A new star chart that departs from the standard and customary method of illustration for such material is described in this article. It has been accepted by competent navigators as without immediate apparent fault, while its benefits are definitely of use.
A perusal of the several, and many, star charts will show that the ordinary practice is to place the north celestial point at the top edge or the center of the page with declination north and south properly shown in a manner similar to latitude north and south. In most rectangular charts right ascension is increasing to the left while in circular charts it increases clockwise.
This practice results in a confusion of direction to the new student who, having become initiated in the customary chart orientation by quadrants, must now invert his viewpoint when considering the stars, or he must hold the chart over his head for true quadrantal relationship.
Star charts should be useful in a normal reading position and still present azimuth as would be expected in all other navigational illustrations. This is accomplished simply, in this new chart, by illustrating right ascension as increasing to the right in rectangular illustrations and counterclockwise in circular layouts. There are two benefits of this method. First, when a rectangular chart is viewed in a normal reading position and facing the north, the celestial directions follow the terrestrial directions, southeast being in the "starboard quarter," southwest being in the "port quarter" locations, etc. Second, when using the chart as a base for a star-finding device (the same would be true if applied to a circular layout) the imposed horizon templates will display azimuth in true quadrantal layout.
With this thought, the writer developed a small-sized star-finder "gadget." One feature has led to another and it is hoped that the results will be useful. A list of features could be tabulated thus:
(1) The size 8" X 8" has been found to be large enough for sufficiently accurate work.
(2) The celestial sphere has been illustrated as a square, which is essentially proper when converting circular to rectangular co-ordinates. Since the angular distance in either direction of declination is, in the actual celestial sphere, equal to one half of the total amount of right ascension, the chart shows a scale measure of 90° declination equal to 12 hours right ascension. Thus a larger proportion of the illustrated constellations are less distorted in their aspect. Only those constellations containing major navigational stars are shown, the lesser groups being omitted.
(3) The Milky Way is given (as is rarely done), and will be found of use, on occasion, by a student as there are stars such as the Vega-Deneb association, or the Aldebaran-Pollux, which may be more readily found by knowing the direction they lie from the Milky Way. It is helpful to know which is on the east or west side of the Galaxy in these and other straddle pairs. A student, or a navigator who is rusty, may benefit by just such help.
(4) The setting of the horizon piece is accomplished by the choice of the nearest latitude template and placing date against local civil time. A few simple statements and an example have been found to be sufficiently dear and concise for a varied list of experimental operators, who were entirely unfamiliar with navigation and its methods, to obtain correct determinations. Below are quotations from the "Description and Instructions."
Description
This finder gives the principal navigational stars and their constellations as well as the Milky Way. The ecliptic and the tropics and circles are indicated. . . . Horizon pieces with centers for each even 100 latitude are given. Dates are arranged on the horizon pieces and are to be placed under the right-ascension scale . . . as if the scale indicated local civil time as labelled, and this will give the proper setting.
Instructions
(1) • • • •
(2) To make the date and time agree it is necessary to move the horizon piece to the left or right until the date coincides with the local civil time. [Note: Your radio time is the correct local civil time for your standard time zone meridian. For every 10 your location is away from the standard meridian your local civil time will be four (4) minutes different. If you are west of the standard meridian your local civil time will be behind the radio time. For example: if your longitude is 76° west, your local civil time will be 11:56 when you receive the noon tick from Washington, and similarly, if you are at 74° west your local civil time will be 12:04. . . .]
For most practical purposes, however, if you set your watch time against date your setting will be sufficiently correct. Remember, your watch keeps the time of your standard time zone meridian.
* * *
When the horizon piece is properly located the altitude and azimuth of the stars may be read. The location of the planets or the moon may be spotted-in on the star chart from the data given in the Nautical Almanac, or other source, for right ascension and declination: then by using the finder as for stars their altitude and azimuth may be determined.
EXAMPLES
North Latitude and West Longitude
Latitude: 22° N. (Use 20° N. template—Slide up to 22° with latitude line intersecting 22° line on star chart.)
Longitude: 79° W.79°-75° (standard meridian) =4°
Difference between watch and local civil time
4 x4 minutes =16 minutes, to subtract.
Watch time: 9:46 P.M. — 16 = 9:30 P.M., which is
9:30+12=21:30 local civil time (24-hour clock)
Date: August 30
Finder shows:
Star Antares will have:
Altitude: 19°; Azimuth: 229°
South Latitude and East Longitude
Latitude: 30° S. (Use 300 horizon piece inverted.)
Longitude 122° E.
122-120° (standard meridian) =2°
Difference between watch and local civil time 2 X4 minutes =8 minutes, to add
Watch time 4:22 A.M. +8 = 0430 local civil time (24-hour clock)
Date: December 13
Finder shows:
The horizon piece lies off the star chart in the eastern portion. Note that the left-hand margin (March 23) of the horizon piece corresponds at 22 hours. Move the star chart to the right so that 22 hours corresponds at the right-hand margin and now it will be found that the missing portion of the horizon lies under the star chart and data may be picked off as follows:
Star Spica will have:
Altitude 37'; Azimuth 80°
Star Identification
Latitude: 400 N.
Longitude: 75° W.
Watch time: 1930—same as local civil time.
Date: October 20
Altitude: 55°
Azimuth: 96°
Finder shows:
The star is Alpheratz.
Right Ascension (approximately): 0°
Declination (approximately): 28° N.
As with other "finders," the approximate meridian angle t may be found and definitely may be determined as to its east or west direction; also a fairly accurate local sidereal time may be read directly. These approximations should be of help to students in preventing major errors. Small accurate finders are almost as useful as large ones, for there is a common limitation which restricts the final usefulness of both in that completely accurate data are not obtainable from either.