Updated December 4, 2018
Right about this time we in the Northern Hemisphere are experiencing the earliest onset of darkness for the year. The Winter Solstice is more than two weeks away but it is already getting dark early. For 40 degrees north latitude, the earliest sunset is December 7 and is now setting only two to three minutes later than that. For example, in Houston, Texas at 30 degrees north, the earliest sunset is 5:21pm local time. Sunset today is at 5:23pm local time. This trend is balanced out by the sunrise: latest January sunrise in Houston is around 7:18 am but now it is rising over one half hour earlier than this, at 6:51 am. For latitude 40 degrees north, the latest sunrise occurs around January 4. These seemingly odd phenomena owe their cause to the Earth’s axial tilt and the eccentricity of its orbit (and perihelion, the date the Earth is closest to the Sun, is January 4).
As the night falls and the stars appear, two of the first are Vega, fairly low in the Northwest, and the planet Mars, fairly high in the South. Both are magnitude 0.0 but each has a very different color. Compare the two as the night darkens and notice the color contrast between them. Binoculars will help enhance the colors of both objects. The brightest star above Vega is Deneb which forms the top of the Northern Cross asterism. The cross appears more or less upright these December evenings, with the base of it burrowing into the northwest horizon around 11:30 pm local time (again as seen from the Northern Hemisphere).
At dusk the Big Dipper asterism is due north on the horizon, The further north you are the easier it is to see; from Miami it is below the horizon. Opposite the Big Dipper is the bowl of the Little Dipper, standing to the left of Polaris, the North Star. Over the course of the evening, like some giant celestial backwards-running clock, the Little Dipper swings down, hanging directly below the North Star by 11 pm or so local time. By this time, the Big Dipper stands upright on its handle, becoming more prominent in this configuration by midnight local time. Six hours later, it hangs inverted (bowl facing down) high in the North at dawn. Also at dawn, if one follows the arc of the Big Dipper’s handle, one arrives at bright Arcturus, getting high in the eastern sky.
Venus is already prominent at dawn as the “morning star”, rising nearly four hours ahead of the Sun and at its maximum brightness of -4.9. The waning crescent Moon just swept past it; on the morning of December 5 it will be well below it as a thin crescent some 45 minutes before sunrise. New moon is at 2:20 am Eastern time on December 7. Mercury is about to make its appearance in the morning sky below Venus, putting on one of its best apparitions of the year. It will be soon joined by Jupiter, making its reappearance in the predawn sky later this month. Meanwhile in the evening sky, the planet Neptune passes very close to Mars. You will need a telescope to see this one, but on the evening of December 6, Neptune will be about 1/3 degree from Mars towards Mars’s east northeast as seen from the Americas. Mars will be some 1400 times brighter than Neptune. On the next evening, Neptune will have moved to about 1/4 degrees to Mars’s southwest as seen from North America.
Saturn is still visible as a “star” of modest brightness low in the southwest at dusk. It is sinking lower and lower in the sky with each passing day, fading into the evening twilight by mid-month.
The Summer Triangle is getting lower in the western sky at nightfall, but is still easy to find. Deneb is now fairly high in the northwest with Vega is further down toward the west-northwest and Altair is low in the southwest. The bright star Fomalhaut crosses the local meridian (passing due south) around 6 to 7 pm local time and Mars is almost directly above it.
One interesting aspect of the night sky this time of year is that the constellations of summertime linger across the western sky at nightfall into early December. These include Sagittarius, Aquila, Cygnus, and Lyra. A wide band of sky going south-southwest to north-northwest contains the traditional fall constellations of Capricornus, Aquarius, Piscens, Pegasus, and Andromeda. The constellation Perseus appears rather high in the northeastern sky trailing Cassiopeia the queen (sporting an “M” shape) and Cepheus the King. This is also the time of year when the constellations of winter begin to make their appearance in late evening: Capella glitters golden in the northeast. Right of Capella is the star cluster (often referred to incorrectly as a constellation) known as the Pleiades. Perseus lies between the two. After midnight, prominent Orion makes his appearance on the celestial stage, bringing the reminder of the winter constellations forward. Finally just before dawn the spring constellations show themselves in the eastern sky, including Leo, Virgo, Bootes and the ascending Big Dipper.
More information on what can be seen in the sky on a weekly basis, including some interesting stellar pairings visible with binoculars near Vega in the western sky, can be viewed at the website http://www.skyandtelescope.com/observing/ataglance. One can go directly to this week’s information by clicking on the link for this week’s (November 30 – December 8, as of this writing) sky-at-a-glance. For subsequent weeks the most current week is at the top with earlier weeks archived in reverse chronological order.
Due to construction of the observatory addition we have not been able to do any further work on the solar observatory telescope. Once this project is complete, the Prairie View Observatory Complex will house 3 domes, including the existing Solar Observatory, and two new domes. For updates on this progress check out https://www.pvamu.edu/pvso/cosmic-corner/project-summary-2/. Also, more information and images about the expansion (along with the existing Solar Observatory) at https://sites.google.com/view/saganti-astro/home. The two new domes will house our Meade 16-inch advanced telescope and a new 0.6 meter (24-inch) PlaneWave Corrected Dall-Kirkham telescope. The design features these two domes situated east and west of a visitor’s center, which is immediately north of the existing Solar Observatory. First light for the new observatory could happen as early as Spring 2019. Keep checking back for updates.
Juno made its 16th perijove flyby of the planet Jupiter October 26th and continues to send back spectacular images. You can find them at https://earthsky.org/space/juno-spacecraft-image-nov-2018-eichstadt-doran and https://www.missionjuno.swri.edu/junocam/processing?ob_from=&ob_to=&phases%5B%5D=PERIJOVE+15&perpage=16. Last year, Juno flew closer to the Great Red Spot on Jupiter than any spacecraft in history, and this year it has been approved to continue orbiting Jupiter until at least July 2021. For more information about this mission in general visit www.nasa.gov/juno. You can also visit http://www.cnn.com/2016/06/30/health/juno-jupiter/index.html which has some additional interesting facts about the mission.