Sextant - Astra IIIB (Split Mirror)

Sextant — Astra IIIB (Split Mirror)

The World’s Most Trusted Training & Offshore Sextant

The Astra IIIB Sextant has earned its reputation as the reference standard for modern celestial navigation training and practical offshore use. With more than 24,000 units sold in the United States alone—and tens of thousands more worldwide—it is the most widely used, most supported, and most recognised serious sextant in service today.

Engineered to deliver professional accuracy at an accessible price point, the Astra IIIB is trusted by beginners, sailing schools, navies, and experienced navigators alike—many of whom choose it specifically so they can leave far more expensive sextants safely at home.

Produced by Celestaire in partnership with Changzhou Celestaire Instrument Co., the Astra IIIB is built to strict quality standards and tested to a level that rivals premium German and Japanese instruments.

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⚓ Why Navigators Choose the Astra IIIB

• Outstanding accuracy at exceptional value — unmatched in its class

• Lightweight, perfectly balanced frame — reduces fatigue and improves sighting stability

• Excellent optics — clear, bright horizons and sharp limb definition

• Beginner-friendly, professional-capable — grows with your skill level

• Unrivalled global support & spare parts availability

This is the sextant most instructors teach with—and the one many professionals quietly rely on.

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🧭 Construction & Handling

The Astra IIIB is built around a lightweight aluminium alloy frame with excellent corrosion resistance. Aluminium has long been favoured for professional sextants where reduced weight improves steadiness, especially in rough conditions.

• Superb balance — easier sights in rolling seas

• White degree markings on black arc — dramatically improved readability in low light

• LED illumination of arc & micrometer drum — powered via the handle

• Comfortable grip geometry — ideal for extended use

Many users report that the Astra IIIB is the easiest sextant they have ever handled.

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🪞 Optical Excellence

• Large rectangular index mirror (56 × 42 mm) — the same size used on high-end sextants

  • Provides greater mirror area for high-angle sights

  • Requires less steadiness during observations

• Horizon mirror choice — whole horizon or traditional split mirror

• Mirror upgrade system — mirrors are easily swapped via two screws

• Every mirror & shade glass tested using Fresnel diffraction for flatness

Randomly tested units have produced results indistinguishable from premium European and Japanese sextants.

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🔧 Modular & Maintainable

The Astra IIIB is especially valued by:

• Navigation schools

• Training fleets

• Institutions with heavy student use

Why?

• Inexpensive, readily available replacement parts

• Easily interchangeable mirrors and accessories

• Robust design that tolerates real-world handling

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📦 Supplied Equipment

Included as standard:

• 3.5 × 40 monocular telescope

• LED illumination (arc & drum)

• Varnished wooden storage case

• Instruction manual

• Certificate of accuracy

• Adjusting wrench

Case dimensions: 165 × 330 × 280 mm (approx.)

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🔭 Optional Accessories (Sold Separately)

• 7 × 35 prism telescope

• Zero-magnification sight tube

• Slip-on rubber eyecup (ideal for glasses wearers)

• Practice bubble horizon (perfect for backyard training)

• Additional horizon mirrors (whole or split, pre-mounted)

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📐 Technical Specifications

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🎯 Ideal For

• 🌊 Offshore and blue-water sailors

• 🧭 Celestial navigation students & instructors

• ⚓ Sailing schools & maritime academies

• 📚 Navigators wanting a dependable “working” sextant

• 🎁 Serious nautical gifts with real function

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Important: This sextant is supplied to order.
Please allow up to 10 working days for delivery.

The Astra IIIB Sextant is not just popular—it is proven.
A professional navigation instrument trusted worldwide for accuracy, durability, and value.

Navigate with confidence. Learn with the world’s standard sextant.