by Jeffrey L. Hunt
The chart above, calculated from data from the U.S. Naval Observatory for Chicago, Illinois, shows the difference in rising time between Venus (green line) and the sun during the planet’s morning apparition. The three phases of twilight are included. Other bright stars that appear near the ecliptic are graphed as well as the time differences for the other bright planets. The moon’s rising time differences are displayed as circles. All this activity occurs in the eastern sky. The setting time differences (circles) for Jupiter, Saturn, and Mars are included as well. When the planets set in the west at sunrise, they are at opposition. For Jupiter, this occurs on July 14, 2020, followed by Saturn six days later. Mars’ opposition occurs on October 13, 2020. Every date after their opposition dates the planets set in the west before sunrise until they disappear from the top of the chart, setting over 5 hours before sunrise.
When the Venus line crosses the lines of other objects, they rise at the same time. A conjunction occurs near the intersection. It is important to note that because two objects rise at the same time, they may not appear close together in the sky. While Antares, Aldebaran, and Pollux generally lie near the ecliptic, the conjunctions with planets can have gaps of several degrees. As an extreme example, Sirius and Venus rise within a few minutes of each other on September 15, 2020. Venus rises in the east-northeast and Sirius in the east-southeast. They are over 40° apart. Objects are selected for the graph that appear near the ecliptic. For this reason, Sirius is not graphed.
If a moon circle is displayed near one of the rising lines, a conjunction may occur on that date, or on the day before or day after the date the moon and that object are plotted together. Notes are on the graph to indicate the dates when the moon is near Venus, along with their angular separations. The closest grouping occurs on June 19, 2020, when they are separated by 1.0°. While they are low in the sky, the scene is that of a classic artist’s celestial painting. Other groupings occur when the moon is higher in a darker sky. Details are in the daily notes.
With the focus on Venus, conjunctions with stars are indicated with boxes on the Venus curve. The greatest morning (west) elongations of Venus and Mercury are indicated with yellow triangles and “GE” labels.
The midpoint (July 8) of the interval of Venus’ greatest brightness is marked with a yellow diamond shape and the “GB” label. While not a formal designation, the change in apparent magnitude is hardly distinguishable to the unaided eye during this period that runs from June 29 through July 17. The midpoint is near the date of the planet’s greatest illuminated extent (July 10). This occurs when the illuminated portion of the planet covers the largest area of the sky. This means the planet is very bright, at its theoretical maximum brightness. For a technical explanation, see https:/tinyurl.com/venus-greatest-illuminated.
For more about Venus as a Morning Star 2020-2021.