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The Sky This Week, 2019 January 2 - 8

A "close shave" with the Sun?
Orion, the Hyades, and the Pleiades, imaged 2017 March 1 from near Boulder, Colorado.
Orion, the Hyades, and the Pleiades, imaged 2017 March 1 from near Boulder, Colorado.
imaged with a Canon EOS Rebel T2i DSLR.

The Moon spends the week in close proximity to the Sun, with New Moon occurring on the 5th at 8:28 pm Eastern Standard Time.  Look for Luna’s slender crescent just over three degrees northeast of Jupiter in the gathering twilight on the morning of the 3rd.  The pair will be low in the southeastern sky, about 10 degrees above the horizon at 6:30 am.  The Moon returns to the evening sky by week’s end, when you’ll find her climbing above the southwest horizon in the fading evening twilight.

For those of you who find it hard to get up in the dark during these early winter mornings, take heart.  This week is when we experience the latest sunrises of the year.  Here in Washington Old Sol crests the horizon at 7:27 am EST on the morning of the 4th.  By the start of next week the time of sunrise will gradually shift earlier, and by the end of the month the Sun will greet us at 7:15 am. 

Earth reaches perihelion, its closest point to the Sun in its annual circuit around our “day star”, on the 3rd at 12:20 am EST.  At this time the center of the Earth will be 147,100,000 kilometers (91,400,000 miles) from the center of the Sun.  The annual variation in our planet’s distance from the Sun is quite small, amounting to a change of around 3 percent between perihelion and aphelion.  This is fortunate for us since it maintains a stable climate throughout the year.  Of all of the major planets only Neptune has an orbit that is more nearly circular.  On Mars the orbital change is closer to 18 percent, and we can observe major variations in global climate conditions on the red planet during the course of its 687-day year.  The eccentricity of Earth’s orbit does vary, however in a cycle that takes place over about 100,000 years.  Even at its extremes, though, the variation is less than half that of Mars, so our planet has been able to support life for billions of years.  The variation in our elliptical orbit is controlled by the giant planet Jupiter, which has a hand in shepherding all of the planets in their paths around the Sun.  Jupiter’s mass is more than two and a half times that of all the other planets combined, which prompted the late science-fiction writer Isaac Asimov to quip that the solar system was “The Sun, Jupiter, and some debris”.

With the Sun now just beginning to wend its way back toward the northern sky we are still experiencing the year’s longest nights.  Fortunately we have a sky full of bright stars to keep us company during the dark hours.  I always enjoy just looking at the stars surrounding the distinctive constellation of Orion, the Hunter.  The different hues ranging from the distinctive ruddy glow of Betelgeuse to the golden glimmer of Capella and the ice-blue dazzle of Sirius are a treat for the eye, and to stand under them on a quiet, snow-covered landscape defines the joy of winter for me.  This is a wonderful part of the sky to explore with binoculars, with treats such as the Pleiades and their mythological half-sisters the Hyades in prime viewing positions.  From a dark site you can trace out the Milky Way coursing through the constellations of Auriga, the Charioteer, Gemini, the Twins, and the obscure constellation of Monoceros, the Unicorn, just to the left of Orion.  This area of the sky is chock-full of star clusters, especially in the region of Auriga and Gemini. 

Mars continues to climb northward among the faint stars of Pisces and has crossed the celestial equator to enter the northern hemisphere of the sky.  The red planet is still prominent in the southwest as evening twilight ends.  Look about 15 degrees above Mars to spot the Great Square asterism of Pegasus.

Venus reaches her greatest elongation west of the Sun on the morning of the 6th.  The dazzling planet will be 47 degrees from the Sun at this time.  She beams brightly in the southeast during the pre-dawn hours and will remain a fixture in the morning sky until late summer.

Jupiter is steadily returning to the morning sky.  The giant planet gets a visit from the Moon on the morning of the 3rd, and he will rise three minutes earlier on each successive morning.  Jupiter and Venus are on a steady course for a beautiful pre-dawn encounter on January 22nd.  The waning crescent Moon will join them at the end of the month.




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