... At the summer date, at the chosen time, the Sun is high in the sky. at point S, while at the winter date, it is low in the sky, at point W. The shadow of the gnomon is always in the plane containing the Sun and the points A and B. If AB is a thin line, the shadow will also be a thin line, the intersection of this plane with the base of the sundial. ... Summer or winter, the shadow is therefore along the same line, the intersection of the above plane and the base of the sundial. ...

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... Each day we feature a different image or photograph of our fascinating universe, along with a brief explanation written by a professional astronomer. August 26, 1995 . Two Tails of Comet West . ... Explanation: Here Comet West is seen showing two enormous tails that wrap around the sky. ... Chronological Archive | Subject Sorted Archive | ... Astronomy Picture of the Day (TM) is created and copyrighted in 1995 by Robert Nemiroff and Jerry Bonnell who are solely responsible for its content. ...

... These experiments followed the movement of the subreflector as the antenna tipped from the zenith to the horizon. We find, relative to a coordinate frame attached to the receiver platform : ffl The axial movement (axial defocussing) is 0.7mm ffl The lateral movement, (in the focal plane, normal to the elevation axis) is 2mm, and no move­ ment parallel to the elevation axis. ffl A rotation of 3 arcminutes about the elevation axis. ... This gave the rotation of the subreflector, shown in figure 3. ...

... And night unto night revealeth knowledge; . ... They noticed that the stars in that celestial canopy, the "firmament," maintained fixed patterns-- constellations --night after night. ... Like a globe, the sphere of the sky has two points around which it turns, points that mark its axis --the poles of the celestial sphere. ... The axis around which the Earth spins points in a certain direction in the sky, and that is also the direction of the pole star (or more accurately, the northern celestial pole...

... connection points . ... The point P3 is the connection between the horizontal and vertical actuators and is the axis of rotation for the tail gunner motion. processing: survey/020204/reduc We can compute P3,P5 (the moveable points) in dome centerline coordinates if we have the actuator distances and we know the positions of the above connection points in dome centerline coordinates for a given position of the tertiary (say the nominal focus position).(see actuator distances to dome centerline ). ...

... In astronomical parlance, an interior planet is at superior conjunction when it is located on the opposite side of the Sun from Earth. ... Water Found in Space Rock . ... HCG 87: A Small Group of Galaxies . ... The Water Vapor Channel . ... It's only Planet Earth, of course ... as seen on the Water Vapor Channel. ... Eclipse Over The Mountain . ... Undaunted by world wide anticipation of the August 11 total solar eclipse, the moon also performed a lunar eclipse just two weeks earlier, on July 28. ...

Next: Star Formation Rate and Up: No Title Previous: Calculation of Evolutionary Tracks . To start calculations, we choose the distributions of the initial binary parameters: the mass of the primary ZAMS component, , binary mass ratio, , orbital separation a . ... whereas the mass ratio distribution is not. ... The zero assumption often made is that the mass ratio distribution has a flat shape, that is binaries with a high mass ratio occur as frequently as those with equal masses. ...

... While the three NICMOS cameras are no longer at a common focus, under many circumstances it is desirable to obtain data simultaneously in multiple cameras. ... From the ground, the infrared background is affected by telluric absorption and emission which limits the depth of astronomical imaging. ... Now, the dominant sources of background radiation will be the zodiacal light at short wavelengths and the thermal background emission from the telescope at long wavelengths. ...

IBIS Data Analysis . ... IBIS . ... Flat Fielding - Introduction . The images obtained by IBIS will have intensity variations across the field of view that are not due to the solar image, but rather caused by instrumental effects that alter the observed intensity in each point of the field of view. ... IBIS Flat Fielding Techniques . ... Therefore, it is desirable to obtain the flat field measurements center on a point along the equator near the heliographic center of the solar disk. ...

... If the Earth is round, the Sun must be north of the equator in northern summer, and south of the equator in northern winter. ... From the Earth's perspective, the Sun is spiraling from north to south and back again along the ecliptic (see figure 7 ). ... The round Earth, at the summer solstice. ... If the rotation axis of the Earth is tilted with respect to its orbit, the equator bobs back and forth, causing the Sun to be north for half the year, and south for the other half (see figure 9 ). ...