This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Saturday, January 6, 2024.
Information updated weekly or as needed.
Times given as local St. Louis time which is Central Standard Time (CST). For definitions of terminology used in the night sky update, click the highlighted text. If relying on times posted in Universal Time (UT), St. louis is -6 hours when CST.
Observing Highlight of the Week
Map showing the bright stars of Canis Major. Map created using Stellarium. The Image of Sirius A nd B was taken by the Hubble Space Telescope in 2003. Image credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester). Bottom right is a diagram of Sirius B’s orbit around Sirius A. The diagram shows the position angle of Sirius B for different years. Diagram created by FrancescoA.
The highlight this week is the constellation, Canis Major. You can find Canis Major rising in the southeast by 7:30 p.m. For most of us, we will have to wait to see Canis Major until closer to 8:00 p.m. when it starts to clear tree lines. The appearance of the Great Dog is heralded by the appearance of its brightest star called Sirius. The brightest stars of Canis Major are Sirius, Mirzam, Wezen, Adhara and Aludra. The first two of these appear as a bright pair that will rise followed by the remaining three which appear as a small triangle shape.
Canis Major covers about 0.921% of the sky making it the 43rd largest constellation of the 88 constellations on the celestial sphere. For northern hemisphere observers it is a member of the winter sky and is bordered by the constellations Monoceros, Puppis, Columba and Lepus.
In Mesopotamia, the stars of CMa and its neighboring constellation Puppis were originally seen as an arrow and bow. Eventually, the bow and arrow were separated into two separate constellations, one of which is the Great Dog Canis Major.
Its brightest star is Sirius, which comes from the Greek term for scorching. This name is appropriate as it is the brightest star we can see at night. It shines with an apparent magnitude of -1.47. The only regularly seen objects that can appear brighter than Sirius are the Moon, the planets Mercury through Jupiter, and a few satellites such as ISS.
Finding Sirius is easy due to its brightness. However, the best way to know for sure you found the Sirius is to locate the three stars of Orion’s Belt. Follow the direction they point to the left of Orion and the first bright star you find is Sirius.
Sirius is a double star which is comprised of a main sequence white dwarf star called Sirius A and smaller white dwarf called Sirius B which is the remaining core of a star that has lost a significant amount of mass while it evolved into its end stage. The pair of stars orbit each other every 50.1 years. They were seen at their greatest separation in 2019 and will appear closest to one another in 2044. It is a double star that can be spilt by backyard instruments, however the large difference in magnitudes makes it difficult to spot the smaller companion even at the pair’s greatest separation.
You will need a moderate sized telescope to spot Sirius B. Some suggest that a 4-inch aperture can be used, however, most indicate 8-inches or larger is necessary. While the instrument used is a major factor, spotting Sirius B finds its largest challenge from seeing conditions. The close proximity of the pair along with the difference in magnitudes makes any atmospheric turbulence problematic. This is why seeing conditions are typically the make-or-break factor for for Sirius B. Nothing short of excellent seeing conditions will do.
Earth’s atmosphere is a collection of gases and particulates that are organized into different layers. As something moves through these layers it will experience variations in temperatures, densities, wind speeds and other variables. Light passing through these layers before it reaches your eyes is distorted impacting how well you see it. A famous example of this is the apparent twinkle of stars called scintillation. As atmospheric conditions become more turbulent, the distortion we see increases.
Additionally looking along the horizon, you are looking through more atmosphere and as such the turbulence will be greater. Because of this, it is best to view a target when it appears highest above the horizon. Sirius is an excellent target to experiment with this. When Sirius is seen low to the horizon, scintillation will cause it to flash varying colors. This is why Sirius has often been confused for a UFO. If you track the star as it culminates each night, you will notice scintillation decreases as the star increases in altitude.
If you plan to attempt splitting Sirius A and Sirius B it is important to monitor viewing conditions. Many observers rely on a weather forecast out of Canada called the clear sky chart. It is a forecast that focuses on seeing conditions over a 96-hour period. You can find the Clear Sky Chart at https://www.cleardarksky.com/csk/. You will have to search for a chart for your location. The St. louis Clear Sky Chart can be found at https://www.cleardarksky.com/c/StLouisMOkey.html
Canis major contains several other stars of interest. The other two I would recommend exploring are EZ Canis Majoris and W Canis Majoris. EZ CMa is a rare Wolf-Rayet star. These are massive stars that are shedding off enormous amounts of mass as they approach their end. Due to their mass Wolf-Rayet stars will end in a spectacular Type Ib or Type Ic supernova. W Canis Majoris is a red giant star that has run out of the hydrogen at its core swelling up in size as it evolved into its red giant phase. Carbon stars are typically red giants that have more carbon in their atmosphere than oxygen. The carbon readily combines with oxygen to form carbon monoxide. As the oxygen is depleted, it frees up carbon to bond with other elements forming other carbon compounds. With this increase of carbon molecules, carbon stars take on a ruby red appearance and can be quite striking to look at. Both of these stars are bright enough to spot in binoculars.
One final object to consider tracking down is Messier 41. This is an open star cluster that contains roughly 100 stars. It is found about 2300 light years away from us appearing as a small patch of stars with an apparent magnitude of 4.5. Its age is estimated to be 190 million years and is modeled to have an age expectancy of 500 million years. There are already several red giants you can easily spot with small telescopes. Binoculars will reveal a few dozen of the brightest stars in Messier 41 while a telescope will offer more stars and distinct colors for several members of the cluster.
Canis Major is best seen in our winter months, and it is one of the many jewels of the winter sky. Over the next few months, step outside a few hours after sunset to see this winter gem.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 7:19 a.m. on Saturday, January 6 and sunset is at 4:54 p.m. providing us with roughly 9 hours and 30 minutes of daylight this week. Even after sunset, light from the Sun will dimly illuminate our sky for about 1 hour and 30 minutes. This period is called twilight, which ends around 6:29 p.m. this week. For those with a sundial, local noon occurs around 12:06 p.m. this week.
| Day | Sunrise | Sunset | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 6-Jan | 7:19 a.m. | 4:54 p.m. | ||||||||||
| 7-Jan | 7:19 a.m. | 4:55 p.m. | ||||||||||
| 8-Jan | 7:19 a.m. | 4:56 p.m. | ||||||||||
| 9-Jan | 7:19 a.m. | 4:57 p.m. | ||||||||||
| 10-Jan | 7:18 a.m. | 4:58 p.m. | ||||||||||
| 11-Jan | 7:18 a.m. | 4:58 p.m. | ||||||||||
| 12-Jan | 7:18 a.m. | 5:00 p.m. | ||||||||||
| 13-Jan | 7:18 a.m. | 5:01 p.m. | ||||||||||
| 14-Jan | 7:18 a.m. | 5:02 p.m. |
Moon
Moonrise for Saturday, January 6 was at 2:24 a.m. and moonset occurred at 12:45 p.m. On Saturday, January 6, the Moon will exhibit a waning crescent phase with roughly 24% disk illumination. By the end of the week the Moon will exhibit a waxing crescent phase with 16% disk illumination. New moon occurs on January 11, 2024, at 5:57 a.m. This starts the first full synodic cycle of 2024.
International Space Station (ISS) Observing
There are several visible passes of ISS from St. Louis for the week of January 6. At the start of the week, they occur during morning hours. On January 12, visible ISS passes will switch to evening passes. The table below lists the best of these passes that will be seen from St. Louis. If you do not live in the area, you can use https://heavens-above.com/ to set your viewing location and get times for where you are.
Catch ISS from St. Louis starting Saturday, January 6, 2024
| Date | Starts | Max. altitude | Ends | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Time | Alt. | Az. | Time | Alt. | Az. | Time | Alt. | Az. | ||
| 07 Jan | -2 | 5:21:49 | 24 | S | 5:21:49 | 24 | S | 5:23:30 | 10 | SSE |
| 13 Jan | -2.6 | 18:43:31 | 10 | SSW | 18:45:54 | 33 | SSE | 18:45:54 | 33 | SSE |
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°.
Detailed information regarding all unmanned exploration of our universe, missions past, present, and planned, can be found at Jet Propulsion Laboratories:
The Visible Planets
Looking south at 6:00 p.m. on January 6, 2024. Credit: Stellarium, EG
Looking southeast at 6:00 a.m. on January 7, 2024. Credit: Stellarium, EG
This week, four naked eye planets will be visible. Saturn and Jupiter are visible in the south once it is dark. Venus will be easy to find in the southeast before sunrise. Mercury becomes visible in the east just before sunrise.
Mercury
Mercury reaches dichotomy this week on January 7, 2023. It will also appear at its highest altitude for the current morning apparition on this date barely clearing 10° above the horizon. Look for Mercury in the southeast about 30 minutes before sunrise. Over the next week, Views of Mercury will be possible provided you have a clear southeastern horizon.
Venus
Venus rises this week around 4:39 a.m. It will be easy to spot for most by 6:00 a.m. If you have a clear view of the planet, telescopes will reveal a gibbous phase with roughly 79.9% disk illumination. Now that Venus is past dichotomy, it is headed back towards the Sun from our perspective. As this continues, Venus’s disk illumination will increase as it heads towards superior conjunction on June 4, 2024.
Jupiter
Jupiter has passed opposition and as such it will rise before the Sun sets. Jupiter will be easy to spot in the south once it is dark outside. Jupiter will set around 2:08 a.m.
Saturn
Start looking for Saturn in the south about 30 minutes after sunset. Saturn will set around 8:42 p.m. Our window to see Saturn is starting to close as the planet approaches solar conjunction on February 28, 2024. As we approach this date Saturn will be found lower to the horizon each day eventually being lost to the Sun’s glare near the end of February.
James S. McDonnell Planetarium
Night Sky Update: January 6-14, 2024