2016: The Evening Sky


 

chicago_evening_2016

The chart shows the setting times of the planets visible without a telescope and stars near the solar system’s orbital plane for 2016.  Mars, Jupiter, and Saturn are also represented with their rising times during the evening.  While the chart represents the activity in the western evening sky, the three outer planets rise in the east and are display until they rise at sunset, their opposition dates.  When they rise at sunset, appear in the south at midnight and set in the west at sunrise.  The earliest event shown begins 5 hours after sunset.  The moon’s appearance for each lunar cycle begins at the bottom the chart and it is represented by circles with indicating the dates.  The three twilight lines are defined at the end of the article.

Summary

The year opens with a single planet in the evening sky, Mercury.  On January 1, it sets about 80 minutes after  the sun in the southwestern sky.  The speedy planet moves quickly between morning and evening sky.  The best evening appearance occurs during mid-April.

Venus begins an evening appearance during the second half of the year as it slowly emerges into the evening sky after superior conjunction.  It passes Mercury twice (mid-July and early August.) Venus passes Jupiter on August 27.  This is another “Epoch Conjunction” between the two planets.  They appear to nearly merge with a separation of only 7 arc-minutes!  This conjunction occurs during  twilight, but the two planets are easily seen.

Venus passes Saturn later in the year,

Notice that Mars enters the chart later in the year.  By year’s end the chart indicates that Venus and Mars are converging.  In early 2017, Venus moves to about 5 degrees of Mars but there is no conjunction.

Twilight Definitions

Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities.

Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is  12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other lighting, general outlines of ground objects may be distinguishable. During nautical twilight the illumination level is such that the horizon is still visible even on a Moonless night.

Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, light from the Sun is less than that from starlight and other natural sources. For a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible. (Source)

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