TO-MORROW’S ECLIPSE

Dominion, Volume 23, Issue 169, 12 April 1930, Page 11

TO-MORROW’S ECLIPSE

MOON PARTLY OBSCURED VISIBLE BEFORE 6 P.M. To-morrow evening’s eclipse of the moon will be well on Its way when people In Wellington first have an opportunity of seeing It. The moon will rise soon after 5 p.m., and at that time the earth’s shadow will be accounting for a small piece of the moon at the top of its disc. This, as a matter of fact, will be practically as much as anyone in the world will see of it, as the eclipse is only a small one. If a sufficiently elevated position can be found, the phenomena at moonrise will be worth watching. The refraction of the atmosphere has the effect of making a heavenly body appear just above the horizon, when it is in reality just below. For this reason, under to-morrow’s conditions, the sun and the eclipsed moon will both be above the horizon for some time, as far as observers in Wellington are concerned. If there were no hills this remarkable occurrence would be visible by everyone, but even with the disadvantage mentioned, the conditions of the eclipse are very interesting. The black shadow will gradually clear off the moon as it rises from the horizon, until at a few minutes past 6 p.m. the moon will be entirely clear of it. On this account, the eclipse will be easily missed.

The accompanying sketch shows the position of the moon and earth’s shadow at 5.30 p.m., one or two minutes after the middle of the eclipse. The earth’s shadow has its centre at O, and the moon has its centre at C. It can be seen that a small section of the moon will be obscured. Relatively to the shadow of the earth, the moon is travelling along the line A B C D at the rate of the width of this column in approximately 5] hours. The circle at P shows the limit of th* 1 penumbra. It has its centre at O, and the ring enclosed between this circle and the shadow circle marks the penumbra, which is a region where some, but not all, of the sun’s surface can be seen. When in this circle, the brilliancy of any part of the moon suffers a decline. The positionsA, B and D are the positions where the moon enters the penumbra, enters the umbra, and leaves the penumbra. The times at which these happenings take place are 3.13 p.m.. 4.51 p.m., and 7.54 p.m. When the centre of the moon crosses the line drawn straight down from O, it is said to be in opposition to the sun, because the line runs north and south on the celestial sphere. The point is indicated by X, and the centre of the moon is at this position at 4.35 p.m. If the sketch is turned to the right so that the bottom right hand corner is directly below O, it will indicate roughly the disposition of the moon shortly after It rises to-morrow evening.