Salutations celestial sight seers!
I'm David Fuller, welcome to Eyes on the Sky; what's up this week?
Over the last two weeks, we looked at stars that are relatively close to Earth.
Many of these stars are Sun-like in size, mass and luminosity.
But what if we go to the other side of that scale?
What about massive stars that shine very brightly?
Let's begin at one of our near stars to find one of those massive ones.
Sirius, the brightest star in the sky after the Sun, is in the southern sky in winter.
Look below and to the left of Orion's belt to find it.
Sirius is the Alpha star of Canis Major, Orion's "Big Dog."
There are several more moderately bright stars in this constellation; Mirzam to the west
of Sirius, and Adhara and Wezen to the south and slightly east.
Draw a line from Adhara, through Wezen, and place it near the edge of a finderscope field
of view.
There will be a 4.9 and a 4.4 magnitude star in the field of view; the more northerly,
dimmer one is 29 Canis Majoris.
The southerly, slightly brighter one is Tau Canis Majoris, and it is here that we will
set our sights.
This star seems unremarkable; at 4.4 visual magnitude, it's not exactly a "stand out"
star.
But there's some interesting things happening here.
First off, Tau is VERY far away; most naked eye stars under a dark sky tend to be within
2,000 light years of Earth.
Tau exceeds that; estimates place it somewhere between 3,200 and 4,800 light years away.
To top that off, it is one of those rare, O-class stars that shines with immense power
and luminosity.
"But wait, there's more!"
Tau is not a single star; it is actually several stars in a multiple star system, two of which
orbit each other in a mere 155 days, and one of those stars is itself a double, with those
ones whipping around each other in just 1.3 DAYS!
Just imagine that while you're looking at this seemingly sedate, 4.4 magnitude star
in a finderscope, or even binoculars.
But Tau Canis Majoris has even more happening around it - but, in a different way.
Dark Sky Fact: A sunset glow has red-shifted light -- this helps your body recognize night
time coming.
But computer screens have blue shifted light -- so download the free program f.lux to automatically
change your computer screen every day to red shifted light when the light outside does,
at sunset.
Open clusters are like snowflakes; there are no two that are alike, and they all have different
sparkles and charm to them.
Appearing almost like a halo around Tau Canis Majoris is NGC 2362, an incredibly young open
cluster that is either actually associated with Tau, or is perhaps a foreground object
with the bright main star just happening to lie right in the middle from our perspective.
Hey, it could happen, right?
This cluster is so young in fact, it is just 5 million years old - that it's 25 times younger
than the Pleiades, which are already considered to be a fairly young cluster by cosmic standards.
And there are only a handful of star clusters considered to be younger; one of them is NGC
2244 in Monoceros, that Eyes on the Sky highlighted around this time last year, that is only 1.9
million years old.
So NGC 2362 came into existence around the time woolly mammoths appeared in Earth's fossil
record.
This is an odd cluster to observe though.
At just five arc minutes across, using higher magnification will help increase the image
size at the eyepiece.
However, many of the cluster's stars are 7-th to 10-th magnitude, quite a bit fainter than
Tau at 4.4 magnitude.
This causes a strange phenomenon to occur while observing; while looking directly at
this area, Tau will appear prominent, while the cluster will appear dim with just a few
stars.
But using averted vision - whereby the observer engages the more light-sensitive rods on the
retina of the eye by looking slightly away from the object, while focusing attention
on the area of the cluster - many of the dimmer stars appear to "pop out" and the cluster
seems to explode with more stellar density.
Also, the size of telescope used will make a difference; smaller scopes will have a harder
time resolving the cluster with direct vision, but can make the cluster "blink" on and off
by going back and forth from direct to averted vision and back.
Larger scopes will make it easier to resolve both the bright, central Tau along with the
dimmer, surrounding cluster.
Along The Ecliptic: Mars is well above 25 degrees elevation by midnight, and has settled
in near Spica over the next several weeks.
That's all for this week.
Keep your eyes on the sky and your outdoor lights aimed down, so we can all see, what's
up.
I'm David Fuller, wishing you clear and dark skies.