This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, July 2, 2021.
Information updated weekly or as needed.
Times given as local St. Louis time, which is Central Daylight Time (CDT). 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 -5 hours when CDT.
Public Telescope Viewings
With the changing recommendations from the CDC regarding COVID-19, conversations regarding the return of star parties at the Saint Louis Science Center have begun. We are close to bringing back our public telescope viewings, but a few details still need to be worked out. We will post future updates as we learn more about when we can bring back telescope viewings.
Observing Highlight of the Week
The Sun on July 3 with Sunspots 2835 and 2837.
Credit: SDO HMI
On July 5, 2021, at 7:00 p.m. CDT, the Earth will reach aphelion. This is when Earth is at its greatest distance from the Sun. When at aphelion, Earth is about 94.5 million miles from the Sun. On the Earth’s orbit, there are two points called apsides. These represent when the Earth is nearest or furthest from the Sun. For the Earth these are called perihelion (nearest) and aphelion (furthest).
Often it is thought that summer is when Earth is nearest to the Sun which is true for the southern hemisphere. For us in the northern hemisphere, winter is when we are nearest to the Sun. The temperature fluctuations we experience during the seasons is not related to solar proximity but rather it is the result of Earth’s axial tilt.
Much like Earth, the Moon has apsides on its orbit. They are called perigee (near) and apogee (far). Each month the Moon reaches these positions on a cycle called the anomalistic month. This month lasts about 27.5 days. Due to the apsidal cycle, the apparent diameter of the Moon varies. This variance is part of predicting eclipses and is relevant to determining if a total or annual solar eclipse is possible. It is also the same cycle connected to what people call a supermoon. This term has become popular when full moon occurs near perigee. This is when the Moon can look about 14% larger. What you rarely hear is that perigee happens every month, it just does not always line up with full moon. The reason for this is the anomalistic month is shorter than the synodic month (moon phase cycle). The next apogee occurs on July 5, 2021, and perigee happens next on July 21, 2021, about two days before full moon on the 23rd.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Sunrise is at 5:41 a.m. on Friday, July 2 and sunset is at 8:29 p.m. providing us with a little less than 15 hours of daylight. Even after sunset, the light from the Sun will dimly illuminate our sky for about 2 hours. This period is called twilight, which ends around 10:26 p.m. this week. For those with a sundial, local noon occurs around 1:05 p.m. this week.
|2021-07-02||5:41 a.m.||8:29 p.m.|
|2021-07-03||5:41 a.m.||8:29 p.m.|
|2021-07-04||5:42 a.m.||8:29 p.m.|
|2021-07-05||5:43 a.m.||8:29 p.m.|
|2021-07-06||5:43 a.m.||8:29 p.m.|
|2021-07-07||5:44 a.m.||8:28 p.m.|
|2021-07-08||5:44 a.m.||8:28 p.m.|
|2021-07-09||5:45 a.m.||8:28 p.m.|
|2021-07-10||5:46 a.m.||8:27 p.m.|
Moonrise for Friday, July 2 occurs at 1:15 a.m. and moonset will occur at 1:56 p.m. On Friday, July 2 the Moon will exhibit a waning crescent phase with 43% of the lunar disk illuminated. New moon occurs on July 9 at 8:17 p.m. This new moon starts lunation 1219. This number indicates that this lunar cycle is the 1219th cycle since the modern Brown Lunation Number system was initiated.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of July 2 occur during morning hours. The best pass this week occurs on the morning of July 7. Use the table below for information about this and other visible passes this week.
Catch ISS from St. Louis starting Friday, July 2
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 West, at 9:00 pm, July 2, 2021
Credit: Stellarium, EG,
Looking Southeast, at 1:00 am, July 3, 2021
Credit: Stellarium, EG
This week, four naked eye planets are visible. Venus and Mars can be found in the west after sunset. Jupiter and Saturn can be found in the southeast after midnight.
Venus is well into another evening apparition. By 9:00 p.m., Venus will be 11.2° above the west-northwest horizon. As 2021 continues, we will see Venus climb higher in the western sky after sunset until October 29 when it reaches maximum eastern elongation. After this date Venus will start to head back towards the Sun as it approaches inferior conjunction on January 8, 2022.
Currently Mars appears as a 1.8-magnitude object that will be visible high in the west about 40 minutes after sunset. Mars sets by 10:20 p.m. If you watch Mars and Venus as we continue into July this year, you will see the two planets are getting closer in the sky. Mars and Venus are headed towards a conjunction on July 13, 2021. The conjunction happens before we seem them that day, so it is best to look for the pair on July 12 about 30 minutes after sunset. You will see the two planets less than 1° apart.
Jupiter is now rising before midnight. Jupiter rises at 11:10 p.m. and will be easy to see in the southeast by 12:30 a.m.
Saturn has returned to our evening sky. Saturn rises at 10:14 p.m. and will be easy to spot by 11:30 p.m. looking southeast.
Night Sky Update: July 2-July 10, 2021