2018: The Morning Sky

This article summaries the planetary activity in the morning sky during 2018.  The articles that follow provide details about the planets visible without optical assistance (binoculars or telescope):

The chart above shows the rising times of the planets, stars near the plane of the solar system, and the moon (circles) compared to the time of sunrise.  The chart is drawn for Chicago, Illinois in the U.S.A. Central Time Zone from data from the U.S. Naval Observatory.  The three phases of twilight are displayed as well.  The activity generally displays activity in the eastern sky, except for the setting lines for Jupiter, Saturn and Mars.  These three planets set in the western sky; their setting times are compared to sunrise.  Each is at opposition during 2018:  Jupiter, May 8; Saturn, June 27; and Mars, July 27.  When at opposition, Earth is between the sun and one of those planets.

The three naked eye outer planets — Mars, Jupiter, and Saturn — are displayed when they are set in the west during the morning.

The white squares on the chart indicate conjunctions between planets or stars and planets.  For Mercury, the yellow triangles with the letters “GE” indicate the planet’s greatest separation from the sun as we see it; this is known as greatest elongation.  For Venus, the yellow diamond with the letters “GB” indicate when the planet is at its brightest.

Four planets are visible in the morning sky early in the year.  Mercury makes one of its two best appearances in January.  The second occurs at the end of the year.  Mars moves past Jupiter and Saturn early in the year.  Mercury makes two more morning appearances during twilight:  April and August.  Venus jumps back into the morning sky late in the year.  Jupiter also re-enters the sky later in the year.

Here are some highlights from planetary events in the morning sky  (Click the images to see the details):

 

The morning sky has a sky full of planets leading up to oppositions from Jupiter, Saturn, and Mars.

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2018: Venus the Evening Star

Photograph of Venus and the moon during twilight on September 3, 2016 -- the most recent evening apparition of Venus.

Figure 1: Venus appears in the evening sky during its 2016 evening appearance.

This article has many details about the appearance of Venus in the evening sky during 2018.  Bookmark it so that you can return to check the details.  Stop back, we’ll update this page with photos throughout the article and display a collection of them at the end.

Venus shines brightly as an Evening Star for most of 2018. It appears in the western sky as the three bright outer planets dance in their retrograde loops throughout spring and summer. 

These articles outline the planetary activity during 2018:

Unless noted, the charts in this article are computed for Chicago, Illinois, in the U.S.A. Central Time Zone (CST, -6 hours).  Daylight Saving Time (CDT, -5 hours) is shown when that occurs.

Figure 2: The chart shows the setting time of Venus compared to sunset, along with the setting time differences of other bright planets, stars and the moon (circles).  The boxes indicate conjunctions with other stars and planets.  The yellow triangle with the letters “GE” indicates Venus’ greatest elongation.  The greatest brightness is marked with the yellow diamond and the letters “GB.”

Introduction

The setting chart above shows the setting of Venus and other planets, bright stars, and the moon (circles) compared to sunset.  The white boxes indicate Venus conjunctions with other planets and stars.  After its solar superior conjunction in early January, Venus slowly moves into the evening sky.  Two months pass before it sets an hour after sunset, shining brightly in the western sky after sunset.  With the lengthening twilight that occurs at mid-northern latitudes (the chart is graphed from data for Chicago, Illinois), Venus reaches its latest setting time after sunset (2 hours, 40 minutes) in late May.  It appears low in the western sky after the end of twilight from March 28 through July 24 (for this latitude).  Meanwhile it passes through the stars of Taurus with a conjunction with Aldebaran, then Pollux, and finally Regulus during the evenings when it sets after twilight.  Because of the low inclination of the ecliptic it reaches greatest elongation and its duration of greatest brightness while it is visible and sets during evening twilight.  This article provides more detail about these events during the early evening hours of 2018.

Superior Conjunction Starts the Evening Apparition

Figure 3: The evening appearance of Venus begins when the planet passes superior conjunction when Venus is on the far side of the sun. At this time it is in the sky during the day and in the south at noon. The noon line on the chart points through Venus, indicating its direction and time.

The Venus apparition begins on January 9, 2018 (1:02 a.m. CST) when it passes superior conjunction. We cannot see Venus as it is on the far side of the sun and is in the sky with the sun. It rises in the east at sunrise, is in the south at noon, and sets in the west at sunset.

After its solar conjunction, Venus climbs slowly in the western evening sky. A month after conjunction it sets about 35 minutes after sunset, setting about 10 minutes later each week.

The chart above (Figure 2) shows the setting times of Venus, other bright stars, and planets compared to Sunset. Moon set is shown by the circles. We should note that these are setting times when Venus and the other celestial objects cross the natural horizon, leaving the sky.  Look for them between sunset and their setting time intervals. By mid-February, Venus appears low in the Southwest after sunset.

While it is the brightest “star” in our sky, it continues to grow in brightness as it slowly catches our planet.  For Venus, Earth is an outer planet, like Mars is for Earth.  Moving on a shorter orbit and at a faster speed — Venus revolves around the sun every 225 days, yet successive solar conjunctions (inferior-inferior or superior-superior) occur every 584 days. These configurations are named from Venus’ position compared to Earth.

Mercury Conjunction, March 18

Figure 4: The first conjunction of this appearance of Venus is with Mercury on March 18, 2018 during evening twilight.

By March 1 Venus continues to set later, now about 100 minutes after sunset. It still sets before the end of twilight . On March 18, Mercury passes about 4° from Venus with the moon nearby. By the end of March (March 28), Venus now sets after twilight ends.  It rapidly moves eastward compared to the background stars.

Venus in Taurus

Figure 5: During late April , Venus moves among the stars of Taurus. On April 24, Venus moves past the Pleiades star cluster. They are about 3.5 degrees apart. Look at the region with binoculars to see the region’s star clusters.

By late April, Venus moves through the stellar background of Taurus with its two bright star clusters:  Pleiades and Hyades.  The Pleiades is a compact grouping of bright bluish stars known to school children as “The Seven Sisters.”  The cluster resembles a tiny dipper.  To the unaided eye, 6 or 7 stars are visible.  A dozen or so through binoculars.  A few hundred through telescopes.  The Hyades are nearby.  This group resembles a check mark, a letter “V” when Aldebaran is included, although it is not part of the cluster.

Astronomical theory describes that stars are formed in bunches from a stellar, gaseous nebula.  Over time the mutual gravitation pull of the stars within the cluster is not strong enough to keep the group together.  The Hyades and Pleaides are close enough (within 400 light years) that they can be seen without a telescope.  Many star clusters are just beyond the perception of our eyes.  Binoculars help reveal them.  If you’re interest in star clusters is piqued, start here.

Figure 6: Venus passes 6.5 degrees from Aldebaran on May 2. With binoculars look at this region every clear night while Venus is there.

During the next week, Venus moves between the Hyades and the Pleiades, passing 6.5 degrees from Aldebaran on May 2.  Venus and the surrounding stars are less than 15 degrees above the west-northwest horizon.  Look at this region with binoculars every clear night.

Figure 7: Venus moves between the horns of Taurus (Zeta Tauri and Elnath during mid-May. It passes within 4 degrees of Elnath on May 13 and about 3.5 degrees from Zeta Tauri the next evening.

Venus and Moon

The moon passes Venus during its monthly succession of phases.  On the setting chart (Figure 2) above, note that the moon and Venus set at nearly the same time on several days.  We chose three of those dates to feature here.  In the charts in this section (Figure 7, Figure 8, and Figure 9)  the moon appears near Venus.  Here are some of the details:

  • May 17, 2018:  Venus and the moon are 6.2 degrees apart at chart time (9:15 p.m. CDT).  They are 14 degrees above the west-northwest horizon.  The moon is only 2.5 days old.  This region of the sky is full of bright stars; Capella is shown on this chart.  To keep the scale of the three charts the same, the view is limited.
  • July 15, 2018:  The nearly 3-day-old moon is slightly less than 2 degrees from Venus.  (The moon is over sized on this charts.)  The star Regulus is 6.75 degrees to the lower right of Venus.  (There is a conjunction with Regulus on July 9.  See the text for more details.)
  • August 13, 2018:  The moon is 2.5 days old and appears 10 degrees to the right of Venus.

Venus & Pollux

Figure 11: Venus passes the Gemini Twin Pollux on June 7.

After its conjunction with Aldebaran, Venus continues its eastward movement against the stars as it moves into Gemini, reaching Pollux in Castor in early June.  It passes 4.75 degrees from Pollux on June 7.  The trio of stars is about 15 degrees above the west-northwest horizon.

Venus in the Beehive

Figure 12: Venus passes the Beehive star cluster on June 19. It is dimmer than the star clusters in Taurus.

After Venus moves through Gemini, it moves into a region with inconspicuous stars known as Cancer.  The Beehive star cluster is in this star field.

Observers with sharp eyesight and a darker sky can see the cluster without binoculars.  For them it appears as a cloudy patch nearly halfway from Pollux to Regulus.

With binoculars stars are visible in the cluster.

The cluster is farther away (500 light years) and consequently dimmer than the Hyades or Pleiades.  Point your binoculars at Venus at 9;30 p.m. CDT, the Beehive cluster is immediately to the left of the brilliant planet.

Venus Meets Regulus

Figure 13: Venus passes within 1 degree of Regulus on the evening of July 9.

Venus continues moving eastward along the ecliptic through the stars Cancer toward Leo.  In early July, Venus passes the next signpost of the ecliptic, Regulus.  This vivid blue star is less than one degree from Venus on July 9.  On the chart above (Figure 13), the pair is 12 degrees above the western horizon at chart time.

See Five Planets

During late July, observers at lower latitudes can see five planets at once.  This will be difficult for observers at mid-northern latitudes.  See the details in this article.

During the time when the five planets are visible, Venus starts setting before the end of twilight on July 24 (at Chicago’s latitude).

Greatest Elongation — East of the Sun

Figure 14: Venus reaches its greatest angular separation from the sun on August 17 when it is 46 degrees from the sun.

Venus is now rapidly catching our planet and growing in brightness.  It continues to move eastward from Regulus and the stars of Leo toward Spica.  On August 17, Venus appears farthest from the sun, known as the greatest elongation (angle).  Venus is about half the distance it was at the Mercury conjunction (March 18) and over 50% brighter.  Venus is now setting about 100 minutes after sunset and its setting time compared to the sun is decreasing about 5 minutes sooner each week.  This is displayed with the yellow triangle and the letters “GE” on the setting chart (Figure 2).  The result is that Venus is lower in the sky each night at the same time interval after sunset.

Venus is now 70 days before inferior conjunction.  It continues to catch Earth and brighten in the sky.

Venus Passes Spica

Figure 15: Venus passes 1.25 degrees from Spica on August 31. Venus appears lower in the sky as it heads toward inferior conjunction.

Two weeks after the greatest elongation, Venus passes 1.25 degrees from Spica. After the conjunction, Venus and Spica continue to set at about the same time — growing in separation — until they disappear into the sun’s glare in October.  Venus sets farther left (south) along the horizon.

Greatest Brightness

Figure 16: Venus reaches its greatest brightness on September 21st.

About September 16 and for the next two weeks, Venus enters its phase of greatest brightness.  The midpoint is September 21st.  This date is displayed with a yellow diamond and labelled “GB” on the setting chart (Figure 2).

Jupiter, But no Conjunction

Figure 17: On September 28, Jupiter closes with 14 degrees of Venus. There is no conjunction during this Venus apparition.

After its opposition, Jupiter appears farther west each night.  During late summer Jupiter sets 80 minutes after sunset and it appears that Venus and Jupiter are headed toward a conjunction.  After the Spica conjunction, Venus rapidly dives toward the sun’s glare as it moves toward its inferior conjunction with the sun.  The closest Jupiter gets is 14 degrees on September 28, setting about 70 minutes after Venus.  See the setting chart (Figure 2) to note the similar setting times of Venus and Spica and the minimum separation of Venus and Jupiter.

Inferior Conjunction Ends the Apparition

Figure 18: Venus overtakes and passes Earth on October 26, moving between our planet and the sun.

During October, Venus rapidly disappears into the sun’s glare and moves between Earth and the sun (inferior conjunction) on October 26 (9:16 a.m. CDT). This completes the evening apparition for Venus during 2018.

After its solar conjunction, Venus quickly moves into the morning sky. By Nov 8 it already rises at the beginning of twilight, gleaming in the morning sky.

Summary

During 2018, Venus appears in the western evening sky.  It passes Mercury, Aldebaran, Pollux, Regulus, and Spica.  While its latest setting time is 160 minutes after sunset, its sets mostly during evening twilight during this appearance.  Late in the apparition, what looks like, an impending Jupiter conjunction never occurs.  There are several opportunities to view Venus and the moon.  Here we highlighted the close passings on May 17, July 15 and August 13.  Venus also passes the star clusters Pleiades, Hyades, and Beehive.  Binoculars help spot the clusters with brilliant Venus nearby.  Happy observing!

With the Moon

The moon is close to Venus on these dates (One degree is the size two full moons appear to our eyes without a telescope:

  • February 16 – 2.5 degrees (d)
  • March 18 – 4d
  • April 17 – 5.5d
  • May 17 – 6.2d
  • June 15 (7.5d) & 16 – 7.3d
  • July 15 – 2.2
  • August 13 – 10.5d
  • September 12 – 9d
  • October 11 – 3.1d

Photos

2018: Mercury in the Morning Sky

Figure 1: An appearance of Mercury in the morning sky.

Introduction

Mercury makes 4 appearances in the eastern morning sky during 2018.  Two of the more promising apparitions occur in January and December.  A third appearance in late August, while not as favorable, presents another view of this elusive planet.  During a fourth opposition, in late April, Mercury rises during bright twilight and is very difficult to locate without optical assistance.

This article describes the observing prospects of these four more money to pay apparitions of Mercury.

Mercury in the Morning Sky

Figure 2: The rising times of Mercury and other bright stars near the ecliptic for 2018. (Data from the U.S. Naval Observatory)

The chart above (Figure 2) displays the rising of Mercury and other bright stars and planets in the eastern morning sky compared to sunrise.  Moonrise is represented by the circles.  The three phases of twilight are graphed as well.  The white boxes indicate conjunctions with other stars and planets.  The greatest elongations are shown by yellow triangles and the the letters “GE.” The chart is calculated from data computed by the U.S. Naval Observatory. The rising times of Mercury are displayed on the brown curves.

 

 

Figure 3: Mercury’s morning apparition begins with inferior conjunction.

 

Because Mercury is always near the sun, its appearance starts shortly after inferior conjunction.  It rises earlier each day until it reaches its maximum separation from the sun, greatest elongation (shown by the yellow triangles and the letters “GE” on the chart).  Then as it moves towards its superior conjunction, its rising time diminishes until it disappears into the sun’s glare.

The best appearances occur around the times of greatest elongation and when the speedy planet arises around the time of astronomical twilight, when the sky is as dark as it gets naturally.

The Mercury Challenge

It is important to note, with these rising time differences shown on the rising chart, that if Mercury rises 1.75 hours before sunrise, it is not visible at that time.  This is when Mercury is at the natural horizon.  The planet is visible about 30 minutes later; yet, it is low in the sky. The sky is brightening, but still dark enough to see it.  Include houses and trees to the scene, you’ll need to find an observing location with a very good horizon.

If the planet rises 45 minutes before sunrise, it is high enough to be seen about 20 minutes before sunrise, after civil twilight.  Optical assistance with binoculars or a telescope is necessary to see the planet.  As morning twilight brightens, Mercury rises higher in the sky. From Earth, Mercury is always low in the sky shining during twilight. The presence of the Moon, Venus, or Jupiter are helpful to locate it as well.

Viewing Mercury is further complicated by our view of the solar system.  As our planet is tilted by 23.5°, the plane of the solar system (called the ecliptic) sometimes makes shallow angles with the horizon. At other seasons, the ecliptic has a higher angle to ease the viewing of the planet.  When the ecliptic is highly inclined during autumn mornings, Mercury can appear several degrees higher than at lower inclinations. Usually though, Mercury is about 5° above the eastern horizon before the sky grows too bright. Having a clear horizon is necessary. My viewing position is limited by trees and neighbors’ houses. Sometimes gaps between the trees provide the space necessary to see Mercury when it low in the sky.  Many times I walked down the street or view it from nearby park lands.

Mercury is not visible at risings times, as indicated on the chart, but several minutes later.  Mercury is almost always visible during some aspect of twilight.  In 2018 look for it in January or December.  August is fair good, but you’ll need binoculars to a telescope to see it during the April appearance.

The Geometry

Figure 4: Mercury at its greatest western elongation on January 1, 2018.

Mercury revolves around the sun every 88 days, at the time earth revolves ¼ of its year. Mercury then takes about another earth month to catch up and pass us (116 days total).

Mercury never appears more than 27° from the sun and never appears at midnight from mid-northern or mid-southern latitudes.  The chart above (Figure 4) shows Mercury on January 1, 2018, when the planet is 23° west of the sun at its greatest elongation.  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 arm’s length.  If the sun were at one end, Mercury would appear near the other end at its greatest elongation.

When the rising time of Mercury intersects with other planets or stars on the rising chart, that indicates that the pair rises at the same time, but they are not necessarily closest.  For example, the Mercury and Saturn rising lines cross on January 12.  The two planets rise at the same time.  A conjunction is near, either a few days before or after the intersection date.   The conjunction is on January 13 when the two planets are ¾ of a degree apart.

The rising circle for the moon is more predictive than for the planets.  For example, on January 15, the moon and Mercury rise about an hour before sunrise.  They are 4 degrees apart.  Of the moon circle coincides with a rising curve, the pair is close on that morning.

Other conjunctions occur with Mercury’s rising time intersections with Regulus (September 6), and Jupiter and Antares (December 21).

Mercury’s morning appearance begins when this speedy planet passes between the earth and sun.  It quickly moves into the morning sky as it moves past and away from us.  It rises earlier until it reaches its maximum separation from the sun.

The chart shows Mercury at greatest western elongation when it is at is maximum separation from the sun.  This chart shows the sky at noon, if the sky were dark.  When a planet is west of the sun, it rises in the east before sunrise.

January 1, 2018 Western Elongation

Figure 5: Mercury’s January 1, 2018 greatest elongation. The planets’ sizes are exaggerated.

On January 1, Mercury has an excellent apparition with an elongation of 23 degrees.  It started with its inferior conjunction on December 12, 2017 (7:48 p.m. CST).   While the greatest elongation is only 23 degrees, the planet rises 1.75 hours before sunrise and stands 15 degrees above the eastern horizon at sunrise.  Like other elongations, Mercury appears low in the eastern sky as the sky brightens.  The ecliptic is inclined with the horizon at about 40 degrees.  While the elongation is not at its greatest, the ecliptic’s angle makes a favorable view.

Figure 6: The Mercury-Saturn conjunction of January 13, 2018.

On January 13, Mercury passes less than one degree from Saturn.  Jupiter is 44 degrees to the upper right of the conjunction with the moon about midway from Saturn to Jupiter.  While dimmer, Mars is about 3 degrees to the lower left of Jupiter and 5 days after its conjunction with the Giant Planet. (See these articles about Mars and Jupiter.)

April 29, 2018 Western Elongation

Figure 7: The April 29 elongation is difficult to see as the ecliptic makes a shallow angle with the eastern horizon and Mercury appears even lower.

The April 29, 2017, elongation is the most difficult to see, but it is has the largest elongation of the year, 27 degrees.  The apparition begins on April 1 at inferior conjunction (12:53 p.m. CDT).  The angle the ecliptic makes is only 25 degrees, and the angle of Mercury’s orbit is less than 20 degrees (See Figure 7).  At sunrise, Mercury is only 9 degrees above the horizon.  It rises about 50 minutes before sunrise, after nautical twilight, when the horizon is distinguishable from the sky.  Look for Mercury with optical assistance, binoculars or a small telescope.

August 26 Western Elongation

Figure 8: Mercury’s August elongation puts the planet in the northeastern sky. The greatest elongation is 18 degrees.

This morning appearance begins at inferior conjunction on August 8 (9:06 p.m. CDT).  By August 26, the ecliptic is again is inclined about 25 degrees to the horizon as is Mercury’s orbit.  Mercury has only an 18 degree elongation, but it rises 90 minutes before sunrise (Figure 8).  By nautical twilight the sky is still dark enough to find this planet in the east-northeastern sky.

Figure 9:  Mercury passes 1 degree from Regulus on September.

As Mercury moves towards its superior conjunction it passes about 1 degree from Regulus on the morning of September 6.    The diagram above shows the pair about 40 minutes before sunrise when Mercury is only 5 degrees above the horizon (Figure 9).  Use binoculars to help with the location of the planets.

December 15 Western Elongation

Figure 10:  December’s greatest elongation is favorable for viewing.  Look in the east-southeastern sky.

The final elongation of the year begins with Mercury’s inferior conjunction on November 27 (4:15 a.m. CST).  Mercury reaches its greatest angular separation on December 15; this elongation is 21 degrees.  It stands nearly 20 degrees above the eastern horizon at sunrise.  While the elongation is small, Mercury’s orbit is inclined over 50 degrees with the horizon (Figure 10).  Mercury rises just before the beginning of twilight.  When the planet reaches 5 degrees in altitude, the sky is still fairly dark, yet beginning to brighten.

Figure 11:  A few days after greatest elongation,  Mercury passes about 4 degrees from Jupiter

Nearly a week after its greatest elongation, Mercury passes less than 1 degree from Jupiter on the morning of December 21 (Figure 11).  Jupiter passes its solar conjunction on November 26 and slowly emerges into morning twilight on its apparition that takes over a year.  In the chart above, Mercury is about 4 degrees above the horizon.

The rising chart above shows Mercury and Antares rising at the same time on December 28, but Mercury is nearest Antares on the same morning as it in conjunction with Jupiter.

Figure 12: Antares rises several minutes after Jupiter and appears lower in the sky on December 21. Mercury is closest to Antares on this morning as well.

By the time Antares rises high enough (5 degrees) the sky is brightening and the diagram shows the triad about 35 minutes before sunrise (Figure 12).

Summary

Mercury is the most difficult planet to see among the 5 naked eye planets.  Because it is so close to the sun, it appears low in the sky during twilight.  During 2018, Mercury makes four morning appearances.  The apparitions in January and December are easily observed.  The August apparition is fairly easy to see, but the April appearance in the morning sky needs optical help.

2018: Saturn With the Teapot

Figure 1:  Saturn as viewed from the Hubble Telescope (NASA photo)

Introduction

(This article has many details about the appearance of Saturn.  Bookmark it so that you can return later for current details.)

Companion Articles about the outerplanets:

One of the most spectacular celestial gems is the view of Saturn through a telescope.  The Ringed Wonder sparkles in a telescope’s eyepiece with its yellowish globe and muted cloud bands.  The bright rings make its identification unmistakable.    Children and adults, alike, marvel at the view and later many state that a telescopic view of Saturn is one of their vivid personal memories.

At its brightest, Saturn is the 8th brightest nighttime celestial jewel, following the moon, Venus, Jupiter, Mars, Sirius, Mercury, Arcturus, Canopus, and Vega.  In a small telescope at around 100x magnification, an oval blob appears.  At first glance Saturn’s is very bright against the starry background.  As your eye adjusts to the planet’s gleam, the rings are clear and bright.  The planet’s globe displays a distinct yellow color.  The clouds show subtle banding.  Showing as a bright star against the velvet background, Saturn’s largest moon, Titan, might be visible just beyond the edge of the rings.  Saturn is stunning through a telescope.

Today the close-up photographs of the planets made by orbiting telescopes and remote robot spacecraft take away the majesty of the personal experience of a view of Saturn.  Should you have the opportunity to see Saturn through a telescope, do not pass.  It is memorable.

During 2018, Saturn has conjunctions with Mercury and Mars; close passings of the moon; and a closing in from Jupiter for a 2020 conjunction.  It has a triple conjunction with Kaus Borealis, the star at the top of the Teapot during this apparition.

Figure 2:  The Teapot region of Sagittarius, Saturn’s location during 2018.
Constellation figure from Starry Night.

At this opposition Saturn appears among the stars of Sagittarius, a celestial character that is part human and part horse.  Sometimes it is referred to as the Archer; as the drawing above (Figure 2) shows, it has a bow and arrow.

Within the stars of the constellation is a popular pattern known as “The Teapot.”  Saturn’s observing year occurs above the stars of this famous asterism — a group of stars, with a familiar shape, that are not a formal constellation.  The Big Dipper and Little Dipper are asterisms and part of larger constellations — The Big Bear and the Little Bear.  The stars of the Teapot are somewhat dim, but they should be visible from your backyard or local park by shielding your eyes from nearby street lights.

The bright band of light we call the Milky Way is full of stars, delicate wisps of gas, and opaque dust clouds.  The center of our galaxy is thought to be far beyond the stars of Sagittarius, behind dust clouds.  We cannot see it visually, but other non-visible “light” (infrared) can reach our telescopes on mountaintops and those revolving around our planet.

Figure 3:  Saturn at solar conjunction, December 21, 2017, when it is behind the sun and invisible to Earth.

This appearance of Saturn begins with its solar conjunction on December 21, 2017.  At this time it is behind the sun and invisible.  Notice that the noon line, on the above diagram (Figure 3), points at Saturn.  The planet rises with the sun, appears in the south at noon, and sets with the sun.

Saturn in the Morning Sky

Figure 4:  This chart shows Saturn rising in the eastern morning sky.
Two Saturn conjunctions are noted.

This chart (Figure 4) shows Saturn, stars, planets and the moon (circles) rising before sunrise, along with the three phases of twilight.  Saturn is displayed until it rises 5 hours before the sun, in late April 2018.  Saturn begins rising during bright twilight late in 2017 and early in 2018.  By mid-January, it rises about 90 minutes before sunrise.  As the new year advances, Saturn rises earlier each day, noticeably earlier each week.  By late February, Saturn rises over 3 hours before the sun.   Two conjunctions of Saturn occur during this morning appearance:  Mercury (January 13, 2018) and Mars (April 2, 2018).  These events are described later in this article.

 

Figure 5: Shows Saturn’s apparent path above the stars of the Teapot during 2018.

Because Saturn takes nearly 30 years to revolve around the sun, it does not move far in its orbit during one Earth year.  During this apparition, Saturn appears above those Teapot stars.  The chart above (Figure 5) and the detailed one below, begin on December 28, 2017, just a week after solar conjunction when Saturn rises during bright twilight.  These charts show the apparent motion of Saturn during its observation year until the next solar conjunction in early 2019.

Figure 6:  Shows more detail of Saturn’s path during 2018 above the stars of the Teapot.
Saturn has a triple conjunction with Kaus Borealis (Lambda Sagittarii) on February 18, June 17, and November 18.

In more detail, showing the top of the lid star in the Teapot (Kaus Borealis), the motion of Saturn is displayed (Figure 6).  It moves eastward against the starry background until April 17.  It retrogrades less than 9 degrees until September 6, passing opposition on June 27.  After its early September stationary point, it resumes its eastward motion against the stars.  During this back and forth motion, Saturn passes the top of the Teapot’s lid (Kaus Borealis) three times:  February 18 (3 degrees), June 17 (3 degrees) during Saturn’s retrograde, and November 18.

Figure 7:  The orange line on the chart shows Saturn rising before
sunrise in late December 2017.  By December 28, it rises less
than 30 minutes 
before sunrise.

In a section of the rising chart (Figure 7) that shows Saturn emerging from solar conjunction into bright twilight, Saturn rises less than 30 minutes before the sun on December 28, the first day on the yearly charts in Figure 5 and Figure 6 above.  Saturn is not yet visible to the unaided eye.

Conjunction With Mercury

Figure 8:  On January 13, 2018 Mercury passes Saturn by
less than 1 degree 
with the moon and other planets nearby.

By mid-January, Saturn rises over an hour before sunrise and stands in the southeastern sky.  On the morning of January 13, Mercury passes about 3/4 of a degree from Saturn.  Mercury is about twice as bright as Saturn.  Just four days before this conjunction, Mars passes Jupiter. On the chart above, Jupiter is over 40 degrees to the upper right of Saturn.  The waning crescent moon appears about mid-way between Jupiter and Saturn (Figure 8).

On February 18, passes 3 degrees north of the top of the Teapot’s lid (Kaus Borealis, Lambda Sagittarii).  See Figure 6 above.

Figure 9:  Saturn at Quadrature West.  The planet
rises  90 degrees from the sun.

The Ringed Wonder continues to rise earlier each week appearing farther south and west.  By early spring it is 90 degrees (quadrature) west of the sun, rising around midnight and appearing low in the south as the sky brightens (Figure 9).  Earth is rapidly catching Saturn, but opposition is three months away.

Conjunction With Mars

Figure 10:  The Mars-Saturn Conjunction, April 2, 2018

In early April, Mars moves past Saturn.  The separation is just over 1 degree.  Mars is growing in brightness and heading toward its own opposition in July, yet it is only slightly brighter than Saturn at this conjunction.  Mars rapidly appears to move away from the eastward-creeping Saturn during the next few weeks.

Figure 11:  The moon passes about 1.5 degrees from
Saturn on April 7, 2018,

one of the closest during this apparition.

A few days later, the moon passes 1.5 degrees from Saturn, making one of the closest passings of the year.  The moon is about 1.5 degrees from Saturn.  (On the chart the moon is oversized, so the grouping looks closer than it is.)  Mars is nearly 3 degrees to the lower left of Saturn (Figure 11).

Figure 12:  Saturn begins to retrograde.

A week later (April 17), Saturn stops moving eastward and retrograde begins (Figure 12).  Mars continues its eastward trek, now nearly 8 degrees from Saturn.  Saturn’s retrograde motion continues until early September.

On June 18, Saturn again passes 3 degrees above Kaus Borealis.  See Figure 6 above.

Saturn in the Evening Sky

Figure 13:  Saturn at Opposition on a full moon night.

Just before Saturn’s opposition, it passes 3 degrees above Kaus Borealis on June 17.

Saturn reaches opposition on June 27, 2018, including a full moon grouping with the moon about 1.5 degrees away (Figure  13).  Saturn is over 10 times the Earth’s distance from the sun, over 840 million miles away.  Sunlight reflected from the clouds and rings take about 75 minutes to reach us.  Like the full moon, Saturn at opposition rises at sunset, appears south at midnight, and sets in the west at sunrise.  Saturn is at its closest to us and brightest in the sky.

Figure 14:  Saturn at Opposition.

On the opposition chart (Figure 14), Earth is between Saturn and the sun.  The midnight line points through Saturn, meaning that it is in the southern skies at midnight.  After opposition, Saturn rises before sunset in the southeastern sky.  As summer progresses, Saturn is higher in the eastern sky at sunset.

Figure 15:  Saturn stops retrograding on September 6, 2018.

Saturn continues to retrograde throughout the summer until September 6.  Coincidentally, Mars retrogrades until late August; on the chart above (Figure 15), Mars is nearly 28 degrees from Saturn and Mars is nearly 10 times brighter than Saturn.  (Mars brightness changes considerably during its apparition. See this article for more about observing Mars when it is near opposition.)

Figure 16:  Saturn’s setting time compared to sunset during late 2017.

The chart above (Figure 16) shows the setting times of Saturn, other planets, bright stars near the ecliptic, and the moon compared to sunset.  Saturn is displayed when it sets 5 hours after sunset,  beginning in mid-September until its solar conjunction in early 2019.  It does not have any conjunctions with any planets during the evening times.  There is a close grouping with the moon on October 14.

Notice, though, how the setting lines of Antares and Saturn are nearly parallel until late November.  Looking back at Figure 6, notice how Saturn is beginning to pick up speed as the separation increases between the daily plots.  Saturn is moving to the east away from Antares.  Also notice that the Jupiter line gets closer to Saturn later in the year.  Jupiter is closing on Saturn, but Jupiter takes two years to catch it.  It is worthwhile noting that there is no visible conjunction with Venus.  A Venus-Saturn conjunction occurs early during the morning hours of the apparition, but it occurs during bright twilight, about 15 minutes before sunrise in late December 2017.

Figure 17:  Saturn at Quadrature East, September 26, 2018

By late September Saturn appears 90 degrees from the sun (Figure 17).  It shines in the southern sky at sunset and sets in the southwest around midnight.  Except for the moon moving through no other bright stars are nearby except for Antares that is setting 2 hours before Saturn.  Mars motors eastward and sets 2 hours after Saturn, when Saturn is at its eastern quadrature.  By early November Mars sets nearly 4 hours after Saturn.  Mars does not reach its eastern quadrature until December.

As Saturn lumbers eastward, it passes about 2.75 degrees above Kaus Borealis (the top of the Teapot’s lid) for the third time during this appearance, a triple conjunction, on November 18.

Figure 18:  Saturn setting the west.
By December 19, Saturn is setting about 50 minutes
after sunset.

The last date plotted on the retrograde charts above is December 19.  By that date, Saturn sets less than hour after sunset and it appears in bright twilight.  Binoculars or a small telescope helps seeing it (Figure 18).

Figure 19:  Saturn at its solar conjunction, January 2, 2019

Saturn passes behind the sun on January 2, 2019 to complete its 377-day apparition.

Saturn’s Appearances With the Moon

The listing below names close passings of the moon with Saturn as viewed from the Central Time Zone.  The angular separations in degrees are included.  The apparent diameter of the moon in the sky is 1/2 degree.  So for a separation of 2 degrees is equal to 4 full moon diameters.  The tip of your index finger at arms length easily covers the full moon

Before Opposition

  • January 15, 2018, 5.5 degrees (d)
  • February 11, 2018, 2d
  • March 11, 2018, 5d
  • April 7, 2018 1.5d  (See text above)
  • May 4, 2018, 5.5d
  • June  1, 2018, 4d

After Opposition

  • June 27, 2018, 1d (Opposition night, see text above)
  • July 24, 2018, 2d
  • August 20, 2018, 4d
  • September 17, 2018, 4.75d
  • October 14, 2018, 1.75d
  • November 11, 2018, 4d
  • December 8, 2018, 3.75d

Photos

Conclusion

Saturn presents an opportunity to see it among the stars of Sagittarius above the Teapot asterism.  Conjunctions with Mercury and Mars, and appearances make this planet easy to track.  This appearance is leading up to an infrequent conjunction with Jupiter in 2020.  During this appearance find a public telescope night at your local planetarium or astronomy club to see the wonders of Saturn.  Happy observing!

2018: Five Planets Visible at Once

During 2018, the five naked eye planets — those visible without a telescope (Mercury, Venus, Mars, Jupiter, and  Saturn) — can be seen during the early evening in late July.  It should be noted that the farther south the observer, the easier they are to see as illustrated in the following diagrams.  From more northern latitudes, such as mine in Chicago (and farther north), Mercury sets or is very close to the horizon when Mars becomes visible in the east.

The summer sky is full of planetary activity.  Venus shines brightly in the western sky.  Jupiter, Saturn, and Mars are passing through their oppositions and displaying their retrograde patterns.  During late July, Mercury pops into the evening sky for a short visit.

These articles outline the planetary activity during 2018:

From Latitude 33 degrees North (Dallas, Texas)

From latitude 33 degrees North, the planets span across the sky from the east-southeast to the west-northwest.

Look for the five planets two to three days before and after the charted date (July 21).  Find a clear horizon to see Mercury; binoculars may be needed to initially identify it.  Twilight is longer, so look for the planets around chart time and before Mercury disappears below the horizon.  The moon appears near Jupiter.  Saturn is low the south-southeast, above the stars of the Teapot (Sagittarius).

Latitude 33 degrees South (Sydney, Australia)

(For my southern hemisphere readers)

From the southern hemisphere where the sun and planets appear in the north, the five naked eye planets are easily visible at 6:30 p.m. AEST.  Tonight the moon is closer to Jupiter than viewed hours later in chart above. Twilight is shorter at this season in the southern hemisphere.  The line-up is the same across the sky as from the northern latitudes.  Mercury in the west-northwest arching back to Mars in the east-southeast.

The farther south, the better the view.

For those at favorable latitudes, look for the planets in late July.  Let us know what you see!

2018: Mercury in the Evening Sky

Figure 1: Mercury’s 2017 spring evening appearance. Mercury is almost always visible during twilight at mid-latitudes.

Introduction

Figure 2: This chart shows the three evening appearances of Mercury during 2018. It shows the setting times of Mercury, other planets, stars, and the moon (circles). The three phases of twilight are displayed. Boxes indicate conjunctions of Venus with other planets, the moon, and stars. The triangles with the GE are the dates of greatest elongation west.

Mercury makes 3 evening appearances in the western sky during 2018.  Because the planet is always near the sun, it rarely appears in a dark sky.  In some instances it sets minutes after the end of twilight.  Most of the appearances occur in bright twilight (as seen in Figure 2 above) when the planet sets during twilight.

The setting chart above (Figure 2) shows the setting times of planets, stars and the moon (circles) compared to sunset. The three phases of twilight are displayed as well.

Mercury zips around the sun every 88 days.  If Mercury starts at inferior conjunction, it rapidly moves around the sun, reaching that starting point in less than three months.  Because of its shorter path and higher speed, Mercury overtakes us in an additional 28 days.  It’s fast!  It seems to bounce from morning sky to evening sky rapidly.  Some apparitions of Mercury are easier to seen than others.

The Geometry

Figure 3: Mercury is at superior conjunction on February 17, 2018.

Mercury’s evening apparitions begin when it passes behind the sun (superior conjunction) (Figure 3).  Near conjunction, Mercury is invisible to us under typical daylight conditions because it is near the sun and in our sky during the daytime.   After conjunction it sets later each day and gradually brightens.  Beginning about two weeks after conjunction it starts appearing low in the western sky during evening twilight. (Figure 2) Binoculars may be needed.  As it heads towards its greatest elongation it brightens and sets later.  As the planet gets closer to us, it brightens.  Unlike Venus, it is impossible to predict its greatest brightness interval because of shadows on the surface from mercurian features and other factors.  For Venus, its cloud tops present a consistent featureless face — allowing greatest brightness predictions.

Figure 4: Mercury at greatest elongation, when Mercury is farthest from the sun. This is a hypothetical view with a dark sky at noon.

After greatest elongation, Mercury sets earlier during brighter twilight as it moves between our planet and the sun.

It is important to note the settings on the setting chart on Figure 2, Mercury is visible before these times.  On March 15 (Figure 4), the planet sets nearly 100 minutes after sunset.  Look for the planet 30 minutes before the setting times.  Mercury will be low in the sky.  The monthly passing of the moon or periodic appearance of other planets aid in its location.  Binoculars help with the initial observation.  Then try to locate it without their assistance.

The best appearances occur Mercury sets near the end of (astronomical) twilight when the ecliptic has a high angle compared to the horizon.  On other apparitions, the angle of the plane of the solar system (ecliptic) makes with the horizon is shallow.  One those occasions Mercury is very low in the sky, setting around the time of nautical twilight.  Even when Mercury has a wide elongation (27 degrees) a shallow inclination of the ecliptic with the horizon makes Mercury set sooner.  During summer twilight lasts about 30 minutes longer than during spring.  A shallow ecliptic inclination and a long twilight makes Mercury spotting challenging during summer.

Autumn apparitions are limited by the extremely shallow ecliptic inclinations.

Spring evenings are the best times for spotting Mercury, if it above the horizon during the evenings at that season.  This year we have such an appearance.

March 15 Elongation

Figure 5: The March 15 greatest elongation is the best one to see Mercury in the evening sky during 2018. The high angle the ecliptic, the planet of the solar system, makes with the horizon is nearly at its greatest. (The planet sizes have been exaggerated in this and other similar diagrams in this article.)

The first and best elongation for seeing Mercury begins with superior conjunction on February 17 (6:27 a.m. CST).  Mercury quickly moves into the evening sky.  Brilliant Venus is in the vicinity and helps finding speedy Mercury.  At its greatest elongation, Mercury is only 18 degrees from the sun.  At sunset (Figure 5), it stands about 16 degrees above the horizon and sets nearly 100 minutes after sunset.  At this time Venus is 4 degrees from Mercury and both fit into a binocular field.  Then once the sky is dark enough, look for Mercury without optical assistance.

Figure 6: The moon and Venus make Mercury easily to located just three days after greatest elongation.

Three days after greatest elongation Venus and the crescent moon help in locating Mercury.  Brilliant Venus is  3.75 degrees to the lower left of Mercury and the moon is nearly 4 degrees from Venus (Figure 6).  All should fit into the same binocular field.

Mercury rapidly moves back into twilight and between Earth and the sun.  Inferior conjunction occurs April 1 (12:53 p.m. CDT).

July 12 Elongation

By summer Mercury reappears in the evening sky, after its superior conjunction on June 5 (9:02 p.m. CDT).  The angle of the ecliptic is shallow and Mercury is only 13 degrees above the horizon at sunset when the planet reaches greatest elongation on July 12.

Figure 7: Mercury’s summer evening appearance is challenging to see because of a low solar system angle and long twilight.

Brilliant Venus is 16 degrees to the upper left of Mercury at this time.  Mercury sets about 90 minutes after sunset.  Twilight ends 130 minutes after sunset in mid-July.  Because of the lengthy twilight, look for Mercury with binoculars.

Figure 8: Mercury passes Pollux on the evening of June 24. While low in the sky, find a clear horizon and use binoculars.

As Mercury moves towards its greatest elongation, it passes 4.75 degrees  Pollux on June 24, though Mercury is only 4 degrees above the horizon when the sky is dark enough to see it.  Venus is 19.5 degrees to the upper left of Mercury.

After greatest elongation, Mercury moves between the earth and sun on August 8 (9:06 p.m. CDT) and into the morning sky.

November 6 Elongation

The final 2018 evening appearance of Mercury begins with superior conjunction on September 21 (8:52 p.m. CDT)  It slowly appears in the west-southwestern sky as it heads toward its greatest elongation (23 degrees).

Figure 9: The third and most challenging apparition to see, Mercury is low in the sky at greatest elongation. Jupiter aids in the location of the speedy inner planet.

While at a favorable angular separation from the sun, Mercury stands only 8 degrees above the west-southwest horizon at sunset, setting less than one hour after the sun.  Clearly this appearance is difficult to see.  The ecliptic has a shallow inclination and Mercury appears below it.  Seeing Mercury requires binoculars and a very clear horizon free from clouds and terrestrial features.  While a challenge, look for these events with binoculars:

Figure 10: Mercury passes 3 degrees from Jupiter on October 28.

Mercury passes 3 degrees from bright Jupiter on October 28.  Locate Jupiter with binoculars, Mercury is in the same field to the lower left of the bright planet.

Figure 11: Mercury has a conjunction with Antares and the moon on November 9. Use binoculars to locate this grouping.

While low in the sky, Mercury passes 2 degrees from Antares on November 9, while a thin crescent moon shines 6 degrees above Mercury.  View the moon through binoculars.  Position the field of view so that the moon appears at the top of the field.  Mercury appears at the bottom of the field.  Jupiter is about 9 degrees to the right of Mercury  A clear view of the horizon is necessary to see this collection of celestial gems.

Summary

Mercury’s best evening appearance occurs during the spring.  Brilliant Venus helps locating the speedy inner planet.  The other two appearances require good horizons and some optical aid with binoculars.  Happy observing!

2017, September 18: Venus, Moon, Mercury and Mars

Brilliant morning star Venus is joined by the 28-day-old moon this morning. The star Regulus appears about 1.5 degrees below the bright planet. Elusive Mercury appears low in the sky. It is easily viewed without binoculars. Dimmer Mars about 1.5 degrees above Mercury and it is emerging from the sun’s glare. It appears near Venus on October 5th.  (Click the image to see Mars easier.)

Notice the earthshine on the moon.  The night portion of the lunar surface is gently illuminated by reflected sunlight from our planet.

For more information about sky watching events: