Image credit & copyright: NASA/ESA Hubble Space Telescope taken on May 12, 2016.
Some of you I know have already been enjoying the view every morning as the Mars, Saturn and Antares trio have been rising before the Sun in close formation recently and what a sight it is. If you haven’t seen this yet I would urge you to do so because it’s a fantastic view that’s peaking right now. In fact, Mars is nearing opposition which will take place on this Sunday, May 22, 2016.
Opposition, in planetary terms is when a superior (outer) planet, dwarf planet or asteroid reaches a point almost exactly opposite the Sun from Earth’s vantage point so we see its full, bright disk. Another way to say it is Earth is directly between the Sun and that object. Opposition also places the object near its closest point that it can get to the Earth in its orbit (perigee). Technically opposition and actual perigee points usually differ from a few hours to a few weeks but again, its close enough for what we’re doing.
Mars reaches opposition every 26 months and this opposition will bring Mars to a mere 0.5 AU (AU being 1 Earth/Sun distance or about 93 million mi.) from Earth, the last Mars opposition which took place on April 8, 2014 was at a distance of 0.62 AU and the next opposition on July 27, 2018 will be at an even closer 0.38 AU! That’s the closest it will get until 2035 (great time to send humans) so take advantage of these next few oppositions. The closest Mars opposition in recent history was on August 27, 2003 where it was 0.37 AU from Earth. It hadn’t been that close for 60,000 years and won’t be that close again until August 28, 2287 so start eating healthy and working out.
It’s important to note that Mars is small and without a decent aperture telescope it will still pretty much appear as an orange ball and seeing any detail will be tough. To put it a different way let’s take a look at how most of us amateur astronomers judge these things; by their apparent properties. In short “apparent” is how objects look on the sky, to us here on the ground. For example, the Sun and Moon both have the same apparent dimensions (also known as angular diameter) at a half-degree on the sky when in reality the Sun is 400 times the diameter of the Moon. At opposition, Mars’s apparent diameter on the night sky will reach about 18.5” arcseconds. For perspective, Jupiter right now is an apparent size of 41.7” arcseconds so you can easily see that even though Mars will be at its best, it’s still a very small target to see detail.
You may be asking why opposition doesn’t also equal perigee or that body’s closest point to Earth. Well, as I said above it pretty much does but you have to remember that orbits are elliptical and two orbits don’t mirror each other so even though a planet may be directly opposite the Sun from us, the elliptical nature of orbits usually means the actual closest points tend to be slightly before or after opposition.
You may also be asking why oppositions have different distances opposition to opposition. The reason is the same as the above paragraph, the orbits of the planets aren’t actually circular they’re slightly elliptical. For example, Mars reaches perigee (closest point to Earth) around the same time it reaches perihelion (closest point to the Sun) every 15 to 17 years. So if Mars reaches opposition at its furthest point from the Sun it will be a more distant opposition than if it were at its closest point to the Sun. Imagine if we happen to be at aphelion (Earth’s farthest point from the Sun) at the same time say, Mars is at its perihelion? What a great sight that would be!
Below I’ve listed the important data as well as a bunch of my favorite links to use and abuse as they’re invaluable assets for sky watching and as always, if you have questions, please ask! I don’t include Planet, Sun or Moon rise and set times because that’s different depending on where exactly you are but the resources are in the links below.
MARS OPPOSITION 2016:
DATE: Sunday, May 22, 2016.
TIME: 11:10 UTC (07:10 EDT).
WHERE IS IT? (Constellation): Scorpius the Scorpion.
WHERE IS IT? (Exact RA/Dec J2000): RA 15h 56m 40s / Dec -21°36′ 10”.
APPARENT MAGNITUDE: A very bright -2.0.
APPARENT DIMENSIONS (Angular Size): 18.5” arcseconds.
ALTITUDE: About 35 degrees for mid-northern latitudes.
DISTANCE FROM EARTH: 0.5 AU (An AU is 1 Earth/Sun distance or 93 million miles).
OPPOSITION FREQUENCY: Every 26 months.
MOON PHASE: Full, 16 days old.
MOON PROXIMITY: Extremely close.
PERIGEE: May 30, 2016.
Naked Eye Planets Mars Oppositions: http://www.nakedeyeplanets.com/mars-oppositions.htm
Dominic Ford’s “In-The-Sky” page for this event: https://in-the-sky.org/news.php?id=20160522_13_100
In-The-Sky’s, Solar System Body Finder Chart: https://in-the-sky.org/findercharts.php
U.S. Naval Observatory (USNO) Solar System Body Dimensions: http://aa.usno.navy.mil/data/docs/diskmap.php
U.S. Naval Observatory (USNO) Rise & Set Times: http://aa.usno.navy.mil/data/docs/mrst.php
Courtney Seligman’s (cseligman) Mars Oppositions page: http://cseligman.com/text/planets/marsoppositions.htm
The Sky Live page for Mars: http://theskylive.com/mars-info
The Sky Live, Mars Tracker: http://theskylive.com/mars-tracker
Chris Peat’s “Heavens-Above” Planet Summary: http://heavens-above.com/PlanetSummary.aspx
The Planets Today (current solar system configuration): http://www.theplanetstoday.com/
Time and Date Sunrise and Sunset calculator: http://www.timeanddate.com/sun/
Time and Date Moonrise and Moonset calculator: http://www.timeanddate.com/moon/