Oppositions

A planet or asteroid is said to be at opposition when it is on the opposite side of the sky as the sun. The planet is up all night at this time. It appears biggest in telescopes because Earth is closest to it at this time. At opposition, the planet may be slightly less than 180° from the sun. That's because it may be a little above or below the ecliptic. The ecliptic is the line on which the sun travels as Earth orbits it.

Opposition for any given planet or asteroid doesn't occur at the same time every year, because as Earth orbits the sun so does the other object. And since none of the planets have perfectly circular orbits, the distance at opposition also varies from event to event.

Only objects farther from the sun than Earth can reach opposition. Mercury and Venus reach points of greatest elongation far less than 180°

Here are the dates and times (in Universal Time) for the planets Mars through Neptune during the 2010 decade along with their distances. Distances are given in astronomical units (the average Earth-Sun distance), kilometers, and miles.

Mars January 29, 2010 - 19:30 at 0.664 AU (99.3 million km or 61.7 million miles)
March 3, 2012 - 20:47 at 0.674 AU (101 million km or 62.7 million miles)
April 8, 2014 - 22:03 at 0.621 AU (92.9 million km or 57.7 million miles)
May 22, 2016 - 10:25 at 0.509 AU (76.1 million km or 47.3 million miles)
July 27, 2018 - 02:30 at 0.386 AU (57.7 million km or 35.9 million miles)

Jupiter September 21, 2010 - 11:35 at 3.954 AU (591.5 million km or 367.5 million miles)
October 29, 2011 - 01:45 at 3.970 AU (593.9 million km or 369 million miles)
December 3, 2012 - 01:47 at 4.069 AU (608.7 million km or 378.2 million miles)
January 5, 2014 - 21:11 at 4.211 AU (630 million km or 391.4 million miles)
February 6, 2015 - 18:17 at 4.346 AU (650.2 million km or 404 million miles)
March 8, 2016 - 10:56 at 4.435 AU (663.5 million km or 412.3 million miles)
April 7, 2017 - 21:38 at 4.455 AU (666.5 million km or 414.1 million miles)
May 9, 2018 - 00:41 at 4.400 AU (658.2 million km or 409 million miles)
June 10, 2019 - 15:28 at 4.284 AU (640.9 million km or 398.2 million miles)

Saturn March 22, 2010 - 00:29 at 8.504 AU (1272 million km or 790.5 million miles)
April 3, 2011 - 23:52 at 8.614 AU (1289 million km or 800.7 million miles)
April 15, 2012 - 18:22 at 8.720 AU (1304 million km or 810.6 million miles)
April 28, 2013 - 08:22 at 8.816 AU (1319 million km or 819.5 million miles)
May 10, 2014 - 18:30 at 8.900 AU (1331 million km or 827.3 million miles)
May 23, 2015 - 01:38 at 8.967 AU (1341 million km or 833.5 million miles)
June 3, 2016 - 06:41 at 9.015 AU (1349 million km or 838 million miles)
June 15, 2017 - 10:21 at 9.043 AU (1353 million km or 840.6 million miles)
June 27, 2018 - 13:27 at 9.049 AU (1354 million km or 841.2 million miles)
July 9, 2019 - 17:08 at 9.033 AU (1351 million km or 839.7 million miles)

Uranus September 21, 2010 - 16:59 at 19.088 AU (2855.5 million km or 1774.3 million miles)
September 26, 2011 - 00:14 at 19.078 AU (2854 million km or 1773.4 million miles)
September 29, 2012 - 07:15 at 19.061 AU (2851.5 million km or 1771.8 million miles)
October 3, 2013 - 14:11 at 19.040 AU (2848.3 million km or 1769.9 million miles)
October 7, 2014 - 20:58 at 19.014 AU (2844.5 million km or 1767.5 million miles)
October 12, 2015 - 03:49 at 18.984 AU (2840 million km or 1764.7 million miles)
October 15, 2016 - 10:44 at 18.951 AU (2835 million km or 1761.6 million miles)
October 19, 2017 - 17:34 at 18.915 AU (2829.6 million km or 1758.3 million miles)
October 24, 2018 - 00:46 at 18.875 AU (2823.7 million km or 1754.5 million miles)
October 28, 2019 - 08:15 at 18.833 AU (2817.4 million km or 1750.6 million miles)

Neptune August 20, 2010 - 10:06 at 29.006 AU (4339.2 million km or 2696.3 million miles)
August 22, 2011 - 23:24 at 28.995 AU (4337.6 million km or 2695.3 million miles)
August 24, 2012 - 12:32 at 28.984 AU (4335.9 million km or 2694.2 million miles)
August 27, 2013 - 01:43 at 28.973 AU (4334.3 million km or 2693.2 million miles)
August 29, 2014 - 14:33 at 28.963 AU (4332.8 million km or 2692.3 million miles)
September 1, 2015 - 03:36 at 28.953 AU (4331.3 million km or 2691.3 million miles)
September 2, 2016 - 16:36 at 28.946 AU (4330.3 million km or 2690.7 million miles)
September 5, 2017 - 05:27 at 28.939 AU (4329.2 million km or 2690 million miles)
September 7, 2018 - 18:27 at 28.933 AU (4328.3 million km or 2689.5 million miles)
September 10, 2019 - 07:23 at 28.928 AU (4327.6 million km or 2689 million miles)