Visibility Of Stars Research Articles

Photogrammetric Determination of Azimuths

Precise azimuth determination to ±1.0 sec of arc over distances of 70 nm to 300 nm is very desirable where electronic survey techniques, such as HIRAN, are used. In January 1962 a series of tests designed to prove the feasibility of a technique of photographic azimuth determinations was conducted by AFCRL. A B-57 aircraft equipped with a flashing stroboscopic light was flown at night at altitudes as high as 35,000 ft between ground camera sites located at Homestead AFB, at Vero Beach, Florida, and at West End, Grand Bahama Island. Six PC-1000 cameras, two located at each site, attempted to photograph the flashing light on the aircraft against a background of stars. The PC-1000 camera has a 1000 mm focal length, and an f/5 lens. Navigation of the aircraft was accomplished by directions from a radar site in the Miami, Florida area. Results of these tests are evaluated from the standpoint of planning this kind of mission, taking into careful consideration haze conditions, star backgrounds, height above horizon for visibility of stars, maximum distances between ground sites and high intensity of the flashing lights.

Athletics in High School

Research—based on the visibility of athletic stars, on most desired achievement, on the composition of the leading crowd, on status criteria in leading-crowd membership, on popularity—demonstrates conclusively that athletics is far and away more important as a value among high school stu dents than intellectual achievement. And the school itself seems to encourage rather than to discourage this relative evaluation. There must be basic reasons for these phenomena, and these may be discerned in the functions performed by ath letics not only in the school but also in the community. Among boys, for example, it has been found that athletics has a demo cratizing effect, breaking up organization based on background and reconstituting it on the basis of common activity or achievement. Athletics serves an important function in moti vating students. It generates strong positive identification with the school ; without athletics the school would be lifeless for the student, deficient in collective goals. With athletics, it is possible for all students to identify with their school through their teams. Not only schools but whole communities depend upon the collective enthusiasm generated by their local high school athletic teams. The problem for the school is to find a way to have the functions now performed by athletic teams performed in ways more conducive to the intellectual aims of the school. Debate used to serve this function, music contests may also, as well as drama contests, and mathematics tournaments. It is possible that social and economic games played by means of complex computers may come to perform, on a far more intellectual level, the integrating function now performed almost exclusively by athletics.

Star Visibility in Daylight at High Altitudes

Star Visibility in Daylight at High Altitudes

Visibility of Stars at High Altitude in Daylight

The daylight visibility of stars has been investigated for an observer altitude of 100 000 ft, using published visual threshold data and calculated sky luminance. Venus, Jupiter, and Sirius, plus Mars at its brighter phases, can be detected with the naked eye if the observer knows where to look for them in the sky. Saturn and Canopus may be seen only under rare circumstances. A random search of the sky will reveal neither planets nor stars except possibly Venus. If a 10-power telescope of large exit pupil is used, there is a possibility of detecting an occasional star by careful search of the sky. The daytime sky will not exhibit nighttime luminance until an altitude of roughly 100 km has been reached, assuming no contribution from airglow.

The Visibility of Stars during Twilight

One of the problems in arctic navigation by astro is the twilight period. At this time, if the Moon is below the horizon, suitable objects for sextant observation are not easy to find. The difficulty is aggravated by the fact that on certain flight paths the arctic twilight may last for many hours. It must also be remembered that in these areas the behaviour of the magnetic compass and of radio aids are often unreliable and this increases the relative importance of astro-navigation. With the introduction of the periscopic sextant into air navigation it has become possible to pre-set the instrument for a given star or planet and satisfactory observations may be possible when the heavenly body is still below the level of casual perception for the unaided eye. In this connection it is necessary to know what stars are likely to be seen under twilight conditions if efficient flight-planning is to be carried out.

Daylight Visibility of Stars from a Long Shaft

Photometric measurements indicate that the presence of a long shaft causes no real change in the contrast of a star against the daytime sky. Moreover, physiological data suggest that contrary to popular opinion such a shaft may actually have an adverse effect on the daylight visibility of stars.

Effect of Spectral Class on Daylight Visibility of Stars

Effect of Spectral Class on Daylight Visibility of Stars

The Visibility of Stars and Planets During Twilight

From known values of twilight sky brightness, atmospheric transmission, and eye sensitivity, the visibility of planets and stars of magnitudes −2.5 to +4.5 is calculated for the twilight period. The results of the calculations are given in charts which can be applied to various altitudes of the observer and various conditions of observation. The twilight belt is about 1100 sea miles in width, from the sunset or sunrise meridian to full night. The charts show that under good conditions in the first 200 miles of the belt the brighter planets and Sirius become visible, in the next 200 miles first magnitude stars appear, and beyond 500 miles practically all navigational stars can be seen.

The Visibility of Stars in the Daylight Sky

From the theory of the passage of light through a telescope and into the eye, formulas are derived for the improvement in the visual threshold of a point source, as a star, viewed in a field of light, as the sky, in terms of telescope parameters, as magnification, transmission, and entrance and exit pupils. For fields of the brightness of the daylight sky the first parameter is the most important and the others are of less importance. Observations of artificial stars in the laboratory and of real stars in the daylight sky are given, which were in fair accord with the theory.Charts and tables are presented of the visual thresholds of stars in various parts of a clear daylight sky in terms of the stellar magnitude, the magnification of the telescope, the use of a polarizer, the altitude of the observer above the surface, and the altitude of the sun above the horizon.New data are given of extra-foveal thresholds of point sources in a field of brightness 360 ft.-c−2.

On the Daylight Visibility of Stars from a Mine Shaft

On the Daylight Visibility of Stars from a Mine Shaft

Visibility of Stars in Great Britain during the Solar Eclipse of 1925 January 24

Visibility of Stars in Great Britain during the Solar Eclipse of 1925 January 24

Historical Sun-Darkenings

Historical Sun-Darkenings

On the Visibility of Stars in the Pleiades to the Naked Eye

On the Visibility of Stars in the Pleiades to the Naked Eye

On the Visibility of Stars in the Pleiades to the unarmed Eye

On the Visibility of Stars in the Pleiades to the unarmed Eye

On the visibility of stars by day

"On the visibility of stars by day." The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 3(15), pp. 238–239