Abstract
MERCURY A MORNING STAR—Mercury will reach its greatest westerly elongation on July 21 (distance from the sun 20°). During the last ten days of July the planet may possibly be glimpsed near the west-north-west horizon at about 3h 30m A.M. The elongation is not a very favourable one, as it does not allow Mercury to remain above the horizon longer than about 1h 35m before the sun rises. The twilight is always very strong at this season of the year, but the planet may be glimpsed on very clear mornings of the period stated by anyone who has fairly good sight and looks in the correct direction. On July 29 the planet's brightness will be equal to - 0.5 mag., which is about the same as Procyon, though not so great as that of Vega, Arcturus, or Capella. The disc of Mercury is so small that its light usually fluctuates or ‘twinkles’ like a fixed star, and this effect is enhanced by the unsteady vapours floating about at the low altitude in which the planet is always observed.
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Our Astronomical Column. Nature 122, 108 (1928). https://doi.org/10.1038/122108a0
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DOI: https://doi.org/10.1038/122108a0
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