Enjoying EarthSky? Subscribe.

231,603 subscribers and counting ...

Moon, Saturn and more on September 8

Tonight – September 8, 2016 – the moon and the ringed planet Saturn pair up together at nightfall. In the same vicinity of sky, note two other bright celestial beauties: the red planet Mars and the ruddy star Antares. You can distinguish Mars from Antares because Mars is the brighter starlike object.

Clouded out tonight? Watch for them tomorrow night, too …

The moon 24 hours before and after nightfall September 8, 2016, as viewed from North America. From the world's Eastern Hemisphere, the moon's position is somewhat offset toward the previous date.

The moon 24 hours before and after nightfall September 8, 2016, as viewed from North America. From the world’s Eastern Hemisphere, the moon’s position is somewhat offset toward the previous date.

Saturn is fainter than Mars but brighter than Antares. And – unlike Mars or Antares (both of which appear reddish) – Saturn displays a golden color. If it’s hard for you to discern color, try observing these planets and the star Antares with binoculars.

Better yet, try observing Saturn with a telescope. You can view Saturn’s glorious rings even with a modest backyard variety. Did you know that, as seen from Earth, the orientation of Saturn’s rings appears to shift regularly, over time? This happens as we orbit the sun yearly, while Saturn orbits once every 29.5 years. In 2016 – as we gaze across space to Saturn – we are seeing the north face of Saturn’s rings. Saturn’s rings are inclined at 26o toward Earth in 2016, which is about as wide open as they ever appear to us from our world.

We see the north face of the rings for about 15 years 9 months years, then the south face for about 13 years 9 months. The difference is due to Saturn’s eccentric orbit, with the planet traveling most swiftly at perihelion and most slowly at aphelion.

The north side of Saturn’s rings will open up most fully on October 26, 2017, to exhibit a maximum inclination of 27o.

Thereafter, the inclination of Saturn’s rings will slowly but surely diminish until the rings appear edge-on in the year 2025. At this juncture, Saturn’s rings will appear invisible to earthly observers for about one and one-half months. That’s because the rings are so thin, in contrast to their width.

View larger. .Saturn oppositions from 2001 to 2019 simulated by a computer program written by Tom Ruen.

View larger. .Saturn oppositions from 2001 to 2019 simulated by a computer program written by Tom Ruen.

This animation demonstrates the 29 year period for oppositions of Saturn from 2001 to 2029, taken from the 28 images of Saturn above.

This animation demonstrates the 29 year period for oppositions of Saturn from 2001 to 2029, taken from the 28 images of Saturn above.

After the year 2025, the south side of Saturn’s rings will start to exhibit itself. Then some seven years later – on May 12, 2032 – the south side of Saturn’s rings will become maximally inclined (27o) toward Earth.

Some seven years after the south side of Saturn’s rings opens up most fully, the rings will appear edge-on and return to invisibility in 2039. Some seven years after that, the north side of Saturn’s rings will become maximally inclined (27o) toward Earth on November 15, 2046.

Contrasting the size of Saturn and its rings with our planet Earth via Hubble Heritage Team.

Contrasting the size of Saturn and its rings with our planet Earth via Hubble Heritage Team.

Saturn’s rotational axis is inclined at 27o to its orbital plane, and – as we said above – this planet takes nearly 29.5 Earth-years to orbit the sun. Therefore, the maximum inclination of Saturn’s rings recurs in a cycle of about 29.5 years, as is shown in the table and diagram below:

Maximum inclination of Saturn’s rings in the 21st century (2001 to 2100)

2003 Apr. 7: South face inclined 27o 01’
2017 Oct. 16: North face inclined 26o 59’
2032 May 12: South face inclined 26o 58’
2046 Nov. 15: North face inclined 26o 56’
2062 Mar. 31: South face inclined 27o 01’
2076 Oct. 9: North face inclined 27o 00’
2091 May 4: South face inclined 26o 59’

Source: page 295 of More Mathematical Astronomy Morsels by Jean Meeus

View larger. The astronomer Christian Huygens (1629 to 1695) explanation for the periodic disappearance of Saturn's rings in Systemma Saturnium 1659

View larger. The astronomer Christian Huygens (1629 to 1695) explanation for the periodic disappearance of Saturn’s rings in Systemma Saturnium 1659

Bottom line: On September 8, 2016, use the moon to locate the ringed planet Saturn as darkness falls. The planet Mars and star Antares are also nearby.

Bruce McClure

MORE ARTICLES