July 1, 2021: Saturn and Mars are in opposite directions in the sky. Mars sets as Saturn rises. In about a week, the two planets are visible in the sky at the same time. This event signals that the planet parade is starting to reorganize. During July, three other planet – planet oppositions occur, leading up to a challenging view of the five bright planets during mid-August.
By Jeffrey L. Hunt
Frequently, the thought of an opposition of a planet is with the sun. The three bright outer planets (BOPs) – Mars, Jupiter, and Saturn – for which this occurs is when Earth is between the planet and the sun. (Of course, all the objects that revolve around the sun farther away than Earth are in opposition with the sun).
When one of the BOPs is at opposition it appears very bright in our night sky. The planet rises in the eastern sky as the sun sets in the west. As Earth rotates, the planet appears southward around midnight. It sets in the west as the sun rises in the east.
Depending on the planet’s orbital characteristics, it is closest to our world around the time of its opposition with the sun.
During July, one planet is in opposition with another planet, occurring four times during the month. The first is the opposition of Saturn and Mars on July 1. They are in opposite directions from each other, 180° along the ecliptic – the solar system’s plane.
On July 1, Mars sets (10:23 p.m. CDT in Chicago) in the west-northwest as Saturn rises in the east-southeast (10:13 p.m. CDT). When Mars rises on July 2 as Saturn sets, the sun is in the sky. Unlike a BOP in opposition with the sun, Saturn’s setting occurs during daytime.
Begin looking for both planets in the sky simultaneously seven – fourteen days following the opposition.
The planet parade begins to regather in the evening sky.
The next planet – planet opposition occurs on July 6, when Venus and Saturn are at opposition. By mid-month, Saturn, Mars and Venus appear in the evening sky simultaneously.
Venus passes Mars on July 12. Then a Venus – Jupiter opposition occurs on July 21. Mars sets before Jupiter rises until July 29. By mid-August, four planets appear simultaneously in the sky. Mercury then zips into the western sky for a poorly placed appearance. Then around the very close conjunction of Mercury and Mars, all five could be observed simultaneously, during a challenging window.
Mars is in a slow slide into bright twilight until it reaches its solar conjunction on October 7. Mercury is low in the western sky until late September. Then it moves into the morning sky for the planet’s best morning appearance of the year during early November.
After the collection of five planets and the disappearance of Mars into bright twilight, Venus, Jupiter and Saturn appear in the evening sky until Venus disappears into bright twilight early next year.
The oppositions: July 1, Saturn – Mars; July 6, Venus – Saturn; July 21, Venus – Jupiter; July 29, Jupiter – Mars.
(Note: The naming of celestial events with the moon and planets uses the convention of naming the brighter planet first, followed by bright planet – moon, bright planet – star, moon – star.)
Articles and Summaries
- Venus as an Evening Star
- Venus Evening Star (Summary)
- Mars during 2021 (Summary)
- Planets during June 2021
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Categories: Astronomy, Sky Watching
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