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

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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

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.

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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.

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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.

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 November 24, 2019 with the next epoch conjunction on April 30, 2022.

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

2017: Mercury in the Evening Sky

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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.

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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)

2016: November Sky Watching

More articles:

Sun

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The sun rises south of east and sets south of west during November.  The chart about shows the length of daylight throughout the year — the red line.  The blue area shows the length daylight during November.  The mid-northern latitudes lose nearly an hour of daylight during the month.

Moon

NASA Photo

NASA Photo

Phase Date/Time Moonrise Moonset
First Quarter 11/07/16 (1:51 p.m.) 12:42 p.m. 11:23 p.m.
Full Moon 11/14/16 (7:52 p.m.) 5:08 p.m. 7:39 a.m. (11/15)
Last Quarter 11/21/16 (2:33 a.m.) 11:05 p.m. (11/20) 12:46 p.m.
New Moon 11/29/16 (6:18 a.m.) 6:46 a.m. 4:57 p.m.
Times are Central Standard Time for Chicago, Illinois, from US Naval Observatory calculations.
(For mjb & afb)

The Supermoon idea is not an astronomical concept and it appears to have originated in 1979.  This is described to when the moon appears at its full phase when it is at its nearest point to earth (perigee).  At this supermoon, the moon reaches perigee nearly 3 hours before it is opposite the sun at its full phase brilliance.  The result is that it appears brighter (although nearly imperceptible) in the sky and about 14% larger than the typical full moon, again not noticeable for most of us.

The moon appears larger when near the horizon and this does not cause a supermoon.  The moon illusion is explained in several ways.  Here’s a way to measure the size of the moon when near the horizon and then higher in the sky.  Locate the moon and extend your  arm.  Notice that the tip of your little finger covers the moon.  Try the same again when the moon is higher in the sky.  Compare the two views.

Morning Sky

Jupiter is the bright “star” in the eastern sky as the sky brightens.  On November 1, Jupiter rises 2 hours, 15 minutes before the sun.  As the month progresses it rises earlier each morning.  By month’s end Jupiter rises nearly 4 hours, 30 minutes before sunrise.

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At mid-month, Spica appears about 10 degrees below Jupiter.

 

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Jupiter, Spica and the moon.  The moon is 7 degrees from Jupiter and Jupiter is 9 degrees from Spica

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Jupiter, Spica and the moon.  The moon is 5 degrees from Jupiter and Jupiter is 9 degrees from Spica.

On the mornings of November 24 and 25, the moon appears near Jupiter and Spica.

Evening Sky

Venus dominates the western early evening sky.  On November 1, it sets about 2 hours after the sun and 3 hours after the sun at month’s end.  Mars and Saturn also appear with Venus in the western sky early in the month.

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On the evening of November 2, the moon appears near Saturn and Venus.  Venus is 6.5 degrees from the moon and 5 degrees from Saturn.  Mars appears over 36 degrees to the upper left of Venus.

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A few nights later, the moon appears 7 degrees to the upper left of Mars.  Venus is 35 degrees to the lower right of Mars and Saturn is 8 degrees Venus.

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Venus and Mars move quickly eastward among the stars and Saturn disappears into the sun’s brilliant glare.  By month’s end, Venus and Mars are 25 degrees apart.

Mercury passed superior conjunction on October 27 and is moving into the evening sky.  More about it next month.

For more details about Jupiter, Spica, Mars and Venus, see the articles linked at the top.