What's Up in the Night Sky -
February
By Fred Barrett
Coronal Mass Ejections and spectacular
views of the Aurora Borealis have been in the news lately and I
thought that a review of Sun basics and what causes CMEs and flares
was in order.
The Sun makes up 99.8 % of the mass of
the solar system and most of the remaining 0.2 % is contributed by
Jupiter. The Earth’s contribution is a tiny fraction of one
percent! To give you an idea of the size difference, the Sun’s
diameter is about 109 times the Earth’s diameter. It could contain
1.3 million Earths within its volume!
The Sun has an internal structure that
is quite complicated but to describe it simply, the visible surface
is called the Photosphere, which has a temperature of about 6000 °C.
Below this is the Convective zone, which starts about 7/10s of the
distance from the center of the Sun to the surface. Here columns of
hot material rise from the inner Sun to the surface and columns of
cooler material fall back down. Next there is the Radiative zone
where heat travels only by radiation. The core of the Sun, where
hydrogen fuses into helium and temperatures reach 14 million °C,
stretches from the center to about 1/5th of the Sun’s radius. Here
are some incredible numbers for you: every second, 700 million tons
of hydrogen is converted to 695 million tons of helium and 5 million
tons is converted to energy.
As you move away from the equator of
the Sun, it rotates at different speeds and this is due to the fact
that the Sun is a ball of gas and not a solid body like the Earth. At
the equator it takes 25 days for one rotation while near the poles it
takes 36 days. Sunspots can be observed moving faster near the
equator than near the poles. Sub-surface portions take an average of
27 days per rotation.
As mentioned earlier, the Photosphere
reaches 6000 °C but this temperature is much less than the Sun’s
atmosphere. The region above the Sun’s surface is called the
Chromosphere and temperatures can reach 10,000 °C. But in the region
above the Chromosphere, called the Corona, 1 million °C is typical.
The Corona spreads out to a volume larger than the volume of the Sun!
Flares and CMEs occur because the Sun
rotates at different speeds at different latitudes. Magnetic field
lines twist and warp and create ropes of magnetism. Where a rope
rises through the surface from the interior of the Sun and then
reenters the surface, 2 sunspots with opposite polarities are formed.
You can think of this formation as a magnet with a north and south
pole. When the ropes or field lines twist enough, they cross and
energy explodes outwards in a Solar Flare. The largest, X class, can
cause radiation storms in Earth’s upper atmosphere (M class are
medium size and C class are small ones. Luckily our atmosphere and
Earth’s magnetic field protects us when the flare’s energized
particles hit us. Satellites can be damaged, though and
communication radio waves that pass through the upper atmosphere can
be disrupted.
On January 24th, a huge Coronal Mass
Ejection occurred on the Sun that blasted out hot plasma and charged
particles directly in the Earth’s direction. CMEs are similar to
flares but are much more violent. The magnetic field lines that twist
to form flares sometimes become so warped that, like a rubber band,
they snap violently and break and then reconnect at different points.
Gaps are created that allow plasma to explode out into space. Most
CMEs and flares are pointed away from the Earth, thank goodness! CMEs
bring charged particles of matter that interact with Earth’s
magnetic field. When the particles reach Earth, they get compressed
on the day side and stretch out like a long tail on the night side.
When connection is made on the night side, a magnetic storm occurs
that races back to the Earth’s upper atmosphere. The spectacular
Auroras that could be seen in northern and southern areas quite far
down from the poles for the best part of the following week, were one
result of that huge CME on the 24th.
CMEs are especially damaging to
satellites, electronic gear and communications due to their
extraordinary violence. As well, voltages are induced in transmission
lines from the magnetic storm and power blackouts can occur as the
power system becomes overloaded.
I hope that my basic introduction to
the Sun and its flares and CMEs tweak your curiosity enough to go out
and do more reading on what is a very complicated subject.
Now let’s move on to this month’s
highlights.
The Full Moon this month is at 4:54 pm
EST. It is variously called the Snow Moon, little Famine Moon,
Trapper’s moon and Storm Moon. All are very appropriate I would
say!
An extremely thin Moon can be seen to
the right of Mercury low in the west about a half hour after sunset
on the 22nd. Mercury reaches its greatest height above the western
horizon, about 10 degrees (1 fist width), on the 28th and maintains
that position until about March 10th. Unless you have excellent
eyesight, binoculars are recommended.
On February 9th, look East after 8 pm
and watch for Mars rising to the left of a gibbous Moon (gibbous
means that lighted part of the Moon bulges outwards). If you follow
Mars from night to night, you will notice that it actually rises
earlier as the month progresses. This is due to its retrograde motion
(westward with reference to the stars) as Earth catches up to it. It
will reach closest approach to Earth on March 5. Its disk grows from
11.8” to 13.8” during February. Good detail can be seen on its
surface with a good telescope.
Between the 9th and 23rd the zodiacal
light can be seen in the west. Watch for a tall cone of faint light
between Jupiter and Venus. It is caused by light from the Sun
reflecting off particles in the plane of the solar system.
On the 28th there will be a nice view
of the Moon passing close to the Pleiades and on the 29th it will be
near the Hyades.
In early evening, Jupiter can still be
seen in the west with Venus far below it. As the month progresses,
the distance between them shrinks and by the end of the month, they
are separated by no more than 10 degrees. On the 25th, shortly after
sunset, the Moon passes close by to the right of Venus and on the
26th, it does the same to Jupiter.
“The Beginner’s Observing Guide by
Leo Enright is an invaluable companion for adventures in the sky and
is available at the Sharbot Lake Pharmacy. It can also be ordered
from the Royal Astronomical Society of Canada at
www.rasc.ca/publications. A subscription to our very own excellent
Canadian astronomy magazine “SkyNews” can be arranged at the RASC
website as well.
Let me know how your observing has gone
this month, especially anything unusual. I enjoy the feedback. If you
have any questions or suggestions you can contact me through this
paper or email me at cygnushill@hotmail.com. Clear Skies! Fred.
If you have questions or suggestions, Fred Barrett may be contacted at cygnushill@hotmail.com
The Beginner’s Observer’s Guide by
Leo Enright is available at the Sharbot Lake Pharmacy or by
contacting the Royal Astronomical Society of Canada
www.rasc.ca/publications, subscriptions for our very own excellent
Canadian astronomy magazine, Sky News, are also available from RASC..
