Category: Sky Events

Sky events

Geminid Meteor Shower

The annual Geminid meteor shower has become one of the most reliable annual meteor showers. First observed over 150 years ago this is a interesting meteor shower. The parent body for the Geminids is not a comet, but rather the asteroid 3200 Phaethon. It is somewhat of a mystery how this mostly rocky body gives rise to the debris stream needed to generate a meteor shower.

Leonids in Orion
A pair of Leonid meteors streak through Orion
The shower peak is predicted for December 14th, at 05:45UT (13Dec 19:45HST). For viewers in the central Pacific this favors the evening of Dec 13th into the morning of Dec 14th, starting around 8pm as Gemini rises in the east.

While the 2013 Geminids are expected to just as numerous as usual, viewing will be hampered by a bright Moon in the sky. Full Moon occurs on the 16th, placing peak just a few days before full. This puts a big, bright Moon in the sky for much of the night. Certainly the brighter fireballs will be easily visible, but the dim meteors will be lost to the moonlight. A dedicated observer might make use of the small window of time between moonset at 5:24am and sunrise about 06:50am on the morning of the 14th.

Watching meteors requires no more equipment than your eyes and a dark sky, and can be enjoyable for just about anyone.

ISON Fades

What is left of the comet is rapidly fading.

During the hours after perihelion the comet brightened again, providing hope that some large fragment had survived. Many commentators were speculating that news of the comet’s demise was greatly exaggerated.

A full sequence of comet ISON passing through perihelion on Nov 28, 2013. Movie prepared from the SOHO LASCO C3 imagery.
I will hold to my original opinion, the comet was substantially destroyed. I may be wrong, but that is the fascination of these things, we observe and we learn.

Watching further is providing further evidence that no substantial fragments remain, the flareup was brief, ices originating from the debris cloud providing one last burst of activity.

Over the last twenty-four hours even this has faded, what is left of the comet continuing to disperse and fade. It will be interesting to see what remains when the comet is at last far enough from the Sun for large telescopes to examine the debris field.

Will anything be visible to small telescopes? Possibly, but if there is anything it will be quite faint, something barely seen visually, or photographic only. I am certain that the amateur community will attempt observations. Again, it will be very interesting to see what is found.

Observing Comet ISON after Perihelion

When will we again see comet C/2012 S1 ISON in the morning sky?

Much depends on how bright the comet has become, thus how far it must be from the Sun’s glare before we can see it well. If the comet has become truly spectacular we may see the tail rising before the comet quite early. If it has disintegrated, we may see nearly nothing.

It is probably on the morning of Dec 3rd that we can start looking for the comet to be above the horizon at dawn. On this morning the comet will be 14° away from the Sun, rising at 05:58 HST as seen from the island of Hawai’i. On the 4th this will be 05:51 and 16°, on the 5th the angular separation will be 19° while rising at 05:43HST.

When planning your comet viewing keep in mind that the comet will rise nearly 25° north along the horizon when compared to where it was rising before perihelion. This is closer to due east, at about azimuth 100°.

Unlike some comets, the comet will not emerge into the evening sky after perihelion. It remains in the morning sky for earthbound observers. It will eventually be visible in the evening sky, but not for some time, a few weeks or more depending on the observer’s latitude. The high inclination of the comet’s orbit will take the comet through the northern constellations, into the circumpolar sky at the end of the year.

What morning will you first see the comet?

ISON After Perihelion
Comet C/2012 S1 ISON rising after perihelion at 6am on the morning of December 3rd, 2013

What Remains of ISON

Fragmented? Probably.

There seems to be something left of comet ISON, perhaps some large fragments. Dimmer than it was going in, more spread out. But something is generating a coma that shows up in the SOHO LASCO C3 imagery.

ISON SOHO LASCO C3
What remains of comet C/2012S1 ISON after perihelion in the SOHO LASCO C3 imagery

So Long ISON?

It does appear that comet C/2012 S1 ISON has come apart at perihelion. Imagery shows the comet coma dimming and smearing out as if the nucleus has totally disrupted. Even worse, the SDO imagery programmed to cover perihelion very near the sun show nothing. The SDO cameras are very good at this sort of thing, it should show traces even if the nucleus had been stripped of the tail by the solar wind.

So long ISON?

SOHO C2 ISON Animation
SOHO C2 camera view of comet C/2012 S1 ISON apparently disintegrating just before perihelion.

Comet C/2012 S1 ISON at Perihelion

Today comet C/2012 S1 ISON will pass through perihelion, its closest approach to the Sun.

At a mere 1,800,000km (1,100,000miles) this will be a close pass indeed. As perihelion is measured from center to center, the distance is even closer if you consider the 695,500km (432,200mile) radius of the Sun. Subtracting the solar radius you realize the comet will pass a mere 1,100,000km (680,000miles) above the surface of the Sun. At this distance the intensity of the solar radiation will be nineteen thousand times more intense than a sunny day on Earth. Hot indeed!!

C/2006 P1McNaught
C/2006 P1 McNaught while 5° from the Sun on Jan 14,2007
While the comet is so close to the Sun volatile gasses will be streaming off the comet in huge quantities creating an extremely bright comet. It is fairly likely that the comet will be visible in the daytime. If so, it will appear much as C/2006 P1 McNaught appeared in January 2007 just a few degrees from the Sun, potentially visible to the unaided eye.

At closest approach the comet will be less than a degree from the Sun, difficult to pick out. An observers best bet will be as it approaches and as it moves away from the solar disk. As the comet nears perihelion it will approach the Sun from the west, best seen in the dawn sky. After perihelion it will exit the Sun’s vicinity to the north, favoring northern hemisphere observers.

The comet should be spectacular in the cameras of the dedicated solar observation satellites. Check out the real time views from SOHO or Stereo.

Observing ISON through Perihelion

Plotted below is the path of comet ISON through perihelion. The image is zenith up on the morning of November 28th from the island of Hawai’i. The actual moment of perihelion will be Nov 28.77501UT (18:36UT or 08:36HST).

A few things are notable… The obvious one is how close the comet will get to the Sun. Not just in absolute terms, which is really close. But rather how close it will look to us. The comet will be under 30 arc-minutes from the center of the Sun, recalling that the Sun is about 30 arc-minutes across. The comet will not pass behind the Sun from our point of view. While we may not be able to see it while lost in the solar glare, it will remain in the view of those solar monitoring spacecraft that are near the Earth.

Separation will help in trying to spot the comet during the day. During the 27th, 28th and 29th the comet will be very close to the Sun. On the morning of the 29th the comet will be only 4.5° from the Sun. Best bet to attempt a daytime peek may be on the 30th or later, when the comet will again be more than 7.5° from the Sun. Look for the magnitude estimates and be prepared to give it a look.

ISON at Perihelion
The orbit of comet C/2012 S1 ISON as it passes through perihelion on November 28th, 2013

Spotting Comet C/2012 S1 ISON in the Daytime

Astrophotography is not normally a daytime activity, but there are exceptions. If a comet is bright enough, about magnitude -2 or brighter, it is possible to spot the comet in the middle of the day. Comet C/2012 S1 ISON may very well be visible near the Sun in the middle of the day.

C/2006 P1McNaught
C/2006 P1 McNaught while 5° from the Sun on Jan 14,2007
The comet will pass through perihelion on November 28th. At a mere 1,860,000km (1,150,000miles) this will be a close pass indeed. As perihelion is measured from center to center, the distance is even closer if you consider the 695,500km (432,200mile) radius of the Sun. Subtracting the solar radius you realize the comet will pass a mere 1,165,000km (724,000miles) above the surface of the Sun. At this distance the intensity of the solar radiation will be nineteen thousand times more intense than a sunny day on Earth.

This sort of solar intensity will cause the comet to emit enormous amounts of gas and dust. It is this cloud of material around the comet, the coma and tail, reflecting the sunlight that makes the comet bright.

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Mercury at Maximum Elongation

Today Mercury reaches maximum elongation, the furthest point it will reach from the Sun in the sky and the highest it will be above the sunrise for this morning apparition. The planet is easily visible as a bright, starlike object about 19° above the rising Sun as the twilight begins. Over the next couple weeks Mercury will slide back into the sunrise, heading for superior conjunction on December 28th.

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