2018: Saturn With the Teapot


Update:  April 10, 2018

 

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

Update:  The conjunction

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

This slideshow requires JavaScript.

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!

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: