Dawn and dusk twilight sky maps by Robert D. Miller. Sky Calendar illustrations courtesy of Abrams Planetarium, Michigan State University. Graphs of planet rising and setting times for School Year 2019-2020 by Jeffrey L. Hunt.

Teachers are encouraged to gather their students for at least one early evening session early in autumn 2019 before Jupiter and Saturn sink low in the southwest twilight glow. Otherwise, the next good views of Jupiter and Saturn will be at predawn sessions in March through early June 2020 (Mars joining Jupiter-Saturn in a compact gathering March 20-31), or at evening sessions in summer and autumn 2020. Venus slowly emerges from the evening twilight glow in autumn 2019, forming striking naked-eye pairs with Jupiter and Saturn on November 23-24 and on December 10. Venus will be at its best for telescopic viewing in the evening sky from late March until late in May 2020, showing half through crescent phases, ever thinner while growing ever larger in apparent size as Venus approaches inferior conjunction between Earth and Sun on June 3, 2020.

Robert D. Miller’s monthly all-sky charts, “Planets and Bright Stars in [Evening or Morning] Mid-Twilight” for August 2019 through August 2020, provide a ready visual representation of where to find the naked eye planets at dusk and dawn. The simplified charts depict positions of only the five naked-eye planets (Mercury, Venus, Mars, Jupiter, and Saturn), and the stars of first magnitude or brighter (plus Pollux’s nearby twin, Castor, of mag. +1.6, included even though it’s fainter). Planet and star positions are for the moment the Sun is 9° below the horizon, which we call “mid-twilight”. Daily planet positions are plotted as dots, labeled every 7th day (1, 8, 15, 22, 29). Positions of bright stars above the horizon at mid-twilight during the month are represented by continuous trails.

Stars trek westward across the sky in the course of any month (a consequence of Earth’s annual revolution around the Sun). Star positions on first and last dates of the month are each indicated by a dot if the star is above the horizon. We will describe evening planetary gatherings first because dusk is a popular time to begin observing. But there are some very worthwhile morning events too, described farther on.

Here are the evening twilight charts for August through December 2019.

The current season for an early evening viewing of the largest planets of our solar system, Jupiter and Saturn, began around the dates Earth overtook them in 2019, on June 10 and July 9, respectively. Each planet then appeared at opposition, on the opposite side of the sky from the Sun, and so above the horizon all night, from dusk until dawn. During the five to six months following opposition, these slow-moving planets remain visible at dusk, starting low in the east-southeast, crossing through the south, and ending low in west-southwest, as a consequence of the Earth’s faster revolution around the Sun.

Both these planets are impressive for telescopic viewing, Jupiter with dark cloud belts parallel to its equator and four moons discovered by Galileo, and Saturn with its beautiful rings. These showpiece planets will remain available for early evening viewing well into autumn 2019. Make plans to hold observing sessions early in this school year, the sooner the better, before these planets sink low into the western twilight glow! We hope you and your students get to enjoy many of the planetary highlights of the coming school year.

Start viewing Jupiter and Saturn now, even if your school year isn’t yet underway! As you receive this issue of California Classroom Science in early August, Jupiter and Saturn are in fine display in the southern sky at dusk. Watch the Moon pass them during August 9-12.

Highlights of August through December 2019 – planets in the evening sky: Follow Jupiter and Saturn drifting toward the southwestern sky, being carried along with the stars, even after each planet ends retrograde and begins slow eastward motion against background stars of their respective constellations. Jupiter ends retrograde in Ophiuchus, within 7° NE of Antares in Scorpius, on Aug. 11, and Saturn does so in Sagittarius, within 4° NE of Nunki (Sigma Sgr), the brightest star in the handle of the Teapot, on Sept. 18. The gap between Jupiter and Saturn reached this year’s maximum of 31° in July, and will slowly narrow, to 25° apart by Oct. 7, to 20° apart by Nov. 17, and to 17° apart by Dec. 11, about when Jupiter will disappear into the twilight glow.

Venus will first become easily noticed in evening twilight in October 2019. It will become ever more engaging to follow the two brightest planets, Venus and Jupiter, as the gap between them narrows, from 30° on Oct. 26, to 20° on Nov. 4, to 10° on Nov. 14.

During Nov. 19-28, Venus-Jupiter will appear no more than 5° apart! Be sure to watch these planets form a spectacular bright pair as Venus passes 1.5° south of Jupiter on Nov. 23 and 24, Saturday and Sunday evenings of the weekend before Thanksgiving. On Sunday, Nov. 24, Saturn will be 19° upper left of the bright pair. On the latter half of Thanksgiving Week, a crescent Moon adds beauty to the scene: On Wednesday, Nov. 27, Moon is 6° lower right of Jupiter and within 10° lower right of Venus. On Thanksgiving, Nov. 28, Moon will be within 3° upper left of Venus (another event not to miss!) and 7° upper left of Jupiter. Saturn will be within 11° upper left of Moon. That’s four solar system bodies fitting within 19°! <On Friday, Nov. 29, Saturn will be just 2° right of the Moon.

Spreading to nearly 5° apart by Thanksgiving, Nov. 28, Venus-Jupiter continues to separate, to nearly 10° on Dec. 3, and 15° on Dec. 8. Venus-Saturn appears no more than 5° apart during Dec. 7-14, and form their closest pairing on Dec. 10, as Venus passes 1.8° south of Saturn. Jupiter on Dec. 10 appears 17° to the lower right of the Venus-Saturn pair. By then, Jupiter is just above the horizon in mid-twilight and sets less than an hour after sunset.

Moon-planet pairings, Aug.-Dec. 2019: The Moon forms pairs or gatherings with planets and bright zodiacal stars every month. Here are some of the most eye-catching of the evening events for the rest of 2019, which are illustrated on the Abrams Planetarium Sky Calendar. Angular distances of planets from the Moon are given for observers in southern California at mid-twilight.

• August 8-12, 2019: Watch the Moon pass Antares, Jupiter, and Saturn. The pairings of Moon-Jupiter on Aug. 9 (2.7° apart in mid-twilight) and Moon-Saturn on Aug. 11 (3.1°) are very striking. (Angular distances are from the center of Moon’s disk.)
• Sept. 5-8, 2019: Watch Moon pass Antares, Jupiter, Saturn. Notable pairings are with Jupiter on Sept. 5 (3.1°), and Saturn on Sept. 7 (5.6°) and Sept. 8 (6.9°).
• Oct. 2-5: Moon again passes Antares, Jupiter, Saturn. On Oct. 3, Moon is 2.8° from Jupiter; on Oct. 5, 3.0° from Saturn.
• Oct. 29-Nov. 2: Moon makes yet another pass by the planets, this time including Venus, and possibly Mercury, in the earlier evening twilight, with the aid of binoculars. Here are daily descriptions, with individual diagrams for the first three evenings:
• On Oct. 29, Venus is within 6° lower right of the Moon. Mercury is within 7° below Moon and 2.8° lower left of Venus. (Mercury was easier to spot, brighter and a bit higher, 1-2 weeks earlier. But this is a poor, very low apparition of Mercury for viewers at mid-northern latitudes.)
• On Oct. 30: Venus 18° to Moon’s lower right. Jupiter 8° to Moon’s upper left; Antares 8° below Moon; and Mercury 2.6° (least distance) lower left of Venus.
• Oct. 31: Jupiter within 6° to Moon’s lower right.
• Nov. 1: Saturn 4° upper left of Moon. Nov. 2: Saturn 9° lower right of Moon; Moon has moved east of the planet gathering.
• Nov. 27-29: Moon passes through the gathering of Jupiter, Venus, and Saturn. Before then, don’t miss the pairing of Venus and Jupiter within 5° apart Nov. 19-28, and at its closest, within 1.5°, on Nov. 23 and 24. See descriptions and illustrations in the section above, about Venus.

By December 2, Jupiter-Saturn is just over 18° apart, and Venus has moved nearly halfway from Jupiter toward Saturn. On Dec. 10, when Venus passes 1.8° south of Saturn, Jupiter is 17° to the lower right of the pair and will drop below the horizon at mid-twilight within a few days.

When the waxing crescent Moon reappears in the southwest at dusk on Dec. 27, Jupiter will be invisible, in conjunction on the far side of the Sun (this time, actually behind the solar disk!), while the 1.8-day crescent Moon will appear 12° lower right of Venus and within 7° upper left of Saturn. By this date, binoculars may be essential for spotting Saturn low in the twilight glow.

In a spectacular event on the next evening, Sat. Dec. 28, the lunar crescent appears within 2° lower left of Venus at dusk and closes in on Venus until moonset. On the next evening, Dec. 29, the Moon will be 10° upper left of Venus at dusk, while Saturn will be 21° lower right of Venus. Saturn sets earlier each evening, and by Jan. 13, 2020, it will be in conjunction, behind the Sun’s disk, as Jupiter was 17 days earlier.

Highlights of January through August 2020 — evening sky:

Here, we extend our summary of planetary visibility in the evening sky into 2020. We’ll follow Venus continuously through late May, catch favorable appearances of Mercury at dusk in Jan.-Feb. and May-June, and welcome the return of Jupiter and Saturn to the southeast evening sky in July 2020. But if you’d first like to peruse the morning highlights for August through December 2019, scroll ahead to that section.

Here are the evening twilight charts for January through August 2020.

Venus is spectacular in the early months of 2020. Venus continues in the evening sky into 2020, getting higher until late in March, near the date of its greatest elongation 46° from the Sun, March 24. The monthly pairings of Venus with the crescent Moon on Jan. 27- 28, Feb. 27, Mar. 28, and Apr. 26 will all be wide, 6°-8° apart, but they can still be used to easily spot Venus in the daytime. At dusk, Venus can help viewers locate Mercury during some of its apparitions: Find our solar system’s innermost planet within 30° lower right of Venus during Jan. 23-Feb. 17, 2020, and as close as 24° during Feb. 4-11. On May 21, a few days before departing from the evening sky, Venus will pass about one degree from emerging Mercury.

From March until late in May 2020, Venus is of increasing interest for observation with telescopes and binoculars, even in the daytime, as it changes through the half and crescent phases, while the planet draws ever closer to Earth. At greatest elongation on March 24, Venus appears half full. Venus brightens for another five weeks, until late in April, when Venus appears in a crescent phase, just over one-quarter illuminated. The crescent continues to get ever thinner and grow in apparent diameter to nearly one arcminute, at inferior conjunction on June 3, 2020. Since Venus passes within half a degree north of the Sun’s center on that occasion, it’ll be unsafe to attempt observation for several days before and after that date. While still in the evening sky during April and May 2020, Venus has striking conjunctions with stars in Taurus, the Bull. On Apr. 3, use your binoculars to watch Venus pass within 0.3° of 3rd-magnitude Alcyone (Eta Tauri), the brightest member of the beautiful Pleiades (Seven Sisters) star cluster. The passage will be fascinating to watch for several evenings, as Venus shifts eastward by nearly 1° per day. On April 14th, Venus makes a wide pass 10° north of Aldebaran. On May 9-12, Venus pauses 1.5° lower left of Beta Tauri, or Elnath, the tip of Taurus’ northern horn. The event is termed a quasi-conjunction, because Venus approaches the star, but does not move past it. Venus instead begins to retrograde (move westward against the stars), and plunge ever more rapidly toward the setting Sun.

Before Venus is lost in the solar glare, Mercury passes superior conjunction on the far side of the Sun on May 4, 2020, and emerges within a week. Look for Mercury to lower right of Venus, by 15° on May 14, by 9° on May 17, and 5° on May 19. Mercury appears only 1.1° south (lower left) of Venus on May 21. That evening, a telescope will show the planets in the same field, Venus as a very thin crescent, its disk 0.9 arcminute in diameter, 5 percent illuminated, and Mercury, in the background, a tiny 0.1 arcminute across and in gibbous phase, 69 percent lit. On May 23, a young, thin, 2-percent crescent Moon joins them, and all three will fit within a 6.5° binocular field! Even on May 27, just one week before Venus’ inferior conjunction, you can still see Venus! Moments after the Sun has set and is safely hidden below the horizon. Venus will be over 8° up in WNW and 10.6° upper left of the recently-set Sun, and, viewed with binoculars or a telescope, displaying a crescent, 2 percent illuminated. Venus departs, but Mercury climbs to its highest in the twilight glow around May 30 and reaches greatest elongation 24° from Sun on June 3. A week later, on June 10, Mercury is 12° below the Twin stars Pollux and Castor, forming an isosceles triangle with them, and thereafter fades quickly and drops out of sight, leaving the early evening sky devoid of planets for a few weeks. Mercury’s inferior conjunction occurs on June 30.

By early July 2020, Jupiter and Saturn will return to the early evening sky, rising in ESE just 6° apart, before evening mid-twilight. Earth will overtake Jupiter and Saturn within a week apart, as the two planets reach opposition and all-night visibility on July 14 and 20, respectively. The planets will remain close companions in the evening sky all summer and fall, spreading to 8.3° apart in late August 2020, and coming back together for a rare, spectacularly close pairing, only 0.1° apart, on December 21, 2020. Jupiter overtakes Saturn about every 20 years, only a few times in a human lifetime, but this event will be their closest pairing since 1623, during the life of Galileo, and the closest until the year 2080.

Now, we return to the start of the school year 2019-2020, to preview the morning sky.

Highlights of August through December 2019 – morning sky

Here are the morning twilight charts for August through December 2019. Notice the stars are in roughly the same positions they will occupy in the evening sky a few months hence. Getting up before dawn is a good way to preview the evening sky of the coming season! The morning charts show the sky at mid-twilight when the Sun is 9° below the eastern horizon, but you may want to begin your predawn sky watches at least 1½ hours before sunup, to include some dark sky time.

In these last five months of 2019, for naked-eye morning planet viewing, we’re limited to two: Mercury during two forays into the eastern twilight glow, both favorable, in August and in November-December; and Mars, after its emergence into the eastern morning sky in October. Mars begins its apparition at mag. +1.8, as faint as it ever gets, improving only slowly at first, and reaching a spectacular mag. –2.6 at opposition in October 2020.

But the most beautiful feature of the morning sky these months is a large number of bright stars, of the constellations Orion, Taurus, Gemini, Canis Major, and Canis Minor, Auriga, and the Hyades and Pleiades star clusters in Taurus. The stars you’ll enjoy before dawn in August through December are the same ones you’ll see in the same places in evening twilight during January through May.

And an advantage of daylight saving time is that the late sunrises we get in autumn before we change back to standard time in early November will enable us to view a dark morning sky without the hardship of getting up very early by the clock.

Use the morning twilight charts for following these constellations’ bright stars from east to west from August into December, and to locate any visible planets. Keep in mind that Mercury is always faint near the start of its morning apparitions, so you may have to wait until several days after the date of its first appearance on a morning chart.

Mercury passed inferior conjunction on July 21, but by August 5, it brightens to the first magnitude, and for several mornings it lingers about 9° lower right of Pollux, the brighter Gemini twin. Mercury reaches greatest elongation, 19° from Sun, on Aug. 9, and attains its greatest altitude in ENE morning twilight about Aug. 11. Conveniently on that date, a line from Castor to Pollux, 4.5° long, extended nearly 10° locates Mercury, now brighter than magnitude zero. Mercury brightens to mag. –1.0 by Aug. 18, and to –1.5 by Aug. 26, but by the latter date, it rises in brighter twilight.

By the middle of August, you should start seeing Sirius, the Dog Star, low in ESE morning twilight. Locate this brightest star, of mag. –1.4, by extending the line of Orion’s belt toward the horizon. If you catch Sirius while it’s still low, you can also spot Altair, low, just north of west. Then you can see both the Summer Triangle (Vega-Altair-Deneb) and the Winter Triangle (Sirius-Procyon-Betelgeuse) simultaneously. On each successive morning, you can find these stars in the same positions 4 minutes earlier, or two hours early each month. By January, you’ll be looking during evening twilight to catch both Triangles simultaneously.

Follow the waning Moon across the morning sky each month, watching for its conjunctions with planets and with these bright zodiacal stars: Aldebaran in Taurus, Pollux, and Castor in Gemini, Regulus in Leo, Spica in Virgo, and Antares in Scorpius. The dates the Moon is in the sky at morning mid-twilight in late 2019 are Aug. 15-29, Sept. 13-27, Oct. 13-26, Nov. 12-25, and Dec. 11-24. Within each set of dates, on Aug. 23, Sept. 22, Oct. 21, Nov. 19, and Dec. 19, the Moon is at or nearest to Last Quarter phase, when it’s half full and 90° from the Sun, and will show wonderful surface detail through binoculars and telescopes! Even at a daytime session at your school, schedule a session within a day or two of Last Quarter phase as the first activity of the morning. Thread a single polarizing filter into the low-power eyepiece of your telescope, aim the telescope at the Moon, and rotate the eyepiece in its tube until the sky foreground is made as dark as possible. (You’ll be using the filter to cross-polarize against the polarized light of the blue sky.) This greatly improves the contrast of Moon against the sky and allows you to see wonderful lunar detail even in the daytime. This works best when the Moon is close to 90° from the Sun (and so half full), on a day when the sky is a deep blue, without much haze. You can order threaded polarizing filters from Orion Telescopes and Binoculars; their website is www.telescope.com

On November mornings, look west to see the huge Winter Hexagon. Beginning with Sirius, its southernmost and brightest star, and proceeding in clockwise order, its other members are Procyon; the “Twin” stars Pollux and Castor just 4.5° apart; Capella, the northernmost member of the Hexagon; Aldebaran; Rigel; and back to Sirius. The red supergiant star Betelgeuse, marking Orion’s shoulder, is inside the Hexagon. High in NE, find the Big Dipper and use its curved handle to “follow the arc to Arcturus” (the bright zero-mag. golden star in the east) and “drive a spike to Spica”, the first-mag. star lower in ESE. In early Nov. 2019, blue-white Spica has a fainter, reddish companion nearby: Mars! They stay within 5° Nov. 4-16 and appear closest, 2.8° apart, on Nov. 10. From then until early June 2020, watch Mars shift eastward against background stars by about two-thirds of a degree per day.

Daytime event: Transit of Mercury on Nov. 11, 2019. Our solar system’s innermost planet passes directly in front of the Sun on the morning of Monday, Nov. 11, a federal holiday, therefore not a school day. To observe this transit of Mercury safely, one should use a filter designed for solar observing, securely installed at the front end of a telescope. Do not use any of those unsafe, eyepiece solar filters often provided with inexpensive telescopes; those should be regarded as throwaways! Unlike during a solar eclipse, or during the transits of Venus in 2004 and 2012, hand-held filters used with unaided eye will not show the tiny disk of Mercury, which will be only 10 arcseconds across, less than 1/180 of the half-degree solar diameter, and only one-sixth of the apparent diameter of Venus at its most recent transit in 2012. From California on Nov. 11, 2019, the transit is already in progress at sunrise and won’t be seen well until the Sun rises higher in the sky. Mercury appears at its minimum distance NNE of the center of the solar disk at 7:20 a.m. PST. For observers in California, the leading edge of Mercury’s tiny dark silhouetted disk reaches the solar limb within a few seconds of 10:03 a.m., and takes only about 1.7 minutes more until egress from the disk is complete. After this transit of Mercury on Nov. 11, there won’t be another visible in California until May 7, 2049.

Next, Mercury enters the ESE morning sky, and very quickly! By Nov. 18, it attains mag. +1.1, and is within 13° lower left of faint Mars, of mag. +1.8. Mercury brightens rapidly, reaching mag. 0.0 by Nov. 22, and lingers about 10° lower left of Mars during Nov. 21-29. The Moon, Full and low in W to WNW on Nov. 12, wanes and makes it over to the busy SE to ESE sky by Nov. 23, when Spica will be within 8° lower right of the 12-percent crescent Moon; Mars 9.1° lower left of Spica; and Mercury 9.6° lower left of Mars. Notice the arrangement of Spica-Mars-Mercury in a nearly straight line, and watch the Moon move downward (sunward) for two more mornings. On Nov. 24, Mars, the middle member of the morning’s evenly spaced lineup, will appear within 4° left of a 6-percent crescent Moon. In the last view on Nov. 25, the old, 2-percent crescent Moon in ESE will be the lowest member of four bodies in a nearly perfect line, and within 7° lower left of Mercury.

Mercury reaches greatest elongation 20° from the Sun on Nov. 28, with the planet steeply upper right of the Sun rather than low to its right as during its greatest elongations of 28° in April 2019 and March 2020. Although Mercury doesn’t range as far from the Sun, the November-December morning apparition of Mercury is by far the most favorable for viewers at mid-northern latitudes during the school year 2019-2020.

But Mercury is heading toward the far side of the Sun, so by Dec. 21, it will rise in bright twilight, leaving Mars once again as the only easy morning planet. On Dec. 12, Mars passes 0.2° north of the 3rd-magnitude star Alpha in Libra, also known as Zubenelgenubi, the northern claw of the Scorpion, as it was formerly imagined. On Dec. 22 the waning crescent Moon will appear 7° upper right of Mars, and on the 23rd, 7° to the red planet’s lower left. In a final easy view on Dec. 24, the 3-percent, old crescent Moon will appear 20° lower left of Mars. Antares, recently emerged from solar conjunction, appears 7° lower right of Moon and 17° lower left of Mars.

Highlights of January through June 2020 — morning sky: Giant planets return, and participate in a rare compact gathering of the three bright outer planets.

Here are the morning twilight charts for January through August 2020. Again, the stars, and now also slow-moving Jupiter and Saturn are in roughly the same positions they’ll be in the evening sky a few months forward in time.

January 2020 opens with Mars in the southeastern morning sky, 12° upper right of Antares, the heart of the Scorpion, on Jan. 1. On Jan. 17-19, Mars passes within 4.8° north of Antares. Compare them in brightness and color, and look up the meaning of the star name. Doesn’t Mars seem lonely with no other planets visible in the morning? But help may already be here! Jupiter was behind the Sun on Dec. 27, 2019, and, owing to Earth’s revolution around the Sun, is now emerging into the morning sky. On Jan. 17, look for Jupiter very low in ESE to SE, 31° lower left of the Mars-Antares pair. Each morning at the same stage of twilight, Jupiter rises a little higher. A waning crescent Moon comes through on Jan. 20-22 and forms attractive groupings with Antares, Mars, and Jupiter.

Mars will soon have even more company. Saturn passed behind the Sun on Jan. 13, 2020. In February Saturn will become easily visible to the unaided eye. By St. Valentine’s Day, Feb. 14, Saturn is only 10° lower left of Jupiter, while Jupiter, in turn, will be 18° lower left of Mars, the three planets spanning 28°.

During February 2020, all three bright outer planets pass the descending nodes of their orbits, which means they cross from above to below the ecliptic, or Earth’s orbit plane. As a result, as seen from Earth, the three planets appear in a remarkably straight line.

Mark Feb. 18-20 on your calendar. The crescent Moon again comes through, actually occulting or covering up Mars in the darkness before dawn on Feb. 18 for California residents. During twilight that morning, after the occultation, Mars will appear very closely upper right of the 23-percent Moon, while Jupiter and Saturn appear 15° and 25° to Moon’s lower left.

On Feb. 19, the 15-percent crescent Moon will appear only 3° right of Jupiter, while Mars will be 13° to Moon’s upper right, and Saturn 12° to Moon’s lower left. The span of three planets, with Moon included, is 25°.

On Feb. 20, the 9-percent crescent Moon will be 2.5° lower right of Saturn, while Jupiter and Mars appear 10° and nearly 25° to Moon’s upper right.

The events involving these three planets in March 2020 will be even more special.Since Jupiter appears to pass Saturn at intervals of about 20 years (next on Dec. 21, 2020), the longest interval between conjunctions for any pair of naked-eye planets. So having Jupiter-Saturn appear within a few degrees of each other, though lasting for a few months, is unusual. Having Mars pass through while the two giants appear only a few degrees apart is even more remarkable.

Mars passes 0.7° S of Jupiter on March 20, 2020. Saturn is then 7.1° east of the pair.

Mars passes 0.9° S of Saturn on March 31. Jupiter is then within 6.3° west of the pair. This is the most compact arrangement of the three bright outer planets between the years 2000 and 2040.

More in March: Mercury brightens from mag. +1 to 0 March 9-31, but is very low, between ESE and E. It reaches the greatest elongation March 24 when 28° from Sun, but is highest in twilight about a week earlier. A waning crescent Moon (38 percent) is 9° west of Mars on March 17. In a truly rare gathering on March 18, a 29-percent crescent Moon is inside the compact gathering of three bright outer planets, about 3° lower left of Mars and Jupiter, and 6° right of Saturn. The gathering of Saturn, Moon, Jupiter, Mars spans only 8.3°. Still more on March 18: A minimum span of the five bodies, Mercury-Saturn-Moon-Jupiter-Mars, 40°. On March 19, a 20-percent crescent Moon is nearly 8° lower left of Saturn, and so outside the compact 3-planet gathering.

On March 20, as mentioned above, Mars passes 0.7° S of Jupiter, with Saturn 7.1° to the east of the pair. Mercury lies 33° east (lower left) of Saturn and 40° east of the Mars-Jupiter pair. The 13-percent waning crescent Moon lies 19° lower left of Saturn and 15° upper right of Mercury.

On March 21, the last, easy, 7-percent crescent old Moon is very low in ESE, 5° lower right of Mercury.

March 24: Mercury’s greatest elongation of nearly 28° from Sun occurs three days before aphelion, and so is nearly the greatest possible. Yet this is an unfavorable apparition of Mercury for mid-northern latitudes because the ecliptic and lineup of the planets make a low angle with the horizon on mornings in March, when the southernmost part of the zodiac, in Sagittarius, is low in the south at sunrise. Contrast with Venus, now at greatest elongation high in the western evening sky, 46° from Sun. At dusk, the northernmost part of the zodiac, in Gemini, is high in the south at sunset, and the ecliptic is nearly vertical.

March 26, morning: 4-planet span Mercury-Mars-Saturn-Jupiter, now 45°, grows by 1° daily as Mercury moves eastward.

March 31: Don’t miss seeing the least span of three bright outer planets as Mars passes 0.9° S of Saturn. Jupiter is within 6.3° W of pair. Mercury is low in ESE to E, 44° E of Mars-Saturn pair and 50° E of Jupiter.

On mornings in April 2020, the 3-planet span of Mars-Saturn-Jupiter expands from 6.° on April 1 to just over 24° on the 30th. The Jupiter-Saturn gap is very slowly closing all month, through 6.0° apart on Apr. 5, and 5.0° on Apr. 28. Mars widens its distance east of Saturn, from just over 1.0° on April 1, to nearly 20° on Apr. 30. The four planet span Mercury-Mars-Saturn-Jupiter widens to nearly 60° by April 7, but Mercury is then very low in morning mid-twilight, just south of east.

The span of three bright outer planets has expanded to 15° on April 15, when the Moon, 44 percent illuminated and just past Last Quarter phase, drops in for a one-day visit, nearly 4° below Saturn and 8° lower left of Jupiter, and just over 8° right of Mars. On the adjacent mornings, the Moon lies just outside the grouping, 6° W of Jupiter on April 14 and 5° lower left of Mars on Apr. 16.

From April 28 through June 6, 2020, the giant planets Jupiter and Saturn appear within 5° apart and reach a minimum separation of 4.7° on May 18. The event is a quasi-conjunction, defined as an approach within 5° without either planet passing the other, at least until after they’ve moved apart. Saturn begins retrograde on May 11, Jupiter on May 14, and the planets reach a minimum separation on May 18 as Jupiter’s westward motion becomes faster than Saturn’s. (The gap between the giants will slowly widen until August 28, when they’ll be 8.3° apart in the evening sky.) In the southern sky in morning twilight on May 12, the waning gibbous Moon (71 percent) appears below the giant pair, 3° lower left of Jupiter and 5° lower right of Saturn. The Moon fits within the larger three-planet gathering for two more mornings, ending at 51 percent (Last Quarter phase) and 8° right of Mars on May 14. On May 15, the 41-percent crescent Moon will lie outside the gathering, 5° lower left of Mars.

In June 2020 morning twilight, the Moon wanes from Full low in WSW on June 5, to a thin crescent very low in ENE on June 19. Along the way, on June 8 and 9, the Moon (at 91 and 84 percent) passes from lower right to left of the Jupiter-Saturn pair 5° apart in SSW. On June 12 and 13, the Moon (at 58 and 48 percent) passes from lower right to lower left of Mars in SE. By these two dates, Venus has emerged very low in ENE and shows a 3-percent crescent nearly one arcminute across, resolvable in binoculars. On the Moon’s last day, June 19, the old lunar crescent will be 3 percent full and just 2° lower left of Venus, which has widened to 8 percent but shrunk slightly in apparent size. Can you see emerging Aldebaran about 3° below the lunar crescent and 4.8° lower left of Venus? As both Venus and Aldebaran rise higher each morning and get easier to see, they’ll stay about the same distance apart through June 28 (max. dist. 5.1° on June 23 and 24, just before Venus ends retrograde).

In July 2020, while Venus shines at greatest brilliancy, watch the Moon pass all five naked-eye planets in morning twilight during July 5-19. But you won’t start seeing Mercury until the last few days of that range after it becomes bright enough. Here’s the sequence of Moon-planet pairings:

On July 5, the Full Moon will be 7° lower right of Jupiter low in SW. Saturn that morning will be 6.3° upper left of Jupiter. On July 6 the waning 98-percent Moon will appear 3° lower left of Saturn and 8° upper left of Jupiter. On July 11 and 12, the still gibbous Moon (64 and 55 percent) will appear 5° and 7° from Mars high in SSE. On the same two mornings, Venus will pass 1.0° N of Aldebaran. On July 17, low, north of east, the 11-percent crescent Moon is 4° lower left of Venus. Look for Aldebaran 3.3° upper right of Venus that morning, and the Hyades cluster just a little farther. With slight optical aid, Venus shows a crescent, then 33-percent full and less than 0.6 arcminute across. By this date, July 17th, Mercury attains the first magnitude in the morning sky and is starting to be visible after its inferior conjunction of June 30. Look for it very low in ENE, 20° lower left of the lunar crescent. Can you see the Moon and all five naked-eye planets simultaneously? Look after Mercury rises and before Jupiter sets. On July 18, the lunar crescent (6 percent) is 16° lower left of Venus and 8° upper right of Mercury. On July 19, the last day of Moon visibility, the 2-percent lunar crescent is very low in ENE, with Mercury 6° to its upper right.

Mercury brightens through mag. 0.0 during July 23-24, but Jupiter, past opposition, is getting lower and setting 4-5 minutes earlier each morning. So the best dates for seeing all five naked-eye planets simultaneously might be July 17-27. Make sure you have unobstructed views toward ENE and WSW to include both Mercury and Jupiter in your sightings.

With the oppositions of Jupiter on the night of July 14, 2020, and Saturn on the night of July 20, it becomes convenient to follow those two planets at dusk for the rest of 2020. In the evening sky, watch Jupiter and Saturn continue to separate until August 28 (8.3° apart), and then come back together for their spectacular close pairing on December 21, 2020, when they’ll be just 0.1 degrees apart. To get an idea of how close that is, observe the double-star Mizar and Alcor at the bend of the handle of the Big Dipper; they are 0.2 degrees apart. So Jupiter and Saturn on December 21, 2020, will have half that separation!

In the morning sky, after July 2020, Mercury will continue to be visible through the first week of August, and a few more days if you search for it low in the brighter morning twilight. Mars continues to brighten in the morning sky until October 2020, but you can switch to evenings at its opposition on Oct. 13, and then the red planet will remain an evening object, fading, until it sinks into the western twilight glow around the end of July 2021. Venus continues to be visible mornings until late January 2021, and a bit longer if you look low in bright twilight.

Abrams Planetarium publishes a monthly Sky Calendar with an evening sky map. The calendar will illustrate many of the events described in this article. Subscriptions are $12 per year at www.abramsplanetarium.org/skycalendar/ for three printed issues mailed quarterly. A sample issue of the Sky Calendar and its evening sky map are posted on that website.To help plan your evening or morning planet viewing sessions from August 2019 through August 2020,download Jeffrey Hunt’s graphic summaries of Moon and planet setting and rising times relative to times of sunset and sunrise, exact for Palm Springs and Sacramento, but each useful over a wide area.

To help plan your evening or morning planet viewing sessions between August 2019 and August 2020, download Jeffrey Hunt’s graphic summaries of Moon and planet setting and rising times relative to times of sunset and sunrise, exact for Palm Springs and Sacramento, but each useful over a wide area.

The graphs of evening planet setting times show the departure of Jupiter and Saturn in December 2019, and the very favorable appearance of Venus visible for 3½ to 4 hours after sunset in March-April 2020, followed by its rapid departure from the evening sky in May. The open circles on the evening charts show setting times of the waxing Moon for several evenings after New.

The graphs of morning planet rising times show the slow emergence of Mars before dawn in autumn 2019, the emergence of Jupiter and Saturn into visibility in January-February 2020, and the sudden rise of Venus into predawn prominence in June-July 2020. The open circles on the morning charts show rising times of the waning Moon for several mornings before New.

These charts also make it easy to pick out the best dates for seeing Mercury in evening and morning skies, when it sets longest after sunset or rises longest before sunrise.

Here’s wishing you many clear nights to enjoy the sky!

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