Fig. 2. Large sunspot group at 07h 14m GMT (UT) Aug. 11 2004;.150mm f/18 OG (prime focus imaging). ISO 640 1/2400 sec. John Vetterlein.

Solar Activity, August 11 2004

There has been a steady build up in solar activity with which the large spot group is associated (Fig. 2).

As the group moves towards the Sun's central meridian this may increase still further and may result in aurora borealis activity.

(This was the case last month.)

The group is again visible to the unaided eye using filters.

Continued Solar Activity

The large sunspot group visible during mid-late July (see archives) is again visible, brought round by the Sun's axial rotation (approximately 26.5 days*).

Fig 1: The Sun 10 August 08h 35m GMT (UT). 100mm refractor x45, ISO 200 1/1000 sec., Baader filter. John Vetterlein.Click the image for enlargement

Such disturbances visible within the Sun's photosphere may last for several months so that they can return again and again and become visible to us for a period of a little over 12 days at a time.

Note, that when close to the limb the appearance of spots will be considerably foreshortened.

* The Sun's rotation as shown by sunspots varies with the solar latitude between approximately 25 days, close to the solar equator, to 27.5 days in higher latitudes. An indication of a spot's position in relation to the Sun's equator may be appreciated by studying the movement of the spot during the course of a few days.urse of a few days.

Perseid Meteors

Dia. 3 The sky looking NNE at 22h 00m GMT (UT) on August 12. The circle between Perseus and Cassiopeia denotes the position of the Perseid meteor radiant. Click the image for enlargement

The meteors associated with the debris from comet Swift-Tuttle are expected to make a good showing this year.

The radiant is well placed for northern observers (Dia. 3).

Meteors associated with this radiant may be seen more or less any time during the dark hours from late July through to late August.

They are likely to peak this year in the early hours on August 12 .