Mars will exceed 24-arc-sec in diameter between July 23rd and August 9th, 2018. This is 97 percent of the maximum of 25.13-arc-sec diameter attained during the last of the ‘favorable’ apparitions, which occurred in 2003.Association of Lunar and Planetary Observers
At the end of this month, on July 27th, Mars will be in opposition and reach its greatest angular diameter — 24.3-arc-seconds — for the year. This is the best opposition since 2003. It’ll be greater than 21-arc-seconds tonight and well worth observing. For an explanation as to why some oppositions are better, what to expect from this year’s event, and accessories to better view and image Mars, see our blog post: Mars Opposition 2018 Preview.
Mars will be growing rapidly in apparent diameter in the weeks up to the big Mars Opposition on July 27, 2018. With Mars peaking this summer, Tele Vue Optics is making it easier to take a peek with rebates on 13mm and shorter focal length eyepieces for customers in the USA, US Territories, and those with APO/FPO Addresses.
It’s important to understand that Mars Opposition is not a one-day event. From June 18th to September 15th – basically the whole summer – the angular diameter of the planet will match or exceed the 18.38-arc-sec diameter it achieved at the 2016 Opposition.
Furthermore, the Association of Lunar and Planetary Observers notes that “Mars will exceed 24-arc-sec in diameter between July 23rd and August 9th, 2018. This is 97 percent of the maximum of 25.13-arc-sec diameter attained during the last of the ‘favorable’ apparitions, which occurred in 2003.” In fact, due to orbital eccentricity, Mars and Earth continue to draw ever-closer after this opposition, with the distance shrinking by another 111,000-miles / 179,000-km when they are nearest on July 31, 2018!
About every 26-months, Earth and Mars get a good look at each other as their orbits cause them to line up together on the same side of the Sun. At the instant that Earth is between Mars and the Sun we have “Mars Opposition” — Mars is opposite the Sun in Earth’s sky. Mars is closest to Earth around this time and amateur astronomers make a point of observing it.