December 31 – Hairy Situation

Today’s factismal: The New Year will start with not one but two comets!

There is something special about comets in the sky. These “long haired” wanderers do more than just provide a spectacular light show; they also create meteor showers and change the way we think about the world. And for the next couple of weeks there will be not one but two comets visible in the sky!

The first one is a regular visitor. Called Comet 45P/Honda-Mrkos-Pajdušáková (after the three people who discovered it), it is a member of the “Jupiter family” of comets. These are short-period comets that cycle between rushing by the Sun before heading back out toward Jupiter to cool their heels for a bit. 45P has a period of about five years; the last time it fly by the Sun was in 2011 and the next time will be in 2022.  And it will come relatively near Earth on February 11, 2017 – it will be just about eight million miles away! (If that sounds too close, remember that the Moon is about thirty times closer.) If you can’t wait, go out just before dawn and look to the East with binoculars. That faint, fuzzy patch? That’s the comet. It will get bigger and brighter over the next few weeks so you’ll have plenty of opportunities to see it.

Comet 45P as it flies from Jupiter's orbit in toward the Sun and back (Image courtesy NASA)

Comet 45P as it flies from Jupiter’s orbit in toward the Sun and back
(Image courtesy NASA)

But that’s not the only comet we can see tonight! There is also comet C/2016 U1 NEOWISE which was discovered by NASA’s NEOWISE project. Using images from the WISE space telescope, which spent a year surveying the sky in infrared, the folks at JPL have identified this long-period comet. Instead of just sprinting between Jupiter and the Sun, these comets run all the way from out past Pluto; as a result, their journeys can take tens of thousands of years. Right now, we aren’t sure how long this particular comet takes to complete an orbit or even if it will be ejected from the Solar System. What we do know is that it has already passed its closest approach to Earth and is heading in toward the Sun. As it gets closer, it will get brighter and may be visible to the naked eye early in the morning between now and January 14th when it passes the Sun and heads back out again.

A timelapse photo from SOHO showing what happens to a comet as it goes around the Sun (Image courtesy ESA)

A time lapse photo from SOHO showing what happens to a comet as it goes around the Sun
(Image courtesy ESA)

As comets get closer to the Sun the outermost ice heats up and spews out gasses that form a globe called the coma (which means “hair”). The gasses in the coma then become ionized and get dragged out by the solar wind forming the long glowing tail that is characteristic of comets; this gas tail always points straight away from the Sun. Little flakes of rock dust can also be lost. Because the dust is denser than the gas and isn’t ionized, it can form a second tail that curves away from the comet. (So straight tail=gas, curvy tail=dust. Now go impress your friends.) That dust is left behind in orbits that sometimes lead it to fall on Earth as fireballs.

The surface of a comet as seen by ESA's Rosetta probe (Image courtesy ESA)

The surface of a comet as seen by ESA’s Rosetta probe
(Image courtesy ESA)

And you can see the show using a pair of good, inexpensive binoculars. Binoculars are preferred by new astronomers because they gather a lot of light, which helps you see faint things, and because they give enough magnification, so you can see things like the moons of Jupiter, and because they are inexpensive (about $50). Or, if you’d like to spend about $1,000,000,000 you could launch another Solar and Heliospheric Observatory or SOHO for short.

This satellite, which was launched in 1995 and is still active today, was intended to observe the Sun and tell us more about how solar flares and coronal mass ejections affect life on Earth. But what NASA hadn’t expected when they launched SoHo was that they would see comets. But it turned out that SoHo saw a lot of comets that came to be called “Sun-grazers” for their death-defying feat of diving in near the Sun before heading back out into the dark depths of the outer Solar System.

Sometimes the stress of passing near the Sun or a planet causes a comet to break into pieces (Image courtesy ESA)

Sometimes the stress of passing near the Sun or a planet causes a comet to break into pieces
(Image courtesy ESA)

SoHo is still in orbit today, looking at the Sun and looking for comets. If you’d like to join the folks that have found more than 2,400 comets using SoHo images, then head on over to Sungrazing Comets:
http://sungrazer.nrl.navy.mil/index.php?p=guide

 

 

 

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