Skywatch Line for Monday and Tuesday, July 25th and 26th, 2016

This is the Skywatch Line for Monday and Tuesday, July 25th and 26th.

The Sun sets at 8:23 PM; night falls at 10:23. Dawn begins at 3:40 AM and ends with the Sun rising at 5:41.

The darkening sky has two planetary visitors. Venus rises very low, about 2 degrees high, in the southwestern sky. If one has an unobstructed horizon, the observer will see minus fourth magnitude Venus, almost full. Mercury, about 5 degrees above Venus, shines at minus 0.4 magnitude and appears about three-quarters illuminated. Both set by 9:21 PM.

Much easier Jupiter, in Leo, is also moderately low in the western sky. It glows at minus 1.8 magnitude. Jupiter is so low that seeing surface features becomes difficult. Jupiter sets about 10:30 PM.

Mars, in Libra, continues eastward motion and slowly closes in on Saturn. Mars appears at minus 0.9 magnitude and slowly dims and shrinks daily. Mars sets at 1:50 AM. Saturn forms the eastern end of the celestial triangle with Mars, 13 degrees west, and the bright star Antares, 6 degrees below Saturn. Saturn proceeds westward and meets up with Mars next month. Saturn, in dim Ophiuchus, glows at zero magnitude and is still a grand vision in any telescope; it sets about 2 AM.

Neptune, in Aquarius, rises before 11 PM and remains up the rest of the night. It appears at 7.8 magnitude and appears as a blue-green dot only 2.3 arc seconds in size. It is best observed at 3:30 AM. Uranus, in Pisces, is brighter, at 5.8 magnitude, and larger, at 3.6 arc seconds. Both require detailed finder charts from astronomical media, since they resemble the neighboring stars. Both remain up the rest of the night.

The Moon rises before Midnight Monday, in Pisces. It appears about 58 percent lit, Monday. Tuesday finds it Cetus, slightly dimmer and less than half illuminated. It is officially Last Quarter at 7 PM Tuesday. The Moon remains up the rest of the night and is visible during daylight.

Appropriate for the current racing season, two horses appear by midnight. The largest horse is, of course, Pegasus. The smallest is Equuleus. This dim constellation is easy to find. Pegasus flies upside down and is easily identified as a Great Square. Two thin chains sweep northward from the upper left. If one sweeps across the chains, binoculars reveal a large hazy oval; this is exposed, in telescopes, to be the Andromeda Galaxy – about two and a half million light years distant, accompanied by two smaller satellite galaxies. You can see it with the naked eye under dark rural skies. Pegasus’ neck flows from the lower right corner and angles up. Equuleus is the small angular line of stars West of the Pegasus’ nose. A globular star cluster, M 15, lies exactly halfway between Pegasus’ nose and Equuleus. This too is easily seen in binoculars.

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