Earlier this month, after a nine-month stay as our evening “star,” Venus moved out of the twilight and into the dawn to become our morning “star.” You can find Venus on any clear morning if you look toward the southeast about 45 minutes before sunrise.
With Venus departed from the evening sky, Jupiter is the brightest planet. Visible above the eastern horizon before sunset and by the end of civil twilight (currently around 5:30 p.m.), it is about a third of the way up the sky. Because this planet is more than 1,000 times the size of Earth, its enormous surface reflects an abundance of sunlight, enabling it to outshine the brightest stars of the night.
Jupiter moves slowly among the stars as it travels through its 12-year orbit around the sun, moving eastward at just one constellation each year. Presently, it is smack in the middle of Gemini, the celestial twin brothers. The bright stars Castor and Pollux, the names of the twins, highlight this stellar backdrop. Jupiter is found just west of the twin stars.
Pollux is slightly brighter than Castor. See if you can notice that Pollux has a slight orange tinge in its light. This color is because its surface temperature is about 1,000 degrees cooler than the sun’s surface. Although fainter, Castor appears whitish, since its surface is many thousands of degrees hotter than the sun’s. Together, the stars represent the sons of Zeus and Leda.
Since professional astronomers cannot use their time at major observatories to continuously monitor the planets, amateur astronomers with good-sized telescopes and electronic imaging devices fill in the gaps. This nightly coverage — with equipment that produces images as sharp as professional images — has resulted in “pro-am” collaborations that have produced some significant discoveries in recent years.
By watching Jupiter, amateur astronomers have noted that its Great Red Spot — a long-lived, giant storm almost the size of three Earths in Jupiter’s clouds — was slimming down and the storm was swirling around slightly more slowly than usual. Two years ago, they also noticed that the spot’s color paled but lately has regained much of its reddish color.
Also discovered by amateurs was a much smaller red spot called “Red Jr.” It was found in 2006 by an amateur astronomer in the Philippines, who noticed the sudden reddening after three 60-year-old white ovals merged. Professional astronomers followed up on this observation with the Hubble Telescope.
In 2009, amateur astronomers also saw a single white oval turn red as it neared the Great Red Spot. This smaller red spot only lasted a few months before it mixed with the big spot. Then amateurs were the first to see that one of Jupiter’s dark cloud bands lightened, probably as whitish material was dredged up from below.
This flurry of activity has led planetary scientists to think that Jupiter is undergoing a global upheaval in which many regions of the planet’s atmosphere become active over several years. No one knows how long this upheaval will last, but astronomers hope to use these observations to better understand what is below Jupiter’s cloud tops.
Many people remember the great collisions that happened in July 1994 between the pieces of a shattered comet and Jupiter. Over a few days, the fragments of Comet Shoemaker-Levy 9 plowed into Jupiter, locally heating its cloud tops, and leaving large brown burn marks that could be seen through amateur telescopes. Astronomers thought that strikes into Jupiter’s clouds were a once-in-a-century event but now amateurs monitoring Jupiter are finding otherwise.
On July 19, 2009, an amateur astronomer in Australia was the first to notice a faint black spot near Jupiter’s south pole. As he watched, the spot moved with the planet’s rotation. Within one day, professional astronomers used NASA’s Infrared Telescope Facility in Hawaii to follow up and confirmed that the spot was an impact site.
Further observations were done with other large telescopes around the world as well as the Hubble. It was determined that this time an asteroid had hit Jupiter and not a comet.
Then on June 6, 2010, the same amateur saw a flash in Jupiter’s clouds.
Fortunately, he was taking video of the planet when this occurred and recorded his observation. This impact, however, was not powerful enough to leave a “scar.” In Racine, Wis., on Sept. 10, 2012, an amateur astronomer observed a sudden faint spot on Jupiter and posted his sighting.
At the same time, an amateur in Dallas had been recording video images of Jupiter; when alerted by the posting, he found a visible flash on 22 frames of his recording. Thanks to these amateur discoveries, we now know that Jupiter experiences more pummeling than once thought.
From west to east and twilight to dawn, we start our current planetary sightings with Mercury low in the west-southwest 45 minutes after sunset. Use binoculars to find this elusive planet in the glowing, twilight sky. Mercury’s position will make it easiest to locate during the coming week. A thin, lunar crescent will be below Mercury on Friday and then above it on Saturday.
Jupiter is at its maximum altitude above the southern horizon around 10 p.m. in early February and then by 8 at the end of the month. Look for a waxing gibbous moon to the lower right of Jupiter on Feb. 10.
Mars is now rising around 11 p.m. and will rise an hour and a half earlier by Feb. 28. Positioned against the spring stars of Virgo, Mars is just above its marker star, Spica, a bluish white, moderately bright star. When Mars rises on Feb. 19, the moon will accompany it; by dawn the next morning, the moon will have moved between the apparent position of Mars and the next planet eastward, Saturn. Saturn rises after 1 a.m.
Of the five naked-eye planets, that leaves Venus. It hovers in the dawn, rising after 5 a.m. from the east-southeastern horizon and will be a dazzling sight when it reaches its greatest brilliancy in mid-February.
Richard Monda is an astronomer living in the Capital Region.