A quiet, petite auroral oval from this earlier this morning. Credit: NOAA
No impact yet from the hoped-for cloud of solar plasma after Thursday’s big solar flare. All’s quiet on the magnetospheric front, but that could change at any moment. For now the Kp index, a measure of potential auroras, sits at “1″, its lowest level, and the auroral oval has shrunk to a mini-donut. During auroral storms, the oval expands southward over northern Europe, Canada and the U.S.
Don’t be lulled by this inactivity – my gut tells me it’s only the calm before the storm.
96P/Comet Machholz showed up this morning around 8 a.m. (CDT) in the narrower field of view of SOHO’s C2 coronagraph. Machholz reaches perihelion today (closest to the sun). In about a week, we’ll see it in the evening sky. Credit: NASA/ESA
Utterly invisible to telescopes on Earth, 96P/Comet Machholz passes only 11.2 million miles from the sun today, well within the orbit of Mercury. The space-based Solar and Heliospheric Observatory (SOHO) sees the small comet clearly using a specialized coronagraph to block the sun’s brilliant disk. The comet shines brightest now at 2nd magnitude and will fade as it speeds away from both the sun and Earth.
96P/Machholz photographed by STEREO-A during its last go-around in 2007. Credit: NASA
Comet Machholz was discovered by American amateur astronomer Don Machholz in 1986 and returns to Earth’s vicinity every 5.2 years. Since it has an orbital period of less than 200 years, astronomers classify it as a short-period comet.
There are about 265 numbered, short-period comets and nearly as many unnumbered ones. Periodic comets get an official number after they’ve been observed through two perihelion passages.
Machholz stands out from many of its brethren in two ways: it has the closest perihelion distance of known, regularly-returning comets and it’s depleted in carbon.
Comets glow green from fluorescing carbon molecules when near the sun. Astronomers suspect Machholz’s lack of this otherwise common element could mean it got baked out during repeated close swings by the sun. Another hypothesis posits an interstellar origin for the comet to explain its singularity.
Comet Machholz will rapidly fade from 7.5 magnitude on July 22 to 10th magnitude on August 1. Time Created with Chris Marriott’s SkyMap software
Machholz’s orbit is related to the Arietid, Southern Delta Aquarid , Quadrantid meteor showers and that of asteroid 2003 EH1, so it’s possible all of them trace their origin to a larger body that was disrupted long ago. You can read more about this comet’s curious connections on Karl Battam’s Sungrazing Comets page.
In about a week, 96P will grace evening twilight in the western sky. You’ll need at least a small telescope to see it. The map above shows its path through Leo Minor, Leo and Coma Berenices as you face west around 10:15 p.m. local time.
UPDATE 10:35 p.m. (CDT): The blast arrived this afternoon when the Kp index hit “5″ and remained through the early evening. At 10 p.m. the index slipped downward to “4″. The present extent of the auroral oval indicates minor aurora for the northern U.S. and southern Canada. This can change at any time overnight. Don’t forget tomorrow morning’s lovely conjunction of the thin crescent moon with Venus and Jupiter. Face east at dawn to see it!