight and the consequences of the lunar part on the tides got here into play. The Allies required a low tide close to dawn, and, on this a part of the Normandy coast, such a tide happens solely close to the instances of both new Moon or full Moon.

Moon, Solar, and Tides

Normal Dwight D. Eisenhower, the Allied Supreme Commander, realized that preparations weren’t full in Might and postponed the assault till June. His 1948 e-book, Campaign in Europe, defined why moonlight and a low tide had been necessary:

…the subsequent mixture of moon, tide, and time of dawn that we thought-about practicable for the assault occurred on June 5, 6, and seven …We wished a moon for our airborne assaults … We needed to assault on a comparatively low tide due to seashore obstacles which needed to be eliminated whereas uncovered.

Admiral Chester W. Nimitz, in his 1960 memoir The Nice Sea Warfare, likewise recalled the importance of the lunar part and the tide instances:

… employees … desired a moonlit night time previous D-day in order that the airborne divisions would have the ability to manage and attain their assigned aims earlier than dawn… the tide … have to be rising on the time of the preliminary landings in order that the touchdown craft may unload and retract with out hazard of stranding…But the tide needed to be low sufficient that underwater obstacles could possibly be uncovered for demolition events.

The Longest Day

This publicity from the 1962 movie, The Longest Day, reveals the early assault waves advancing on foot by mined seashore obstacles, a combination of stakes and hedgehogs.

Prime Minister Winston Churchill, in his 1951 e-book Closing the Ring, burdened the astronomical and tidal elements:

Solely on three days in every lunar month had been all the specified situations fulfilled. The primary three-day interval…was June 5, 6, and seven…If the climate weren’t propitious on any of these three days, the entire operation must be postponed not less than a fortnight—certainly, a complete month if we waited for the moon.

The Allies initially meant to invade on June Fifth, however dangerous climate compelled a postponement of at some point.

Calculating the Results of Moon and Solar

An almost full Moon rose 1½ hours earlier than sundown on June Fifth, reaching its highest level on June Sixth at 1:19 a.m., simply because the American airborne assault started. Slanting moonlight illuminated the bottom under for the troops of the 82nd and the 101st Airborne as they began dropping from the sky between 1:15 and 1:30 a.m., following pathfinders who had jumped about an hour earlier. These instances are expressed in British Double Summer season Time (two hours forward of Greenwich Imply Time), as employed by the Allied invasion forces.

Brigadier Normal James Gavin of the 82nd Airborne supplied an eyewitness account in a 1947 monograph titled Airborne Warfare. As his C‑47 plane approached a drop zone west of Sainte-Mère-Église, Gavin may clearly see the bottom under:

…the roads and the small clusters of homes within the Normandy villages stood out sharply within the moonlight.

Significance of the Tides

The German defenders had employed a number of forms of mined obstacles on the seashores, as proven within the accompanying illustrations.

Beach obstacles

Left: This German plan of seashore obstacles reveals barbed wire connecting stakes, ramps, hedgehogs, Belgian Gates, and tetrahedrons, because the seashore would seem close to low tide. Higher proper: This Belgian Gate seashore impediment is preserved on the Omaha Seashore Memorial Museum in Saint-Laurent-sur-Mer. Decrease proper: Don Olson poses with a tetrahedron seashore impediment within the assortment of the Battle of Normandy Memorial Museum in Bayeux.
Higher proper: © John Hamill; Decrease proper: Marilynn Olson

Normal Omar Bradley described in his 1951 memoir A Soldier’s Story how the plans for the demolition groups trusted the tides:

At low tide the seashore defenses lay uncovered … We might assault when a rising tide reached the impediment line and provides the engineers 30 minutes to clear it earlier than the water turned too deep. Successive assault waves would then trip the rising tide nearer the ocean wall by gaps within the impediment belt.

Tide Calculations for Omaha Seashore

Our Texas State group wrote a pc program to calculate the tide ranges at Omaha Seashore. The calculated morning tide vary was about 18 toes, with a speedy rise from low water at 5:23 a.m. to excessive water at 10:12 a.m.


The 150mm weapons of the German battery at Longues-sur-Mer had been positioned close to the coast between Omaha Seashore and Gold Seashore. Members of the Texas State group pictured listed below are Laura Shiny, Don Olson, and Hannah Reynolds.
Russell Doescher

This speedy rise had a big impact. The preliminary landings at Omaha Seashore happened at 6:30 a.m. Over the subsequent 30 minutes, the water degree rose 2.four toes because the demolition groups struggled to position explosives whereas the obstacles had been nonetheless uncovered. By 7 a.m. the water degree was already rising by one foot each 10 minutes, and that fee solely accelerated. Even a small delay had severe penalties. These calculations assist clarify why demolition crews cleared solely 5 of the deliberate 16 gaps among the many obstacles earlier than the advancing tide compelled them to wade ashore.

Whereas tidal and astronomical concerns meant that the date of the Normandy invasion needed to fall close to a full Moon, its gravitational results had been then chargeable for the quickly rising spring tide. The remaining fields of mined seashore obstacles contributed to the lack of momentum of the next assault waves and helped earn Omaha Seashore its nickname: “Bloody Omaha.”

D-Day Timetable

The 5 touchdown seashores had the code names Utah (American forces), Omaha (American), Gold (British), Juno (Canadian), and Sword (British), so as from west to east. Astronomical calculations are for the Caen Canal and Orne River bridges close to Bénouville, France (49° 15′ North Latitude, zero° 16′ West Longitude), simply inland from Sword Seashore. The instances are expressed in British Double Summer season Time (two hours forward of Greenwich Imply Time), as employed by the Allied invasion forces.

June 5, 1944

eight:30 p.m.       Moonrise, Moon is 99% lit
10:01 p.m.       Sundown

June 6, 1944

12:16 a.m.     First British glider lands on the Caen Canal bridge, brilliant Moon in southeastern sky
12:26 a.m.     Radio message despatched: British captured the canal bridge and Orne River bridge intact
1:15 a.m.       American paratroopers start to land inland from Utah Seashore
1:19 a.m.       Lunar transit, Moon at its highest level within the sky for the night time
5:17 a.m.       Starting of civil twilight
5:23 a.m.       Low water exposes the seashore obstacles on Omaha Seashore
5:50 a.m.       Naval bombardment of Omaha Seashore begins
5:57 a.m.       Dawn
6:02 a.m.       Moonset, Moon is 99% lit
6:30 a.m.       First assault wave lands on Omaha Seashore, on a rising tide
7:25 a.m.       First assault wave lands on Sword Seashore, on a rising tide
10:12 a.m.     Excessive water covers Omaha Seashore nearly to the ocean wall
1:00 p.m.       Approximate time when Lord Lovat leads British commandos inland from Sword Seashore and so they hyperlink up with the airborne forces on the canal bridge

Moon over Pegasus Bridge

Six hours earlier than the amphibious landings even started, British troopers carried on gliders had already descended silently from the night time skies and landed on French soil. Their aims had been two essential bridges over two parallel waterways, the Caen Canal and the Orne River, simply inland from Sword Seashore. A brilliant Moon was essential for this assault.

At 10:56 p.m. on June Fifth at Tarrant Rushton airfield in England, the engines of the huge Halifax bombers serving as tugs surged from a gradual hum to a deafening roar. Inside minutes six gliders had been pulled into the air. Within the moonlight over England, the plane fashioned up and headed out for the flight over the Channel.

Horsa glider

The British employed six Airspeed Horsa gliders to land the assault forces close to the Caen Canal and Orne River bridges. This full-size Horsa reproduction, constructed in line with the unique wartime glider plans, was unveiled on the Memorial Pegasus museum in 2004 for the 60th anniversary of D-Day.
Amanda Slater

James Wallwork, pilot of the lead glider, realized when his tug had reached France, as a result of within the moonlight he may see the surf breaking on the Normandy shoreline. Wallwork recalled how he may see the waterways because the Moon shone from between clouds:

And there are the river and canal like silver ribbons within the moonlight.

With pardonable exaggeration, Wallwork described the moonlit scene as his glider approached the canal bridge goal. (The interview will be seen within the movie proven on the Memorial Pegasus museum):

I may see the goal. The Moon was on it. I may see the bridge. I may see the whites of their eyes nearly.

Pegasus Bridge and a Horsa glider

This aerial reveals the Memorial Pegasus museum within the distance, the unique 1944 Pegasus Bridge in its everlasting place on the museum grounds, and the total measurement Airspeed Horsa glider reproduction within the foreground. The touchdown zone for the three British gliders on D-Day is simply seen on the excessive higher proper.
Michel Dehaye

Wallwork’s glider was the primary to land, skidding to a halt close to the canal bridge at 12:16 a.m. Two extra gliders adopted into this touchdown zone, and the British troopers rapidly overwhelmed the German defenders. The group on the Orne River bridge had related success, with their descent likewise aided by the moonlight.

The canal bridge turned often called “Pegasus Bridge,” a reputation that refers back to the British airborne insignia that includes the mythological “airborne warrior” Bellerophon using the winged horse Pegasus. 

A “Late-rising” Moon?

Many authors writing about D-Day mistakenly think about that the Allied forces wished a darkish night time till the airborne divisions reached their targets. We positioned the first supply for this error within the memoirs of Walter Bedell Smith, one among Eisenhower’s closest aides. Smith’s article for the June eight, 1946, Saturday Night Put up made the inaccurate declare that for “the airborne landings … we would have liked a late-rising full moon, so the pilots may method their aims in darkness, however have moonlight to select the drop zones.” Cornelius Ryan’s traditional 1959 e-book The Longest Day used Smith as a supply, and Ryan wrote “crucial demand was for a late-rising moon.” A Google search with related key phrases (D-Day late‑rising Moon) will carry up many subsequent authors who adopted Ryan and repeated this unlucky error concerning a “late‑rising” Moon.

Astronomical calculations present that the Moon was positively not “late‑rising.” Moonrise truly occurred very early – the Moon had already risen into the sky about 1½ hours earlier than sundown on the previous day (June Fifth). The Moon then remained within the sky throughout all the night time of June Fifth-Sixth, 1944.

American Cemetery at Colleville-sur-Mer

The stone monuments of the American Cemetery at Colleville-sur-Mer dominate the foreground of this aerial . The cemetery is positioned on a bluff overlooking Omaha Seashore and the English Channel, each seen within the background.
Michel Dehaye

Because the 75th anniversary of D-Day approaches, the commemorations will rightly give attention to the heroism of the Allied troopers, sailors, and airmen who started the liberation of France. Readers of Sky & Telescope may also use this month to acknowledge the significance of the astronomical elements that decided the date of the invasion after which affected the course of occasions for each the airborne and amphibious forces on that historic day.

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