This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, February 10, 2023.
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.
Public Telescope Viewings
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 March 3, join us indoors in our planetarium theater for “The Sky Tonight”. Showtime is at 7 p.m.
Observing Highlight of the Week
Hubble Space Telescope image of Saturn taken as part of Hubble’s OPAL program. In the image, ring spokes are visible heralding the start of a new ring spoke season. You can find the NASA release of this image here. Image credit: NASA, ESA, and Amy Simon (NASA-GSFC); Image Processing: Alyssa Pagan (STScI).
This week we will highlight the planet Saturn which may come as a surprise as currently we cannot see Saturn at night. I chose Saturn for this week’s highlight for two reasons; preparations for the 2023, 2024 and 2025 apparitions Saturn, and the new image of Saturn taken by the Hubble Space Telescope.
In astronomy, the term apparition refers the period when an object in our solar system is visible. Saturn’s’ current apparition has ended as it approaches solar conjunction on February 16, 2023. Solar conjunction occurs when an object appears closest to the Sun in the sky. For superior planets like Saturn, this occurs as Saturn passes behind the Sun. As the object approaches and passes by solar conjunction, it is lost from view due to the glare of the Sun. Due to this, views of Saturn are not possible until the second or third week of March 2023 when Saturn becomes visible in morning twilight.
As we wait for the next apparition of Saturn, now is the time to prepare for the next few apparitions. The best time to see Saturn is when its near opposition. Opposition is when a solar system object appears near the anti-solar point in the sky. This is when Saturn appears its brightest. Saturn next reaches opposition on August 27, 2023.
While we wait for opposition later this year, Saturn will returns to our morning skies, looking a little different. The ring system Saturn is known for will appear tilted a little less then you may remember. Like Earth, Saturn is tilted on its axis of rotation. This axial tilt is 26.73° with respect to its orbital plane. Due to its axial tilt, Saturn experiences seasonal changes like Earth does. Each of Saturn’s season last a little over 7-years due to its greater distance from the Sun. Saturn orbits the Sun at an average distance of 9.54 AU. At this distance, Saturn takes about 29 years to complete a revolution of the Sun.
During summer and winter on Saturn, our view from Earth sees one of the polar regions inclined towards the Sun. During these seasons, Saturn’s rings appear tilted more face on. As Saturn approaches an equinox, the rings appear more edge on. This edge on appearance is called a ring plane crossing which occurs next on March 23, 2025, with Saturn’s equinox occurring on May 6, 2025. Unfortunately, Saturn will be at solar conjunction on March 12, 2025, which means it will be difficult to observe Saturn on the day of the ring plane crossing. Saturn will only appear roughly 10° from the Sun and the angle of the ecliptic will be low. Chances are we will have to settle for near edge on views of Saturn’s rings about a month before and after the ring plane crossing.
Tracking the tilt of Saturn’s ring system is a project you can do if you have any telescope. Additionally, this is a time to catch shadow transits of Saturn’s larger moon Titan. For most observers, Titan is the only moon large enough to see its shadow transit the clouds of Saturn. However, those with larger aperture telescopes can see other shadow transits as well. Shadow transits occur when a moon passes between the Sun and its planet. As this occurs the moon’s shadow can be seen cast onto the cloud tops of the planet’s atmosphere. For backyard observers, it is possible to see these on Jupiter and Saturn. Shadow transits on Jupiter a common, but for Saturn, it requires Saturn to be approaching a ring plane transit. If you miss out on this chance to see shadow transits on Saturn, you will have to wait another 15 years for the next equinox on Saturn.
2025 will be a great year to train our telescopes on Saturn. The most interesting views occur a few months before and after the ring plane crossing that year. If this feels a bit far off in the future, recently, the Hubble Space Telescope captured a new image of Saturn revealing the start of ring spoke season. Ring spokes were discovered in Saturn’s rings by Voyager 1 and 2 as they flew by Saturn. Ring spokes appear as dark or bright transient smudges in Saturn’s B-ring. Their appearance depends on the Sun angle being low for dark or high for bright. This behavior indicates they are collections of dust-sized ice particles in the rings. What they are and what causes them is not fully understood but they appear to be seasonally variable. Ring spokes appear to be more common as Saturn is near an equinox. These also appear to be related to Saturn’s magnetic field and its interaction with the solar wind. A prevailing theory suggest they are the result of electrostatic forces generated from the interaction of the solar wind and Saturn’s magnetic field. The resulting electrostatic forces hold clouds of dust sized ice particles aloft from the rest of the rings.
The image recently taken by the Hubble Space Telescope has revealed the presence of ring spokes signaling the start of ring spoke season. The image was part of Hubble’s Outer Planet Atmospheres Legacy (OPAL) program which is intended to help understand atmospheric dynamics and evolution of the gas giant planets.
I have never attempted to see ring spokes myself, so I was curious to see if they were a target available for backyard telescopes. Regarding visual observations, what I found was inconclusive, whereas planetary imagers have found success in imaging ring spokes. For visual observers, many report seeing ring spokes in moderate sized telescopes. Others are far more skeptical suggesting that what is seen as spokes are likely optical illusions or atmospheric interference. One of the better conversations I found was a thread from a Cloudy Nights forum back in 2010. For me the debate remains inconclusive. However, with the appearance of ring spokes in the new Hubble image, now is the time to start planning for Saturn as it starts a new apparition this March. We will have to wait and see what is possible. Whether we see them or not, is not what is important. Rather, it is the pursuit of exploring something new that is of interest.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sunrise is at 6:58 a.m. on Friday, February 10 and sunset is at 5:33 p.m. providing us with roughly 10.5 hours of daylight. Even after sunset, light from the Sun will dimly illuminate our sky for roughly 1 hour and 30 minutes. This period is called twilight, which ends around 7:03 p.m. this week. For those with a sundial, local noon occurs around 12:14 p.m. this week.
| Day | Sunrise | Sunset | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10-Feb | 6:58 a.m. | 5:33 p.m. | ||||||||||
| 11-Feb | 6:56 a.m. | 5:34 p.m. | ||||||||||
| 12-Feb | 6:55 a.m. | 5:35 p.m. | ||||||||||
| 13-Feb | 6:54 a.m. | 5:36 p.m. | ||||||||||
| 14-Feb | 6:53 a.m. | 5:37 p.m. | ||||||||||
| 15-Feb | 6:52 a.m. | 5:38 p.m. | ||||||||||
| 16-Feb | 6:51 a.m. | 5:40 p.m. | ||||||||||
| 17-Feb | 6:49 a.m. | 5:41 p.m. | ||||||||||
| 18-Feb | 6:48 a.m. | 5:42 p.m. |
Moon
Moonrise for Friday, February 10 was at 10:27 p.m. and moonset occurred at 9:48 a.m. on the following day. Friday, February 10, the Moon will exhibit a waning gibbous phase with 78% of the lunar disk illuminated. Last quarter moon occurs on February 13, 2023, at 10:01 a.m.
International Space Station (ISS) Observing
There are several visible passes of ISS from St. Louis for the week of February 10. They occur during morning hours. The best passes for this week are listed below. Use the table below for information about these passes.
Catch ISS from St. Louis starting Friday, February 10
| Date | Starts | Max. altitude | Ends | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Time | Alt. | Az. | Time | Alt. | Az. | Time | Alt. | Az. | ||
| 16 Feb | -1.3 | 5:36:46 | 10 | S | 5:39:22 | 22 | SE | 5:42:00 | 10 | E |
| 18 Feb | -3.5 | 5:36:23 | 17 | SW | 5:38:47 | 68 | SE | 5:42:06 | 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:
The Visible Planets
Looking south at 6:00 p.m. on February 12, 2023. Credit: Stellarium, EG
This week, three naked eye planets are visible. Venus and Jupiter are found in the southwest after sunset. Mars is found overhead after sunset.
Venus
Venus is climbing out of the Sun’s glare as it starts another an evening apparition. Once high enough above the horizon, Venus will be a bright target in the west after sunset until August 2023 when it approaches inferior conjunction. This week, look for Venus in the southwest about 20 minutes after sunset. Venus sets at 7:42 p.m.
Mars
Mars now rises before sunset becoming visible once it is dark. Look for it overhead about 30 minutes after sunset. Mars sets by 2:44 a.m.
Jupiter
Now past opposition, Jupiter will be visible about 30 minutes after sunset. Jupiter reaches superior conjunction on April 11, 2023. As we progress towards this date, we will see Jupiter slowly wander towards the Sun. Jupiter now sets at 9:08 p.m.
James S. McDonnell Planetarium
Night Sky Update: February 10 – 18, 2023