13.5 Eclipse Observing
193
annular/total, eclipse caused by the eclipse transitioning from total to annular as the
Moon’s shadow tracks across the Earth’s surface.
Solar eclipses are divided into four phases, the start of each being marked by a
specific event. First contact occurs in a solar eclipse when the leading edge of the
Moon makes contact with the Sun, which is when the observer enters the penumbra.
Second contact occurs when the trailing edge of the Moon contacts the edge of
the Sun. This occurs when the observer enters the umbra for total eclipses or the
antumbar in the case of annular eclipses. Third contact occurs in a total or annular
solar eclipse when the leading edge of the Moon touches the far edge of the Sun and
totality ends. This is effectively the point when an observer reenters the umbra. The
eclipse ends with Fourth contact, occurring when the trailing edge of the Moon is
no longer in contact with the Sun and the eclipse ends. This is the point at which the
observer leaves the penumbra.
Safety is paramount when you are undertaking observations of solar eclipses.
There is no point during a partial or annular eclipse at which it is safe to observe
without using either a solar filter or projection. The only period during which a total
solar eclipse can be observed without a solar filter or projection is during the brief
period of totality.
During an eclipse, if you are not using an instrument, you should always use
specialist eclipse glasses from a reliable supplier. During the American 2012 solar
eclipse, there were problems with online suppliers selling eclipse glasses that did not
cut out the harmful UV from the Sun and therefore endangered the user’s eyesight.
Unfortunately, this put off many users from looking at the eclipse, even though they
had purchased safe solar eclipse glasses. Before using eclipse glasses, just as with any
solar filter, you should check for damage. You should do this by looking at the glasses
for signs of damage and shining a bright light through them. The amount of light
allowed to pass through them should be uniform, with no bright spots or scratches. If
there is even a hint that the glasses are damaged, they should be destroyed to ensure
that they are not used. Even a small hole could cause irreparable damage to the retina.
During the eclipse, you may wish to take images using a camera. The same rules
apply to cameras as for the human eye. Always use a solar filter during the entire
eclipse, except for the period of totality for a total solar eclipse. Failure to do so
can cause catastrophic damage to the camera and if viewed through a DSLR, eye
damage.
As a general rule of thumb, it is always best to set an alarm to go off with 30 s
of warning of the end of totality so that everyone can get their eyes and equipment
suitably protected before totality ends (Fig. 13.8).
There is very little “science” to be achieved during a partial eclipse, as most of the
desired effects are not seen until at least 90% totality is achieved. However, in recent
years there has been much interest in the temperature drop that has been reported
during eclipses, and therefore you may wish to measure the local temperature during
the eclipse.
During a total eclipse, there are a number of features that can be observed and
recorded that are not available at other times, such as the corona, the outer atmosphere
of the Sun.
193
annular/total, eclipse caused by the eclipse transitioning from total to annular as the
Moon’s shadow tracks across the Earth’s surface.
Solar eclipses are divided into four phases, the start of each being marked by a
specific event. First contact occurs in a solar eclipse when the leading edge of the
Moon makes contact with the Sun, which is when the observer enters the penumbra.
Second contact occurs when the trailing edge of the Moon contacts the edge of
the Sun. This occurs when the observer enters the umbra for total eclipses or the
antumbar in the case of annular eclipses. Third contact occurs in a total or annular
solar eclipse when the leading edge of the Moon touches the far edge of the Sun and
totality ends. This is effectively the point when an observer reenters the umbra. The
eclipse ends with Fourth contact, occurring when the trailing edge of the Moon is
no longer in contact with the Sun and the eclipse ends. This is the point at which the
observer leaves the penumbra.
Safety is paramount when you are undertaking observations of solar eclipses.
There is no point during a partial or annular eclipse at which it is safe to observe
without using either a solar filter or projection. The only period during which a total
solar eclipse can be observed without a solar filter or projection is during the brief
period of totality.
During an eclipse, if you are not using an instrument, you should always use
specialist eclipse glasses from a reliable supplier. During the American 2012 solar
eclipse, there were problems with online suppliers selling eclipse glasses that did not
cut out the harmful UV from the Sun and therefore endangered the user’s eyesight.
Unfortunately, this put off many users from looking at the eclipse, even though they
had purchased safe solar eclipse glasses. Before using eclipse glasses, just as with any
solar filter, you should check for damage. You should do this by looking at the glasses
for signs of damage and shining a bright light through them. The amount of light
allowed to pass through them should be uniform, with no bright spots or scratches. If
there is even a hint that the glasses are damaged, they should be destroyed to ensure
that they are not used. Even a small hole could cause irreparable damage to the retina.
During the eclipse, you may wish to take images using a camera. The same rules
apply to cameras as for the human eye. Always use a solar filter during the entire
eclipse, except for the period of totality for a total solar eclipse. Failure to do so
can cause catastrophic damage to the camera and if viewed through a DSLR, eye
damage.
As a general rule of thumb, it is always best to set an alarm to go off with 30 s
of warning of the end of totality so that everyone can get their eyes and equipment
suitably protected before totality ends (Fig. 13.8).
There is very little “science” to be achieved during a partial eclipse, as most of the
desired effects are not seen until at least 90% totality is achieved. However, in recent
years there has been much interest in the temperature drop that has been reported
during eclipses, and therefore you may wish to measure the local temperature during
the eclipse.
During a total eclipse, there are a number of features that can be observed and
recorded that are not available at other times, such as the corona, the outer atmosphere
of the Sun.