The brilliant colors of our leaves are beginning to transform our landscape. As we slowly get closer to winter, the nights are getting longer by a few minutes each day. The northern hemisphere is tipping ever so slowly further away from the sun, until its lowest point will be reached on the winter solstice.

Autumn is a great time to enjoy the beauty of the night sky, because much of North America tends to have its best weather in this season, with fewer clouds and less haze and humidity. Look up into the crystal-clear skies this month and you will see Jupiter at its best, a chance to see the elusive zodiacal light, two meteor showers and even another comet.

The king of the planets, Jupiter, will rule our night sky all this month. Just past opposition now, Jupiter rises before sunset and sets shortly before sunrise. Jupiter is now in the middle of its retrograde loop, which lasts four months. It is moving westward against the fixed background of stars, crossing from Pisces back into Aquarius for a while.

Jupiter takes 12 years to orbit the sun, so it will spend one year in each constellation on the average. However, it does appear to be traveling backwards for one third of that year, so it may loop back into a previous constellation.

All the planets are constantly orbiting the sun in a counterclockwise manner, but from our perspective in this ecliptic plane, Jupiter appears to be going backwards for a while as we pass it in our faster orbit around the sun. All of the superior planets from Mars out to Neptune go through this illusory motion when they are near opposition.

Through a telescope you can watch the endless dance of Jupiter’s four large Galilean moons, Ganymede, Callisto, Io and Europa as they are forever trading places. Most of those moons are even visible in a good pair of binoculars. You will also notice that Jupiter still shows only one band instead of its usual two prominent cloud bands. Its South Equatorial Belt, where the Great Red Spot resides, has not reappeared yet, but may do so any time or it may take another year or two.

The Draconid meteor shower will peak on Friday night Oct. 8 into the morning of Oct. 9. Caused by periodic Comet Giacobini-Zinner, this is not a very prolific shower. The best you could expect is 10 meteors per hour, which is only a little above the background rate of stray meteors of about three to five per hour from a dark-sky site.

The next shower, the Orionids, on Oct. 21, are usually much better, but this year they will be washed out by a nearly full moon. Caused by the most famous of all comets, Halley’s, the Orionids will all appear to originate in the constellation of Orion the hunter. The May 6 Eta Aquarids are also caused by this famous comet.

ZODIACAL LIGHT

The zodiacal light is an amazing phenomenon that is always there, but best visible for us in the northern hemisphere this time of year in the eastern morning sky about two hours before sunrise or in the western evening sky after sunset in the spring.

You should be able to see it if you are far away from any light pollution and there is no moon in the sky. Look for a cone of light slanted to the right along the ecliptic through Regulus in Leo and the Beehive star cluster in Cancer.

Composed of primordial interplanetary dust, the zodiacal light is always there but we can’t usually see it because it is so subtle. This dust is generated by all the comets and asteroids in the plane of our solar system. On the average there may only be a single one millimeter particle every 5 miles to create this extremely tenuous glow.

These individual dust particles are slowly spiraling into the sun, but there is a constant source of new particles being created in the plane of our solar system by asteroid collisions and more comet dust as comets get close to the sun and release some of their mass.

This incredibly ancient interplanetary dust is 4.6 billion years old. Even as more of this dust is being generated by new collisions, it is all the same age, since our sun and solar system were formed 4.6 billion years ago. There is nothing that ancient left on Earth because of our constant weathering and erosion and plate tectonics.

Although usually only visible as a cone of ghostly light extending a little above the horizon, be aware that the zodiacal light actually extends uniformly all the way around the sky. Only the part near the horizon reflects enough sunlight back to us to become visible.

Comet Hartley 2 will pass high through our northern sky this month, traveling below Cassiopeia, very close to the double cluster in Perseus on Oct. 9, and on through Auriga and Gemini. Discovered in March 1986 by Australian Malcolm Hartley, this little comet has a 6-year orbit around the sun.

This appearance will be its closest approach since its discovery and one of the closest approaches of any comet in the last few centuries. It will pass only 11 million miles from us on Oct. 20. Comet Hyakutake also passed about that close to us back in March 1996. That was a once-in-a-lifetime comet with a brilliant green gas tail and was closely followed by an even brighter once-in-a-lifetime comet named Hale-Bopp in March 1997.

Comet Hartley 2 should reach 6th magnitude, which is right at the limit of being visible without binoculars, by the start of this month as it passes below Cassiopeia. Then it may even brighten another magnitude as it passes near the double star cluster in Perseus. It should be visible in binoculars in any case, so don’t miss this opportunity to see another ancient primordial visitor from deep space.

Venus is getting very low in our western sky now and will disappear completely by the middle of this month, not to reappear until early November in our morning sky.

OCTOBER HIGHLIGHTS

Oct. 4. On this day in 1957 the Soviets launched Sputnik 1, the first man-made satellite ever, beginning the space age. Look for a waning crescent moon near Regulus and above Mercury low on the eastern horizon 30 minutes before sunrise.

Oct. 7. New moon is at 2:44 p.m. EDT.

Oct. 9. Use binoculars to see the moon directly between Mars and Venus low in the southwestern sky 20 minutes after sunset. Also look for Comet Hartley directly below the double cluster in Perseus, which is just visible to the naked eye below Cassiopeia.

Oct. 14. First quarter moon is at 5:27 p.m.

Oct. 19. Jupiter is directly below the moon shortly after dark below the Great Square in Pegasus.

Oct. 22. Full moon is at 9:37 p.m. This is also called the Hunter’s Moon.

Oct. 25. The moon will pass just below the Pleiades star cluster in Taurus high in the western sky one hour before sunrise.

Oct. 28. On this day in 1971, Britain becomes the 6th nation to launch its own satellite.

Oct. 30. Last quarter moon is at 8:46 a.m.

Oct. 31. On this day in 2005, the Hubble Space Telescope discovered two more moons of Pluto, named Nix and Hydra. Its largest moon, Charon, was discovered in 1978. 

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