The Sacred Hour Before Dawn and an Evening Comet Surprise

By: Bob King September 26, 2018 6

Silence can sometimes be in short supply, but one sure place to find it is under a starry sky before the first blush of dawn. Comet 29P/Schwassmann-Wachmann erupts again!

Sneak a peek at dawn — Orion stands high at the start of dawn in late September.
*Bob King*

Recently, I set my alarm for 4 a.m. for an hour of observing before the start of dawn. Fall brings later sunrises that make it possible to go to bed at 10 p.m. and still garner enough sleep to make it through the following 8-hour workday. Winter's even better, but yes, much colder.

The wee hours have always been special ones for me since the time I began exploring the night sky. From an early age I learned to tiptoe through the halls of my home when everyone else was asleep so as to make as little noise as possible. I zipped up my jacket deliberately and closed every door on the way out by hand to avoid slam-backs. Once under the sky, I was an animal escaped from its cage. I loved the morning stars and my dark-hour freedom spiced with a dash of danger should I accidentally wake up a family member coming or going.

As skywatchers know well, the Earth rotates through the night. In the evenings we see the familiar seasonal sights, but wait until morning and a new season's stars fill up the eastern sky. Getting up before dawn let me see into the future, one of my only magical super powers. In September, when the Summer Triangle would begin the night, I'd wake to Orion and that glorious belt.

When the world is in bed and traffic calms, mornings bring a hush that we rarely experience during evening observing. It's the quietude that adds a sacred quality to morning observing. Just you and the crickets. Silence is in such short supply these days, the experience of it makes you stop and catch your breath. Not only are quiet and solitude calming, they uncork the senses, allowing a keener awareness of the natural world and a deeper connection to our surroundings. This is a good feeling.

Small but lots of character — Returning Comet 38/Stephan-Oterma displays one and possibly two tails in this photo taken on September 17th. It's well placed in the morning sky this fall.
*Mikhail Maslov*

Once dawn blues up the eastern sky, I pack away the telescope and quietly slide back into bed, happy to have found my way back to the universe again.

I got the scope out before dawn a couple weeks ago and looked for and found the newly-returning comet 38P/Stephan-Oterma in Orion and its brighter relation, 21P/Giacobini-Zinner, in Gemini. Both comets still ply the sky during the small hours; I've included maps to help you find them when the Moon bows out next week.

A cool catch — This map plots Comet 38P's position nightly through late October. Dates are 0^h UT. Convert UT to local time here. Click the map to enlarge, then save the file and print to use outdoors.
*SkyMap with additions by the author*

Both are also visible in modest telescopes, with 21P still bright around magnitude 7.6 and flashing a 1° westward-pointing tail. 38P shines about three magnitudes fainter and appears much less condensed with a 5-arc-minute coma. With an orbital period of 37.7 years, most of us only get two chances in a lifetime to spot it. Carpe cometa!

Take a trip down south — Comet 21P/Giacobini-Zinner swiftly moves south in the next few weeks, passing close to numerous NGC star clusters. Sirius makes an easy place to start your search for the comet, which is still bright enough in a moonless sky to see in 50-mm binoculars.
*SkyMap with additions by the author*

Mid-September marks the beginning of the dawn zodiacal light season. After finishing up at the telescope I made a short field trip to a big field with a wide open vista of the eastern sky. Whoa! At 5:15 a.m. the tapered glow of the zodiacal light reached from the Sickle of Leo at the eastern horizon all the way to Milky Way in Taurus, a span of 60°. It was an incredible sight, towering over the distant trees like some giant, headless comet.

Glorious dust — The photo, taken on September 13th at 5:15 a.m., gives a good visual impression of the zodiacal light seen from a fairly dark sky. You can spot the giant, tapered cone a half-hour before the start of dawn, but it's tallest and brightest at the very start of morning twilight. The knot of stars halfway up the column is the Beehive Cluster in Cancer. Orion and the winter Milky Way are visible at upper right.
*Bob King*

And that's exactly what it is — primarily comet dust, with some added debris from asteroid collisions, lingering in the plane of the solar system.The material scatters sunlight well, and since it lies in Earth's orbital plane, we see it along the ecliptic, the same path taken by the planets, Sun, and Moon.

In fall, the ecliptic tilts up steeply from the eastern horizon before dawn, lifting this fat finger of dust up and away from the horizon murk and into a dark sky. The cone of light is brightest and widest at its base because that part is physically closest to the intensely bright Sun. The farther up you gaze, the narrower and fainter the finger. To see the light in its glory, find a spot with a great view to the east and start looking about a half-hour before the beginning of morning twilight. You'll see it best when the Moon's out of view from October 7–23 and November 5–21.

Compact comet — Comet 29P is small, bright, and strongly condensed in this image taken on September 23rd.
*Jean-François Soulier*

Now for some great news for evening skywatchers. On about September 20.5 UT, Comet 29P/Schwassmann-Wachmann underwent a bright outburst, morphing from a vague, diffuse 13th-magnitude patch to a bright little ball of light. At the moment, it's about magnitude 12 and ~20″ (arcseconds) across, like a small planetary nebula. It's possible it will get brighter still, so I strongly encourage you to take a look. The Moon should be out of the way by the 26th — just in the nick of time.

Comet pops near the Water Jar — Track down Comet 29P with this detailed map. Positions are shown every 5 days on the UT dates.
*SkyMap with additions by the author*

The comet's been very active this year and more outbursts are expected. To learn more about 29P's explosive nature and possible causes, check out my earlier blog. Clear skies!

Comments

Anthony Barreiro

September 26, 2018 at 7:50 pm

Carpe stella crinita per cauda.

Even here in a light-polluted city, the hour before dawn is the best time for back yard skywatching. All my neighbors are still in bed, so no extra lights from their windows. Fewer cars on the roads, fewer businesses open. There's less air pollution so if the weather is clear the air is clearer, and everything has cooled down overnight so the seeing is steadier than in the evening, when all the streets and buildings are radiating heat.

One early morning in 2016 I got a perfectly steady view of Mars at 100x through a 70 mm refractor. The northern polar cap, Syrtis Major, and Hellas Basin were all perfectly clear. I was exceedingly happy all day at work.