Two skies · One turning Earth
The sky is the clock.
The stars are its hands.
Live astronomical instruments for your wall. The Hand of the Cross carries the Southern Cross around the pole, while civil time, the sidereal hour and the Moon read from the corners.
Live now. This is the clock itself, running in your browser, exactly as it runs on the wall.
Why a sidereal clock
At a known season, the Cross tells the hour; at a known hour, it tells the season.
For most of human history the heavens were our clock, calendar and compass. Sidereal Clocks brings that back — instruments that put civil time and the turning sky in one readable field, so a glance tells you not just the hour, but where you stand in the night and the year.
The instruments
Three ways to bring the sky indoors.
Each runs live from the real positions of the Sun, Moon, planets and stars. The collection runs today in software; the physical wall editions are in early development.
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Square screen · always on
The Sidereal Wall Clock
The Southern or Northern dial, with the time, the sidereal hour and the Moon reading from its four corners.
See the wall clock →
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Large touch screen · in development
The Grand Orrery
The solar system on a wall or table, turned by hand: spin it, pinch to zoom, roll the years forward and back.
See the orrery →
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Round screen · by commission
The Building Clock
A round instrument tuned to the exact meridian of the building it stands in, for a lobby, a library, an observatory.
Commissions →
How to read it
Four corners, one glance.
Behind the dial, the same engine that drives our astronomy runs the whole face. The corners translate it into readings you can take at a distance.
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The Hand of the Cross
The Southern Cross itself becomes the hand, drawn from the pole and sweeping the night sky as the Earth turns.
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Local time
Ordinary civil time for where you are, so the instrument reads as a clock first.
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Sidereal time
The hour by the stars for your meridian — the sky's own clock, which gains on the Sun's a full turn each year.
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The Moon
Its phase and how much of the disc is lit tonight, named in plain words.
Designed in New South Wales
Made to be lived with.
Each instrument is conceived as a piece of furniture as much as an astronomical tool — a quiet, always-on object with the weight and finish to hold a wall for years. Frames in warm timber, housings true to the horologist's eye, a face that is accurate to the second and never needs winding.
The designs are ours, drawn in New South Wales and first published at CalculationTime.com. The physical editions are in early development; register your interest to be the first to know when they are ready.
- Students and teachers Learn the sky Live field guides to both skies, and a free classroom lesson on the two poles. Field guides and lesson →
- 1300 to today The story of the Cross How sailors read the hour and the season from the Southern Cross, and why it became the hand. Read the story →
- Full screen The dials, live Open either face full screen on any display — a phone, a desk monitor or a wall panel. Open the dials →
Be the first to bring one home.
The wall editions are being readied now. Register your interest and we will write to you — no spam, just word when the instruments are ready and how to reserve one.