2016, May 22: Mars at Opposition


Mars at Opposition 2016.

For more about Mars at opposition see this posting.

NASA to Provide Coverage of May 9 Mercury Transit of the Sun


Image from http://www.eclipsewise.com

To view a NASA ScienceCast video on the rare opportunity the Mercury transit poses for professional astronomers and backyard sky watchers alike, go to:


NASA is inviting media and viewers around the world to see a relatively rare celestial event, with coverage of the Monday, May 9 transit of the sun by the planet Mercury. Media may view the event at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Mercury passes between Earth and the sun only about 13 times a century, its last trek taking place in 2006. Due to its diminutive size, viewing this event safely requires a telescope or high-powered binoculars fitted with solar filters made of specially-coated glass or Mylar.

NASA is offering several avenues for the public to view the event without specialized and costly equipment, including images on NASA.gov, a one-hour NASA Television special, and social media coverage.

Mercury will appear as a small black dot as it crosses the edge of the sun and into view at 7:12 a.m. The planet will make a leisurely journey across the face of the sun, reaching mid-point at approximately 10:47 a.m., and exiting the golden disk at 2:42 p.m. The entire 7.5-hour path across the sun will be visible across the Eastern United States – with magnification and proper solar filters – while those in the West can observe the transit in progress after sunrise.

For more information about the transit on NASA’s website, click here.

For the circumstances of the transit in Chicago, see our article.

2016: Mars and Saturn, Two Oppositions


Mars and Saturn reach opposition during late Spring.  Mars (astronomically) appears opposite the sun, just after it sets, as seen from the Chicago area, on May 22.  On the previous evening, Mars appears near the moon, Saturn, and the star Antares.  On the chart above, the moon appears about six degrees to the upper left of Mars and Saturn is 12.5 degrees to the lower left of Saturn.

At opposition, a planet rises in the east at sunset, it is in the south at midnight, and sets in the west at sunrise.  It is closest to our planet and at its brightest in our sky.


Mars revolves around the sun once every 687 days, that’s nearly 1.9 times an Earth year.  To keep the arithmetic simple, Mars moves around the sun on a larger orbital path about half the speed of Earth.  So about every two years, Earth passes Mars and we see the Red Planet gleaming in the sky.  Actually opposition occurs every 778 days; that’s about every 25.5 months.


At this opposition Mars is only half Earth’s distance to the sun from us.  The planet has a slightly irregular orbit.  Since its distance from the sun varies, its opposition distance varies from about 63 million miles to about 45 million miles.  During the 2018 and 2020 oppositions, Mars is closer than this year.  However, its brightest rivals that of Jupiter which shines high in the southern skies during the early evening hours.  See this article about Jupiter during May 2016.  At this opposition, Mars is about 7 times brighter than Saturn.

Interestingly, Venus and Mercury never appear near Mars and Saturn when the latter are at opposition.  Venus and Mercury are always seen near the sun, and can appear with the outer planets when these remote planets are near their solar conjunction when they are far from Earth.   So we never see a brilliant Mars along with a brilliant Venus.  When the two appear together, Mars is much dimmer because it is far from us. Here’s a view of them during 2015, as Mars emerged from its solar conjunction.

The next opposition of Mars is July 27, 2018.



Just 12 days after the Mars opposition, Earth passes Saturn, placing it at opposition.  The chart above shows Saturn and Mars on the night opposition occurs.  The event occurs at 1:37 a.m. CDT on  June 3.


Unlike Mars, Saturn is much slower.  Its solar year is nearly 30 earth-years long.  Opposition occurs every 378 days as our planet catches the Ringed Wonder that quickly.  While Saturn is much larger than Mars and it is about 840 million miles from us, it shines with the brightness of a typical bright star; it is about 2.5 times brighter than the distant Antares.

The next opposition of Saturn is June 15, 2017.

2016: Jupiter During May


Jupiter shines brightly from the southern skies during the early evening hours of May 2016. It appears among the stars of Leo with its bright star Regulus that shines about 13 degrees to the upper right of Jupiter.  The planet is about 25 times brighter than this star. At mid-month the moon passes through the region.  Here are the events of the three evenings.

May 13:  The First Quarter Moon appears 3.5 degrees to the lower right of the star Regulus.

May 14:  The moon appears 4 degrees to the lower right of Jupiter.

May 15.  The moon appears 9 degrees to the lower left of Jupiter.

Cassini Explores a Methane Sea on Titan

From NASA News

Fast Facts:

› A new study finds that a large sea on Saturn’s moon Titan is composed mostly of pure liquid methane, independently confirming an earlier result.

› The seabed may be covered in a sludge of carbon- and nitrogen-rich material, and its shores may be surrounded by wetlands.

Of the hundreds of moons in our solar system, Titan is the only one with a dense atmosphere and large liquid reservoirs on its surface, making it in some ways more like a terrestrial planet.

Both Earth and Titan have nitrogen-dominated atmospheres — over 95 percent nitrogen in Titan’s case. However, unlike Earth, Titan has very little oxygen; the rest of the atmosphere is mostly methane and trace amounts of other gases, including ethane. And at the frigid temperatures found at Saturn’s great distance from the sun, the methane and ethane can exist on the surface in liquid form.

For this reason, scientists had long speculated about the possible existence of hydrocarbon lakes and seas on Titan, and data from the NASA/ESA Cassini-Huygens mission does not disappoint. Since arriving in the Saturn system in 2004, the Cassini spacecraft has revealed that more than 620,000 square miles (1.6 million square kilometers) of Titan’s surface — almost two percent of the total — are covered in liquid.

For the complete article, click here.

Curiosity Mars Rover Crosses Rugged Plateau

NASA’s Curiosity Mars rover has nearly finished crossing a stretch of the most rugged and difficult-to-navigate terrain encountered during the mission’s 44 months on Mars.

The rover climbed onto the “Naukluft Plateau” of lower Mount Sharp in early March after spending several weeks investigating sand dunes. The plateau’s sandstone bedrock has been carved by eons of wind erosion into ridges and knobs. The path of about a quarter mile (400 meters) westward across it is taking Curiosity toward smoother surfaces leading to geological layers of scientific interest farther uphill.

The roughness of the terrain on the plateau raised concern that driving on it could be especially damaging to Curiosity’s wheels, as was terrain Curiosity crossed before reaching the base of Mount Sharp. Holes and tears in the rover’s aluminum wheels became noticeable in 2013. The rover team responded by adjusting the long-term traverse route, revising how local terrain is assessed and refining how drives are planned. Extensive Earth-based testing provided insight into wheel longevity.

The rover team closely monitors wear and tear on Curiosity’s six wheels. “We carefully inspect and trend the condition of the wheels,” said Steve Lee, Curiosity’s deputy project manager at NASA’s Jet Propulsion Laboratory, Pasadena, California. “Cracks and punctures have been gradually accumulating at the pace we anticipated, based on testing we performed at JPL. Given our longevity projections, I am confident these wheels will get us to the destinations on Mount Sharp that have been in our plans since before landing.”

Inspection of the wheels after crossing most of the Naukluft Plateau has indicated that, while the terrain presented challenges for navigation, driving across it did not accelerate damage to the wheels.

For the entire article, click here

2016, August 27: A Venus-Jupiter Epoch Conjunction

The June 30, 2015, Venus-Jupiter Conjunction.  The 2016 conjunction is closer.

An Epoch Conjunction

Just 424 days after the last Epoch Conjunction, Venus and Jupiter pass again in the western evening sky on August 27, 2016, shortly after sunset.  The image above shows the two planets when they were about one-third of a degree apart during the 2015 conjunction.  The 2016 conjunction is three times closer.  This article outlines the circumstances of conjunctions between Venus and Jupiter, the events of this conjunction, and concludes with a list of future Venus-Jupiter conjunctions.

See this article for more as Venus as an Evening Star during 2016-2017.

Conjunctions of the bright planets occur when they appear to move past each other in the sky.  Sometimes they seem to nearly meet, although they are millions of miles apart.  A Venus-Jupiter conjunction occurs between 34 days and 449 days, depending on the relative positions of the three planets (this includes Earth).  Venus revolves around the sun once in about 225 days.  Because our planet is moving, Venus catches up to and passes by Earth every 584 days.  Jupiter is a slower moving participant in this celestial waltz as it revolves around the sun once in nearly 12 years.

Venus-Jupiter conjunctions occur somewhat frequently; the close ones of are great visual interest, because to the unaided eye, the planets appear to merge together.  While not a “once-in-a-lifetime”event, these close conjunctions are infrequent enough to attract the attention of even the casual sky watchers.  Robert C. Victor, former staff astronomer at Abrams Planetarium, calls these close conjunctions “epoch conjunctions.”

Venus is always visible near the sun as it is closer to the sun than Earth.  From our planet it never appears more than about 45 degrees from the sun.  When it is east of the sun, it appears in the western sky just after sunset.  When it is west of the sun, it appears in the eastern sky, just before sunrise.

Jupiter’s movement in the sky largely follows the earth’s revolution around the sun and mostly reflects the annual westward advancement of the starry background.  Jupiter first makes a morning appearance in the eastern sky, just past conjunction when Jupiter is on the far side of its orbit behind the sun.  Each week it appears higher in the sky and farther west at the same time each morning.  Several months later, it appears in the western sky just before sunrise from this slow westward celestial migration.  At this time it is at opposition with Earth between the sun and Jupiter; they are on opposite sides of our sky.  At this time, Jupiter rises a sunset, appears in the south at midnight and sets at sunrise — appearing in between at other times during the night.  Jupiter continues to rise earlier each week, eventually appearing in the south at sunset.  As Jupiter heads for conjunction (behind the sun) it appears in the western sky at sunset, eventually setting with the sun.  This entire cycle takes 399 days.

Because Venus’ orbit is inside Earth’s orbit, Venus never appears more than 45 degrees from the sun, the Venus-Jupiter conjunction appears within region of the sky when Jupiter is near conjunction.  Additionally, if the Venus-Jupiter conjunction occurs too close to the sun, the planets are hidden in the sun’s brilliant glare.  In recent times, 75% of the conjunctions occur when Venus and Jupiter are very close to the sun.


During the August 2016 conjunction, Venus is emerging from behind the sun (superior conjunction).  Venus is only 22 degrees from the sun, setting 56 minutes after the sun, and before Nautical Twilight.  Jupiter is nearing its solar conjunction which is caused more by the earth’s revolution than Jupiter’s orbital movement.  The two planets are about 450 million miles apart, although they appear about 7′ (7 minutes= 0.10 degrees, much less than a full moon diameter) apart.

The Conjunction

Here are the events leading up to the conjunction.


On August 1, Venus is low in the western sky.  Find a clear horizon to see it.  Bright Jupiter is 26 degrees to the upper right of Venus.  Mercury is  about 8 degrees to the upper right of Venus.


While not a good appearance, the evening of August 4, 2016, presents another opportunity to view all five naked eye planets simultaneously.  Locate a clear horizon looking west.  Venus stands about 3 degrees above the western horizon.  While it is bright in the twilight, binoculars may be needed to first locate it.  A thin crescent moon appears 10 degrees to the upper left of Venus, with Mercury  2 degrees to the upper right of the Moon.  Jupiter is higher to the upper left of the moon (14 degrees).  Saturn and Mars in the southern sky, near the star Antares.


On August 6, the separation between Venus and Jupiter decreases to 21.5 degrees with the moon 10 degrees to the upper left of Jupiter.


On August 15, Mercury is rapidly disappearing from the sky.  Tonight Venus and Jupiter are 12 degrees apart.


By August 20, the Venus-Jupiter distance is 7.5 degrees.


On August 24, the pair is 3 degrees apart.


Two evenings later and the evening before the conjunction, the Venus-Jupiter distance is 54′ apart.


August 27, 2016 is conjunction evening when the two planets are 7 arc minutes apart!


In a telescope at about 80 power, Jupiter and its four largest moons are visible along with Venus.  The view through your telescope may be inverted or backwards left to right, depending on the optical design.  The four largest moons are in a plane that is along the cloud bands of the planet.


On the evening following the conjunction, the planets are 1 degree apart. with Jupiter to the lower right of Venus.


On August 30, the planets have separated to 3 degrees.

The planes continue to separate and Jupiter disappears into the sun’s glare heading for solar conjunction (September 26, 2016).

Upcoming Venus-Jupiter Conjunctions

The table below shows the next 7 close Venus-Jupiter conjunctions.  The November 2017 conjunction and the February 2025 event rival this conjunction in separation.   Following the conjunctions mentioned on this list, a close conjunction (28′) occurs on August 23, 2038 followed by a closer conjunction occurs on November 2, 2039 (13′).  Other more widely spaced Venus-Jupiter conjunctions (30′ to 2 degrees) occur in the interim.

Conjunction Dates Separation Location Visibility
November 13, 2017 20’ Morning(east) During this conjunction the planets rise in the east-southeast about 75 minutes  before sunrise.  In separation, it rivals the June 2015 conjunction, but it appears low in the sky.
November 24, 2019 1 degree, 28 minutes Evening(west) The planets in this widely spaced conjunction are nearly 3 full moon diameters apart.  They are visible low in the southwestern sky during twilight and early evening, setting about 1 hour, 35 minutes after sunset.
January 22, 2019 2 degrees, 24 minutes Morning (east) The planets in this widely spaced conjunction are far apart visually, but easily seen as they rise about 3 hours before sunrise and appear in low in the southeastern sky as morning twilight begins.
February 11, 2021 26’ Morning This pairing is very difficult to see in the eastern sky as the planets rise in bright twilight just 25 minutes before sunrise.
April 30, 2022 29’ Morning The planets rise in the eastern sky about 90 minutes before sunrise.  In separation, this rivals the June 2015 conjunction, although it is lower in the sky.
March 1, 2023 32’ Evening This conjunction rivals the June 2015 pairing, with the planets high in the west after sunset, setting 2 hours, 30 minutes after the sun.
May 23, 2024 15’ Morning This pairing is impossible for casual observers  to see as it occurs when the planets are nearly behind the sun hidden in the solar glare.

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