The most convenient time for most of us to observe the planets is in the early evening. With that in mind, I’ve prepared an ephemeris of favorable evening times to view each of the eight major planets of the solar system over the next ten years. Some interesting patterns emerge, which I will comment on.
With the exception of Mercury, what follows is a range of dates when each planet is at least 10° above the horizon at the end of evening twilight at latitude 43° N. Mercury, however, is never even above the horizon at the end of evening twilight.
Altitude at 43° N |
Angle |
Twilight |
| Civil | ||
| Nautical | ||
| Astronomical |
Here is a list of dates when Mercury is highest above the western horizon at the end of evening civil twilight.
| Dates – Highest Above Evening Horizon |
||
| July 18, 2017 | ||
| November 28, 2017 | ||
| March 15, 2018 | ||
| July 2, 2018 | ||
| November 10, 2018 | ||
| February 27, 2019 | ||
| June 16, 2019 | ||
| October 20, 2019 | ||
| February 11, 2020 | ||
| May 30, 2020 | ||
| September 25, 2020 | ||
| January 25, 2021 | ||
| May 14, 2021 | ||
| September 2, 2021 | ||
| January 9, 2022 | ||
| April 28, 2022 | ||
| August 14, 2022 | ||
| December 24, 2022 | ||
| April 11, 2023 | ||
| July 28, 2023 | ||
| December 8, 2023 | ||
| March 24, 2024 | ||
| July 11, 2024 | ||
| November 20, 2024 | ||
| March 8, 2025 | ||
| June 25, 2025 | ||
| November 1, 2025 | ||
| February 20, 2026 | ||
| June 9, 2026 | ||
| October 10, 2026 | ||
| February 4, 2027 | ||
| May 24, 2027 | ||
| September 15, 2027 |
Mercury, the innermost planet, whips around the Sun every 88 days (116 days relative to the Earth—its synodic period). It never strays more than 28° from the Sun.
As you can see in the graph below, Mercury is presently highest above our evening twilight horizon when it reaches greatest eastern elongation in April, and lowest in October.
Similarly, greatest eastern elongations that occur in the constellations Taurus and Aries present Mercury highest above our evening twilight horizon, and Libra, the lowest.
Now, let us turn to Venus. Unlike Mercury, Venus usually spends a considerable number of days well above the horizon near greatest elongation. This occurs because Venus orbits further from the Sun—reaching a maximum angular separation of 47°— and because its orbital period is only 140.6 days shorter than the Earth’s: the Earth “keeps up” with Venus reasonably well as the two planets orbit the Sun (the synodic period of Venus is 583.9 days), so it is a long time between successive elongations. In the next ten years, we will see Venus high above the evening horizon during only three intervals, though for a generous three or four months each time.
| Dates – At Least 10° Above the Horizon at the End of Evening Twilight |
Constellation |
| January 2, 2020 – May 7, 2020 | |
| February 26, 2023 – June 3, 2023 | |
| November 30, 2024 – March 2, 2025 |
Now, we turn to the superior planets: Mars, Jupiter, Saturn, Uranus, and Neptune. These planets are visible in our evening sky during and after opposition.
Mars has the longest synodic period of all the major planets—780 days—so it takes an unusually long period of time for the orbital positions of Mars and the Earth to change relative to one another. Approximately every two years we get the opportunity to see Mars at least 10° above the horizon at the end of evening twilight. The number of evenings Mars is visible varies quite a lot (due to its significant orbital eccentricity): 293 evenings during the 2018 perihelic opposition of Mars, down to 145 evenings during the aphelic opposition of Mars in 2027. In any event, Mars spends a considerable amount of time during these intervals very far away from Earth and therefore disappointingly small in our telescopes. The best time to observe Mars is during the early weeks of the intervals listed below when Mars is at or near opposition.
| Dates – At Least 10° Above the Horizon at the End of Evening Twilight |
Constellation |
| July 21, 2018 – May 10, 2019 | |
| October 5, 2020 – May 27, 2021 | |
| November 28, 2022 – June 11, 2023 | |
| January 7, 2025 – June 22, 2025 | |
| February 12, 2027 – July 7, 2027 |
Jupiter orbits the Sun every 11.9 years, so it is easy to see why it is in a different constellation along the zodiac each year.
| Dates – At Least 10° Above the Horizon at the End of Evening Twilight |
Constellation |
| March 30, 2017 – July 24, 2017 | |
| April 29, 2018 – August 29, 2018 | |
| May 28, 2019 – October 19, 2019 | |
| June 26, 2020 – December 10, 2020 | |
| July 30, 2021 – January 22, 2022 | |
| September 10, 2022 – March 1, 2023 | |
| October 21, 2023 – April 5, 2024 | |
| November 28, 2024 – May 5, 2025 | |
| January 1, 2026 – May 28, 2026 | |
| February 2, 2027 – June 16, 2027 |
The orbital periods of Saturn, Uranus, and Neptune are 29.5, 84.0, and 164.8 years, respectively, so we can see why they take a successively longer amount of time to traverse their circle of constellations. You’ll also notice that the interval of visibility shifts later each year, but the shift is less with increasing orbital distance. The synodic periods of Saturn, Uranus, and Neptune are 378.1, 369.7, and 367.5 days, respectively.
| Dates – At Least 10° Above the Horizon at the End of Evening Twilight |
Constellation |
| May 31, 2017 – October 25, 2017 | Oph |
| June 10, 2018 – November 11, 2018 | Sgr |
| June 20, 2019 – November 28, 2019 | Sgr |
| June 30, 2020 – December 12, 2020 | Cap – Sgr |
| July 12, 2021 – December 27, 2021 | Cap |
| July 24, 2022 – January 9, 2023 | Cap |
| August 7, 2023 – January 23, 2024 | Aqr |
| August 21, 2024 – February 4, 2025 | Aqr |
| September 5, 2025 – February 17, 2026 | Psc |
| September 20, 2026 – March 2, 2027 | Cet – Psc |
| Dates – At Least 10° Above the Horizon at the End of Evening Twilight |
Constellation |
| October 2, 2017 – March 16, 2018 | |
| October 7, 2018 – March 20, 2019 | |
| October 12, 2019 – March 23, 2020 | |
| October 15, 2020 – March 27, 2021 | |
| October 20, 2021 – March 31, 2022 | |
| October 25, 2022 – April 4, 2023 | |
| October 30, 2023 – April 7, 2024 | |
| November 3, 2024 – April 12, 2025 | |
| November 8, 2025 – April 16, 2026 | |
| November 13, 2026 – April 20, 2027 |
| Dates – At Least 10° Above the Horizon at the End of Evening Twilight |
Constellation |
| August 13, 2017 – January 30, 2018 | |
| August 16, 2018 – February 2, 2019 | |
| August 19, 2019 – February 4, 2020 | |
| August 21, 2020 – February 6, 2021 | |
| August 24, 2021 – February 8, 2022 | |
| August 27, 2022 – February 11, 2023 | |
| August 30, 2023 – February 13, 2024 | |
| September 1, 2024 – February 15, 2025 | |
| September 4, 2025 – February 17, 2026 | |
| September 7, 2026 – February 17, 2027 |
