Hidden Hollow 2012
Solar Observing on the Pavillion
Have you ever wondered what our Sun really looks like? Everyone knows you'll go blind if you look at the Sun, but it's perfectly safe if you use the correct type of solar filter to block the dangerous light rays. As a matter of fact, studying our nearest star and all of its changes can be very fun!
During your visit at Hidden Hollow, we'll have a solar observing session set up on the Pavillion in front of the speaker hall during the lunch break for you to enjoy viewing the Sun in different wavelengths of light. Although we can't promise you that there will be sunspots at the time of your viewing, we do guarantee that if the skies are clear that you'll never forget the view! Sunspots are observed with land-based solar telescopes as well as ones on Earth-orbiting satellites. These telescopes use filtration and projection techniques for direct observation, in additional to filtered cameras of various types. Specialized tools such as spectroscopes and spectrohelioscopes are used to examine sunspots and areas of sunspots. Artificial eclipses allow viewing of the circumference of the sun as sunspots rotate through the horizon. This is how the Sun looks through a white light solar filter.
A sunspot is an area on the Sun's surface (photosphere) that is marked by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. They can be visible from Earth without the aid of a telescope. Although they are at temperatures of roughly 4,000–4,500 K, the contrast with the surrounding material at about 5,800 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of T (temperature) to the fourth power. If a sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc.
Sunspots, being the manifestation of intense magnetic activity, host secondary phenomena such as coronal loops and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars are commonly called starspots and both light and dark spots have been measured. The photo you see here is how the Sun would appear through a white light solar filter which produces an orange image.
Although the details of sunspot generation are still somewhat a matter of research, it is anticipated that sunspots are the visible counterparts of magnetic flux tubes in the convective zone of the sun that get "wound up" by differential rotation. If the stress on the flux tubes reaches a certain limit, they curl up quite like a rubber band and puncture the sun's surface. Convection is inhibited at the puncture points, the energy flux from the sun's interior decreases, and with it the surface temperature. The photo you see here is how the Sun will appear through a specialized filter call h-alpha. We will have at least two h-alpha filtered telescopes for you to look through!
The Wilson effect tells us that sunspots are actually depressions on the sun's surface. This model is supported by observations using the Zeeman effect that show that prototypical sunspots come in pairs with opposite magnetic polarity. From cycle to cycle, the polarities of leading and trailing (with respect to the solar rotation) sunspots change from north/south to south/north and back. Sunspots usually appear in groups. Sunspot activity cycles about every eleven years. The point of highest sunspot activity during this cycle is known as Solar Maximum, and the point of lowest activity is Solar Minimum. While we are currently going into a maximum phase, there is no guarantee that there will be sunspots during our demonstration - or that the skies will be clear. However, should it be cloudy, we will present a "Solar Show" inside so you can learn more!
PS - If you will be a guest astronomer at Hidden Hollow and will be bringing your solar telescope, won't you please join us? Thank you so much!!