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.
Credit: NASA

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.

DaySunriseSunset
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.

Moon 

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

Credit: NASA

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

Date Starts  Max. altitude  Ends  
TimeAlt.Az.TimeAlt.Az.TimeAlt.Az.
05 Jul-1.2 02:00:3421NE 02:00:3421NE 02:01:5410NE
05 Jul-0.9 03:34:1710NW 03:36:0113NNW 03:37:4510NNE
06 Jul-1.2 02:47:4416NW 02:48:3417NNW 02:50:5110NNE
07 Jul-1.2 02:01:5421N 02:01:5421N 02:03:5410NNE
08 Jul-0.8 01:16:0016NNE 01:16:0016NNE 01:16:5210NE
09 Jul-0.7 02:02:5612NW 02:03:5413NNW 02:05:3810NNE
10 Jul-0.8 01:16:4816NNW 01:16:4816NNW 01:18:4310NNE
10 Jul-0.6 04:30:2510NNW 04:32:2515NNE 04:34:2610NE

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 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

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.

Mars

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

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

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.

James S. McDonnell Planetarium

Night Sky Update: July 2-July 10, 2021