... 12c. Venus transit (1) . ... Predictions for the transit give four "contact" times, at which the dark Venus disk touches the edge of the Sun's disk (marked by numbers on Figure 3 )" . First contact - Venus disk touches the Sun from the outside , on entry . Second contact - Venus disk touches the Sun from the inside , on entry . Third contact - Venus disk touches the Sun from the inside , on exit . Fourth contact - Venus disk touches the Sun from the outside , on exit . ... sin? sin? ...

Hipparchus (and possibly Aristarchus before him) also derived the Moon's distance from the duration of a lunar eclipse . Because the Earth casts a much larger shadow than the Moon, such an eclipse usually darkens the entire Moon, for several hours. ... If the Sun is assumed to be very distant, and if the Moon crosses the middle of the shadow (if not, corrections must be made), the width of the shadow is expected to be about 2r , twice the Earth's radius r . ... Last updated 4 February 1999 Moon. ...

Educator's Guide to Sunspots . ... Naked eye observations of the Sun will result in blindness. The improper use of telescopes or binoculars will cause blindness much faster. ... Binoculars, with the front of one ocular covered, can be used to project a sharp image of the Sun on to a white piece of paper. ... Aim the binoculars by tilting them up and down and back and forth until the Sun shines through. ... Sharpen the image of the Sun on the paper by using the binocular's focusing knob or lever. ...