September marks the beginning of autumn for us in the Northern Hemisphere. The autumnal equinox will occur at 11:09 p.m. Wednesday the 22nd. Three other interesting events will happen within just one day of the equinox. Both Jupiter and Uranus will reach opposition the day before and the famous full harvest moon will occur just 6 hours and 8 minutes after the equinox.

The spring and fall equinoxes are the only two days each year when the sun rises due east and sets due west for everyone on Earth except at the poles. If you live near the ocean, try to see how much the position of sunrise varies each day.

You will find that it averages nearly half a degree per day, which is the width of the sun in the sky.

The sun reaches its northernmost point in our sky at the summer solstice, when it rises about 40 degrees north of due east and sets about 40 degrees north of due west, tracing a high arc through the sky. By contrast, notice that the sun rises about 40 degrees south of due east and sets about 40 degrees south of due west and traces a very low arc through our sky on the winter solstice.

Within a few days of the equinoxes are also the only two days each year that the days and nights are exactly of equal length for everyone on Earth, except for the poles. This serves as a unifying event, showing us how much more the 7 billion Earth inhabitants have in common than our minor differences.

Both Jupiter and Uranus will reach opposition on Sept. 21. They are located only 1 degree apart, which can be measured by holding up one finger at arm’s length. You will need a telescope to see Uranus just to the upper right of Jupiter because it is 13 times smaller and 2,000 times fainter than the King of the Planets. They will both rise at sunset that day and remain in the sky all night, not setting until sunrise. They can be seen just below the great square of Pegasus in Pisces, the fish in the eastern sky.

Discovered in 1781 by William Herschel, Uranus is named after the ancient Greek deity that is the father of Saturn and the grandfather of Jupiter. All eight members of our family of planets are unique, but Uranus exhibits more extreme differences. It is tilted completely on its side, so it seems to roll around the sun as it orbits. Half the planet experiences a 42-year night and the other half a 42-year day before it reverses for the next 42 years to complete its 84-year orbit around the sun.

Located 2 billion miles away or three hours at the speed of light, or about twice the distance of Saturn, Uranus is the third-largest planet after Jupiter and Saturn. It has rings like all four of the gas planets have, but it has only 27 moons instead of 63 for Jupiter and Saturn. Most of its moons are named for characters in Shakespeare’s plays. One of its five largest moons, named Miranda, is one of the strangest moons in our solar system, seemingly made of a combination of features of other moons stitched together. About 300 miles in diameter, Miranda has a giant chevron etched on one side and it looks like at least two different moons sandwiched together. There was a tremendous collision that tore this moon apart a long time ago, and it has since coalesced itself back together.

Uranus shows as a very interesting pale greenish-blue dot through a telescope. That is because the methane in its very cold atmosphere absorbs all red light. At 32,000 miles in diameter, it is four times the size of Earth and it has an earth-sized solid core that may be highly compressed carbon, which is the substance of a diamond.

While Jupiter was hiding below the horizon this winter and early spring, it went through a great change. It re-emerged missing a stripe. Jupiter usually has two distinct bands visible in small telescopes, called the north and south equatorial bands. The south equatorial band is now missing, veiled by a thick deck of cirrus clouds composed of tiny crystals of frozen ammonia. What is even more interesting is exactly how this band will revive itself. This band has already faded and revived itself 15 times since 1919, but not on a regular basis. The last time was in 2007. It could revive itself anytime between now and a couple of years from now.

An extremely dark spot will appear near the southern edge of this band and immediately encounter tremendous wind shear in the form of 200 mph winds blowing in one direction around Jupiter and the 300 mph south equatorial belt jet stream blowing in the other direction. This dark upwelling material will then quickly spread out in both directions and several more sources of this dark material will probably occur. After just two or three months, the entire south equatorial belt will be restored to its original darkness. Hopefully, this will happen while Jupiter is well placed in our sky to watch all this action through an amateur telescope. Try to get a better sense of the tremendous forces always at work deep within Jupiter as we get a better insight into its inner workings during this event.

Our neighbors, Venus and Mars, continue to distance themselves from Saturn.

Look low in the west-southwestern sky half an hour after sunset and you will see brilliant Venus and orange Mars 5 degrees apart forming an ever-elongating triangle with Saturn 10 degrees to their lower right.

The star Spica in Virgo will be directly between Venus and Mars on the first of the month. Venus is 250 times brighter than Mars and 200 times brighter than Saturn. The ringed planet will sink below the horizon by the middle of the month, just as Mercury becomes visible in the morning sky half an hour before sunrise in Leo the lion.

SEPTEMBER HIGHLIGHTS

Sept. 1. Last quarter moon is at 1:22 p.m.

Sept. 5. On this day in 1977, Voyager 1 was launched.

Sept. 8. New moon is at 6:30 a.m.

nSept. 10 & 11. Watch the slender waxing crescent moon pass directly below Spica, Mars and Venus these two evenings half an hour after sunset.

Sept.13. The moon passes near Antares, the brightest star in Scorpius one hour after sunset this evening.

Sept. 20. Jupiter and Uranus are closest to the Earth tonight.

Sept. 21 Jupiter and Uranus are at opposition tonight.

Sept. 22. Jupiter and Uranus are 6 degrees below the nearly full moon tonight. Autumn begins in the Northern Hemisphere at 11:09 p.m.

Sept. 23. The full Harvest Moon is at 5:17 am. This is called the Harvest Moon because it only rises about half an hour later each night instead of the usual 50 to 60 minutes later, giving the farmers more consistent light to harvest their crops well into the night for several nights.

Sept. 27. The Pleiades in Taurus will rise around 9 p.m. two degrees to the left of the waning gibbous moon.

Sept. 30. Last quarter moon is at 11:52 p.m.

 

Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.