Delicious Comet Lemmon-cluster pairing; moon greets 7 Sisters at dawn

Comet C/2012 F6 Lemmon cruises by the open cluster NGC 7789 in Cassiopeia last night July 2, 2013. Click to supersize. Credit: Damian Peach

It’s a beautiful thing when two completely different celestial objects pair up. Seen side by side, we can appreciate the unique qualities of each by contrast with the other. Two fine examples stand out this week.

Comet Lemmon, which has been chugging across the sky for months, pulled up alongside the rich star cluster NGC 7789 this week. The cluster is sandbox of pinpoint stars tucked off to one side of the W of Cassiopeia. I’ve been watching the scene the past two nights through the telescope. Last night both comet and cluster shared the same field of view.

Compared to the pointillistic stellar swarm, the comet looked ghostly and ethereal. And to think that one of these belongs to our solar system and the other resides on the far edge of the galaxy at a whopping 7,600 light years from Earth … well, it simply jazzes the brain cells. What can I say?

Then there’s composition to consider. Comets and the sun are made of virtually the same materials – hydrogen (frozen H2O in a comet’s case) and a dusting of carbon, nitrogen, oxygen, silicon and on and on. Yet comets are cold, relatively uncompressed dust. Not the sun. Put enough dust in one place and gravity will eventually crush it into a sphere hot enough to start its innards burning. A star is born. Interstellar dust left by earlier stellar generations is their common bond.

Watch the moon come up below the Pleiades star cluster tomorrow morning. The crescent will be only three days from new moon. This map shows the sky facing northeast at early dawn. Stellarium

Tomorrow morning we’ll see another auspicious duo. The waning lunar crescent rises at dawn below the Seven Sisters star cluster. Also known as the Pleiades (PLEE-uh-deez), the dipper-shaped group is more closely associated with the winter sky than the summer. In July it re-emerges during morning twilight, stalks the wee hours in August and looks down on earthlings from overhead on December evenings.

You can watch both moon and sisters with the naked eye, but binoculars will enhance the view. Next to the cluster, will the tweezers moon look closer to home than ever before? Take a look and see what you think.

Lizard Lemmon Comet loses tail, grows a new one

Comet C/2012 F6 Lemmon photographed on May 15 showing its bluish, ion tail (bottom) beginning to peel away from the comet. The dust tail sticks out to the left. A wispy, new gas tail is already growing above the departing one. Credit: Damian Peach

Solar winds snapped off Comet Lemmon’s ponytail this week and sent it reeling into space. Not to worry. Comets possess the remarkable ability, shared by many species of lizards, to grow new ones. A lizard loses its tail to distract and escape a predator; a comet because its charged atoms – called ions – interact with the breezy blasts of charged particles from the sun called the solar wind.

Magnetic fields in the solar wind tore off Comet Lulin’s tail on Feb. 4, 2007. You can clearly see it falling away in the bottom frame. Credit: Joseph Brimacombe

One day Comet Lemmon was minding its own business and then on Wednesday morning, one of its two tails underwent a “disconnection event”. Comets frequently grow two tails when they orbit near the sun – a pale yellow one of fine dust and a blue one of ionized (electrically charged) gas. The blue color comes from ionized carbon monoxide which fluoresces blue when excited by ultraviolet light from the sun. The larger particles in a comet’s dust tail have no electric charge and aren’t affected by the solar wind; they get pushed away from the comet’s head by the pressure of sunlight.

Charged particles from the sun – electrons and protons – plow through the solar system and continuously interact with comets creating picturesque kinks and ripples in their ion tails. Wrapped up into this electrical mix are solar magnetic fields with north and south-directly poles similar to those on a horseshoe magnet.

 

Invisible magnetic field lines are made visible around a bar magnet when you sprinkle iron filings around it. The sun’s wind likewise has lines of magnetic force embedded within it created by moving charged (electric) particles.

Electricity and magnetism go hand in hand. A spinning magnet creates an electrical field and an electric current creates a magnetic field. Every time you turn on a lamp, the wires inside the cord are looped by invisible but very real magnetic fields.

Solar flare eruptions like the powerful X-class flares earlier this week can direct huge clouds of magnetized (and electrified) clouds of gas called coronal mass ejections or CMEs into space. When one smacks into a comet, it can rip its tail right off.

Magnetic field lines bound up in the sun’s wind pile up and drape around a comet’s nucleus to shape the blue ion tail. Notice the oppositely-directed fields on the comet’s backside. The top set points away from the comet; the bottom set toward. In strong wind gusts, the two can be squeezed together and reconnect, releasing energy that snaps off a comet’s tail. Credit: Tufts University

Comets present obstacles to the solar wind. The magnetic field carried by the sun’s constant wind gets pushed back by the comet’s electrified gases causing it to drape and flow around the comet’s head. That’s what forms the streamlined blue ion tail in the first place. But when an especially powerful blast of wind blows by, it can elbow its way around the backside of the comet and reconnect with itself, releasing a burst of energy that snaps off the tail.

Diagram showing how a CME slams into a comet (B) to create a tail disconnection event, known in the biz as a DE. Soon enough the comet grows a new one (D). Credit: NASA

In a very real sense, Comet Lemmon experienced a space weather event much like what happens when a powerful solar wind reconnects streams around Earth’s magnetic field and reconnects on the back or nightside of the planet. The energy released sends zillions of electrons and protons screaming down into our upper atmosphere where they stimulate the air molecules to produce auroras. One wonders whether comets might even have their own brief displays of northern lights.

As the solar wind flows away from the Sun, it creates a spiral-shaped interplanetary magnetic field (IMF). Two to four sectors – where the field is pointed toward or away from the sun – spin out every solar rotation (27 days). Each sector Credit: NASA

It’s unclear what pinched Lemmon’s tail since all four large flares from sunspot group 1748 and their associated CMEs weren’t directed at Comet Lemmon.

Maybe the comet crossed a sector boundary where the magnetic field carried across the solar system by sun’s steady breeze changed direction from south to north or north to south. When it sped across the older field wrapped around Lemmon, the two once may have linked up in a burst of energy.

When a lizard loses its tail, it may gain its life, but still suffer for the trouble. For a time, its sense of balance is compromised and important fat reserves stored in the tail aren’t available. Comet Lemmon will be no worse for the wear. As soon as the old tail drifts away, a new one sprouts in its place, cooked up by the ever-steady sun.

Read more about tail disconnections HERE; check out a map for finding Comet Lemmon HERE.

Sweeten your May mornings with Comet Lemmon

Comet C/2012 F6 Lemmon cruises up the side of the familiar Great Square of Pegasus this month. Look for it starting about 90 minutes before sunrise low in the eastern sky. Let the W of Cassiopeia point you toward Alpha Andromedae; from there you can star-hop to the comet using binoculars. Stellarium

Looks like Comet PANSTARRS has company.This week Comet Lemmon begins nudging its way into the early dawn sky. Watch it to slowly climb up the eastern side of the Great Square of Pegasus in the coming weeks. Both comets are now below the naked eye limit and glow around 7th magnitude.

A beautiful pairing of Comet PANSTARRS and two bright nebulae – NGC 7822 (top) and Cederblad 214 (center) – in the constellation Cepheus on April 30. The colors of the comet and nebula are strikingly different. Sunlight reflected by dust colors the comet’s tail yellow; the light of hot, young stars embedded within the nebulae causes hydrogen gas to fluoresce red. Credit: Michael Jaeger

From a dark sky 7×50 and 10×50 binoculars will easily show Lemmon as a fuzzy spot, and you might even spot a long, thin tail. The comet slowly fades during the month while rising higher and becoming easier to see in the morning sky. You can use the map here to help guide you to it; for more details, check out this recent article I wrote that appeared in Universe Today.

Lemmon of a comet slices through the Southern Cross

The Southern Cross, officially named Crux, is tipped on its side in this photo taken off Comet F6 Lemmon on Jan. 18, 2013 local time in Bright, Victoria, Australian by amateur astronomer Rob Kaufman. He used a 134mm telephoto lens setting. The inset photo is a blowup from the main image.

I apologize. I discovered the joy of puns around the age of 13 and have been making family and friends groan ever since. The title refers to Comet C/2012 F6 Lemmon, which has turned out to be anything but.

Lemmon was discovered in March 2012 by A.R. Gibbs during the Mount Lemmon Survey based in the Catalina Mountains north of Tucson. At the time it was spectacularly faint. Not anymore. The comet became much brighter than expected when it first appeared in the morning sky late last fall. I recall it as a big, puffy glow shining at 10th magnitude in my scope one chilly December dawn.

Comet Lemmon’s been on a roll ever since; this week it’s 7th magnitude glowing ball with a bright center easily visible in binoculars from a dark sky. One caveat. The comet’s moving south through the famed Southern Cross in the pre-dawn sky. While you might just catch sight of it from Key West, where it clears the horizon before the start of twilight, southern observers have the edge on this fuzzy blob. From Down Under, Lemmon’s very well placed for viewing between 2 and 4 a.m.

It’s not often a brighter comet crosses in front of the Southern Cross. This compact constellation has three stars (labeled) around 1st magnitude. Acrux is the brightest. The tick marks show the comet’s position each morning (Australian Eastern Daylight Time) starting Jan. 18. Created with Chris Marriott’s Skymap software

Comet Lemmon reaches perihelion – closest approach to the sun – in late March, when it could gleam at 4th magnitude, bright enough to see with the naked eye. Unfortunately, it will be too near the sun to see at that time. We’ll hope that when it slips into a dark morning sky in May, it will still be bright enough to see in a small telescope for observers in both hemispheres.

Comet L4 PANSTARRS in mid-March, Lemmon (perhaps) in May and Comet ISON in fall. Keep the comets coming I say!