2017-2019: Mars Observing Year with a Perihelic Opposition, July 27, 2018

Photo Credit:  NASA

Every few years, Earth passes Mars. The Red Planet shines brightly in our skies, and prompts many Internet claims that the planet will appear larger than the moon.


Photo credit

In recent history observations of Mars spawned stories of great martian cities and unusual beings.  Mars is a planet that inspires intrigue and speculation.

Once every 15 or 17 years, Mars appears at opposition when it is nearest the sun (perihelion).  Just after midnight (12:13 a.m. Central Daylight Time) on July 27, 2018, opposition occurs and this is near Mars’ closest point to the sun (perihelion).  Opposition is just not one flash-in-the-pan event.  During the evenings leading up to opposition, the Mars grows in brightness and in size, although its planetary globe is not discernible to normal human sight.  A telescope is needed to see the orb of Mars.  More about the appearance of Mars during its 2017-2019 observing year follows.

Morning Appearance

The 768-day observing season begins with Mars’ solar conjunction on July 26, 2017 (7:57 p.m. CDT).

At this time, Mars is behind the sun as viewed from Earth and lost in the sun’s brilliance.  It rises with the sun, lies in the south at noon, and sets around sunrise.  The planet gradually emerges into the morning sky.  This process is slower than most planets as it revolves around the sun every 687 days about half the speed of our planet.

On the chart above notice the scale drawings of the planets’ orbits.  Earth’s orbit is nearly a circle, while Mars’ orbit is more elliptical.  Opposition occurs nearly a year after the conjunction date.   The planets are over-sized on the chart to easily demonstrate their positions.  The yellow line that extends from Earth through the sun defines noon, the morning side of the sky and the evening sky.  The line pointing away from the sun, defines midnight.

This chart was calculated from data by the United States Naval Observatory for Chicago, Illinois, in the Central Time Zone.

The chart shows the rising time of Mars (the red line) compared to sunrise beginning with its solar conjunction (7/26/17) until the time it rises more than 5 hours before the sun (May 23, 2018). The rising time differences for the moon (circles) and other bright planets are included as well as the rising time differences for bright stars that appear near the plane of the solar system (ecliptic) where the planets appear to move in the sky.  The time differences are included for Civil Twilight, Nautical Twilight and Astronomical Twilight.  These events occur in the eastern sky, except for the Saturn sets and Jupiter Sets circles.  Those planets are setting in the morning western sky.

Mars is hidden in the sun’s glare until late August, although it can be found with optical assistance.  Mars appears near a celestial object when its rising line crosses other celestial objects’ rising lines or when the Mars rising line appears near a circle indicating the rising of the moon.  During this morning appearance, the Red Planet has conjunctions with Mercury, Venus, Spica, Jupiter, Antares and Saturn.

As it rises and sets from Earth’s rotation, it rises earlier each morning from our revolution around the sun and its revolution around the sun.  At its solar conjunction we are 180 degrees from Mars and are moving nearly twice its speed, so it’s a slow catch-up game.  Meanwhile the other celestial objects rise earlier from our revolution around the sun, except for Mercury, the moon and Venus.

Mars-Mercury Conjunction

As Mars emerges from the sun’s glare, it is dim in our skies.  In late August and early September it appears near Regulus, Mercury. Venus and the moon.

On the morning of September 16, Mars and Mercury appear very close together, less than 0.2 degrees apart!  The pair is only 17 degrees from the sun and near the horizon when the sky begins to brighten.  Mars is over 240 million miles away, appearing as a not-so-bright star in the morning sky.

Our view on this morning puts Mercury and Mars, in conjunction, near the eastern horizon with Regulus 7 degrees above Mars with Venus and the waning crescent moon higher in the sky.  Find a clear horizon and use binoculars.  This view shows them one hour before sunrise, about the time of nautical twilight, when the horizon is first distinguishable.

Venus-Mars Conjunction

Mars and Venus were last in conjunction on November 3, 2015 when they were about 3/4 degree apart.  As with the last conjunction the 2017 conjunction occurs in a sky full of planets as noted here.  Also note that these conjunctions occur farther east along the solar system’s (ecliptic) plane.

As Venus heads toward its solar superior conjunction, it passes Mars on the morning of October 5.  On the rising chart above notice that the Venus rising time(the green line) diminishes during the autumn of 2017.  Mars’ separation from the sun has grown to 23 degrees.  Earth is slowly catching Mars, yet opposition is months away.  From this scale drawing notice that Venus’ orbit is closer to Earth than Mars.

The separation of the pair is about one-fourth of a degree.  This would be spectacular conjunction if Mars were brighter.  However, Venus-Mars conjunctions only occur when Mars is far away from our planet and near the sun (where Venus appears).  For more about the appearance of Venus, see this article.  The planets are close for a few mornings before and after this close passing.

The moon moves through its orbit about every 27 days and its cycle of phases nearly every 30 days.  The circles on the chart indicate the rising times of the moon.  If a moon circle appears near a planet or star on the chart, there is a good chance they are together in the sky.  For example on October 17, the moon circle appears with Mars and Venus (the green line) rises less than an hour later.

The view of that morning is a close appearance of the waning crescent moon and Mars (1.3 degrees) with Venus 7 degrees to the lower left of Mars.

Mars-Spica Conjunction

Mars then slowly lumbers eastward compared to the starry background, moving eastward along the solar system’s ecliptic plane.  Earth is slowly catching up to the Red Planet and it has brightened only slightly since its first morning appearance.


On the morning of November 30, Mars passes slightly more than 3 degrees from the star Spica. The pair is close for a few days before the closest pairing.  Jupiter began its morning appearance in late October is now about 16.5 degrees to the lower left of Mars.  Watch Mars catch up with Jupiter during the next six weeks as the two pass early in 2018.

Jupiter-Mars Conjunction

By early 2018, Mars is now nearly 60 degrees from the sun, rising about 4.5 hours before sunrise, nearly 45% brighter than when it first appeared in the morning sky, and about 180 million miles from Earth.  Earth is slowly catching.  Recall, that Mars moves at about half the speed of Earth, so it’ll over six months to catch Mars from this point.

On a few mornings around January 7, 2018, Mars passes close to Jupiter near the stars of Libra with the star Antares nearly 23 degrees to the lower left of the planetary pair.  Jupiter is over three times farther away than Mars, yet it outshines the nearer planet by 20 times.  Jupiter’s brightness is from its enormous size compared to Mars and its highly reflective cloud tops.  Jupiter’s clouds reflect nearly 40% more sunlight than Mars’ rocky and dusty surface.  Since it is over 3 times farther away than Mars early in the new year, it receives only 11% of the sunlight that reaches its red neighbor.  Jupiter is highly reflective and much larger, yet it receives much less sunlight than Mars.

Future Jupiter-Mars Conjunctions

Jupiter and Mars are in conjunction in spans of 26-27 months.

The next conjunction is March 20, 2020 when the two planets are about 0.7 degree apart when they rise in the morning sky before the beginning to twilight.  A close conjunction occurs (0.3 degrees) on August 14, 2024 when the two planets rise in the northeastern sky after 1:30 a.m.  The conjunction occurs among the bright stars of Taurus  near Aldebaran and the Hyades.  A conjunction slight closer than the 2018 conjunction (0.2 degree) occurs on December 1, 2033.  The planets appear in the evening sky in front of the dim stars of Aquarius, setting at about 10:30 p.m.

Mars-Antares Conjunction

During the next 30 days, Mars continues to ramble eastward among the stars and growing nearly 40% in brightness.  On the morning of February 10, Mars passes 5 degrees from the star Antares.  Jupiter is 17 degrees to the upper right of Mars and the waning crescent moon is 14 degrees to the lower left.  Mars is the Roman name for this planet.  The Greeks called it Ares.  Antares is sometimes called the “Rival of Mars.”  When are both are in the sky the resemble each other in brightness and color.  Another way to consider this is the prefix “Ant,”  sometimes meaning against: Antares = Against Mars.  Yet another way is to think that “Ant” can be replaced with “Not:” Not Mars.  This star is Antares, not Mars; it’s not Mars.

Mars at Quadrature West

By late March, Mars is well past Jupiter with an upcoming conjunction with Saturn, yet still in the morning sky.  It has grown in brightness nearly 2.5 times since the beginning of the year.  On March 23, it is 90 degrees from the sun (quadrature), rising about four hours, twenty minutes before sunrise and shines from the southern skies at sunrise.  Earth is beginning to approach Mars, still 110 million miles away, but the opposition is still 3 months away.

Mars-Saturn Conjunction

Mars continues eastward march against the starry background, reaching Saturn on April 2, 2018 when the two planets are about 1.25 degrees apart.  The Red Planet is slightly brighter (about 23%) than Saturn.  The color contrast is distinct, with Saturn’s pale yellow-orange color distinguished from Mars’ red-orange hue.  This conjunction occurs north of the main stars of Sagittarius, also commonly called “The Teapot.”

Mars Retrograde

After the Saturn conjunction, Mars continues to move eastward compared to the stars, yet it rises in the east and sets in the west as Earth rotates.  It moves away from the region of the Tea Pot toward the stars of Capricornus.  On June 26, Mars stops its eastward motion among the stars and begins to appear to move backwards, retrograde.  Since its conjunction with Saturn, this brightness grows over times and its distance diminished 2.5 times.  For the next month, Mars continues to retrograde as it reaches opposition, rising in the east at sunset and setting in the west at sunrise.  Its brightness grows another 20%.  Because Mars’ orbit is noticeably elliptical, opposition night is not the closest night.  Four nights later Mars is closest it has been since August 28, 2003.

This chart shows the close opposition of Mars.  The planet orbits are to scale, the planet sizes are not to scale.  Mars appears as a bright star at opposition.  (It will not appear the size of the moon.)  The “midnight” indicates that Mars is south at midnight, opposite the time when the sun is south.

On Opposition night the full moon appears about 7 degrees from Mars as they rise in the east at sunset.  On the evenings around opposition, Mars outshines all other stars and planets except Venus, although the moon is 10000 times brighter than Mars.

Other close historic perihelic oppositions:

  • August 10, 1971, 0.376 A.U. (1 A.U. is about 93 million miles, the average earth-sun distance)
  • August 18, 1845, 0.373 A.U.

The next perihelic opposition is September 15, 2035 (0.382 A.U.).  The next Mars opposition is October 13, 2020 (0.42 A.U.).  A more extensive list of oppositions appears at the end of this article.

Mars continues to retrograde until August 27, dimming slightly as it moves westward motion against the stars.

Resuming its eastward motion, Mars dims considerably, nearly 2.5 times as our planet now moves away from it as the last date displayed on the chart is displayed (October 13, 2018).

For more details about the opposition, see this article.

Mars in the Evening Sky

After opposition, Mars is in the eastern sky during the early evening, in the south in the middle of the night and setting in the west well before sunrise.

On December 1, 2018, as Earth pulls away from Mars, it is 90 degrees east of the sun, now in the evening sky.  (The angle Sun-Earth-Mars angle is 90 degrees.)  It appears in the southern sky around sunset.

On New Years Day 2019, Mars is in the southern sky after sunset and setting in the west around midnight.

In early March 2019, Mars “appears” on the evening sky chart showing when planets, the moon (circles) and bright stars near the ecliptic set after sunset.  This chart refers to activity in the western sky after sunset.  The Jupiter rises and Saturn rises circles refer to activity in the eastern evening sky.

Mars continues to move eastward compared to the stars, now much dimmer than it was a few months ago.  On the evening of March 11, 2019, the moon appears about 7 degrees to the upper left of Mars.

On March 31, 2019, its eastward motion carries it near the Pleaides star cluster and its brightest star Alcyone.  Away from bright lights, Mars is easily distinguishable from the tiny star cluster.

Through binoculars, the stars cluster stands out.  The contrasting colors of the stars with Mars is easy to see.

During Spring, Mars continues to set earlier each night as it slowly ambles eastward against the stars. By May it is 30 times dimmer than it was at opposition.  While it is one of the brighter celestial objects, Earth is pulling away from Mars making it appear dimmer in our sky.  On May 7, Mars appears near several brighter stars that are prominently displayed in the southern sky during the evening hours of winter.  The moon is 3.75 degrees to the lower left of Mars.  Prominent Betelgeuse, Aldebaran, and Elnath appear in the same region.

Mars begins setting during twilight in early June 2019.  On June 18 Mercury passes 0.2 degree from Mars.  Mercury is over 1.5 times brighter than Mars, yet the Red Planet is over 230 million miles away heading toward its solar conjunction.

Mars setting earlier during twilight each evening becoming a binocular object as it sets in deeper twilight.

As it sets in bright twilight, it passes Pollux and Regulus.  In late August 2019, Venus and Mars pass each other, but the pair sets about 10 minutes after sunset.

Mars reaches its solar conjunction on September 2, 2019, again rising with the sun, is in the southern noon sky, setting in the west with the sun, and ending its 768-day apparition with its perihelic opposition.

Mars Appearances With the Moon

Morning Appearance (Can be seen in the sky before sunrise)

  • August 20, 2017, 8 degrees (d) separation(During twilight)
  • September 18, 2017, 4 d
  • October 17, 2017, 1.3 d (See text)
  • November 15, 2017, 5.5 d
  • December 13, 2017, 4.75 d
  • January 11, 2018, 4 d
  • February 9, 2018, 4.3 d
  • March 10, 2018, 5.75 d
  • April 7, 2018, 4.2 d
  • May 6, 2018, 2.5 d
  • June 3, 2018, 2.3 d
  • July 1, 2018, 6 d

Evening Appearance (Can be seen in the sky after sunset)

  • July 27, 2018, 7 degrees (d) separation  (Opposition Night!)
  • August 23, 2018, 8 d
  • September 19, 2018, 4.25 d
  • October 17, 2018, 5.25 d
  • November 15, 2018, 2.3 d
  • December 14, 2018, 4 d
  • January 12, 2019, 5.3 d
  • February 10, 2019, 6.25 d
  • March 11, 2019, 7.3 d (See text)
  • April 8, 2019, 6.5 d
  • May 7, 2019, 3.75 d (See text)
  • June 5, 2019, 6 d
  • July 3, 2019, 2.75 d
  • August 1, 2019, 2.3 d (twilight)

Future Mars Oppositions

  • October 13, 2020
  • December 7, 2022
  • January 15, 2025
  • February 19, 2027
  • March 25, 2029

A perihelic opposition occurs July 27, 2018.  This close oppositions provides an infrequent opportunity to watch Mars emerge from behind the sun climb into the eastern morning sky.  It gradually increases in brightness to brightly appear at opposition.  Then it slips back into the bright twilight of the sun to complete its dramatic close appearance.

“Imagination is but another name for super intelligence.” — Edgar Rice Burroughs

2017, March 28: Mercury and Mars

After several days of rainy and cloudy weather in the Chicago area, clear skies prevail this evening as Mercury begins its best evening display of the year.  At about 45 minutes after sunset Mercury stands less than 10 degrees above the horizon, so a clear viewing spot is needed.  Mars is nearly 17 degrees to the upper left of Mercury.

Tomorrow evening (March 29), the crescent moon joins the planetary pair.  If you can’t find Mercury, the moon is a guide with binoculars:  Mercury is about 9 degrees to the lower right of the moon.  In typical 7 x 50 binoculars, Mercury stands just outside the field of view if the moon is placed at the 10 o’clock part of the field.  Slowly move the binocular toward the 4 o’clock direction.  Mercury will appear in view.

Link to YouTube video.

For more information about Mercury’s evening appearances this year, see this article:

For more information about current sky events, see these articles:

2017: Mercury’s Spring Evening Appearance

Mercury’s best evening appearance at mid-northern latitudes occurs during spring evenings.  This year, Mercury appears farthest from the sun on April 1.  A few days earlier (March 29), the moon helps in locating this speedy and elusive planet.  Look to the west at 8 p.m. CDT as observed from the Chicago area.  For other time zones, look about 45 minutes after sunset.  The crescent moon stands nearly 13 degrees above the western horizon.  Mercury is about 9 degrees to the lower right of the moon.  In typical 7 x 50 binoculars, Mercury stands just outside the field of view if the moon is placed at the 10 o’clock part of the field.  Slowly move the binocular toward the 4 o’clock direction.  Mercury will appear in view.

Mars is fading in brightness quickly and appears 11 degrees above the moon.

Link to YouTube video.

For more information about Mercury’s evening appearances this year, see this article:

For more information about current sky events, see these articles:

2017, Late March: Venus as a Morning and an Evening Star

This is likely visible only with optical assistance, such as through binoculars or a small telescope.  WARNING!  NEVER POINT BINOCULARS OR TELESCOPE DIRECTLY AT THE SUN!   Such activity can cause permanent damage to your vision and/or the optical device.

As Venus rapidly disappears into the sun’s brightness during the next few weeks of March, it is visible in the morning sky and evening sky with optical assistance.  (Not to be redundant, but heed the warning above.)

Venus reaches inferior conjunction on March 25, 2017.  At this time Venus moves between the Earth and the sun.  Because the orbits  of the planets line nearly in a plane, but not a perfect one, Venus does not move directly across the face of the sun.  It either passes above or below the sun.

At this conjunction, Venus is about 8 degrees above or north of the sun.  When an object is north of the sun, it can appear in both the morning and evening sky.  The Big Dipper is far north of the sun.  In March, during the early evening from mid-northern latitudes, the Big Dipper appears to stand on its handle high in the northeast.  In the predawn hours, it appears to be dipping down from the northwestern sky.  The Big Dipper is an extreme case of the concept.  But is shows that anything north of the sun can be both seen in the morning sky and in the evening sky,

The chart above (click the image to see it larger), shows Venus’ invisible orbit at noon on inferior conjunction day.  With appropriate shading, the planet is visible with optical assistance.  It is north of the sun.

Starting at mid-March and until inferior conjunction, Venus rises just ahead of the sun in the morning and sets just after it in the evening, during bright twilight, and so the need for optical assistance.  The optimum date is March 22 when Venus rises about 30 minutes before the sun and sets 30 minutes after.

At 6:45 a.m. CDT in the Chicago are (check your local sunrise time for other locations), about 10 minutes before sunrise, Venus stands 4 degrees above the the horizon and about 11 degrees from the sunrise point.  A crescent moon is in the southeast, over 70 degrees from Venus and not much help with its identification.

That evening, about 15 minutes after sunset (7:10 p.m. CDT in the Chicago area), Venus is 4 degrees above the horizon and 8 degrees from the sunset point.  Dimmer Mercury is about 13 degrees to the upper left of Venus.

While not easily seen, it is possible to see Venus as both a morning and evening star.

For more information about current sky events, see these articles:

2017: Venus as a Morning Star

Venus on July 14, 2017

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Venus last appeared in the morning sky in 2015 and 2016, when it appeared with Mars and Jupiter.

Introduction

Brilliant Venus zips into the morning sky during April  2017 and dominates the morning sky until year’s end.   During this morning appearance, Venus makes close appearances with the star Regulus and the planets Jupiter and Mars.

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This chart shows the rising time of bright planets, the moon, and stars near the planets’ orbital plane (ecliptic) compared to sunrise as calculated from U.S. Naval Observatory data for Chicago, Illinois in the Central Time Zone.  Additionally, the times when Jupiter sets and Saturn sets are charted compared to sunrise.  On April 7, Jupiter is at opposition and it sets in the west at sunrise.  The time differences are also displayed for Civil Twilight, Nautical Twilight and Astronomical Twilight.  At Astronomical Twilight, the sky is as dark as it gets naturally.

The rising time of Venus is represented by the green line on the chart.  It enters the chart in mid-March, reaching its maximum rising time difference during the summer, and leaves the sky in early 2018.  Notice that during the summer months of this appearance of Venus, the brilliant planet rises well before the beginning of twilight.  It stands low in the eastern sky as the sky brightens.

As Venus appears earlier in the morning sky, Jupiter shines brightly in the western sky, until about May 20 when Jupiter sets as Venus rises. (Notice on the chart, Jupiter sets line crosses the Venus rises at May 20.)  After this date Jupiter sets before Venus rises.  Similarly, Saturn, while not as bright as Jupiter or Venus, reaches opposition on June 15, setting in the west as Venus rises in the eastern sky.  Venus appears in the eastern morning sky and Saturn appears in the western sky until about July 25 when Saturn sets as Venus rises.  After this date Saturn sets before Venus rises.

Later in the year, Venus appears near Regulus.  This occurs near the date when the rising lines of Regulus and Venus intersect.  The same occurs for Mars, Spica, and Jupiter.  As Venus moves back into bright sunlight later in the year, it appears near Mercury, Antares and Saturn, although they appear together during bright twilight and out of view for most observers.

Venus has a close conjunction with Mars on October 5, followed by a very close (Epoch) conjunction with Jupiter on November 13.

The moon passes Venus each month, as our nearest celestial neighbor moves through its celestial path.  Two dates (May 22 and July 20) are especially noteworthy when Venus and the moon appear about 3.5 degrees apart.

Inferior Conjunction

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Venus moves between Earth and Sun on March 25, 2017; this is known as inferior conjunction.  Since Venus has a shorter orbital path and faster speed, it quickly moves into the morning sky.  The red line on the chart shows the division between morning and evening.  The line pointing from the earth to the sun indicates noon.  So at inferior conjunction, Venus rises with the sun, appears in the south at noon, and sets in the west at sunset.

Venus does not appear in the sky at midnight at mid-northern latitudes.  That occurs when a planet is opposite the sun in the sky as seen from Earth.  On the chart notice that the midnight line does not point toward Venus.

As Venus reaches this inferior conjunction, it passes above the sun.  Because it is north, above the sun, it rises earlier than the sun.  On conjunction morning it rises about 40 minutes before the sun.  On the rising chart above, it first appears on the chart on March 14, 11 days before it reaches conjunction!

Venus was last at inferior conjunction on August 25, 2015, 589 days between inferior conjunctions.

Greatest Brightness

The planet rapidly moves into the morning sky, rising earlier each morning.  It is very close to our planet and sparkles in the morning sky.  The brightness is from the proximity of the planet to Earth, its highly reflective clouds and the phase of the planet.  (Yes, Venus shows phases when viewed through a telescope.)  At this time Venus is about 170 times the moon’s distance, relatively close compared to other planets.

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From April 15 through May 13, Venus appears brightest in our skies, with the mid-point on May 1, 2017.  This is shown with the GB (greatest brightness) designation on the rising chart above.

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Update:  This image is from the beginning of the period of peak brightness.  Venus rises during twilight during maximum brightness during this appearance.

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Venus continues to rise earlier each morning. On the morning of May 22, the crescent moon appears about 3.5 degrees from Venus.

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Update May 22:  Venus and the moon appear together.

Greatest Elongation

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Venus reaches its greatest angular separation (46 degrees) from the sun on June 3.  This is shown by the GE symbol (greatest elongation) on the rising chart above.  It rises about 2 hours before sun near the beginning of twilight.

Venus Dazzles Morning Sky

 Venus continues rising earlier as summer begins.

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On July 14, Venus moves past Aldebaran.  The closest approach is about 4 degrees.

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The Binocular View

Update: Image of Venus and Aldebaran on July 14, 2017.  Click the image to see the Hyades and the Pleiades.

More striking is the star cluster near Venus and Aldebaran: Hyades.  The Hyades cluster is about 2.5 times farther away than ruddy Aldebaran.  Through binoculars, Venus, Aldebaran and the jewel-like stars of the cluster sparkle against the black velvet of the  predawn sky. Several dozen stars can be seen.

To the unaided eye, the Hyades resemble a check mark or a letter “V” if Aldebaran is included.

Clusters, like the Hyades, are used to refine distance measuring techniques as well descriptions of the lives of stars.  These clusters are thought to form at approximately the same time.  Stars that burn their nuclear fuels faster convert into other stellar forms sooner, such as red giants and red super giants.  From these stellar models, the estimate of the sun’s total lifespan is about 10 billion years.

Over time these clusters break apart; the gravitational forces between the stars are not strong enough to keep the cluster together.  The stars go their own way in their orbital path around the galaxy.

Our sun was likely formed in such a cluster and is now a lone star since it has gone into its own orbit around the Milky Way galaxy.

ven_lun_170720

On the morning of July 20, the crescent moon again appears with Venus.  The pair is separated by about 3.5 degrees.

In early August Venus rises about 3 hours before sunrise and begins to rise later each morning as displayed on the rising chart.  For the rest of the year, it loses about 30 minutes each month.

ven_beehive_170901

On September 1, Venus passes about 1 degree from the Beehive star cluster.  Like the Hyades described above, this is a stellar nursery.  It is too far away to be easily seen.  Binoculars will help with the view.  Look around 5:15 a.m. CDT.


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In late summer and early Autumn look for Venus and Sirius at the same time.  Both are about the same height (altitude) above the eastern horizon.  Venus stands in the east-northeast and Sirius appears in the southeast.  Only the sun and moon shine brighter than Venus and Sirius is the brightest star in the night sky. See this link to view the last time Venus and Sirius appeared together in the morning sky.

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Venus continues its rapid eastward movement as compared to the stars and descent toward the sun’s glow, passing about a half degree from Regulus on September 20.  This pair rises about 2 hours before sunrise.

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Over a month later, Venus passes Spica.  The gap is nearly 4 degrees.

Mars Conjunction

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The first planetary conjunction of this appearance is with Mars.  On the morning of October 5, Venus passes 0.2 degrees from the Red Planet.  The planets are close on a few mornings before and after the conjunction.

For more about Mars’ appearance during 2017-2019, see this article.

Venus-Jupiter Epoch Conjunction

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Another Epoch (close) Conjunction of Venus and Jupiter occurs before sunrise on November 13.  The distance is about .2 degrees.  This conjunction is visible during twilight as the pair rises about 70 minutes before the sun.

The next conjunction between the pair is January 22, 2019 with the next epoch conjunction on April 30, 2022.

For more about the Venus-Jupiter Epoch Conjunction, see this article.

Superior Conjunction

Venus continues its rapid descent into bright sunlight.  Conjunctions occur with Mercury, Antares and Saturn, but they occur in bright twilight, out of the view of most observers.

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On January 9, 2018 passes behind the sun at its superior conjunction and reappears in the evening sky.

Lunar Conjunctions

The moon appears with Venus on the following dates:

April 23: 8 degrees

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May 22: 3.5 degrees (See description in text)

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June 20: 7 degrees

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July 20: 3.5 degrees (See description in text)
August 19: 4.5 degrees
September 17: 6 degrees
October 18: 5.5 degrees

Other Images

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Venus on April 2, 2017

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Venus:  May 8, 2017 (Even visible from the brightest city lights)

 

Venus:  June 21, 2017

Venus:  July 14, 2017

Venus provides a dazzling view of planetary, stellar and conjunctions during its morning appearance in 2017.

2017: Mercury in the Evening Sky

mercury_2017

This chart shows the setting times of Mercury, other planets, and stars in the western sky compared to sun during 2017.  The vertical axis shows hours after sunset.  The horizontal axis shows the dates every seven days.

Mercury makes three appearances in the evening sky during 2017.  The brown curves on the chart above represent Mercury’s setting times compared to the times of sunset.  The three appearances peak around their greatest elongation dates:  April 1, July 29, and November 23.

The Geometry

The greatest elongation is the planet’s greatest angular separation from the sun.  As Mercury speeds around the sun it rapidly moves from the sun’s glare into the evening or morning sky and then back into the sun’s brilliance.

The planet revolves around the sun every 88 days.  Because our planet is revolving, yet at a slower speed and on a longer path, Mercury catches up and passes us every 116 days.

merc_orbit_170401

Mercury never appears no more than about 27 degrees from the sun and never appears in the sky at midnight from the mid-northern latitudes.  So it is in the sky mainly during the daytime and sometimes during twilight.  The chart above shows Mercury on April 1, 2017, when it is at its greatest elongation or maximum separation (19 degrees) from the sun.  This chart shows the sun and Mercury at noon, if the sky were dark.  The red line represents Mercury’s invisible orbital path.

Hold a ruler (12 inches) at arms length.  If the sun were at one end, Mercury would appear near the other end when it is at its greatest separation from the sun.

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Mercury passes behind the sun on March 6, 2017.  It is invisible because it is hidden in the sun’s glare.  The planet then moves into the evening sky, east of the sun, until it reaches its greatest separation from the sun on April 1.  It then rapidly moves into the sun’s glare and passes between Earth and sun  (inferior conjunction).  Mercury then moves into the morning sky, west of the sun.  After reaching its greatest elongation it moves back into the sun’s brilliance reaching superior conjunction.  The chart above shows the configurations if the earth were stationary.

The April 1 Elongation

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Our view of the planet is further complicated by our seasonal view of the plane of the solar system, known at the ecliptic.  The chart above shows the plane and Mercury’s orbit at the planet’s greatest elongation (19 degrees), just after sunset.  The narrow elongation would be particularly challenging to see, but the angle the ecliptic makes with the western horizon is very large.  During spring evenings, the ecliptic makes its highest angle with the horizon.  Venus and Mercury stand very high in the western sky during these times.  In the morning, the ecliptic makes its sharpest angle on autumn mornings.

On the evening of April 1, Mercury sets over 100 minutes after sunset.  Astronomical twilight ends 96 minutes after sunset, and nautical twilight, 61 minutes.  At astronomical twilight, see the chart at the top of this article, the sky is as dark as it will ever get naturally.  At nautical twilight, the horizon is visible, so that mariners can take measurements of star’s heights (altitudes) above the horizon.

So at this appearance, Mercury can be seen low in the western sky.  First locate the planet with binoculars, then try with optical help.  Look for Mercury a week before and after April 1.

The July 29 Elongation

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At the next greatest elongation on July 29, the angular separation is 27 degrees, but the angle of the ecliptic is very unfavorable.  Mercury sets about 60 minutes after sunset, but nautical twilight occurs 70 minutes after sunset.  Astronomical twilight occurs nearly 115 minutes (almost two hours) after sunset.  Mercury is less than 15 degrees at sunset.  This is likely a binocular or small telescope only apparition, from the unfavorable position of the ecliptic.

The November 23 Elongation

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Similarly, the November 23rd apparition has unfavorable observing conditions.  At sunset, the planet is less than 10 degrees above the horizon and sets nearly 70 minutes after sunset.  Saturn is 4 degrees above Mercury and sets nearly a 30 minutes after the speedy planet.  Nautical twilight occurs at nearly the same time as Mercury sets and astronomical twilight is nearly 35 minutes later.  Like the summer appearance, Mercury can be seen with optical aid.

Mercury appears in the western evening sky three times during the year.  Because of favorable seasonal circumstances, the April 1, 2017, view is the best of the year.

2017: Evening Planets

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(All charts and times are calculated for Chicago, Illinois in the Central Time zone.)

The evening sky in 2017 presents the five naked eye planets for easy viewing.  The year begins with Venus and Mars shining brightly in the western sky during early evening hours.

The chart above shows the times that planets, moon, and bright stars, near the plane of the solar system, set compared to sunset.  This activity occurs in the western sky.  Moon set is represented by circles;  two days each lunar cycle are labelled with their dates.  The exceptions are the Jupiter Rises and Saturn Rises lines.  Their graphs indicate when those two planets rise in the eastern sky.  When the planets rise at sunset earth is between the planet and the sun.  The planet is at opposition.  When the sun sets in the west, the planet rises in the east.  The planet is south at midnight and sets in the west at sunrise.  Jupiter is at opposition on April 7, Saturn on June 15.

Venus and Mars

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These two planets are well placed in the western evening sky for easy observation on New Years Day. Venus sets nearly 4 hours after sunset and Mars follows about an hour later.  Venus and the Moon are 4 degrees apart with Mars about 12 degrees to the upper left of Venus. During January, Venus and Mars appear to move closer together as the setting lines of the two planets begin to converge.

On January 12, Venus reaches is greatest angular separation from the sun (47 degrees) and sets 4 hours after the sun.

On February 3, the planets close to 5.5 degrees, with Mars setting 19 minutes after Venus.  The chart above shows their close angular proximity, but they are nearly 126 million miles apart in space, over 300 times the distance between the earth and the moon.  On this date, Venus enters a 30-day period when it is at its maximum brightness with the greatest brilliance date of February 17.  Venus dazzles the late winter sky in the west with the bright stars of Orion, Canis Major, Canis Minor, and Auriga shining in the southern sky.

Image from February 3, 2017

The planets then separate with Venus rapidly moving into the sun’s brilliant glare passing its solar inferior conjunction on March 25 and moving into the morning sky.

Mars is on a slow trail of descent into the sun’s glare that ends at conjunction on July 26 and the planet enters the morning sky.

On March 1, the moon appears 5 degrees to the lower left of Mars with Venus 13 degrees to the lower right of Mars.

In late April, Mars moves through the region of the sky with Aldebaran (Taurus) and two bright star clusters (Pleiades and Hyades).  This article explains more about Mars’ movement and the Venus-Mars encounter.

Mercury

Mercury’s best evening appearance of the year occurs during Spring this year.  On April 1, this speedy planet reaches its greatest angular separation from the sun (19 degrees) and sets 100 minutes after sunset.

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A few nights earlier, the waxing crescent moon appears 10 degrees to the left of Mercury and Mars is 16 degrees to the upper left of Mercury.  (The chart shows the sky 70 minutes after sunset.  For other observers at mid-northern latitudes determine your local sunset time and 70 minutes to get a similar view.)  At this time Mercury is less than 6 degrees in altitude.  Find a clear horizon, free from houses, buildings and trees.  Use binoculars to locate Mercury; then locate it without optical aid.

Mercury and Mars on March 28, 2017.

Jupiter

Jupiter enters the evening sky in the east when it appears at opposition on April 7.  During the spring it appears in the eastern evening sky.  It “enters” the setting chart shown at the top of this article on June 22 when it sets 5 hours after sunset.  Jupiter is near the bright star Spica.  This article provides more details about its conjunctions with Spica during its 2016-2017 appearance.

A conjunction occurs as Jupiter and Spica disappear into the sun’s glare as Jupiter heads for its solar conjunction (October 27).   At the planet-star conjunction, shown in the chart above, the objects are separated by 3.3 degrees.

Saturn

On the planet setting chart, the “Saturn Rises” circles indicate that the planet is rising in the east at those times.  When it rises in the east at sunset, it is at opposition.

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Saturn appears in the south during the mid-summer evenings.  On August 2, the waxing gibbous moon appears about 4 degrees from the Ringed Wonder and Antares is about 13 degrees away from the planet.

The Saturn setting line then enters the chart again in early September when it is setting less than 5 hours after sunset.

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On November 20, the waxing crescent moon appears near Saturn when the pair is low in the west, setting abut 110 minutes after sunset.

Other dates when the moon appears near Saturn:

  • August 29
  • October 23

Moon

NASA Photo

NASA Photo

Full Moon Dates (Central Time)

  1. January 12
  2. February 10
  3. March 12
  4. April 11
  5. May 10
  6. June 9
  7. July 8
  8. August 7
  9. September 6
  10. October 5
  11. November 4
  12. December 3

As a closing note:  In the U.S. Daylight Saving Time runs from March 12 (2 .m. local time set clocks forward) to November 5 (2 a.m. local time set times back).

End Notes: Twilight Definitions

Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities.

Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is  12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other lighting, general outlines of ground objects may be distinguishable. During nautical twilight the illumination level is such that the horizon is still visible even on a Moonless night.

Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, light from the Sun is less than that from starlight and other natural sources. For a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible. (Source)