skytalk

What’s in a name? Kerberos and Styx join Nix, Hydra and Charon


Greek mythology guides the naming convention for Pluto’s two most recently identified moons, more may be discovered when the New Horizons spacecraft flies past Pluto in July 2015. Tonight marks the onset of the month-long Muslim observance of Ramadan, it’s start is based on the lunar calendar. See the moon below Venus Wednesday evening after sunset, Saturn high in the south / southwest all night.


July 8, 2013

[Dave Heller] Now on the downside of Solstice, the earliest sunrise and latest sunset of the year, we’re embarked on another astronomically-driven observance. Let’s take out the calendar with Derrick Pitts, chief astronomer at the Franklin Institute. Derrick, July 8 is … ?

[Derrick Pitts] The beginning of Ramadan. I really love how the cycles of astronomical objects affect our life here on the planet. One of the best examples of this is the Muslim observance of Ramadan. It’s a month-long observance that goes right along with the religion, and in this case the date of the beginning of Ramadan is tied to the lunar cycle. So that date slides around the calendar during the course of a number of years. So in this case, Ramadan actually begins at sunset tonight, making tomorrow the first full day of Ramadan.

Is that slide a little swifter though because the moon is very small right now?

[Laughs] Very clever, but no. And if anybody was outside observing the moon over the weekend, I wonder how many people may have noticed how small the moon may have appeared. Not really so much, but in fact, as it turns out, Saturday night was the smallest moon of the year. It was the Mini Moon of the year! So if you remember a couple of weeks ago, we were all in a tizzy about the Super Moon, the biggest moon of the year. Well, here we are now at the Mini Moon, the smallest moon of the year.

So in the moon’s orbit there are these points that we know of as the closest point to Earth and the most distant point from Earth — we call them perigee, that’s the close point, and apogee, the most distant point. Well these two points happen every month, so there’s a monthly perigee and a monthly apogee. As it turns out, this month’s apogee is the most distant apogee of all of the apogees this year. So that in turn renders the moon as being very small. Now one way you might be able to measure it is by the change in the tides. So the tides would not be as strong on this day as they were for the Super Moon.

Ok, let’s migrate from the Mini Moon to the miniest of mini planets, at least it once was: Pluto and its micro moons.

Its micro moon system, it has an incredible system of moons. And most people might recall that Pluto has at least one moon, Charon. Well after Charon was discovered in the late 1970’s, we were able to identify a decade and a half later that Pluto actually had two other moons which have been named Nix and Hydra. We may have thought that was remarkable for Pluto, considering that Pluto had its status changed or its classification changed from being a planet, the smallest planet of the solar system, to becoming the largest of the dwarf planet category of objects in our solar system. Now Hubble Space Telescope in 2011 and 2012 identified two other objects in orbit around Pluto and they had been named, appropriately at that time, P4 and P5 (Pluto4 and Pluto5), the fourth and fifth moons of Pluto. Well there was a contest held by “Pluto Rocks” at seti.org, to crowd-source names for the two new moons. And with 500,000 votes submitted, 30,000 write-ins provided, the International Astronomical Union finally approved the next two names of Kerberos and Styx. The International Astronomical Union approved names that were directly related to the underworld of either Greek or Roman mythology. So it turns out that Kerberos and Styx are — Kerberos is the three-headed dog from Greek mythology, and Styx is the name of the river that separates the realm of the living from the realm of the dead. But perhaps we’ll find out more, considering that the NASA space craft New Horizons is due to fly past Pluto in July of 2015. At that point we’ll get close-up images and collect a lot more information about the Plutonian system, and maybe even a few of the Plutonians will come out to visit the space craft as it passes by.


“The International Astronomical Union approved names that were directly related to the underworld of either Greek or Roman mythology … Kerberos and Styx.”

Derrick Pitts


  • An Update on the Moons of Pluto (SETI Chats)

Derrick, approximately how far away are these objects and what size are they?

They are way smaller than our own moon, which is about 2,000 miles in diameter. So these are well under 1,000, maybe even under 500 miles in size. They are tiny, there’s no question about it. And the distance from us, well, the average distance from Earth to Pluto is about 3.6 billion miles out. So they are way, way out.

Amazing sleuthing, and I’m wondering if when merely turn our lens on say, our moon, can we see just the finest detail now compared to when the Apollo missions were taking place?

That’s a really great question, and I hear that question frequently. You would think with the magnification power we have on these telescopes and light-gathering capability, that we could really see some stuff close up. As it turns out, there’s a bit of disconnect in that with a telescope with the capability of Hubble looking at the moon, you can dramatically overpower the sensors because the moon is so close and reflects so much light from the sun it really overpowers the sensors. So the sensors would be completely washed out in gathering any light that might let us look at something. And then the other thing is that an interesting thing happens as magnification goes up in an optical system: resolution goes down. So we might be able to magnify an area and try to blow it up big enough, but then the clarity of the image would then decrease dramatically.

  • Pluto and its moons

    Composite image of several Hubble Space Telescope observations of Pluto’s system showing orbit movement. (NASA)

Well then let’s do it the old fashioned way, let’s head out of doors and what would the moon look like overhead?

In the evening coming up on Wednesday, you’ll see the moon just after sunset below Venus — about 6 degrees below Venus — and it’s a very thin crescent moon, so it should be a very pretty sight. Don’t forget, Saturn is still very prominent in the south / southwestern potion of the sky; easy to see, great target for telescope and is up a fair portion of the night. So, with the warm temperatures it’s a perfect time to look for that.



Share this story:




Share a comment:


Please keep your community civil. All comments must follow WHYY's terms of service; WHYY reserves the right to remove any inappropriate comments. See also WHYY's privacy policy.


Comments are closed.


More Like This