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The Large Sunspot Groups of 2004 October, a Giant Prominence
and Gigantic Solar Flares: The Sun's Continuing Saga Howard L. Cohen Alachua Astronomy Club, Inc. 2003 Oct. 24 (Revised 2003 Oct. 25, Oct. 26, Oct. 28, Oct. 30, Nov. 4, Nov. 6)
SEVERAL PEOPLE HAVE ASKED about the large sunspot (no. 484) that appeared on the Sun during late 2004 October including the spot's relative size compared with Venus on the day of the Transit of Venus in 2004. (Sunspots are dark areas on the Sun cooler than their surroundings.) This spot first appeared as a disturbed area on the Sun's western limb 2004 October 17. This spot group grew rapidly over the next few days as the Sun's rotation began to carry the group across the Sun's face. (The Sun rotates or spins once about every four weeks.) Although most people call this object a spot, it is, in fact, an extremely complex sunspot "group" rather than a single spot. The group may look like a single spot to the eye or when the resolution is poor (e.g., under low magnification, poor seeing, etc.). However, when with a high quality telescope, one can easily see several large umbral spots surrounded by dozens (yes dozens) of small umbral spots all contained within a complex penumbral pattern. Indeed, the larger dark spots in the group are not exceptionally large but may appear so when they blend with their penumbral areas under poor resolution. The longest diameter of the spot group (as of 2004 October 23) was very close to 3.0 arc minutes. When compared with the current solar diameter, this makes the spot group about 130,000 km long, which is 90% of Jupiter's equatorial diameter. Note: Other large spot groups have appeared in recent years. For example, the large sunspot group of 2001 March was about 1.7 times longer than the present group but was not as wide. The more rounded form of the current group helps give the current "spot" its huge, impressive appearance. WHEN VENUS TRANSITS THE SUN NEXT JUNE 8, the diameter of this planet will be 58 arc sec, or nearly one arc min. Therefore, the spot group (or "spot) is now about three times the width Venus will have at the time of transit. One arc sec is, in fact, roughly the size of the lead spot (umbra + penumbra) as seen now (2004 October 23 The disk of Venus is currently (2004 October 23) 10.4 arc sec across By the time of next year's transit, the diameter of Venus will grow nearly six times larger.) People with good eyesight may be able to see the disk of Venus against the Sun's disk during its transit of the Sun in June 2004! Note: For those still thinking about observing the Transit of Venus next year, I plan to escort a group to Crete next June. ANOTHER VERY LARGE SUNSPOT GROUP became visible (at the eastern limb of the Sun) several days after the first large group! This spot grew even bigger than the previous. Is is unusual to have two such large sunspot groups on the Sun at the same time. It will be interesting to see what develops with this new "spot" (no. 486). In fact, this may be the first time two Jupiter-size spots have been observed on the solar disk at the same time. A GIANT PROMINENCE NEXT APPEARED on the western limb and became visible on SOHO images taken early on 2004 Ocotber 26! This prominence is vividly seen in SOHO extreme ultraviolet images at a wavelength of 30.4 nanometers. This prominence rises above the solar surface to at least a distance equal to half the solar radius, or 350,000 km (220,000 mi). This distance is nearly the same as the separation between Earth and Moon! NEXT, THE THIRD LARGEST SOLAR FLARE EVER RECORED appeared eary on Tuesday, October 28, 2003. High speed particles from this flare headed for Earth with potential for communications disruptions, bright aurorae and loss of electric power. MEANWHILE A THIRD NAKED EYE SUNSPOT GROUP DEVELOPED during October 17–18 2003 (spot 488). The first spot group (#484) is now (Oct. 28) rotating out of view but the latter two groups (#486 and #488) should remain visible into early November. Keep looking up (safely). GIANT SUNSPOT 486 DOES IT AGAIN. After Tuesday's (Oct. 28) gigantic solar flare (category X17.2), this sunspot group sent out an X10 flare Wednesday (Oct. 29). A coronal mass ejection (CME) swept past Earth on Oct. 30th, at about 12:00 noon EST 1700 UT. This makes conditions favorable for a strong geomagnetic storm as a result of the impact. Sky watchers should remain alert for aurorae. Faster moving particles from the new faster moving storm are catching up with slower moving particles from the previous storm. Having two such storms erupt one after the other with both directed toward Earth is almost unprecedented. All this excitement on a solar disk that only one week ago was nearly "spotless"! (And yet the Sun is now on the declining slope of its eleven year sunspot cycle.) For more info see Sky & Telescope, "Auroras Possible from Three Naked-Eye Sunspots" by Cary Oler and David Tytell. SUPERFLARE. However, the Sun hasn't given up! Sunspot 486, one of the giant, naked-eye sunspot groups visible on the Sun during late October, a sunspot group that sent out two enormous solar flares on October 28 and 29—so strong that observers in Central Florida witnessed the Northern Lights—HAS DONE IT AGAIN! At 2:50 p.m. EST November 4, sunspot 486 unleased a gigantic solar flare and caused severe radio blackouts across North America. This flare proved the largest ever recorded —the largest explosion ever recorded in our Solar System (X28)! Fortunately, sunspot 486 was on the Sun's limb at this time so the blast was not directed toward Earth and its effects were relatively small. |
