Davis Instruments Artificial Horizon - Celestial Navigation Practice Kit for Any Location - Includes 2 Sun Shades, Lid and Full Directions - Great for Beginners or Experienced Navigators

Summing up - this clever and well-made bit of kit lets you take sights from your backyard or building rooftop day or night using a completely still pool of water protected from the elements. Whatever your desire to measure the altitude of celestial bodies, whether astronomy or to do practice shots for celestial navigation, this tool will make it easier and more accurate. The artificial horizon comes with two clear glass panes, two colored ones for taking sun sights, and two triangular supports. All pieces fit neatly inside a 4x6x1” water reservoir which doubles as a sturdy storage box. It is a breeze to set up. The panes shield the water against wind, creating a completely still image. This is the central advantage of this artificial horizon over a bucket or deep dish. Altitudes below 10 degrees get challenging on account of the reservoir's rim. High altitudes are limited to half your sextant’s arc, 65 degrees for most but 50 for the Davis Mark 3. And do not expect to take sights other than the Sun, its planets or the brightest stars. Otherwise the reflection off the water will be too weak. Remember to adjust your sight for index error and then divide by two because the reflection doubles the altitude. Then apply all other corrections except dip and height of eye. A winning tool to elevate your sight practice.

Since it comes with two shades, this is much better than just water in a bucket, because you will not accidentally get blinded by a solar reflection. Compare your readings against a good astronomy program like Starry Night Professional - or try the free program Stellarium - to find out how accurate you can get. Or just plot your data on a piece of paper and check if they look consistent or not. For celestial bodies at most altitudes, remember to correct for atmospheric refraction, which is a hefty 34 (!) minutes of arc exactly on the horizon. Even at 45 degrees above the horizon, the atmospheric refraction is 1 minute of arc and therefore should not be ignored. For accurate sights, even small errors need to be corrected for! When using the artificial horizon on celestial bodies low in the sky, you will need to fill up the water level to the brim. Also, in this case, keep the sextant as close as possible to the artificial horizon, or you might not find a useful reflection of the target. Repeat practice sessions as required. The artificial horizon could be used also for checking and adjusting the sextant. This method could be handy in case you don't have a real horizon or a suitably distant object available for reference. Instead of getting stuck on that important part of operating the sextant, try this: Fill up water in both the bowl and the lid and set them properly apart in order to produce two sun reflexions, one for the index mirror and one for the horizon mirror of the sextant. Engage a suitable set of shades for the index and horizon mirrors, look through the eyepiece and point the scope at the water surfaces in order to catch both reflexions. Then proceed as usual with checking or adjusting index error. Pro: Pointing the scope downwards is more comfortable, particularly on extended practice sessions. Cons: 1. Outdoor use is practical only if the provided glasses - as well as additional covering - are used to protect water surfaces from air currents. 2. Altitude measurement range is limited to 65 degrees at most on a regular sextant.

I've hesitated to purchase this after hearing some complaints but Davis has such a good reputation I took the leap. The artificial horizon works as advertised and easier to assemble than write this review. Nice piece of work.

Really very handy to practice with.

Artificial Horizon is a top product, already own sextant Davis Mark 25. Had a scratch on blue filter glass, notified Davis and got a replacement sent to Europe. Am very satisfied with 2 Boater and Davis!

pricey for what it is, but works well for the purpose

Great for practice, fog or obscured horizon...has lots of filters for every condition...will not work with your celestial overhead or at a high angle.

The product is delivered in a box without any instructions on use or even assembly, not even an website to refer. Another disappointment about Davis products.

Oggetto perfetto spedizione veloce

組み立て式の人工水平線です。蓋を開けて中身を取り出したら水を入れ(光を反射することができば、海水・真水どちらでもOK)、三角形の部品2つを箱の長辺に差し込み、付属のガラス板又は色付きアクリル板をはめ込むだけです。 水平線・地平線が見えない陸上で、太陽または月(半月以上から満月に近い時)を利用した観測に使っています。 しかし欠点が2つあります。第1点、強風のときは水面が揺れます。わずかな隙間から風が入ることがあります(セロテープ等で「目張り」をすれば隙間風が入りません)。2点目、気温と水温差等から、水蒸気が発生してガラスの内側が曇ることがあります。こうなるとガラス板の表裏をひっくり返して結露を拭きとるか、くもり止め等の表面処置をする必要があります。いずれも手早く計測したいときの障害になります。(太陽は刻々と動きます。六分儀をお使いの方ならおわかりですよね。) 正直に申し上げて、Hou much?Too much. 高過ぎます。この人工水平線の原理は単純な(水平な面を使い、反射した観測対象をみる。角度は2で割る)ものなので、材料が揃えられ、加工できるのであれば自作するのも一手です。(評価を一部修正しました。鏡を使う方法もありますがお薦めできません。鏡を水平に正しく置く必要があるため手間がかかります。また鏡の材質によっては太陽や月が二重に映ることがあるため、間違いの元になります。)

Ideal para practicar con el sextante y poder calcular la altura de los astros en casa o con condiciones meteorológicas adversas.

The AH works exactly as expected. It nicely collapses into its 'water tank' and fits conveniently into my sextant case. Comes with a helpful instruction pamphlet.

good