This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Tuesday, December 18. Times are given as local St. Louis time in Central Standard Time due to the time change coming this Sunday. For definitions of terminology used in the night sky update, click the highlighted text.

Information updated weekly or as needed.

Join us for our next star party, Friday, January 4, 2019 held in association with the St. Louis Astronomical Society. For details, see the information at the bottom of this page.

The Sun and Moon

Sunrise is at 7:13 a.m. on Tuesday, December 18 and sunset is at 4:42 p.m. providing us with about 9.5 hours of daylight. Even after sunset, the light from the sun will still dimly illuminate our sky for about 1.5 hours. This period is called twilight, which ends around 6:17 p.m. this week. For those with a sun dial, solar transit or local noon occurs around 11:58 a.m. this week.

Day

Sunrise

Sunset

18 Dec

7:13 a.m.

4:42 p.m.

19 Dec

7:14 a.m.

4:42 p.m.

20 Dec

7:15 a.m.

4:42 p.m.

21 Dec

7:15 a.m.

4:43 p.m.

22 Dec

7:16 a.m.

4:43 p.m.

23 Dec

7:16 a.m.

4:44 p.m.

24 Dec

7:16 a.m.

4:45 p.m.

25 Dec

7:17 a.m.

4:45 p.m.

26 Dec

7:17 a.m.

4:46 p.m.

 

2018 Winter Solstice

The first day of winter will occur this week on December 21. This day is called the Winter Solstice which has been celebrated by ancient and modern cultures around the world. The winter solstice marks the day when one end of Earth’s axis is tilted away from the Sun. For northern hemisphere observers this occurs in December and for those in the southern hemisphere it occurs in June. It might come as a surprise that our winters in the northern hemisphere coincide with Earth’s nearest point to the Sun. This point is called perihelion which occurs on January 2, 2019. At perihelion the Earth is roughly 91 million miles from the Sun. To learn more about the solstice and Earth’s seasons visit http://aa.usno.navy.mil/faq/docs/seasons_orbit.php

Moonrise for Tuesday, December 18 occurs at 2:05 p.m. and moonset will occur at 3:34 a.m. on the following day. On Tuesday, December 18 the moon will be exhibiting a waxing gibbous phase with roughly 80% of the lunar disk illuminated. Full moon occurs on December 22. The full moon of December is sometimes known as the Long Night Moon.

International Space Station (ISS) Observing

Visible passes of ISS from St. Louis for the week of December 18 occur during morning hours. The best of these occur on the mornings of December 24 and 26. Use the table below for information about these and other visible passes of ISS.

Catch ISS from St. Louis starting Tuesday, December 18

Mag

Starts

Max. altitude

Ends

Time Alt. Az. Time Alt. Az. Time Alt. Az.

22 Dec

-0.9 06:11:46 10 S 06:14:19 21 SE 06:16:51 10 E

24 Dec

-3.1 06:02:53 10 SW 06:06:05 54 SE 06:09:19 10 ENE

25 Dec

-1.7 05:12:52 22 SSE 05:13:56 26 SE 05:16:45 10 ENE
26 Dec -3.8 05:56:39 31 WSW 05:57:58 56 NW 06:01:14 10 NE

Magnitude (Mag): The Measure of brightness for a celestial object. The lower the value is, the brighter the object will be.

Altitude (Alt): The angle of a celestial object measured upwards from the observer’s horizon.

Azimuth (Az): The direction of a celestial object, measured clockwise from an observer’s location with north being 0°, east being 90°, south being 180° and west being 270°.

For information about ISS flyovers and other visible satellites, visit www.heavens-above.com

Detailed information regarding all unmanned exploration of our universe, missions past, present, and planned, can be found at Jet Propulsion Laboratories:

http://www.jpl.nasa.gov/

The Planets Visible Without a Telescope

This week all five of the naked eye planets are visible. The two that will be easy to see are Venus and Mars. Venus has started a morning apparition rising before the sun and Mars will be seen shortly after sunset in the south. The other three will be difficult to find if you have trees or builds in the east or west. Saturn has a small window after sunset to see and the pair of Mercury and Jupiter are rising just before the sun.

Mercury

The nearest planet to the sun is exhibiting a brief morning apparition. Mercury rises at 5:33 a.m. which is just 1.45 hours before sunrise. There will be a brief window around 6:20ish to see Mercury.

Venus

Venus has started another morning apparition. You can find the brightest planet rising in the east by 3:30 a.m. By 4:00 a.m. should be high enough to clear trees and buildings. Venus will spend the first half of 2019 as an early morning target

Mars

The red planet can be found in the south as the sun sets. With opposition having come and gone the bright appearance of Mars will begin to fade. Mars will set by 11:25 p.m.

Jupiter

The king of the planets is beginning another apparition. Like Mercury it rises just before sunrise. In the coming weeks it will be easier to see Jupiter but this week you can find Jupiter with Mercury about 40 minutes before sunrise.

Saturn

Saturn has been visible in the southern sky for some time, but the angle of the summertime ecliptic has kept the ringed planet low in the southern sky. Saturn has now shifted to the southwestern sky and will be difficult to see. Saturn sets at 5:35 p.m.

Our next Star Party will be held on Friday, January 4, 2019, from dusk until 10 p.m.

As part of the Saint Louis Science Center’s First Fridays, weather permitting, the St. Louis Astronomical Society and the Science Center will set up a number of telescopes outdoors and be on-hand to answer your questions. Telescope viewing begins once it is dark. Regardless of the weather on January 4, join us indoors in our planetarium theater for “The Sky Tonight”. Showtime is at 7 p.m.

This free, indoor star program will introduce you to the current night sky, the planets, and the seasonal constellations. Doors open 15 minutes before show time. Shows begins at 7 p.m. Sorry, no late admissions due to safety issues in the darkened theater.

The St. Louis Astronomical Society helps host the monthly Star Parties at the Saint Louis Science Center which are held on the first Friday of each month. Our Monthly Star Parties are open to the public and free of charge. Telescope viewing is scheduled to start around 7:00 p.m.