THE ASTRA IIIB SEXTANT Deluxe with Traditional Mirror


The Astra IIIB has somewhat revolutionized celestial navigation. Never before has such a high quality, accurate metal sextant been available at such a low price. Over 18,000 sextants of this model have been sold in the US alone in the past 20 years; far more than any other serious sextant. Its popularity has spread throughout the rest of the world as well, making it the the most recognized (and supported) sextant worldwide.

Its low price, excellent optics, and choice of horizon mirrors and other accessories makes it the perfect selection for beginners. Yet, we know several professional navigators who prefer the ASTRA IIIB merely because they can leave their expensive models at home without sacrificing noticeable accuracy. The Astra IIIB is made by the Changzhou Celestaire Instrument Co. in China, with whom Celestaire is joint-ventured, and it is produced in accordance with Celestaires specific quality guidelines.

Construction Details:
The frame is made from lightweight aluminum alloy which resists corrosion. Aluminum alloy is not new to sextant construction. It has long been used by many manufacturers for lightweight versions of their heavier brass or bronze sextants in order to reduce arm fatigue and unsteadiness among infrequent users. The sextant is electrically lighted by an LED on the arc and drum. The index mirror is rectangular in shape, and has the silvering applied to the front, rather than the rear surface. This is similar to the way astronomical telescopes are silvered. From an engineering standpoint, the rectangular shape allows for a better reflecting profile during high angle observations, and the front surface silvering provides better reflection brightness for all sights. From a more practical standpoint, the biggest advantage is in the durability of the silvering itself. When applied to the front surface it is easy to keep clean and free of saltwater contamination and it is further protected by a durable oxide coating. In contrast, rear silvered mirrors need resilvering more frequently if saltwater becomes trapped between the mirror and its housing, and is not faithfully rinsed out. An index mirror upgrade kit is available for older models having round, rear-silvered index mirrors. It comes mounted in a rectangular frame and has instructions for easy installation.

Celestaire is impressed with the degree to which each component of the sextant is tested. For example, each mirror and shade glass is tested for perfect flatness by the Fresnel diffraction pattern method. The sextants are assembled and tested in a clean, professional, environment. Random units have been tested by us and several professional navigators, with results that rival the most expensive German and Japanese models.

Arc -5 + 130, radius 153mm
Accuracy 20", throughout the arc
Micrometer Drum 1' scale, vernier to 0.2'
Horizon Mirror 51mm diameter
Index Mirrors 56x42mm
Shades 4 index - 3 horizon
Weight 2 lbs., 10 oz

Add to Cart:

  • Model: 0502D
  • Shipping Weight: 16lbs
  • Manufactured by: Celestaire

This product was added to our catalog on Thursday 13 October, 2005.