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RADIO AGE for October, 1927
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| iQurrent ^cience |
Venus Now Visible in Daylight!
By JAMES STOKLEY
Science Service Staff Writer (Copyright 1927 by Science Service, Inc.)
LOOK for Venus in the daytime! . Ordinarily, the only astronomical * body that we are privileged to observe during daylight is the nearest of all the stars, the sun. Sometimes, when the moon is near first or last quarter we see it, in the former case in the afternoon, in the latter in the morning.
But to these two this month is added the planet Venus. Brightest of all the planets when it is brightest, the brilliancy of Venus this month is inferior only to the sun and moon. On October 17, it attains its greatest magnitude, and for perhaps a week or more either side of that date it will be easily visible in the morning sky, if you know where to look for it.
One way of finding it in the day time would be to get up before sunrise. Then it will be blazing in the east, and there will be no doubt of its identity. By watching it carefully until the run rises, you can easily see it in day light. But a simpler method, and one not requiring such early rising, is to use the celestial guide, the moon, on October 21.
On that date the moon and Venus are in conjunction. That means that they will be as close together as they will get on this particular circuit of the moon around its orbit. At 8 :00 a. m., eastern standard time, Venus will be about seven and a half degrees south of the moon. The moon itself is about half a degree in diameter, so if you
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find the moon in the south on the morning of the twenty-first, and then look about fifteen times its diameter to the south, there you will see Venus. On the 15th of the month, Venus will be directly south at 9:17 a. m. local time, so that will also help you to find it.
Invisible Light Shows Star in Day Of course, Venus is not a star. It is a planet. The only star that can be seen in the day, as was said before, is the sun. But
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with the aid of the photographic plate and invisible light, the stars can be photographed in full daylight.
If we were on the moon, the stars would all be visible even if the sun were above the horizon. The sky would look black, either at day or night. The reason why the earth's sky doesn't look black is because, unlike the moon, we are surrounded by a gaseous atmosphere. It is the atmosphere that reflects the short waves of light, the blue ones, and makes the sky look blue.
All day, the stars are in the sky above us, just as at night. If you look to the north, about 40 degrees above the horizon, you are looking at the pole star just as when you look at the same part of the sky at night. But in the daytime, the blue light from the sky enters your eye also. It is much more intense than the light from Polaris. The star is therefore invisible.
But the sky light consists predominantly of the short waves of light — the blue, and ultraviolet ones. The light from the star contains these rays, but it also contains a large proportion of longer waves, the wave that we call the infra red. These are invisible, because the retina of the human eye is not affected by their relatively slow vibrations, but a photographic plate can be treated so that it will record their impressions. And a dyed filter can be made that (Continued on pag'e 30)