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Dudley Observatory
Supporting research and education in astronomy, astrophysics, and the history of astronomy |
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Skywatch November 2007
Skywatch line for Wed. and Thurs., November 28 and 29, 2007:
by Ray Bogucki
Probably the most interesting and most closely watched object in
the night sky is the comet, Holmes17P. Last October 24, this
normally unremarkable comet, which is usually not visible even in
binoculars, suddenly flared up when it puffed out a huge cloud of
dust, becoming easily visible to the naked eye in the constellation
Perseus. Binoculars showed it as a large, round, bright cloud with
well defined edges. Over the past month, the dust cloud, or coma,
has been expanding rapidly at about 1,200 miles each hour, so that
it is now over a million miles in diameter. This makes it larger in
diameter than the Sun, and, thus, the largest visible object
currently in the Solar System. As it expands, the dust cloud
becomes thinner and shows less surface brightness, so it does not
look as bright in binoculars or telescope as it did originally. The
edges have become more diffuse and less distinct, while its shape
is somewhat asymmetrical, giving a hint of a faint tail. Its
position currently is just a bit east of Mirfak, the brightest star
in Perseus. We will continue to monitor and report on this unusual
object.
Another spectacular sight is coming upon the celestial scene in
the east at mid-evening, the constellation Orion, the Hunter. This
most brilliant of all constellations visible from our mid-northern
latitudes is, in our era, the harbinger of winter, much as the three
bright stars of the Summer Triangle announce the arrival of summer.
I mention "in our era" because 13,000 years from now, when the Earth
is halfway through its 26,000 year precessional cycle, the situation
will be reversed, with Orion's evening arrival marking the beginning
of summer and the Summer Triangle being renamed the Winter
Triangle. These two groupings of bright stars make an interesting
comparison. Stars appear bright in our skies either because they
are relatively close to us or, if they are more distant, because
they are truly superbright giant stars. The two brighter stars in
the Summer Triangle, Vega and Altair, are quite close to us at 25
and 17 light years respectively. Vega is somewhat larger than our
Sun and 50 times more luminous. On the other hand, the blue-white
stars in Orion, sparkling like diamonds in our frosty w inter skies
are much more distant, typically 800 to 1,000 light years away. To
shine as brightly as it does in our sky, Rigel, the brightest star
in Orion, at 820 light years distant, must be a hot, young, truly
giant star, 36,000 times more luminous than our Sun. We will
explore some of the fascinating aspects of this bright constellation
in next week's Skywatch line.
This is the Skywatch Line for Monday and Tuesday,
November 26 and 27. Dudley Observatory's Skywatch Line for Friday, November
23, through Sunday, November 25, written by Alan French. This is the Skywatch Line for Monday and Tuesday,
November nineteenth and twentieth. The Sun sets at 4:27 PM, with night falling at 6:07. Dawn
breaks at 5:12 AM, ending with sunrise at 6:52. This is Dudley Observatory's Skywatch Line for Friday, November 16, through Sunday, November 18, written by Alan French. The annual Leonid meteor shower will peak during the early morning hours on Sunday. The best chance to catch some of the fast moving meteors from this shower will be between moonset on Saturday night – which occurs at 25 minutes after midnight - and sunrise on Sunday morning. Although the Leonids produces major storms about every 33 years, this will be a more typical year with perhaps 10 to a dozen meteors visible in an hour of watching under dark skies away from city lights. Comet Holmes does not sport a fine tail like many comets, but it is unique and worth seeing. It surprised astronomers by suddenly becoming almost one million times brighter and visible to the unaided eye – an apparent first for a comet out past Mars. The comet is now very close to Mirfak, the brightest star in the constellation Perseus. If you look to the northeast around 8:00 PM, you will find the familiar "W" of Cassiopeia high in the sky and standing on its side, with the top of the "W" facing left. If you look a bit right of the "W" and downward, the first bright star you come to is Mirfak. Comet Holmes is just to the left of and below Mirfak. It looks bigger than a star to the unaided eye. If you look at Mirfak in binoculars, the comet should also be visible in the same field, appearing as a round, glowing cloud. A telescope may reveal some stars shining through the cloud of dust that forms the visible part of Comet Holmes. If you have trouble finding the "W" of Cassiopeia, look for the brightest star above the northeastern horizon. This is Capella, in the constellation Auriga. Mirfak is the bright star almost directly above Capella and 20 degrees away. (Note that your fist held at arms length spans 10 degrees across the knuckles.) As a final resort, visit www.skyandtelescope.com for a chart showing the constellations in the northeast at 8:00 PM and the location of Comet Holmes. Weather permitting; the Albany Area Amateur Astronomers will host a public star party in Glenville's Indian Meadows Park beginning at 8:00 PM on Saturday, November 17. The park is on the west side of Droms Road, which runs between Swaggertown and Charlton Road. The park entrance is about 1/2 mile south of the Parkside YMCA and is marked by a large wooden sign. After passing the park buildings on your right, bear left at the next fork in the road. Telescopes will be aimed at Comet Holmes, the first quarter Moon, and other celestial wonders. Guests of all ages are always welcome at star parties and there is no charge. Be sure to dress very warmly – it feels 20 to 30 degrees colder when you are inactive and under the clear night sky. The star party is cancelled if the skies are mostly cloudy. If in doubt, call 374-8460 after 6:00 PM Saturday.
Skywatch line for Wed. & Thurs., Nov. 14 & 15, 2007.
by Ray Bogucki
Several interesting sights this week await those sturdy
skywatchers who are willing to brave the increasingly chill nights.
As a bit of unsolicited advice, we might mention that the best
strategy for keeping warm is to wear several layers of warm clothing
and when you think you have enough, take one more layer. A warm hat
and boots are essential. Four out of five visitors who leave early
from a late fall or winter star party claim they are about to
freeze.
For early risers, this is the last week that you can see Mercury
rise into a dark sky just before the onset of morning twilight.
This is a good apparition of Mercury for mid-northern latitudes
because at this time of year the ecliptic rises from the eastern
horizon at a very steep angle. Mercury, shining at brighter than
zero magnitude and travelling close to the ecliptic, rises very
steeply and achieves an altitude for good observing very quickly, at
least a half hour before sunrise in the east-southeast.
In the early evening, Comet Holmes continues to be the most
fascinating object to view. Two weeks ago, this comet suddenly
flared up in brightness quite unexpectedly. Now close to the bright
white star Mirfak or Alpha Persei, in the constellation Perseus, the
comet continues to move toward Mirfak. On or about Nov. 21, it will
pass very close to, or perhaps, between us and Mirfak. The huge
coma, or "head", of the comet has passed in front of several stars
and they are easily visible shining through the thin dust cloud that
forms the coma. The coma continues to expand and is now easily
distinguishable by the naked eye, not as a star, but as a small
round cloud of reflected fuzzy sunlight, close to Mirfak. It is not
known how much longer the comet will remain bright, so look soon.
On Saturday night, between midnight and sunrise Sunday morning,
the Leonid Meteor Shower is expected to peak. Generated by cometary
debris left in our orbit by Comet Tempel-Tuttle, which swings in
around the Sun just inside of Earth's orbit every 33 years, the
Leonids have, in certain years, produced spectacular meteor storms
with thousands of meteors per hour. This year is expected to
produce a much more modest display with perhaps a dozen meteors per
hour. These meteors are known for their bright lights travelling at
high speeds and often leaving long, persistent trains. Expect the
best viewing after midnight when the quarter Moon will have set and
the radiant, the point from which all Leonid meteors will seem to
originate, will be above the horizon.
This is the Skywatch Line for Monday and Tuesday,
November twelfth and thirteenth. The Sun sets at 4:35 PM, with night falling at 6:13. Dawn
breaks at 5:05 AM, and ends with sunrise at 6:43. This is Dudley Observatory's Skywatch Line for Friday, November 9, through Sunday, November 11, written by Sue French. Weather permitting, this weekend will feature two public star parties. The first will start at 8 PM on Friday at the George Landis Arboretum in Esperance. For further information, contact Alan French at 374-8460. The second will start at 5 PM in Grafton Lakes State Park. For this, contact Dave Hubicki at 274-0947. Public Star parties are free and open to folks of all ages. They are canceled if the sky is mostly cloudy. Maps and directions can be found on the web page of the Albany Area Amateur Astronomers at: www.timesunion.com/communities/astronomy/ At public star parties, members of the astronomy club set up a variety of telescopes to entertain you with views of the night sky. Star parties this weekend will feature views of Comet Holmes, an astounding comet that brightened over the course of a week from an object that could be seen only with the largest amateur telescopes to naked-eye visibility. If you can't attend a star party, and would like to find the comet, you can visit Sky & Telescope's web page: www.skyandtelescope.com/ and follow the link for observing Comet Holmes. The comet is a nice sight even through binoculars or a spotting scope. Other views at the public star parties will include young open clusters, groups of tens to thousands of stars born together and gathered like gems in a jewel box. Then there are the ancient globular clusters, with hundreds of thousands of stars packed so densely that they look like mounds of glittering sugar. There are also nebulae, glowing clouds that mark areas of star-birth and star-death. All these wonders inhabit our own galaxy, but you can see other galaxies far beyond, including the great Andromeda Galaxy. All weekend during evening twilight, the brightest object low in the southwestern sky is the planet Jupiter. See if you can spot Jupiter at about 4:45 PM on Sunday. With a pair of binoculars, sweep about two binocular fields to the lower right of Jupiter and try to spot the extremely thin crescent Moon near the orange star Antares. Imagine Jupiter at the center of a clock and sweep toward the five o'clock position. You'll need an unobstructed horizon and a bit of luck. Few people have seen a crescent Moon this slender. Each evening during the upcoming week, the crescent Moon will be a little higher, a little brighter, and a little fatter than the night before. By Saturday, the Moon will be at First Quarter phase and appear half lit in the southern sky as darkness falls.
Skywatch line for Wed. and Thurs., Nov. 7 & 8, 2007:
by Ray Bogucki
Eight Solar System objects are strung out like beads along the
ecliptic tonight, and all can be seen between sunset tonight and
sunrise tomorrow morning. Their order of appearance, from west to
east, is: Jupiter, Neptune, Uranus, Mars, Saturn, Venus, Mercury
and the Moon.
Taking them in order, the first to look for is Jupiter, shining
brightly low in the southwest shortly after sunset in the
constellation, Ophiucus. Jupiter sets about 7 p.m, roughly two
hours after sunset. Although telescopic views will continue to show
the four Galilean moons all through this month, clear images of
surface markings on Jupiter's surface will become increasingly
difficult as the giant planet sinks ever lower into the turbulent
atmosphere just above the Earth's surface.
The two distant gas giants, Neptune and Uranus, are higher in the
southwest in the constellations Capricornus and Aquarius,
respectively. Their precise locations are provided by the charts
published in the July issue of Sky and Telescope magazine. They
each appear in a telescope as a small pale blue disk, always an
interesting sight.
About an hour and a half after Jupiter sets in the southwest, Mars
appears, rising in the northeast in the constellation Gemini, near
8:30 p.m. You can't miss it because, at magnitude negative one, it
is much brighter than any of the stars in the area and has a
distinct orange color. The Earth is rapidly approaching Mars, which
is now only about 65 million miles away. Next week Mars will appear
to pause in its normal eastward motion among the stars and then
begin to move backwards in retrograde motion as the Earth begins to
overtake it in our faster inside orbit. The disk of Mars has grown
to 13 arc-seconds, large enough to show, in a telescope, the
characteristic dark markings on the light orange surface, which were
once mistakenly interpreted as "canals" that would imply the work of
intelligent beings. Mars will continue to grow in size and
brightness until our closest approach, a week before Christmas, when
the white polar ice caps should be at their visible best.
The next planet to appear is the lovely ringed giant Saturn,
rising about 2 a.m. in the constellation Leo, close to the bright
star Regulus. By 5 a.m., when morning twilight begins, Saturn is
high enough for excellent viewing. Observers will notice that
Saturn's rings are closing down to a much thinner appearance as we
approach closer to the plane of the rings.
About an hour after Saturn rises, super-bright Venus bursts upon
the scene. With a magnitude of negative 4.5, this dazzling "morning
star" completely dominates the eastern sky. A telescope shows that
Venus is about 50% illuminated, looking like a small last quarter
Moon. The last planet to appear is the innermost planet, Mercury,
rising about 5 a.m. just at the beginning of morning twilight, in
its best morning apparition for this year. When the razor thin
waning crescent Moon rises a half hour after Mercury, it provides
the anchor for the spectacular line of six bright objects, Moon,
Mercury, bright star Spica, Venus, Saturn and bright star Regulus,
all shining in the early morning twilight.
This is the Skywatch Line for Monday and Tuesday,
November Fifth and Sixth. Now that Daylight Savings Time has ended, the Sun sets early,
at 4:43 PM. Night falls at 6:19. Dawn breaks at 4:57 AM, ending with
sunrise at 6:35. This is Dudley Observatory's Skywatch Line for Friday, November 2, through Sunday, November 4, written by Alan French. This weekend's Skywatch Line again features the amazing naked eye Comet Holmes, and a chance to see the International Space Station in the morning sky. Until October 24, distant periodic Comet Holmes was too faint to see in all but the largest amateur telescopes, and out past the orbit of Mars quietly moving away from the Sun. Unexpectedly, the comet quickly brightened almost a million times, and became easily visible to the unaided eye. Comet Holmes is in the constellation Perseus, not far from Mirfak, the brightest star in the constellation. It is up all night, and should be easy to see with the unaided eye now that the evening hours are dark and moonless. Under dark skies, it is obviously non-stellar, and can be distinguished from the stars. If you have a planisphere or star chart that can show the sky for November evenings, the comet forms a triangle with Mirfak, also known as alpha Persei, and delta Persei. Early in the evening, Perseus is in the northeast, above the very bright star Capella and below and to the right of the familiar "W" pattern of Cassiopeia. A web search should reveal several finder charts for the comet. Through binoculars or a telescope, the disk of dust that was released from the comet and caused the sudden brightening is visible. The dust cloud is slowly growing, but the comet should remain bright and easily visible for some time. On the next clear night, look at this unusual comet. It may not be spectacular, but it is rare - perhaps unique - to see a comet by eye alone when it is out past Mars. The comet is now 230 million miles from the Sun, and 151 million miles from our Earth. For more details, and a finder chart, visit http://www.skyandtelescope.com/observing/home/10775326.html The International Space Station has been joined by the space shuttle Discovery, now docked to the station. You can see the ISS pass over our area on Monday morning. With the Discovery there, the ISS will appear brighter than any of the stars in the morning sky, and will only be outdone by the Moon and Venus. The ISS will appear just after 5:52 AM on Monday morning in the south-southwest. It will be highest at 5:55 AM when it will appear 39 degrees above the southeastern horizon. It will vanish in the east-northeast just before 5:58. Its path across the sky will bring it up through Canis Major, the Big Dog, just above and close to the Moon and Venus, and down past Arcturus. The Moon and Venus themselves will be close together and a pretty sight on Monday morning.
Skywatch line for Wed. and Thurs., October 31 & November 1,
2007:
by Ray Bogucki
On a typical night of observing, most amateur astronomers make up
a list of objects that they plan to study. These might include star
clusters, nebulas, galaxies, planets, comets and the Moon. The star
clusters and nebulas are fixed in position among the stars and the
astronomer knows precisely where to find them. The other objects
that belong to the Solar System move at various speeds, usually
slow, among the stars, but their paths are well defined, and so,
again, the astronomer knows where to look. It is also uncommon for
the brightness of an object to change suddenly, so surprises in
location or brightness are very rare. It is true that a couple of
times a year a very faint star may suddenly flare up in brightness
by a factor of several thousand. These stars are known as nova
stars, and the mechanisms that cause the sudden eruption in emitted
energy are well known. When one is observed, it causes quite a
stir.
By contrast, all of the objects in the Solar System other than the
Sun are relatively cold and can be seen only by reflected sunlight.
A particularly interesting group are the comets - large chunks of
ice and embedded dust and solid particles that sweep into the inner
Solar System from far out and swing around the Sun. The heat of the
Sun causes the solid ice to sublime into gaseous water molecules,
thus releasing large clouds of dust and sand grain-sized particles
to surround the comet, and reflect sunlight which we see as the
"head of the comet" or coma. The dust particles falling behind the
moving comet forms the usual "tail" of the comet. As the comet
slowly approaches the Sun, the size and brightness of the comet
gradually increases, almost imperceptibly from night to night, over
a period of months.
A comet now approaching the Sun, but still well out between the
orbits of Mars and Jupiter, is designated as Comet Holmes (17P). It
is not well known to the general public, unlike Comets Halley or
Hale-Bop, because even at its brightest, it typically reaches only
magnitude 13, which is too faint to be seen by the naked eye, or
even in binoculars, but it can be seen in backyard telescopes.
Imagine the amazement of the astronomer on the Canary Islands who,
just a week ago, discovered that overnight, Comet Holmes had
brightened by a factor of 10,000, from magnitude 18 to magnitude 8.
A few hours later, it's brightness had increased about a million
fold to a magnitude of 2.7, which is easily visible to the naked
eye. Having found this information in the magazine Sky &
Telescope's website (skyandtelescope.com), this observer brought out
binoculars and telescope to view this phenomenon. The view through
12x50 binoculars was incredible. Instead of a tiny speck of light,
there shone a surprisingly large yellowish ball of diffuse light.
The telescope showed a large, perfectly round coma with a bright,
almost star-like center. No tail was visible, but that may be
because the Sun is almost directly behind us when we look at the
comet. The tail streams away from the Sun so it is pointing almost
directly away from us in space.
Reports and images have been pouring in from astronomers all
around the world. Hypotheses concerning the reason for the sudden
brightening of the comet include a large meteorite striking the
comet and raising a huge cloud of dust, and the possibility of a
sudden fragmenting of the comet, which would greatly increase the
comet's surface area so much more dust could be released. To find
Comet Holmes, first use any star atlas to find the constellation,
Perseus. The brightest star in Perseus is Mirfak, near the center
of the constellation. About 2 degrees east of Mirfak is a bright
starlike object that does not appear on the atlas. This is the
comet and it shows the best image in binoculars or telescope.
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