Skylights: October 2022

With October comes earlier and cooler nights. As the temperature dips, so does the chorus of our night singers. A few crickets may remain within earshot of our observing station, and the distant, raspy chirp of a lone katydid reminds us of the warm nights gone by. The nights are getting quieter.

The Milky Way still arcs high overhead after twilight, but it quickly turns away from the summer star clouds as the autumn star patterns take over, and hints of winter sky begin to appear low in the east.

The Sun spends the entirety of October, save for a few hours on the 31st, within the boundaries of Virgo, and on the 17th it is located close to the constellation’s brightest star, Spica, which is 1.8° to the south. The 17th is also the first morning when the Sun begins to rise after 7am. The last 6pm sunset occurs the following day, on the 18th..  

October begins with the Moon in first quarter on the 2nd. The Moon is 5.6° southeast of Saturn on the 5th, 3.4° south of Neptune on the 7th, and .2° east of Jupiter on the 8th.

The Full Hunter's Moon occurs on the 9th, in Pisces. This month’s full Moon is notable as being the first one since March to occur north of the celestial equator. If you notice that the Full Moon appears higher and brighter, this is the reason why.

The waning gibbous Moon appears close to the Pleiades on the 12th-13th, passing just 2.5° south of the cluster at midnight. On the 14th, the Moon is 2.8° north of Mars.

The Moon is at last quarter on the 17th, when it resides near the twin stars of Gemini, Pollux and Castor. 

On the 21st, the waning crescent is your guide to locating our closest dwarf planet, Ceres, which will be 3° north of the Moon. Also on this morning, the Moon lies within 1° from the galaxies M95, M96, and M105. A medium-sized telescope will be needed to see the galaxies.

The Moon is new on the 25th.

October mornings present a good opportunity for observing Mercury. The elusive innermost planet reaches its greatest elongation on the 8th, and although this is one of the shortest possible elongations, the high angle of the ecliptic gives Mercury a few days of visibility exceeding 90 minutes before sunrise. It remains at a favorable distance from the Sun up until the last week of October, and is joined by the Moon on the 24th, when the 1.1% illuminated 27-day crescent lies just 1.5° above the planet.

Venus rises just 30 minutes before sunrise at the beginning of October, and is at superior conjunction on the 22nd. It then returns to the evening sky, but will not be easily visible again until late November.

The evening sky belongs to our three bright outer planets. Saturn, in Capricornus, becomes stationary on the 23nd, and resumes prograde motion. This is the best time to view the ringed planet at its maximum shadow angle, giving the planet its most dramatic three-dimensional appearance. Note how close Saturn appears to be to iota Capricorni, and continue to watch it over the coming weeks as it moves east, back towards Nashira (gamma) and Deneb Algedi (delta Cap).

Jupiter, in Pisces, is the brightest starlike object in the sky and is visible for much of the night, setting before morning twilight.

We are entering the best time to watch Mars. Moving eastward through Taurus, until it reaches its stationary point on the 30th, the Red Planet brightens to magnitude -1 and grows to 15 arcseconds by month’s end. In mid-October, Mars passes within 2° of the supernova remnant M1, the Crab Nebula, though bright moonlight might interfere with seeing it.

Mars reaches its stationary point on the 30th and begins to move westward, until January 12, when it resumes eastward, prograde motion.

Beyond the bright outer planets, the ice giants are also well-positioned for viewing during October evenings.

If you haven’t seen Uranus yet, an opportunity exists on the night of the 11th-12th to locate it with ease. When the waxing gibbous Moon rises, Uranus will be 3° to its east, but just after 2am, you can find Uranus just 0.2° south of the Moon.

However, it is worth waiting until the bright Moon is out of the way, and trying to find it from a dark site. Uranus, at magnitude 5.7, is just at the cusp of naked-eye visibility, and presents a worthy challenge for keen-eyed observers. From less than ideal conditions, it is easily visible in binoculars, and a sizeable telescope with high magnification under reasonably steady skies will reveal its featureless teal-toned disk about 3.7 arcseconds across.

Neptune, located 8° west of Jupiter along the ecliptic, is ideally placed for early evening viewing. Directly south of the Circlet asterism of Pisces by 5° is a 1.5° elongated diamond of 6th and 7th magnitude stars. Neptune is close to the easternmost star. A small telescope will reveal its bluish, 7.8 magnitude glow fairly readily.

While Pluto is still visible in the evening sky, it is getting fairly low  by the time the Moon moves out of view.

Our nearest dwarf planet, Ceres, is in central Leo in October, and the waning crescent Moon appears 3° to its south on the 22nd.

Asteroid 4 Vesta, shining at 7th magnitude in southeastern Capricornus, is an easy target for binoculars or small telescopes. It can be located about ⅖ of the way along a line connecting Saturn and Fomalhaut (alpha Piscis Austrinus), and a few degrees to the east-northeast of globular cluster M30.

You may notice meteor activity picking up in October, as there are two notable showers occurring. In early October, the Draconids peak around the 8th-9th, when a bright gibbous Moon interferes with all but the brightest of the approximately ten meteors per hour you can expect to see.

Later in the month, conditions are more favorable for the Orionids, which peak on the 20th-21st. This shower, consisting of dust left behind from Comet 1P/Halley, originates from northeastern Orion and can produce up to 20 meteors per hour.

Every few months we notice that the Big Dipper’s pointer stars align with cardinal points around the north celestial pole (approximately the location of Polaris, the North Star) at an even hour of our clock. These alignments typically occur in December, March, June, and September. 

While these positions do not occur during October, it is notable that during early October, the celestial coordinate grid neatly aligns with local time. This occurs on the night of October 2-3 for the range of longitudes covering Rhode Island.. 

To understand what this means, go out and look due south at any time during the hours of darkness on that night. Any star crossing the meridian, or culminating directly over the southern horizon, will have a right ascension that is almost exactly the current local time.

This could be a fun exercise  to familiarize yourself with the coordinates of some of the sky’s notable stars, the planets, or deep sky objects. First, you must identify true south from your observing location. If you can see Polaris, this should be fairly straightforward, but if the North Star is obstructed from view, you’ll need to find another method. Using a compass will give you magnetic south, with which you will need to add your magnetic declination. An easier method would be to use an online mapping service. Locate your observing site, and determine its orientation and your direction due south. Additionally, many weather apps, or services such as TimeAndDate, will tell you what time the Sun transits the meridian, so you can mark your south point during the day.

Once you’ve oriented your observing site within a reasonable degree of accuracy, begin your observations and take note of the time some of your favorite objects cross your meridian, then take out your star catalog and look up the right ascension coordinate for each object. Note that this will be more accurate if you use current year epoch, as the J2000 coordinates will be slightly off due to precession.

On the flip side of this exercise, if you know the coordinates of a star, and you have the current time, you can determine your meridian to within about a degree of accuracy.

What if you are not able to check the coordinates of your favorite objects on the night of the 2nd-3rd? Each successive night, the stars will transit approximately four minutes earlier, and each night before, they transit about four minutes later. Note also that if you observe from a significant difference in longitude east or west of Rhode Island, the synchronization between the celestial grid and local time will occur on a different night.