[The planetary nebula M 2-9, winds from a dying star. Credit: NASA / ESA / Hubble Legacy Archive / Judy Schmidt]
What I’ve recently written on the blog, ICYMI
[M87’s black hole is launching a jet of material away from it at a decent fraction of the speed of light. From Friday’s article. Credit: The EHT Multi-wavelength Science Working Group; the EHT Collaboration; Hubble Space Telescope, ALMA (ESO/NAOJ/NRAO), the Chandra X-ray Observatory]
Tuesday 6 April, 2021: A new way to find gigantic black holes paired up at the dawn of the Universe
Wednesday 7 April, 2021: If these brown dwarfs spun much faster they'd tear themselves apart
Thursday 8 April, 2021: A dead comet that doesn't chafe
Friday 9 April, 2021: A fleet of telescopes on and above the Earth zoom in on M87’s enormous black hole
A brief synopsis of some interesting astronomy/science news
I recently wrote about the asteroid Apophis, a 370-meter-wide rock that, unfortunately, has an orbit that brings it underwear-changingly close to Earth. It’ll pass just under 32,000 km from Earth’s surface in 2029, which is close enough that it will be naked-eye visible! Happily, though, astronomers have ruled out an impact from Apophis for at least a century. Since that would create a crater 5 km across and explode with a yield 2,400 times bigger than the largest nuke ever detonated, this is A Very Good Thing.
… but that name. The original designation for the asteroid was 2004 MN4, after the year and date it was discovered. In 2005 it was given the official name Apophis. That’s the Greek name for the Egyptian god Apep, the god of chaos and destruction.
But Apophis is also the name of the main villain for the first few seasons of the TV show Stargate SG-1. He was a goa’uld, a serpent-like alien inhabiting the body of a human (Apophis the god was represented as a serpent in mythology, too).
[The Goa’uld Apophis, from Stargate SG-1. Credit: MGM]
As a massive Stargate dork, I wondered if this was coincidence that they named the asteroid Apophis; he isn’t as well known a deity as Ra or Osiris, and the name for the asteroid was given to it in 2005, well after the series aired. A quick online search showed a lot of other Stargate fans wondered about this as well.
As it happens, one of the discoverers of Apophis the asteroid is astronomer Dave Tholen, with whom I used to chat back in the old Usenet bulletin board days (kids, ask your grandparents about that). So what the heck. I sent him an email and asked.
His response was interesting. While he and his co-discoverers were familiar with Stargate, that was a “happy coincidence”, he told me.
Now bear with me here. There are different classes of asteroids based on their orbits. Aten asteroids, for example, have orbits where their semi-major axis (half the long axis of an elliptical orbit, a convenient unit for orbits) is less than 1 AU (for Astronomical Unit, the average distance of the Earth to the Sun which is about 150 million km), but also have an aphelion (greatest distance from the Sun) larger than 0.983 AU — the Earth’s orbit is elliptical and varies between 0.983 and 1.017 AU. By definition, then, Atens are Earth-crossers, and they spend most of their time closer to the Sun than Earth.
Apollo asteroids are the opposite, kind of. Their semi-major axes are greater than 1 AU and have a perihelion (closest approach to the Sun) of less than 1.017 AU. So again they cross Earth’s orbit but they spend most of their time farther than Earth from the Sun.
[Apollo asteroids (teal) orbit mostly outside Earth’s orbit (black) but get near/cross over it at perihelion, while Aten asteroids (red) are mostly inside Earth’s orbit but get near/cross over it at aphelion. Credit: Phil Plait]
Here’s the fun bit: Atens are traditionally named after Egyptian gods, and Apollos after Greek gods.
So what? Well, at the moment Apophis is an Aten asteroid, but after the 2029 pass of Earth, our gravity will change its orbit so much it will become an Apollo asteroid. Naming it Apophis is a sly tip o’ the hat to this change; the Greek name for an Egyptian god! Clever.
And, of course, given the chaos the asteroid could cause, the name works that way as well.
Tholen also mentioned that the weapon of choice for the humans of Stargate SG-1 is a compact submachine gun called a P90, and Apophis was discovered using the Bok Telescope, which has a 90-inch mirror. A coincidence, he noted, but they didn’t have anything they could use for the letter P.
When I read that I laughed, and replied, “Maybe if Apophis starts outgassing it can be renamed to P/2004 MN4 (Apophis) and you'll get your wish.”
That’s an astronomy inside joke. Sometimes objects first thought to be asteroids turn out to have cometary activity, where ice on and just under the surface warms when the object approaches the Sun and turns into a gas. When that happens the asteroid is designated as a comet, and the designation is changed. Officially, if the orbit is periodic (note the P in periodic) the designation will be changed to “P/” with the year it was discovered. So it would be called P/2004 MN4 (Apophis), and it all works out.
[The orbit of 2004 MN4 (Apophis) takes it extremely close to Earth. This shows its position on 6 March 2021 when it was observed with radar. Credit: NASA/JPL-Caltech]
I’ll note that when I looked up the naming of the asteroid, the Wikipedia page says that the discoverers were fans of Stargate and it was “thus likely why the asteroid was named after (the alien)”. Heh. As we now know: nope. If any Wikipedia editors are reading this, you can use me as a source.
To be clear: The asteroid was not directly named after the Stargate character, but they knew of the show. So the coincidence is just that: happenstance.
… but come to think of it, Tholen is similar to the Tollan, a race of humans featured many times in Stargate SG-1. Hmmmm. Coincidence again, surely.
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