Group 1 - The core event of Neptune's opposition occurs on September 23, 2023, providing the best opportunity for observation as it will be at its closest distance to Earth, with maximum brightness and apparent diameter [2][4] - Neptune's brightness during this opposition is approximately 7.7 magnitude, making it invisible to the naked eye and requiring a telescope with a minimum aperture of 10 centimeters for observation [4][6] - The opposition of Neptune happens every 367 days, with the previous one occurring on September 21, 2024, indicating a consistent cycle for astronomical events [2] Group 2 - The proximity of Saturn and Neptune during this period allows observers to use Saturn, which has a brightness of about 0.6 magnitude, as a reference point to locate Neptune in the night sky [6] - Observers are advised to utilize telescopes with larger apertures, ideally 20 centimeters or more, to potentially view Neptune's blue disk [6]

Group 1 - The core event of Neptune's opposition occurs on September 23, 2023, providing the best opportunity for observation as it will be at its closest distance to Earth, with maximum brightness and apparent diameter [2][5] - Neptune's brightness during this opposition is approximately 7.7 magnitude, making it invisible to the naked eye and requiring a telescope with an aperture of at least 10 centimeters for observation [5][7] - The opposition of Neptune happens every 367 days, with the previous one occurring on September 21, 2024, and this year's event coinciding with the autumn equinox [2][5] Group 2 - Observers are advised to use Saturn, which has a brightness of about 0.6 magnitude, as a reference point to locate Neptune in the night sky [7] - The close timing of Neptune and Saturn's oppositions, occurring just two days apart, indicates that both planets are moving in a similar manner through the constellation Pisces during late September [5][7]