EVENTS AND NAKED EYE VIEWING
NOTE: All Sky Charts Courtesy of SkyGuide App Unless Otherwise noted.
September 4 (Monday) Neptune at Opposition. Since Pluto was reclassified as a "Dwarf Planet," Neptune became the farthest known planet in our Solar System. Even when Pluto was still designated as a planet, it's eccentric orbit crossed Neptune's orbit in two places causing both worlds to "take turns" being the farthest from the Sun.Tonight it reaches opposition (closest annual separation between Earth and the ice giant) at 11 PM MDT. Although this is the one night of the year that Neptune will shine at its brightest and look the largest it can through Earth based telescopes, that's not saying much for this distant denizen of the Sun's realm. When Neptune is farthest away from us, it's 2.9 billion miles distant. Closest approach on this night is 2.7 billion miles which is only 6% closer. Therefore, it'll only be 2 tenths of a magnitude brighter than it's dimmest point. Translation: Neptune looks best when sky conditions are best for viewing as long as the blue planet is prominent in the night sky. Neptune shines at magnitude 7.8 which is too dim to view naked eye. 10x50 binoculars gather enough light to see Neptune, but you have to have them on a fixed tripod so you can study the surrounding stars in order to pick out which one is Neptune. Even then, it's extremely difficult to locate. I suggest using a computerized telescope to find it.
Neptune will be high above the SE horizon at its time of opposition on September 4. Note that the waxing gibbous Moon is nearby with it's bright shining disk interfering with your view of the distant planet. In fact, the next night, the Moon will be less than a degree south of Neptune in a near occultation. Your best views of Neptune should be any day in September from the ninth to the end of the month between the hours of 9 PM and midnight when the Moon's glare will no longer interfere. Don't forget to slide your scope to the east or scan your binoculars to find planet Uranus (easier to see than Neptune).
September 10 (Sunday) Near Occultation of Mercury and Regulus. Mercury is always difficult to find and when first viewed, many mistaken it for Mars because it has a similar ruddy orange appearance. This is your chance to see Mercury in a glorious alignment with the alpha star in the constellation Leo The Lion along with lower to the horizon and much dimmer planet Mars. Venus will most likely grab your attention first because it is (by far) the brightest object in the morning sky besides the Sun which will rise 40 minutes after the predawn sky image you see below.
September 6 (Wednesday) Full Harvest Moon. Arguably the most famous of all Full Moons, the Harvest Moon occurs in September this year because it's closest to the Fall Equinox
September 22 (Friday) Autumnal Equinox. At 2 minutes past 2 in the afternoon, the track of the Sun reaches its midpoint between its farthest travel north (Summer Solstice) and farthest travel south yet to come (The 2017 Winter Solstice). Summer officially ends and Fall begins in the northern hemisphere. Already, the aspens in the Sangre de Cristo mountains have changed to golden yellow contrasting well with the deep blue sky and green spruce and ponderosa pine. Steller's Jays have returned and there are an unusually high number of bear sightings as they look for food to prepare for their long winter hibernation. Elk cows are being herded by bugling Bulls as they build their harems for the mating season. Even I have joined the ritual by purchasing a new snow blower! This is a melancholy time for me. Although I adore the Fall colors, it saddens me to see the Summer go. But each season here in the mountains has its unique appeal. For skywatchers, Fall in the Sangre de Cristos affords more clear nights because the monsoon season ends and the Sun sets earlier every day. This allows us to more frequently enjoy the grotto of stars cascading over us.
October 5 (Thursday) Full Hunter's Moon. Before the age of supermarkets and big box stores, this Full Moon signified an important time for hunting animals whose meat and furs would sustain and protect us through the coming cold season.
October 8 (Sunday) 3 AM MDT Peak of Draconid Meteor Shower. This shower and the constellation it emanates from (Draco the Dragon) are almost equally difficult to see. The Draconids come from the debris trail behind comet 21 P/Giaconbini-Zinner which completes its orbit around the Sun every 6.6 years. That's a short period as comets go, but it's relative nearness to the Sun means that much of its volatile gasses have escaped and the debris trail it leaves is thinning out. That, along with the fact that there will be a bright waning gibbous Moon in the way, means that this will probably not be a crowd pleaser like the Persieds or Geminids.
October 15 (Sunday) Algol At Minimum. Algol is back! Most of us remember the Great American Solar Eclipse on August 21, but did you know that you can view two stars eclipsing each other? The eclipsing binary star in Perseus is once again in a favorable position to view its near vanishing act. So you won't freeze or be bored to death waiting for it to happen, look to the NE at 7 PM to see Algol before its larger dimmer companion star passes in front of its smaller brighter buddy. Go out again at 9:46 PM (mid eclipse) to see it at its dimmest possible state. The contrast will be alarming! Although binoculars or a telescope will show more detail, your naked eyes are all you need to see this eclipse...and...you won't have to worry about wearing special protective eclipse glasses!
You can see Algol when it's relatively bright by viewing it rising above the NE horizon at 7 PM MDT. Look for the bright star Capella near the NNE horizon and the "tiny little dipper" cluster of bright blue stars known as the Pleiades. Draw an imaginary line connecting Capella and the Pleiades to form the baseline of a triangle cocked slightly to the right. Complete the triangle as shown in the image above to find Algol. To help you orient your perspective, I've included the "W" zigzag pattern of stars known as Cassiopeia as well as the dim but naked eye visible galaxy Andromeda. Don't mistaken Algol for the brighter star Mirfak which is to the left and slightly above Algol.
Here's what the sky will look like when Algol is almost fully eclipsed by its larger dimmer companion star. The Capella-Pleiades-Algol triangle is higher in the sky and is now centered above the ENE horizon. Compare the relative brightness of Algol with what you saw almost 3 hours ago. You just witnessed a near total eclipse of one star by another! Imagine what the ancients thought when they saw this phenomena. To them, the stars were considered constant and unwavering. To have one of them "blink" like this caused many to think the worst...it was the Evil Eye! Thanks to astronomy, we have (in my opinion) much more interesting and exciting views of celestial events. We now know that some stars eclipse each other and that many stars occur in pairs or multiples. In fact, Algol is a three star system with Algol A and B eclipsing each other nearly every three days and Algol C completing a wider non eclipsing orbit around the inner pair nearly every 2 years.
The image on the left is Algol at maximum brightness while the one to the right is its minimum. The other stars in the field are too dim to see naked eye, but Algol is bright enough (magnitude 2.1 at its brightest) to be seen by most people with good night vision. Some of us older folks may not see Algol at all when it's at its dimmest. If you're having trouble viewing this star, try using a pair of binoculars. Most everyone can see Algol throughout the eclipse by using optical aids such as binocs or telescopes.
October 17 (Tuesday) And Every Predawn Sky For the Remainder of October THE ZODIACAL LIGHT. Once again, another Equinox means we get another view of the dusty disk plane of our Solar System. This time, the reflected sunlight from the primordial stuff that formed our star system is best seen during the predawn hours when the sky is still predominantly dark from 3 to 4:30 AM MDT. It will look like a "false dawn" dim foggy triangle of light rising above the eastern horizon. If you live in an area where the eastern horizon is light polluted, you won't see the Zodiacal Light. You can help yourself and others by shielding your outdoor lights so that they won't shine up and kindly ask your neighbors to do the same! If we all show how much we care for our environment and the health of Earth's nocturnal creatures, we will be rewarded by the mind boggling spectacle of our rich and mysterious universe!
October 19 (Thursday) Planet Uranus at Opposition. Here's your chance to view Uranus at its brightest in 2017. Although it will shine at only a tenth magnitude brighter than at other times, Uranus' disk will be larger (3.7 arc seconds wide) and at least two of its brightest moons (Titania and Oberon at 14.0 and 14.1 respectively) may be visible when viewed through a high power eyepiece on an 8 inch or larger telescope. Under pristine conditions, at the right moment in their orbits, and using a telescope with a sensitive planetary camera, it's possible to see 4 of Uranus' 27 moons. Ariel and Umbriel are the most challenging at magnitude 14.3 and 15.0 respectively because they are smaller and closer to Uranus than Titania and Oberon. At 1.7 billion miles, Uranus is "out there," so don't be discouraged if bad weather won't allow you to see it at opposition. It'll still be a fine sight during the entire month of October and well into November.
October 21 (Saturday) Orionid Meteor Shower. This shower is not the best, but it occurs at a time of year when it's not so beastly cold and you can expect as many as 20 meteors per hour during its predicted peak. Orion will be high enough over the ESE horizon on October 20 at 11 PM MDT to properly expose the radiant, but the peak of the shower will occur at 6 AM on October 21...only 20 minutes before sunrise. So, you may see some Orionids (debris trail from comet Halley) between these time periods. Understand that Orion will travel from the eastern horizon through south to the southwestern horizon by dawn. My best recommendation is to get up early and set up a lounge chair with your feet facing WSW and lie down so you can see as much of the sky as possible between 4:00 and 5:15 on Saturday morning.
Uranus is still in the constellation Pisces The Fishes which is not surprising considering it takes 84 years for Uranus to complete one orbit around the Sun. That means it spends an average of 7 years passing through each sign of the Zodiac. I've provided a reasonable time on its night of opposition to view Uranus comfortably high over the ESE horizon and not too late in the evening when most people are still more or less...awake! Try binoculars first to find Uranus, then look at the same spot naked eye using the averted vision technique to see if you can still spot this distant ice giant planet.
This image is from Software Bisque's Gas Giants App. It shows the orientation of 5 of Uranus' brightest moons at the time stamp for the night of the planet's opposition. The image is mirrored to simulate a view through an SCT telescope with a star diagonal attached. Good luck seeing all of them! The best I've been able to do with the 14" SCT at Mount Sangre Observatory using an Atik Infinity camera is 3 moons (Titania, Oberon, and Umbriel).