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Citizen BY1010-57L Super Titanium™ 'Tsuki-Yomi' Moon Phase Watch - W38381
Ref. BY1010-57L
Sits in Citizen’s upper tier here — more premium than three quarters of the Citizen watches we list, which start at £139.
Price range £139 to £1,145 across 113 Citizen watches in stock.The Tsuki-Yomi — moon-reading in Japanese — was built to mark thirty years of Citizen's radio-controlled technology, and the H874 movement inside it earned its own milestone: the first light-powered calibre in the world to combine a fully analogue moon phase with atomic timekeeping synchronisation. That pairing is the whole point of the watch's existence, and Citizen's Luna Program is what makes it work, applying a proprietary mathematical formula to signals from multi-band radio transmitters to calculate the current lunar phase and adjust the display at six o'clock automatically, correcting for whether the signal originates in the Northern or Southern hemisphere. The dial earns its name. The moon phase aperture carries a textured rendering of the lunar surface rather than a generic disc, and against a deep blue field with a black outer ring it reads as something genuinely considered. At 43mm the case is substantial, but Super Titanium brings it in at 105 grams, and at 10.9mm it sits flatter than most watches carrying this much complication — it disappears under a cuff in a way a steel equivalent at this depth rating simply would not. The five-month power reserve means the solar cell rarely faces a serious deficit, and with radio synchronisation handling accuracy, there is very little the owner needs to do.
- Reference
- BY1010-57L
- Brand
- Citizen
- Collection
- Tsuki-Yomi A-T
- Case size
- 43mm
- Case thickness
- 10.9mm
- Lug width
- 22mm
- Case material
- Titanium
- Case shape
- Round
- Dial
- Blue
- Crystal
- Sapphire
- Movement
- Solar
- Calibre
- H874
- Functions
- Moonphase
- Water resistance
- 100m
- Bracelet / strap
- Titanium bracelet
- Strap colour
- Silver
- Clasp
- Deployant clasp
- Lume
- Luminous
- Retailer
- F.Hinds
Additional specifications
- Lug-to-lug
- 53mm
Learn more about Citizen
The Shokosha Watch Research Institute began in Tokyo in 1918, and the Citizen name was given to its first pocket watch in 1924 by the then mayor of Tokyo, Shinpei Goto, who wanted a watch that would be available to ordinary citizens rather than only the wealthy. The company formally took the name in 1930.
That founding intention has held. Citizen is the largest watch manufacturer in the world by volume and is fully vertically integrated, making its own movements, cases, and electronic components.
Its most significant technology is Eco-Drive, introduced in 1976 and refined over decades. A photovoltaic cell beneath the dial converts any light — including indoor light — into stored energy, so the watch never needs a battery change. Citizen has sold well over a hundred million Eco-Drive watches, and the environmental argument is substantial: hundreds of millions of cells not discarded.
The company also produced the first analogue quartz watch with a titanium case in 1970, the first professional dive watch with an electronic depth sensor, and the Caliber 0100, an Eco-Drive movement accurate to within one second a year — the most accurate independent watch movement ever put into production.
Citizen owns Bulova, Frederique Constant, Alpina, and the movement manufacturer Miyota, whose calibres power a large share of the affordable mechanical watch market worldwide.
- 1918
- The Shokosha Watch Research Institute is founded.
- 1924
- The Citizen name is given to its first pocket watch.
- 1976
- Eco-Drive light-powered technology is introduced.
- 2018
- The Caliber 0100 achieves accuracy of one second a year.
Also in 3 collections
This watch appears in Blue Dial Watches (994), Solar & Kinetic Watches (263) and Titanium Watches (186).
Manufacturer’s guarantee
Best of 2 retailers
What the specifications mean
Strengths
- 100m water resistance covers swimming and watersports
- Sapphire crystal, which resists scratching
- Luminous hands and markers for low light
- One of Citizen's more premium watches
Worth knowing
- 43mm sits at the larger end
Citizen BY1010-57L Super Titanium™ 'Tsuki-Yomi' alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification |  BY1010-57L | SFJ005P1 | GMW-BZ5000BD-1ER |
|---|---|---|---|
| Price | £599 | £560 | £619 |
| Case size | 43mm | 42mm | 43.6mm |
| Water resistance | 100m | 100m | 200m |
| Movement | Solar | Solar | Solar |
| Strap | Titanium bracelet | Stainless steel bracelet | Stainless steel bracelet |
| This watch | Closely matched |
|
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 100m it is rated for swimming and snorkelling, though not for diving.
Water resistance explainedWill the glass scratch?
Unlikely. Sapphire is second only to diamond in hardness and shrugs off everyday marking.
Sapphire, mineral and acrylic comparedDoes it need a battery?
No. It charges from light, and the cell behind that is designed to last a decade or more.
Quartz, automatic and solar comparedWhat size strap does it take?
22mm. Any strap of that width will fit, and on most modern watches quick-release bars make the swap a two-minute job with no tools.
Will it fit my wrist?
Lug-to-lug is 53mm, which suits wrists from roughly 17.5cm (7 inches) upward.
Lug-to-lug decides fit more than case diameter does.
How to size a watch to your wristIs it a men's or women's watch?
Listed as men's.
Cheapest place to buy
F.Hinds at £599, against £699 at Goldsmiths. Two UK retailers stock this reference.
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