THE OBSERVER Newsletter of The Tri-State Astronomers December 2020 Volume 35 Number 12 MONTH AT A GLANCE The next TSA Virtual Meeting December 16, 7:00 PM This is the final monthly edition of the OBSERVER.

The OBSERVER has been published for 35 years since November 1985.

©BlueMarmot / CalculatorCat.Com There are plans to publish a special remembrance edition after the Last Quarter Mon Dec 07 first of the year. Please submit any suggestions you have for the OBSERVER Remembrance Edition by January 15. New Moon Star Party (Club Members Only) Fri Dec 11 or Sat Dec 12, Dusk Geminids Peak Mon Dec 14, 2:00 AM New Moon Mon Dec 14 TSA Virtual Meeting Wed Dec 16, 7:00 PM Virtual Meeting Jupiter/Saturn conjunction 0°6 This is their closest in 397 years. Next closest will be in 2080 Mon Dec 21, 4:50 PM - 6:55 PM Winter Solstace Mon Dec 21, 5:02 AM First Quarter Mon Dec 21 Full Moon Tue Dec 29 TristateAstronomers.org December Sky Map

Early December 7:00 PM - Late December 6:00 PM

2 Our Friendly Skies By Alicia Kutzner Robertson, WCPS STEM/Planetarium Resource Teacher And Andy Smetzer, Tristate Astronomers

THE DECEMBER SKY December is the season of celebration! Whether you celebrate Hanukkah, Christmas, Kwanzaa, Boxing Day or Omisoka, this is a time of year that we look forward to as it means family and friends will gather together, if only virtually, to enjoy each other’s company. What better way to spend time together than looking at the stars with a great big cup of cocoa! After all, no matter where your family is you are all going to be looking at the same sky!

THE DECEMBER STARS This has always been my favorite time of year as it means that my friend, the constellation , will be hunting the skies for an- other season. Orion is part of the Winter Circle or Winter Hexagon, an that is made up of stars from 6 different constel- lations. Orion is easily identified by first locating the three stars that make up his belt. From the lowest star on his belt, move up to the bright star, , which is located in Orion’s armpit. Betelgeuse is a red supergiant that will eventually go supernova, leaving Orion arm pitless! However, it is not Betelgeuse that we will use to make our way clockwise around the Winter Circle but , which can be found down and to the west of the highest star in Orion’s belt.

Traveling down and to the east of Rigel, you will find the bright star , the nose of Orion’s hunting dog in the constellation . For the month of December, I prefer to believe it is the nose of a reindeer that Orion uses to carry his hunting equipment - similar to another jolly man that we know! Of course, both Orion and Canis Major are accompanied by the con- stellation , Orion’s small hunting dog. You can find him by looking up and east of Sirius to the bright star .

From Procyon, head straight up and you will see two stars stacked one almost directly above the other. These stars, Pollux and Castor, are the brightest stars in the constellation Gemini. Watch out for the twins on December 2 as Castor tries to punt the moon across the sky!

Continue looking up and to the west you will find the star , located at the top of the Winter Circle. Capella is the brightest star in the constellation , the Charioteer. Although Capella appears to be one star, if you had a telescope strong enough to see it well, you would notice it is actually 4 stars arranged in 2 binary star systems. The stars in each system appear to dance a slow waltz around one another, having chosen their partner long ago.

Continue clockwise and down to the great red eye of the Bull, our final constellation in the Winter Circle. At first glance, the eye, , may seem to be the same size as any other star. In actuality, Aldebaran is approximately 44 times larger than our own Sun, not a star to be trifled with!

THE DECEMBER SOLAR SYSTEM Just as December heralds the end of the year, it also brings us to the end of a spectacular season of planet watching, including one final show! Before we begin talking about planets, there are a few notes I would like you to keep in mind. As we discuss the visibility of planets from Earth, we talk in terms of their or how bright objects in space appear to us as we view them from Earth. On the apparent magnitude scale, the lower the apparent magnitude, the brighter the object appears to be. Also, viewing notes are made assuming you are observing over a flat horizon from Hagerstown, MD. However, you may be viewing the skies from a different location and/or mountains, trees and buildings may obstruct your view of the horizon. Both of those factors can affect when the object rises and sets and how visible it is from where you are.

Morning Planets 3 MERCURY is closing out the year as fickle as ever. He will start the month visible in the morning, rising at 6:22 am and end the month visible in the evening, setting at 5:20 pm. Mercury also has a hard time deciding which constellation to settle down in and travels quickly from one constellation to another this month. He starts December in Libra, but travels through Scorpio and Ophiuchus to end the month in Sagittarius on December 19, shining more brightly then he did at the beginning of the month with a magnitude of -1.

VENUS remains a bit more steady throughout the month, rising before sunrise and setting at approximately 3:25 pm each day, shining with an apparent magnitude of approximately -4. Just like Mercury, she too tends to wander this month, moving from Libra into Scorpio over the evening of the 17th and ending the month in Ophiuchus on the 22nd.

Evening Planets JUPITER and SATURN continue their friendship in the early evening December skies. Jupiter rises at 10:32 am on Dec. 1 and sets at 8:07 pm at the beginning of the month, but rises earlier and earlier throughout the month until he is rising at 8:56 am and setting at 6:41 pm on the 31st. He remains the jewel of the sky, shining with a magnitude averaging -2 throughout the month and travels from the constellation of Sagittarius into Capricorn over the night of the 16th.

Not one to be left alone, SATURN rises and sets just minutes behind Jupiter throughout the month as she strives to catch up to Jupiter, even moving from the constellation of Sagittarius into Capricorn on the same evening as Jupiter. However, the ever shy Saturn still allows Jupiter to be the star of the friendship, shining with a lesser average magnitude of 1.

SPECIAL EVENTS This is a month filled with celestial events to celebrate. From the 10th to the 12th, Venus and the moon will rise together at sunrise, being closest together on the 12th. This will be a great time to look at the dark side of the moon as it is illuminated by earthshine or sunlight that is reflected from Earth to the moon and back again.

The Geminids meteor shower will emanate from the constellation of Gemini on the 13th and 14th. For the best viewing, head out around 2:00 am on Dec. 14. During the peak of the shower, you may be able to see 50 - 100 meteors per hour! And, lucky for us, the Geminids coincide with the new moon, so you will not have to worry about moonlight obscuring your view of the shower.

The Winter Solstice occurs on Monday, Dec. 21 at 5:02 am. The Winter Solstice marks the shortest day of the year in the north- ern hemisphere when the sun is directly over the Tropic of Capricorn in the southern hemisphere and everything above the Arctic Circle spends the day in darkness. Celebrate by building a yule altar to honor the return of the sun with a gold, silver or yellow candle surrounded by evergreens and pinecones!

The 21st will also see the great conjunction of those friendly planets Jupiter and Saturn. Conjunction happens when 2 or more objects meet up in the sky. This conjunction is called a “great” conjunction as Jupiter and Saturn are the largest planets in our solar system. At their closest, Jupiter and Saturn will only be .1 degree apart, which is the diameter of the moon and is a much smaller distance than the width of your little finger when your hand is held at arm’s length. Jupiter and Saturn will be so close that they may appear as one very bright star. However, don’t delay your observing of this great conjunction! Jupiter and Saturn will be visible at sunset, 4:50 pm, but they will set at 6:55 pm. Blink and you may miss the conjunction, which would be unfortu- nate as this is the first great conjunction since 2000, the closest since 1623 and won’t be matched until March 15, 2080.

On December 23, the moon is just below Mars with Uranus trailing Mars to the SE. On December 24, however, the moon will be directly below Uranus with Mars directly to the West. Don’t forget - you will need binoculars or a telescope to view Uranus.

We end the month, New Year’s Eve, with the great star of Sirius, the brightest visible from earth, reaching its highest point in the sky, culmination, at midnight. FINALLY As we close out what we can only consider to be a very strange and sometimes lonely year, I hope you will take a few minutes to bathe in the comfort of our evening skies and enjoy the steady friendship offered by our stars and planets. I wish you all a happy holiday season and joyous New Year! 4 Geminids December 14, 2020 2:30 AM

Moon, Uranus, Mars, Neptune December 24, 2020 9:30 PM

5 6 December 21, 6:25 PM 0°06ˈ Separation

7 TSA MEMBER ONLY EVENT WEATHER PERMITTING

NEW MOON STAR PARTY DATES

December 11/12

FACE COVERINGS AND SOCIAL DISTANCING MANDATORY

8 Visitors to Both Jupiter and Saturn

By David Prosper

This article is distributed by NASA Night Sky Network The Night Sky Network program supports astronomy clubs across the USA dedicated to astronomy outreach. Visit nightsky.jpl.nasa.org to find local clubs, events, and more!

Have you observed Jupiter and Saturn moving closer to each other over the past few months? On Decem- ber 21, the two worlds will be at their closest, around 1/5 of a full Moon apart! While the two gas giants may appear close, in reality they are hundreds of millions of miles apart. Despite this vast distance, a select few missions have visited both worlds by using a gravity assist from giant Jupiter to slingshot them towards Sat- urn, saving time and fuel.

Pioneer 11 was the first mission to visit both worlds! Launched in 1973, the probe flew past Jupiter in late 1974, passing just 26,400 miles above its stormy clouds. In 1979, it became the first spacecraft to encounter Saturn. Pioneer 11 took the first up-close photos of Saturn and its satellites, and made many exciting discov- eries, including the detections of its magnetic field and a faint “F” ring, before departing Saturn and eventual- ly, the solar system.

The Voyager missions quickly followed up, taking a “Grand Tour” of the four largest and most distant plan- ets in our solar system. Both probes were launched within two weeks of each other in 1977. Voyager 1 flew past Jupiter in March 1979, discovering Jupiter’s faint ring and two new moons, along with active volcanoes on Io’s surface! The probe then flew past Saturn in November 1980, discovering five new moons, a new “G” ring, mysterious ring “spokes,” and “shepherd moons” shaping the rings. After a brief encounter with Ti- tan revealed evidence of complex organic chemistry and liquid on the moon’s frigid surface, Voyager 1 was flung out of the plane of the solar system. Following close behind, Voyager 2 took detailed photos of Jupiter’s moons and cloud tops in July 1979. Flying past Saturn in August 1981, Voyager 2 measured the thickness of Saturn’s rings and took detailed photos of many of its moons. This second explorer then captured images of Uranus and Neptune before leaving our solar system.

Cassini-Huygens was the last mission to visit both worlds. Launched in 1997, the mission flew past Jupiter in late 2000 and took incredibly detailed photos of its stormy atmosphere and faint rings. Cassini entered into Saturn’s orbit on July 1, 2004. The Huygens probe separated from Cassini, landing on Titan to become the first probe in the outer solar system. Cassini discovered geysers on Enceladus, fine details in Saturn’s rings, many more moons and “moonlets,” the changing oceans of Titan, and seasonal changes on Saturn itself. After revolutionizing our understanding of the Saturnian system, Cassini’s mission ended with a fiery plunge into its atmosphere on September 15, 2017.

What’s next for the exploration of the outer worlds of our solar system? While Juno is currently in orbit around Jupiter, there are more missions in development to study the moons of Jupiter and Saturn. Discover more about future NASA missions to the outer worlds of our solar system at nasa.gov.

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The difference in technology between generations of space probes can be stunning! The top two photos of Jupiter and Saturn were taken by Pioneer 11 in 1974 (Jupiter) and 1979 (Saturn); the bottom two were taken by Cassini in 2000 (Ju- piter) and 2016 (Saturn). What kinds of photos await us from future generations of deep space explorers?

10 TREAC

There are NO scheduled OutReach Events for December

New Hubble Data Explains Missing Dark Matter (The image used for the December Banner)

New data from the NASA/ESA Hubble Space Telescope provides further evi- dence for tidal disruption in the galaxy NGC 1052-DF4. This result explains a previous finding that this galaxy is missing most of its dark matter. By studying the galaxy’s light and globular cluster distribution, astronomers have concluded that the gravity forces of the neighbouring galaxy NGC 1035 stripped the dark matter from NGC 1052-DF4 and are now tearing the galaxy apart.

More Info: https://www.spacetelescope.org/news/heic2019/

Image credit: ESA/Hubble, NASA, Digitzed Sky Survey 2. Acknowledgement: Davide de Martin.