Bernard Reim
If you could photograph the sun at high noon every few days throughout the year, you would see that it traces a figure eight in the sky, called the analemma. This giant graph in the sky is loaded with information if you know how to read it. It tells you the tilt of the earth, the fact that we are orbiting in ellipses, your latitude on earth, sunrise and sunset times, the equation of time, when we are moving faster and slower around the sun, and many more things. If the earth was not tilted and our orbit was a perfect circle, the whole analema would just be a single dot in our sky, since the sun would always be at the same place at high noon.
Starting from the North Pole, you would only see half of this analema, because the sun doesn’t rise at all for half a year. By the time you get down to the Arctic Circle, would see the whole thing and it would be upright and each loop would be the same size. Then it gets more and more tilted over and the top loop gets smaller. By the time you get to the equator, it is completely horizontal and then the top loop gets larger and it starts tilting the other way as you get farther south until it is upright and even again as you get to the Antarctic Circle and then part of it starts disappearing again, as it did above the Arctic Circle.
You can actually measure the tilt of the earth for yourself at either of the solstices by just measuring the shadow of a level stick and knowing your latitude. You could even trace the entire analemma on the ground with a sundial, which is much easier than photographing it in the sky over the course of a whole year.
Many exciting highlights abound once again this month that will make it well worth it to brave any cold weather that we may get. Getting up an hour or so before sunrise for several mornings this month will also reap great rewards for you, as it did for me last month.
Our four brightest planets will all grace our morning sky this month, the Geminid Meteor Shower will happen without the moon in the way, a lesser meteor shower called the Ursids will peak near the winter solstice, a new comet will be visible in the morning sky, and the moon will occult Venus in the daytime sky on Dec. 7.
Jupiter starts the month rising about half an hour after midnight and will end the month rising two hours earlier. Then Mars rises next around 2 a.m. and it will only rise about half an hour earlier by the end of the month. Then brilliant Venus rises around 4 a.m. and Saturn will join the trio by the middle of the month rising only about one hour before sunrise.
So there you have your morning planetary line up along the ecliptic plane of our solar system. To add some real drama to these planets, watch the last quarter moon pass near Jupiter on the 3rd and 4th, then close to Mars on the 5th and 6th, and then very close to Venus on the morning of the 7th about one hour before sunrise. Later that same day, as the thin waning crescent moon creeps ever closer to our brightest planet, it will actually cover up Venus completely starting at 12:40 p.m. Then the waxing gibbous Venus will reappear from the moon’s dark limb, which will be invisible in the daylight, about one hour later, at 1:40 p.m. This shows you that the moon is always moving eastward in our sky at the rate of half a degree per hour, which is its own width.
I have seen an event like this before. It is quite amazing to witness and it really demonstrates many interesting aspects of the relative sizes and motions of neighboring objects in our solar system along with great excitement in trying to capture it on film. You will need a telescope or a good pair of binoculars to see this daytime event.
The best meteor shower of the year, the Geminids, will peak a week later on the morning of Monday the 14th. They are expected to reach 120 meteors per hour, which is a fantastic rate of 2 meteors per minute. They are one of only two annual meteor showers that are caused by an asteroid instead of a comet. The Geminids are caused by 3200 Phaethon, named after the driver and sun god of Helios’s chariot.
All of these meteors will appear to emanate from the constellation of Gemini the Twins in the famous winter hexagon, just above Orion. It will be high in our eastern sky by 11 p.m., but you will be able to see meteors anywhere in the whole sky all night long as well as the next night and even some on Saturday night the 12th. Just bundle up, find a good open sky by the ocean or a large field, and enjoy a great, quiet show brought to you by nature and our protecting and life-giving atmosphere. If you watch for at least one hour, you can even do a scientific meteor count for the International Meteor Organization.
A comet named Catalina, discovered by the Catalina Sky Survey in Arizona on Halloween night two years ago, just reached perihelion last month and will be climbing higher into our morning sky near all the planets all month long and into next month. This comet is zipping along at 100,000 miles per hour and is already sporting two tails, one of which is 500,000 miles long. It should become visible without binoculars early this month. See how soon you can spot it and photograph it along with all of our solar system neighbors in the morning sky.
Dec. 2: On this day in 1974 Pioneer 11 flew by Jupiter. It is now passed the heliosphere.
Dec. 3: Last quarter moon is at 2:40 a.m. EST.
Dec. 4: The moon passes just below Jupiter this morning.
Dec. 5: The moon passes near Mars this morning, one hour before sunrise.
Dec. 7: The moon passes very close to Venus this morning and will occult the planet this afternoon, starting at 12:40 p.m. and ending one hour later.
Dec. 11: New moon is at 5:29 a.m. Annie Jump Canon was born on this day in 1863.
Dec. 13: The Geminid meteor shower peaks tonight and into the next night.
Dec. 14: Tycho Brahe was born on this day in 1546, three years after Copernicus died.
Dec. 17: On this day in 1903 the first powered flight was accomplished by Orville Wright. We flew all the way to the moon less than 66 years later.
Dec.18: First quarter moon is at 10:14 a.m.
Dec. 21: The winter solstice happens at 11:48 p.m., marking the longest night of the year.
Dec. 23: The Ursid meteor shower peaks, emanating from Ursa Minor near Polaris.
Dec. 25: Isaac Newton was born on this day in 1642. Full moon is at 6:11 a.m. This is also called the Long Night Moon or Moon Before Yule if it happens before Christmas.
Dec. 27: Johannes Kepler was born on this day in 1571. He discovered the three laws of planetary motion, one of which you can clearly see demonstrated in the shape of the sun’s analemma. He worked closely with Tycho Brahe, who was the greatest observer in the world at that time.
Dec. 28: Arthur Eddington was born on this day in 1882. He led the solar eclipse tour in 1919 that was the first concrete proof of Einstein’s General Theory of Relativity, which came out exactly 100 years ago in 1915.
Dec. 29: On this day in 1980, the very first space shuttle ever, STS-1, left the Vehicle Assembly Building and was rolled out to the launch pad in Cape Kennedy.
— Bernie Reim is an amateur astronomer and teaches astronomy lab courses at the University of Southern Maine.
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