Tag: comet

The Final Fate of Comet ISON

Like many I was watching as comet ISON passed through perihelion. A better show than many other holiday offerings. It is clear that the comet has failed to survive perihelion passage. Disrupted by tidal forces and the extreme solar heating, the comet appears to have come apart even before closest approach.

I have assembled a better resolution animation of the demise of ISON from SOHO LASCO C2 imagery. Fifty frames at the full 1k x 1k resolution of the camera that shows the event from entry to exit from the field of view. Click on the image below for the full resolution version.

Note the lack of a distinct coma, simply a smeared out debris cloud. A cloud of debris and fragments continues along the original orbit. How large are some of these fragments? This is a question that may have to wait for a few days, allowing observations from a larger telescope further from the Sun.

Best laid plans? Not much hope remains for dawn photos as the comet emerges from the Sun’s glare. There remains comet C/2013 R1 Lovejoy in the morning sky, perhaps another photo session?

ISON Perihelion from SOHO
SOHO C2 camera view of comet C/2012 S1 ISON apparently disintegrating just before perihelion. (click on image for animation)

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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ISON, Mercury and Saturn in the Dawn

Not quite the dramatic comet in the dawn shot I was hoping for. The comet is just barely able to compete with the dawn glow. Still, a beautiful morning.

Waiting to see what fate holds in store for this dirty snowball as it travels through the hell of the solar corona. I will try another photo session after perihelion.

ISON in the Dawn
Comet C/2012 S1 ISON, Mercury and Saturn in the dawn over Hilo

Three Comets in the Dawn

While comet C/2012 S1 ISON is getting all of the attention, it is not the only comet currently visible. There are a couple other good comets available to observe or photograph. On Sunday morning I tracked down and photographed three comets.

The Astrophoto Rig
The ZEQ25, TV-76mm and Canon 6D setup and taking photos of comet ISON
Comet ISON is sharing the stage with comet 2P/Encke and comet C/2013 R1 Lovejoy. All three are bright enough to be spotted in a small telescope. Encke was about magnitude 8, Lovejoy and ISON were both about magnitude 5 on Sunday morning.

Despite following comet ISON for the last year, I had never actually observed it myself. Attempts to change this repeatedly ran into problems, either work commitments or bad weather. Over the last month cloudy skies have been more common than clear, even the big ‘scopes on the mountain losing a large amount of time to poor conditions.

Continue reading “Three Comets in the Dawn”