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The night sky is changing this August — here's which planets to watch
Venus dominates the evening sky while Mercury and Jupiter stage a beautiful dawn pairing you won't want to miss.
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Venus dominates the evening sky throughout August, but early risers have a special treat too, as Mercury and Jupiter draw together in a beautiful dawn conjunction around mid-month.
From our vantage point on Earth, Venus reaches the end of its tether to the sun on the evening of Aug. 15, when it is at greatest elongation 46 degrees to the east of the sun. And yet, paradoxically, instead of appearing high up in the west, Venus is getting noticeably lower to the west-southwest horizon as the month progresses. This is because its declination in the sky is taking it well to the south of the sun. In fact, Venus's greatest elongation coincides with the time that it sets right at the end of evening twilight.
During the second half of August, into September, Venus will no longer be setting in a dark sky, but rather in a progressively brighter twilight sky. This is all due to its increasing southerly declination and the fact that the ecliptic — the apparent path of the sun, moon and planets through the zodiacal constellations — appears to slope closer to the western horizon at sunset during late summer and early fall.
The planet best positioned for telescopic observation this month is the "Lord of the Rings," Saturn, which comes up during late evening and is in a commanding position, well up in the south-southeast at the break of dawn.
Mars becomes evident a few hours before sunrise. During August, Earth approaches it at an average daily rate of 425,800 miles (685,100 kilometers). Still, even at month's end, Mars will be 172.2 million miles (277.1 million km) away, so while it continues to brighten, that process will still be quite slow.
Mercury and Jupiter are morning objects. Mercury will be evident during the first half of August, low in the east-northeast within about an hour of sunrise. It will be joined at midmonth by Jupiter as that big world emerges into view out of the glare of the rising sun.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm's length measures roughly 10 degrees. Here, we present a schedule below which provides some of the best planet viewing times while directing you as to where to look to see them
Mercury reaches greatest elongation from the Sun (19 degrees) on the morning of Aug. 2; it should be an obvious, +0.2-magnitude point low in the east-northeast if you look 50 minutes before sunrise. About a week later, look for Mercury very low in the east-northeast about an hour before sunrise. This small fleet world gets lower each dawn in early August, but it also rapidly brightens, from magnitude -0.7 on Aug. 9 to -1.3 (a trifle fainter than the brightest star, Sirius) by Aug. 16.