Image credit & copyright: NASA/JPL/USGS of Mars’s Schiaparelli Crater (front & center) by the Viking 1 Orbiter.
If you’re a fan of the night sky, you’ve been noticing the trio of Jupiter, Saturn and Mars rising one at a time in the East as it’s been quite a treat for the past few months. If you haven’t seen this yet I would urge you to do so because it’s a fantastic view that’s at its peak right now. Jupiter reached opposition back on May 8. Saturn reached opposition on June 27 and on Friday, July 27, 2018 Mars will attain its closest opposition since August 27, 2003 (which was its closest opposition in 60,000 years) and will be its closest until September 15, 2035 though unless you’re a planetary imager the exact date and time of opposition doesn’t really matter.
Mars reaches opposition about every 2 years (26 months, or 113 weeks or 791 days) and in addition to that, every 15 or 17 years opposition happens within a few weeks of Mars perihelion or Mars closest point to the Sun in its orbit which means its closer than a normal opposition. This opposition will bring Mars to within 44 million mi. (70.8 million km) from Earth. That’s not quite as close as the 2003 opposition but it’s the closest one since then. And if you’re wondering, that 2003 opposition distance of 34.6 million mi. (55.8 million km) will stand until August 28, 2287. To help paint a picture of the vast distances in our solar system, when Mars is at its furthest point from Earth (known as conjunction) on the opposite side of the Sun its roughly 2.65 AU (250 million mi. or 401 million km) from Earth.
NOTE: Please don’t believe or share any ridiculous hoaxes in regard to the opposition of Mars. Even at its closest for example, it will be 24.4” arcseconds in diameter on our sky which is still very small. Jupiter for example is 44” arcseconds at opposition and the Sun and Full Moon is about 1,800” arcseconds. On the night sky it’s certainly brighter than usual but through a telescope you still see some dark regions and some polar caps mixed in with the red that’s about it.
NOTE (Take 2): The same night that Mars reaches opposition, we (some of us) will experience a total lunar eclipse. In fact this event will be the longest total lunar eclipse of this century, so if you have an opportunity to experience it, please do. My post on the event will be forthcoming.
What is Opposition?:
Opposition, in planetary terms is when a superior (outer) planet, dwarf planet or planetary body 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 positioned directly between the Sun and that object. This occurs because as the outer planets orbit more slowly than the inner planets so every so often we come up on the inside like turn 1 at Laguna Seca, make the pass and we’re on our way until next time. Though Mercury and Venus can never reach opposition as seen from Earth; Earth reaches opposition as seen from them. Opposition also places the object near its closest point that it can get to the Earth in its orbit (perigee). Technically opposition and the actual closest point usually differ from a few hours to a few weeks.
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 no two orbits mirror each other, so even though a planet may be directly opposite the Sun from us, the elliptical nature of orbits usually means that the actual closest point tend to be slightly before or after opposition.
Why oppositions have different distances from 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 opposition around the same time it reaches perihelion (closest point to the Sun) every 15 to 17 years so when that happens opposition is closer. Conversely, 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.
Also, during the immediate hours of opposition look for a phenomenon known as the Seeliger Effect; also known as Opposition Surge, Opposition Effect or Opposition Spike. This is a sudden brightening of the planet (especially Saturn and the Moon) right before through right after opposition. The main culprit for this phenomenon seems to be coherent backscattering and shadow hiding. To use the Moon as an example of shadow hiding; just hours before full moon, the suns light is hitting the lunar surface squarely and almost all major shadows on the lunar surface from our vantage point are gone. When this occurs the Moon can brighten by about 40 percent and usually lasts until a few hours after full phase. When this happens during an opposition of Saturn for example, the rings actually become brighter than the planet itself for those few hours.
Mars Basic Data:
Name: Mars, the Roman God of War and the Red Planet
What is it?: 4th planet from the Sun, 4th and final terrestrial planet
Size (diameter): 4, 212 mi. (6,778.5 km) or roughly half the size of Earth
Size (mass): 6.42 X 1023 kg or about 10 times less than Earth
Orbital Period (a Martian year): 1.88 Earth years or 686.97 Earth days
Rotational Period (Sol or Martian day): 1.02 Earth days or 24h 37m 22s
Satellites (moons): 2; Phobos and Deimos
Discovery: Unknown; pre-historic
Mars Opposition 2018 Data:
Date of Opposition: Friday, July 27, 2018
Time of Opposition: 01:07 EDT (05:07 UTC)
Date of Closest Point to Earth: Tuesday, July 31, 2018
Time of Closest Point to Earth: 03:50 EDT (07:50 UTC)
Where is it? (constellation): Capricornus
Where is it? (exact RA/Dec J2000): RA 20h 31m 30s / Dec -25d 33’ 15”
Apparent Magnitude: a very bright -2.8
Apparent Size (Angular Size): 24.4” arcseconds and 100% illuminated. For perspective Jupiter is around 44” arcseconds at opposition.
Altitude: It will reach about 22 degrees in altitude
Distance from Earth: 0.39 AU (44 million mi. or 70.8 million km)
Opposition Frequency: just over 2 Earth years (26 months, or 113 weeks or 791 days)
Moon Phase: 14 day old, waxing gibbous, 99% illuminated or basically full
Moon Location (constellation): Capricornus, same as Mars which will impact opposition greatly
Current Visiting Spacecraft: Many
Former Visiting Spacecraft: Many
Naked Eye Planets Mars Finder Chart: http://www.nakedeyeplanets.com/mars.htm
Dominic Ford’s “In-The-Sky” page for this event: https://in-the-sky.org/news.php?id=20180727_12_100
In-The-Sky’s, Solar System Body Finder Chart: https://in-the-sky.org/findercharts.php?objtxt=mars&year=2018&duration=7
The Sky Live page for Mars: https://theskylive.com/mars-info
The Sky Live, Mars Tracker: https://theskylive.com/mars-tracker
The Sky Live, Mars Planetarium: https://theskylive.com/planetarium?obj=mars
The Sky Live, Mars Rise & Set Times: https://theskylive.com/mars-info#riseset
Chris Peat’s “Heavens-Above” Planet Summary: https://www.heavens-above.com/PlanetSummary.aspx?lat=0&lng=0&loc=Unspecified&alt=0&tz=UCT
U.S. Naval Observatory Planet Rise and Set Times: http://aa.usno.navy.mil/data/docs/mrst.php
Time and Date Sunrise and Sunset calculator: http://www.timeanddate.com/sun/
Time and Date Moonrise and Moonset calculator: http://www.timeanddate.com/moon/
Time and Date Lunar Calendar: https://www.timeanddate.com/moon/phases/
Moon Calendar: https://www.calendar-12.com/moon_calendar/2018/june
Moon Giant Moon Phase: https://www.moongiant.com/phase/06/19/2018
Heavens-Above Moon Data: http://www.heavens-above.com/moon.aspx?alt=0&lat=0&lng=0&loc=Unspecified&tz=CET
The Planets Today (current solar system configuration): http://www.theplanetstoday.com/
NASA JPL Small Body Database: https://ssd.jpl.nasa.gov/sbdb.cgi#top