The December Solstice

EARTH —  The coming week already marks the first day of winter in the northern hemisphere, with the December Solstice on Thursday the 21st.

Earth is tilted on its axis, and as we make our way around the sun, the sunlight strikes the planet at different angles throughout the year.

Now, the southern portion of our planet is tilted more toward the sun than is the north. Where the sun strikes more directly, it appears higher in the sky, the days are longer, and the weather warmer. It is the beginning of summer in the southern hemisphere.

Conversely, the opposite must be true in the northern hemisphere, where we live. The sun appears lower in the sky, the days are shorter, and decidedly colder. It is the beginning of winter for us, the Winter Solstice.

During the solstice, we experience the day with the least amount of daylight, the sun appears furthest south. But from that day onward, the hours of daylight will begin to lengthen, the sun will move higher, and that means that spring is just around the corner.

So, this coming Thursday, we will have the shortest day, the beginning of winter.

Amazingly, Earth is moving closer to the sun right now, in our elliptical orbit. In fact, we are a full three million miles closer to the sun this week, than we were back at the beginning of July. But the distance to the sun has little to do with the seasons on Earth.  Summer temperatures in the south are less than one degree warmer than they are in the north, due to the varying distance in our orbit from the sun.

The good news for stargazers is we are blessed with the most hours of dark skies, for celestial viewing. Also, the winter constellations are much more distinctive, brilliant, and easy to identify, than what we see during the shorter summer nights. So, if you don’t mind the colder conditions, skies also appear clearer when temperatures are lower, ideal conditions for viewing.

This week, Saturn is further from Earth by more than 122 million miles than when it was at its brightest. Though it is dimming as we move away from it, the moon will join Saturn in our night sky this week.

On the evening of Sunday, Dec. 17, go out about an hour after sunset.  In the south-western sky, you can easily find the crescent moon. About two degrees above the moon is distant Saturn. It is rapidly blending in with the surrounding stars, but with the assistance of the moon on Sunday night, you can easily find the fading ringed planet.

To the east of the pair, high above, is brighter Jupiter. Jupiter is larger than Saturn, and much nearer to Earth, so it always outshines the more distant Saturn.

Next week, the moon will encounter Jupiter as it passes through the sky. The planets orbit the sun, of course, but the moon orbits Earth, so it moves across the sky at a more rapid rate. The moon will traverse, generally speaking, about fifteen degrees each day, most of that motion due to its orbit around the Earth.

So, the moon will move from its position near Saturn on Sunday, to a position near Jupiter on Friday, traveling nearly eighty degrees across the sky, in five days.

The motion of the moon between the planets is due to the moon’s orbit around Earth. The motion of the moon, with the planets and stars, across the sky each night, is due to the rotation of the Earth.

But this week, what we have to watch for is the moon and its encounter with Saturn in our evening sky. It comes just a few days before the solstice. So, with our long, dark nights, we have plenty of time for star gazing and planet watching.

With our dark skies here, they only need to be clear, so keep your eyes on the skies from sunset to sunrise.

Thanks for the positive feedback about our featured columns, and your continued interest in astronomy. If you have any questions or article requests, contact us at spacescape@rocketmail.com, or follow us on Twitter @ColoSpacEScapE for updates and additional viewing opportunities.

Sun Set = 4:42 p.m.

1 minute later than last week

91.484 million miles from Earth

71,008 miles nearer than last week

3.022 million miles nearer than its

furthest in July

Mercury Set = 5:36 p.m.

23 minutes earlier than last week

54 minutes after the sun

68.095 million miles from Earth

14,216,821 miles nearer than last week

65.216 million miles nearer than its furthest in October

Moon Set = 8:52 p.m.

75 minutes later than last night

228,608 miles from Earth

172 miles nearer than last night

11,228 miles nearer than last week

Nearest is 221,557 miles

Furthest is 252,665 miles

Saturn Set = 9:59 p.m.

25 minutes earlier than last week

936.935 million miles from Earth

10,175,190 miles further than last week

122.356 million miles further than its nearest in August

Jupiter Set = 3:11 a.m.

30 minutes earlier than last week

397.756 million miles from Earth

7,495,586 miles further than last week

27.431 million miles further than its nearest in November

Venus Rise = 3:48 a.m.

13 minutes later than last week

101.193 million miles from Earth

4,399,084 miles further than last week

74.355 million miles further than its nearest in August

Mars Rise = 6:28 a.m.

3 minutes earlier than last week

37 minutes before the sun

229.116 million miles from Earth

1,632,720 miles nearer than last week

7.868 million miles nearer than its

furthest in October

Sun Rise = 7:05 a.m.

5 minutes later than last week

91.478 million miles from Earth

5,336 miles nearer than last night

69,696 miles nearer than last week

3,027,527 miles nearer than its

furthest in July

First Quarter Moon occurs on Tuesday, Dec. 19, at 11:39 a.m.  We’ve lost four minutes of daylight since last week, and 31 minutes since last month, and a full five5 hours five minutes since the June Solstice.  Our nearest planetary neighbor currently is Mercury.

William J. Bechaver is the director of SPACE • Spanish Peaks Amateur Cosmos Enthusiasts, the premier Astronomical Society for Southern Colorado and Northern New Mexico.