- Review of a discarded 2003 National Geographic Society 50mm Refractor
- Daystar Filters’ SR-127 ‘QT’ Dedicated Hydrogen Alpha Solar Telescope (Chromo...
- Software Bisque Paramount MyT 10 Year Review
- Unitron Model 114 - a quick look
- Review of the 20” f/3.4 Reginato Supermaser
- Celestron PowerSeeker 127EQ
- North Star Equatorial Platform
- OGMA AP26CC Review
- iOptron HAZ-46 Alt Azi Mount Review
- Brandon Vernonscope 94mmF7 APO first impressions.
- A quick review of the iStar Phantom FCL 140-6.5
- Explore Scientific, 16 inch / F 4.5 Truss tube Dobsonian
- Celestron PowerSeeker 70AZ Telescope ($10 Scope)
- Orion EQ-26 Mount Review
- Review of Explore Scientific First Light 8
CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Binocular Universe: Some Crown Jewels
Discuss this article in our forums
Some Crown Jewels
If you're like me, then you probably noticed certain star patterns even before you became "an astronomer." One of mine was Corona Borealis. I remember looking up at this semicircular pattern of six stars and thinking that the sky was smiling at me.
Above: Spring star map from Star
by Phil Harrington.
Finder chart for this month's Binocular Universe. Chart
adapted from Touring
Binoculars Atlas (TUBA)
Corona Borealis has been portrayed as many things over the
course of history. It all depended
on one's point of view. For
instance, my celestial smile was interpreted as a boomerang by Australian
Aborigines. To the Cheyenne Native
Americans, the stars were huts set in a camp circle.
To Welsh stargazers, the stars were Caer
Arianrhod, "the Castle of the
History records that the second century AD astronomer
Ptolemy was first to portray them as Corona Borealis, the Northern Crown.
And not just any crown, mind you, but the crown worn by Ariadne, the
daughter of Minos of Crete, during her wedding to the god Dionysus. After
the ceremony, her crown was placed in the sky for all to see.
Although only one of its crown jewels shines as brightly as
second magnitude, the constellation's distinctive shape lets it stand out among
this season's constellations. And
while none of the Crown's nonstellar deep-sky denizens breaks the binocular
barrier, it does hold many interesting stars for us to seek out.
Centered among the Crown's stellar jewels is one of the
sky's most unusual variable stars, R
Coronae Borealis. This odd star
usually shines around 6th magnitude, looking like just another point of light.
But every now and then, suddenly and unpredictably, its brightness
plummets to magnitude 13 or 14 in a matter of ten days to two weeks.
Many liken its behavior to a "reverse nova."
As Margaret W. Mayall, late director of the American Association of
Variable Star Observers, once wrote, R Coronae Borealis is "one of the most
interesting and most peculiar of all variables, and is often called the 'ideal'
irregular variable. Its times of
minima are distributed absolutely at random, according to the laws of pure
chance." These unannounced
descents usually last for several months, although some have continued for
years. Then, just as unpredictably
as it faded, R will ascend from the depths of obscurity back to its
"normal" brilliance, often in irregular steps.
Discovered in 1795 by British amateur astronomer Edward
Pigott, R Cor Bor, as it's often nicknamed, is the prototype of a class of
spectral F and G yellow supergiant stars that are unusually rich in carbon.
Although these stars are similar to our own Sun in terms of surface
temperature, they differ in many important ways.
Studies show that occasionally these stars expel a carbon-rich cloud of
celestial soot that surrounds the star. In
the process, the star's light-producing photosphere is partially blocked,
causing the star's brightness to fall off. What
mechanism produces this sooty exhaust remains a mystery, although astronomer
Geoffrey Clayton has come up with a leading theory behind the behavior.
He describes it as the Dust Puff Theory.
Writing in the March 1996 Publication of the Astronomical Society of
the Pacific, Clayton theorizes that the sooty cloud comes from the star
itself as it undergoes internal pulsation. Material
is thrown off from the star and slowly drifts away.
As it moves outward, its temperature falls until it reaches the
condensation temperature of carbon. As
the opaque cloud of carbon forms, the star itself is partially blocked from
view. Eventually, radiation pressure
from the star dissipates the cloud, returning the photosphere to view.
If you are interested in following R Cor Bor, the chart
below, from the American Association of Variable Star Observers' on-line Variable
Star Plotter, shows R and its surroundings.
Compare its magnitude to the neighboring stars and watch for the next
drop in brightness. Objects like R
Coronae Borealis prove that our universe is dynamic, violent, and changeable.
And the greatest part of that is you only need a modest pair of
binoculars to see our active universe at work right from your own backyard.
T Coronae Borealis
is another odd variable found within the Northern Crown. For
the most part, this star leads an unspectacular life at 10th magnitude.
But all this has changed abruptly on at least two occasions in the past
when T unexpectedly erupted to about 2nd or 3rd magnitude.
T Coronae Borealis is an example of a recurrent nova.
In this binary system, a red giant star is bound gravitationally to a
white dwarf companion. As the two
continue their orbital dance, the white dwarf's intense gravitational field
pulls material off of the red giant. When
the amount of transferred hydrogen reaches a high enough level, a nuclear
detonation is triggered, exploding the material off of the white dwarf and
causing the system to burst in brightness. Will
T Coronae Borealis burst again, and if so, when?
If we play the odds, then perhaps around 2026.
But, of course, it could be sooner. Who
knows, it could happen tonight!
For double-star fans, the Crown holds a couple of targets
worth scoping out. Let's first visit
Nu Coronae Borealis, set near the
constellation’s eastern border. Here,
we find two nearly twin 5th-magnitude suns separated by about 6 arc-minutes.
That’s just wide enough to be resolvable without any optical aid at
all, making them a great naked-eye test as long as light pollution doesn’t
wipe them out. They form a striking
couple through just about any pair of binoculars.
Studies show that the “Nus” are a little more than 500
light years away; the eastern star, red giant Nu-1, is 555 light years, while
orange giant Nu-2 is a little closer at 545 light years.
While nearly the same distance, and even though they are about the same
age, it turns out that the Nus do not form a true binary system.
We know this from studying their motions; one is going one way and the
other is going another way in their travels through the Milky Way.
As the saying goes, “close only counts in horseshoes and hand
grenades,” but apparently not with these two stars.
And finally, for those who have 70-mm and larger
binoculars, try your luck with the true binary system H V 38, just to Nu’s south. H
V 38, from William Herschel’s catalog of binary stars, was originally assigned
to Hercules as 23 Herculis, but now finds itself with Corona Borealis.
Large glasses are needed for the best view, although the two component
stars may be separately resolved using smaller binoculars under dark skies.
Look for a 9th- magnitude secondary star next to the system’s
6th-magnitude primary sun. They are
separated by about 35" of arc, with each shining pearly white.
Looking for still more crown jewels? Here are some additional targets within this month’s Binocular Universe.
be back next month to delve headlong into the summer sky.
Until then, remember that two eyes are better than one.
About the Author:
Phil Harrington is the author of nine books on astronomy, including Star Ware and Star Watch. Visit his web site at www.philharrington.net .
|Phil Harrington's Binocular Universe is copyright 2013 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.