Sidereal Clocks: questions & answers
What a sidereal clock is, how the Southern Cross hand works, and what to expect from the physical editions: sizes, finishes, pricing and commissions for architects, designers and private clients.
What is a sidereal clock?
A sidereal clock keeps time by the stars rather than the Sun. The Earth turns once against the stars every 23 hours 56 minutes 4 seconds, about four minutes shorter than a solar day, so a sidereal clock shows where the sky actually stands overhead. Observatories have used them for centuries to know which stars are crossing the meridian.
What makes a Sidereal Clock different from other astronomical clocks?
Its fourth hand is the Southern Cross. One needle runs from the south celestial pole, exactly halfway between the stars Acrux and Gacrux, and turns with the real sky once per sidereal day. Around it sit a familiar twelve-hour face and the Sun, Moon, planets and months. The Northern Movement mirrors the design around Polaris and the Big Dipper, turning anticlockwise.
Can I buy a Sidereal Clock now?
Not yet. Every instrument in the collection already runs live in software, and the physical editions are at the prototype-specification stage with specialist display, enclosure and calibration makers. The first editions will go to the people who register their interest now through the enquiry form.
What sizes are planned?
Three physical editions are planned: the 600 mm Salon edition for residences, galleries and boardroom walls; the 900 mm Architectural edition for atriums, lobbies and installation-scale interiors; and the Twin Clocks, a paired Northern and Southern installation. Bespoke sizes can be discussed for a specific project.
How much will a Sidereal Clock cost?
Each physical edition is priced as a commission. Series 01 pricing will be published once prototype quotations from manufacturing partners are in. Register your interest, with a note of the space you have in mind, to receive pricing first.
What frames and finishes are available?
The envisioned finishes include dark anodised aluminium, brushed brass and bronze, and timber frames including American walnut, oak, cherry, maple, teak, rosewood, ebony and burl. Final materials are specified with the manufacturing partners and can be matched to a project’s interior palette.
Does it work in the Northern Hemisphere?
Yes. The Northern Movement is the same clock mirrored for the northern sky, with the hand turning anticlockwise around Polaris and the Big Dipper. The Twin Clocks pair both faces, so one room can read the sky from both ends of the Earth.
How is a clock set for where it hangs?
Every clock is calibrated to a meridian. The hand reads exactly zero at standard-time midnight at the end of 31 March 2026 on the reference meridian through Cumnock, New South Wales, and every time zone has one such midnight-zero meridian, about 15.04 degrees from the next. Each physical clock is calibrated to the midnight-zero meridian of the time zone it hangs in.
How do you read the sky from the clock?
Two rhythms. Through one night, about two hours takes the Crux hand from one number to the next. Looking at the same time each night, about a month produces the same step, which is why a month sits in every five-minute space around the face. The clock is both a timepiece and a calendar of the sky.
Can I change the face?
Yes. A Sidereal Clock is a live display, so the same clock can wear any of its faces: the Crux Movement, the Crux Movement with a turning month bezel that always points at today’s date, the Northern Movement with mirrored or clockwise hands, and a mirrored Southern face for clocks seen through glass. On the Northern faces the Southern Cross can be shown on the hand or switched off. New faces can be added over time. See them all, live, on The Faces.
Can the clock face be in my language?
Yes. The month ring can be set in English, Spanish, French, German, Italian, Portuguese, Russian, Arabic, Hindi, Chinese, Japanese or Korean, and further languages can be added for a commission. The Roman numerals, the Southern Cross hand and the sky stay the same on every face. Try the Face menu beneath the live clocks on the home page.
Does the clock follow daylight saving?
No. The sky does not observe daylight saving, so the clock keeps standard time all year and stays true to the stars.
Can architects and interior designers specify a Sidereal Clock for a project?
Yes. The enquiry form takes project details such as the space, wall, preferred size and finish, and timeline. Architects, interior designers, hotels and private clients are welcome to start the conversation at concept stage, and installation is planned with the design team.
Where are Sidereal Clocks designed and made?
Sidereal Clocks is designed in New South Wales, Australia. Each edition will be made with specialist dial, enclosure and calibration makers, with assembly and delivery partners appointed country by country.
Can I see the clocks running?
Yes. The live Southern and Northern dials run on the Sidereal Clocks home page, and the collection was proved in public at CalculationTime.com, where the Southern Cross Clock, the Crux Perpetual, the Crux Movement and the Twin Clocks of Earth all run live.
Another question? Write to concierge@siderealclocks.com or register your interest.