EAS BUSINESS…
July Meeting Recap
The speaker was Kevin Krisciunas of the UW Astronomy department talking
about “Observations of Type 1A Supernovae, and what they can tell us”, with musical excerpts.
The Table Mt. Star Party was a big success, with good weather, (a more reasonable) 1200 attendees, lots of
Eta Aquariid and early Perseid meteors, and A MAJOR TWO-NIGHT DISPLAY OF THE
AURORA BOREALIS!!! The northwest also
had clear weather to observe a partial solar eclipse a day later as well.
Next Meeting – Saturday August 26th At
Providence Pacific Clinic Hospital – Monte Cristo Room – 7:00 PM
The
Everett Astronomical Society's next meeting will be Saturday August 26th, at
7:00 PM, in the PROVIDENCE Monte Cristo Room at Providence Hospital
PACIFIC Clinic at 916 Pacific Avenue in Everett. The speaker will be member Henry Schnackenberg on Telescope
Making
Scheduled Meeting Topics:
Aug 26 –
Henry Schnackenberg – Telescope Making
Sep 30 –
John Armstrong UW - Mars climate modeling/astrobiology
Oct 28 –
Vandana Desai of UW
Nov 18 –
Brad Snowder, WWU, Native American star lore
Dec 16 –
Holiday party
Member News
“I put some unedited digital snapshots of Table Mountain
2000 on my website. They can be
accessed via: http://www.bassnotes.com/table/table.html - Jim Ehrmin - KB7SOK”
Jim Bielaga got a chance to try out and demo his new “Almost
30” Starmaster/Coulter telescope at Table Mt.
At its eyepiece height, it apparently required a flashing red warning
beacon for low flying aircraft! Ask Jim
about the new details discovered in M-27.
Don’t forget about the wonderful
star party at Camp Delaney sponsored by the Olympic Astronomical Society,
coming up on September 22, or the Orion Star Party at Table Mt, an informal
event put together by EAS member Jim Bielaga, for the following weekend,
September 28-30th. “This is an annual event where astronomers from all
over the state come to view the Orion Nebula from a dark site. This year
we will have a 29.25" f/4.5 Starmaster Dobsonian telescope to view
through, free observing lists, and t-shirts $12.00 and sweatshirts $20.00 for
sale. Last year we had 20 astronomers and nice chilly 20 degree weather
in October. We also had a comet, northern lights, great steady skies for
planetary viewing and of course the Orion Nebula for those that braved the
cold. Our new theme is "Freeze with a Friend". So if you
decide to come dress warm and bring something hot to drink. Hope to see you there and if you have any
questions email me jimb@buytelescopes.com
or phone 360-293-8137 until August 31st then 360-675-8734.”
Financial Health
The club maintains a safe $1450+ balance. We try to
keep approximately a $500 balance to allow for contingencies.
Club Star Party Info
Dates for
this season’s club star parties:
Sept 2 Sept 30 Oct 7
The next star party on September 2, and is scheduled
to be held at Ken and Judy Ward’s, north of Monroe, east of Snohomish.
We try to hold
informal close-in star parties each month during the spring and summer months
on a weekend near the New moon at a member’s property or a local park. (call
Dave Mullen at (425) 347-3151 or club officers for info.) During the winter, phone tree is used to
arrange spur-of-the–moment events during clear weather spells when there are
significant celestial happenings.
Club Scopes’ Status
Scope Loan
Status Waiting
10-inch
Dobsonian On loan No wait list
8-inch Dobsonian On
Loan No wait
list
60 mm Refractor Available No wait list
Astro Calendar
August 2000
Aug 01 - Moon Occults
Venus
Aug 01 - Alpha
Capricornids Meteor Shower Peak
Aug 05 - Asteroid 9
Metis At Opposition (9.5 Magnitude)
Aug 05 – EAS Star Party – at the Ashforth’s, Lake Roesinger
Aug 05 - Neil
Armstrong's 70th Birthday (1930)
Aug 06 - Southern
Iota Aquarids Meteor Shower Peak
Aug 09 - Mercury At
Perihelion
Aug 09 - Asteroid 3
Juno At Opposition (8.7 Magnitude)
Aug 09 – Ast. 88 Thisbe
Occults GSC 0599 01001 (10.8 M Star)
Aug 10 - Mercury
Passes 0.1 Degrees From Mars
Aug 11 - Uranus At
Opposition
Aug 12 - Perseids
Meteor Shower Peak
Aug 12 - Comet C/1999
T2 LINEAR Closest To Earth (2.9AU)
Aug 12 - 40th
Anniversary (1960), Echo 1 Launch
Aug 13 - Moon Occults
Neptune
Aug 25 - Northern
Iota Aquarids Meteor Shower Peak
Aug 26 - EAS Meeting 7:00 PM
– Providence Pacific Clinic
Aug 28 - Moon Occults
Mars
Aug 31 – Sep 3 Oregon
Star Party – Ochocco National Forest, Prineville Oregon
September 2000
Sep 02 - EAS Star Party – Ward’s
house
Sep 14 - John
Dobson's 85th Birthday (1915)
Sep 22 - Autumnal
Equinox, 17:11 UT
Sep 28 - Venus
Occults 158372 (7.6 Mag.)
Sep 22-24 – OAS’ Camp Delaney
Star Party – Sun Lakes St. Park – Best family star party of the year!
Sep 30 - EAS Meeting 7:00 PM
– Providence Pacific Clinic
Sep 28-31 Orion Star Party – Table Mt. – Ellensburg WA
Asteroid Observing
(Especially if you have a camera or CCD camera…)
Aug 17 - 135 Hertha
At Opposition (9.6 Mag.)
Aug 23 - 393 Lampetia
At Opposition (10.6 Mag.)
Aug 30 - 3 Juno
Occults GSC 5204 00253 (11.7 Mag.)
Aug 31 - 626 Notburga
At Opposition (11.0 Mag.)
Sep 01 - 914 Palisana
Occults TAC +37 06955 (10.5 Mag.)
Sep 01 - 85 Io
Occults TYC 0770 00300 (8.6 Mag.)
Sep 02 - 22 Kalliope
At Opposition (10.7 Mag.)
Sep 02 - 471 Papagena
At Opposition (10.1 Mag.)
Sep 03 - 27 Euterpe
At Opposition (9.8 Mag.)
Sep 05 - 78 Diana
Occults TYC 6883 00093 (10.3 Mag.)
Sep 06 - 626 Notburga
Occults HIP 111044 (8.8 Mag.)
Sep 11 - 55 Pandora
At Opposition (10.7 Mag.)
Sep 11 - 324 Bamberga
Occults GSC 2343 01660 (11.9 M)
Sep 18 - 223 Rosa
Occults TYC 1896 01563 (10.7 Mag)
Sep 19 - 48 Doris At
Opposition (11.0 Mag.)
Sep 20 - 192 Nausikaa
Occults TYC 1213 00825 (9.2 Mag.)
Sep 20 - 37 Fides
Occults TYC 6833 00485 (10.6 Mag.)
Sep 21 - 412
Elisabetha Occults TAC +01 00912 (10.9 Mag)
Sep 21 - 336
Lacadiera Occults TYC 0572 00380 (9.3 Mag)
Sep 22 - 88 Thisbe At
Opposition (10.2 Mag.)
Sep 23 - 743
Eugenisis Occults TYC 1310 02435 (9.2 Mag.)
Sep 24 - 2453 Wabash
Occults HIP 10375 (9.2 Mag.)
Sep 26 - 38 Leda
Occults TYC 1876 00850 (11.5 Mag.)
Sep 26 - 328 Gudrun
Occults YTC 2484 00937 (8.5 Mag.)
Sep 26 - 31
Euphrosyne Occults TYC 2375 02899 (10.3 M)
Sep 28 - 469
Argentina Occults TYC 1779 01415 (10.2 Mag)
Sep 29 - 21 Lutetia
At Opposition (9.5 Mag.)
Over The Airwaves
E.A.S.
members, Jim Ehrmin, Pat Lewis, Greg Donohue and SAS member Ted Vosk present
the astronomy radio show, "It's Over Your Head", on radio station
KSER. The show is broadcast every
Wednesday morning at 7:20 AM to KSER FM 90.7.
The six minute astronomy segment gives a weekly look of what's up in the
night sky over Snohomish County. Pat would appreciate your suggestions about subjects
for scripts that you would find interesting.
If you have information on a good subject, send her a copy. If you think of a good subject but don't
have the information, call her; she may be able to research it. Send to Pat Lewis, 5307 30th N.E., Seattle
WA 98105, or call (206) 524-2006.
If you are a listener of the program show your support by giving the
program director of KSER a call! KPLU
88.5 FM National Public Radio has daily broadcasts of "Star Date" by
the McDonald Observatory of the University of Texas at Austin, Monday through
Friday at 8:58 A.M. and 5:58 P.M. Saturday and Sunday). The short 2 minute radio show deals with
current topics of interest in astronomy.
The
University of Washington TV broadcasts programs from NASA at 12:00 AM Monday
through Friday, 12:30 AM Saturday, and 1:30 AM Sunday on the Channel 27 cable
station.
EAS Library – Book & Video List
The EAS has a library of books, videotapes, and software
for members to borrow. We always value
any items you would like to donate to this library. You can contact Mike Eytcheson to borrow or donate any materials.
MEMBERSHIP BENEFITS & INFORMATION
Membership in the Everett Astronomical Society (EAS) will
give you access to all the material in the lending library. The library, which
is maintained by Mike Eytcheson, consists of several VCR tapes, over 40 books,
magazines, and software titles.
Membership includes invitations to all of the club meetings and star
parties, plus the monthly newsletter, The Stargazer. In addition you will be able subscribe to Sky
and Telescope for $29.95 that
is $7 off the normal subscription rate, contact the treasurer for more
information. When renewing your subscription to Sky
& Telescope you should send your S&T renewal form along with a
check made out to Everett Astronomical Society to the EAS address. The EAS treasurer will renew your Sky and Telescope subscription for
you. Astronomy magazine ($29) offers a similar opportunity to club
members once a year in September.
EAS is a member of the Astronomical League and you will
receive the Astronomical League's newsletter, The Reflector. Being a member also allows you the use of
the club's telescopes, an award winning 10 inch Dobsonian mount reflector,
built as a club project or the 60mm refractor.
Contact Dave Mullen (425-347-3151) to borrow a telescope. EAS dues are $25. Send your annual dues to
the Everett Astronomical Society,
P.O. Box 12746, Everett, WA 98206.
Funds obtained from membership dues allows the Society to publish the
newsletter, pay Astronomical League dues and maintain our library.
OBSERVER’S INFORMATION…
Lunar Facts
Aug 15 Full
Moon
Aug 22 Last
Quarter Moon
Aug 29 New
Moon
Sep 06 First
Quarter Moon
Sep 13 Full
Moon
Sep 20 Last
Quarter Moon
Sep 27 New
Moon
Up In The Sky -- The Planets
MERCURY is moves from inferior conjunction with the sun on July 6th and then gradually becomes visible for both northern and southern hemisphere observers during the last half of the month, rising ahead of the sun over the eastern horizon.
VENUS and MARS are in the dawn twilight and not visible.
JUPITER and SATURN are rising before morning twilight about a degree apart in the ENE sky, about 3 hours before sunrise. Jupiter is the brighter planet, to the lower left.
URANUS and NEPTUNE are rising around 10 PM, transiting the meridian a
couple of hours or so before sunrise, and are at magnitude 6 and 8
respectively.
PLUTO is in Ophiuchus in the south in the evening transiting
around 10 PM, but at mag. 14, requires an 8 to 10-inch scope a dark sky, and a
good map.
Constellation(s) of the Month
LACERTA: (The Lizard). With a
midnight culmination date of August 28th, Lacerta (pronounced “luh-sir’-tuh”)
is well-placed for summer viewing.
Lacerta borders on the constellations of Andromeda, Cassiopeia, Cepheus,
Cygnus, and Pegasus, and contains no asterisms. Lacerta ranks 13th in overall
brightness among the constellations, but 68th in size; it takes up
approximately 201 square degrees of the sky (0.487%). Lacerta contains no known meteor showers and no Messier
objects. This constellation is
completely visible from latitudes North of –33 degrees, and completely
invisible from latitudes South of –55 degrees.
It has 23 stars brighter than magnitude 5.5, and its central point is at
RA=22h25m, Dec.= +46 degrees. The solar
conjunction date of Lacerta is February 27th.
Lacerta is
one of the seven constellations still in use invented by Johannes Hevelius; it
was included in a 1690 star atlas accompanying his stellar catalogue. While Lacerta has no meteor showers or
Messier objects, it does contain one very important object to astronomy. BL Lacertae (BL Lac) is a very distant,
extremely compact, and violently variable extragalactic object resembling a
quasar in both size and energy output, and is the prototype for similar objects
in the sky. BL Lac objects are
different from quasars however, in that they appear to be related to distant
elliptical galaxies (and indeed most appear to lie within elliptical host
galaxies), and because there are no lines (neither emission or absorption) in
their spectra (although some may demonstrate very weak emission lines during
periods of faint luminosity). Lack of
emission or absorption lines hampers distance measurements. However, surrounding nebulosity does contain
weak absorption lines, making it possible to measure a redshift. BL Lac objects are a form of active galaxy,
and about 100 of them are known. BL Lac objects are most easily identified from
X-ray and radio surveys (most known ones are strong radio sources), but the
peak of their emission lies in the infrared (similar to quasars). BL Lac objects demonstrate intense magnetic
fields, which rapidly vary in both strength and direction; these objects are
also violently variable in luminosity at all wavelengths, and can flare up to
five magnitudes brighter in a matter of only a few weeks. BL Lac objects are most prevalent in the
low-redshift universe; as a result, their space distribution appears very
different from other active galaxies, including quasars.
Young
Astronomer’s Corner
This month, the Young Astronomer’s
Corner will briefly talk about a very timely topic in amateur astronomy: Star
Parties!! If you can go to an official
Star Party this summer with family or friends, such as the upcoming Oregon Star
Party or the Orion Nebula Star Party at Table Mountain in Ellensburg, you
should. And less formal Star Parties
given year-round and locally by amateur astronomers are also lots of fun. It is a wonderful experience to look at the
beautiful night skies, and to meet lots of great people and perhaps make new
friends. Your experience can be even
more enjoyable if you follow a few certain practices that are tried and true in
amateur astronomy circles, to help make your experience the most enjoyable and
rewarding it can be. Some of these
suggestions may even be star party rules that must be followed in courtesy to
other observers (these rules will be noted as such). So if you follow these rules and specific practices, you’re sure
to have a great time at the next Star Party you attend:
** Dress warmly, or be prepared to dress warmly. Just because the evening starts out warm, it
doesn’t necessarily mean that it will end up that way. So take warm clothes with you just in case.
** The warmest clothes include polypropylene worn directly against
the skin; other warm clothes include those made of wool. Layered cotton materials can also be warm,
but you tend to need more layering, and if they get wet, cotton clothes do not
transport moisture away from the body (like polypropylene and wool), and are
more likely to chill you.
** Make sure you have a good hat that covers the ears, and also
good gloves as well. Polypropylene
glove liners make excellent astronomy gloves because they are not bulky, making
it easier to use flashlights, eyepieces, and charts, for example.
** Never underestimate the power of a good hooded piece of
clothing. Wearing a hood cuts down, and can sometimes almost eliminate, cool or
cold wind from going down your neck and down your back or front. Wearing a hood
serves two purposes: it cuts down on the aforementioned wind, and also helps to
keep body heat in, as the head radiates more heat away from the body than any
other area. A good hat that covers the
ears is also essential in keeping body heat in.
** Always wear warm socks.
Again, socks that conserve heat and take moisture away from the skin
(such as polypropylene or wool) are excellent.
It doesn’t hurt to have an extra pair or two on hand either just in case
it’s extra nippy for you.
** A good windbreaker (such as Gore-tex or nylon), which also has
an integral hood, is an excellent way to conserve body heat and minimize chill,
and can be used over other layered clothing as necessary.
** Always eat well and drink plenty of fluids to avoid
dehydration. Good nutrition (and yes, including carrots or other sources of
Vitamin A which improves night vision) and hydration helps to maintain
alertness, body warmth (especially by using drinks like hot chocolate), and
helps to battle fatigue. Being hungry
and thirsty, like in many other areas of life including school work, does not
make for an enjoyable experience. Most
areas allow camp stoves, but open fires are usually prohibited. Importantly, alcohol and nicotine use can
also interfere with the conservation of body heat.
** Always follow established Star
Party etiquette. Use red flashlights
ONLY, and point them downwards so as not to shine them in someone’s eyes. Using any color other than red will cause
your night adapted vision (the ability to see some contrast in the dark, and to
see beautiful telescope objects more clearly) will be interrupted, and will not
return to where it was at least for a good 20 minutes to a half-hour. (Night vision is never perfect, so it is
also important to know your immediate surroundings and move slowly and ask
questions if you are unsure of them; this helps to protect you from injury and
from damaging other people’s equipment).
The use of red lights is a basic star party rule, and is a courtesy to
other astronomers as well. No white
lights (including car headlights!) are ever allowed in proximity to an official
and large Star Party after darkness has arrived. Note: you may also want to have extra batteries for your red
light, just in case.
**Everybody has different tastes
in music. If you would like to listen
to music while you observe, it is best and most often a Star Party rule (as
well as a courtesy to your neighbors) to wear headsets. Star Parties may also have rules about pets,
so be sure to check those rules out as well.
If they are allowed, they should not be roaming freely.
** Always ask an amateur astronomer if it is OK to look through
his or her scope. They make be taking
pictures, or they may want to take a rest for a while without being
disturbed. It is common courtesy to
always respect another’s wishes. Many,
if not most, astronomers are very friendly and love to have people look through
their telescopes, but always be sure to ask.
** Star Parties are frequently held in remote areas. It is never a good idea to go to unknown or
remote areas alone. Also remember that
such areas are also remote from medical attention. If you have bee-sting allergies, or other potential serious
conditions, always be prepared, and be prepared for the fact that you may be an
hour or more from medical attention.
Always let someone at home know where you are and where you will be,
including expected time of arrival back home.
** It is not necessary to have a telescope to enjoy a star
party. A lawn chair and a blanket,
perhaps with a pair of binoculars and a good, basic book of the sky, can give
you countless hours of enjoyment and learning about astronomy without spending
much money. IT IS NOT NECESSARY TO
SPEND LOTS OF MONEY TO ENJOY THE NIGHT SKY.
Going to a Star Party sponsored by your local astronomy club, or perhaps
even joining your local astronomy club, is a GREAT way to learn about
astronomy. Star parties also give you
the opportunity to meet new people, ask lots of questions (and perhaps share
your knowledge of astronomy too), as well as to look through many telescopes
and possibly binoculars as well.
** Finally, respect for your fellow astronomers by following the
simple rules as listed above, and respect for the environment (never leave
trash around, and stay away from fragile areas of grass and wilderness) will
also make your Star Party experience more enjoyable. See you at an upcoming Star Party!!
Astronomy and Telescope “Lingo”
ASTRONOMY
LINGO: A-TYPE ASTEROID:
A rare class of asteroid with both a moderately high albedo and a
reddish spectrum. A spectral absorption
characteristic around 1.05 micrometers in the near-infrared is thought to be
due to the mineral olivine.
TELESCOPE
LINGO: APERTURE
RATIO (OR RELATIVE APERTURE): The ratio (d/f) of the effective diameter ‘d’
(i.e., aperture) of a lens or mirror to its focal length ‘f’. (The ratio ‘f/d’ is the focal ratio).
Astronomy Fun Facts
August Fun Facts:
** The sunspot
cycle reaches a maximum approximately every 11 years; during that time, the sun
is considered to be in its most active phase. One of the largest sunspots ever
recorded appeared during one such maximum in 1947, covering more than 1% (one
percent) of the solar disk’s area. This
particular sunspot was estimated to be large enough to contain about 100 Earths
(all of which of course would be totally incinerated!).
** The
massive Hellas basin on Mars was hollowed out by an asteroid with a diameter of
at least 100 miles. This asteroid
impacted Mars at a velocity of about 36,000 mph, producing an explosion equal
to 100 trillion tons of TNT! Just one
(1) ton of TNT can destroy a small city block of buildings.
** Most
sunspots last only a few days; a few however can last about a month, completing
a full solar revolution. However, there
was a very famous sunspot that was observed around 1840. This sunspot lasted 18 months(!!) – this is
220 times longer than the duration of the worst Earthly hurricane on record!
“MIRROR”
IMAGES
“MIRROR”
IMAGES”: “Mirror
Images” is a bimonthly column, and was last published in July. It will return in September, when the topic
will be active galaxies.
Astronomical
Notes --
On & Off the Net...
Researchers may have solved a
20-year-old geological mystery surrounding Jupiter's icy moon Europa. Louise Prockter of APL and Robert Pappalardo
of Brown report evidence of "folds" on the moon's frozen surface. The
researchers say the mountain-like features - found in three regions - are the
first indication of compression on the fractured Europan crust, and provide
unprecedented insight into the history and behavior of the Jovian satellite.
"We learned from
Voyager images in the late 1970s that there was a lot of extension on Europa -
that the surface was pulling apart and a slushy material was moving up through
the gaps - but no one could find out how this new material was being accommodated,"
Prockter says. "Now, we have finally found folds where the icy surface
material compresses, and this will help us start to understand how Europa
evolved and how it resurfaces."
Prockter and Pappalardo first
noticed the folds in high-resolution images of Europa's Astypalaea Linea
fracture region, taken by the Galileo spacecraft. Near the large fracture zone
they spotted fine-scale features that typically occur in fold structures (such
as the Appalachian Mountains) on Earth: regional patterns of fractures and
small ridges which mark adjacent crests and valleys. The folds' direction and location along Astypalaea Linea
coincide with models of tidal stress, the gravitational pull from Jupiter that
scientists believe creates the pattern of large, canyon-like cracks on Europa's
rotating surface. The size and nature of the folds - crests possibly tens to
hundreds of meters high and spaced about 25 kilometers (16 miles) apart - also
tell the researchers about the surface itself. They indicate warping of a thin
brittle lithosphere covering a thicker region, or asthenosphere, of
"warmer" and mobile glacier-like ice.
The researchers spotted
similar folds in two other regions, and believe they could exist in other
areas. One reason the folds have been hard to find is the planet does a good
job of hiding them; over time, the researchers hypothesize, the folds
"relax away" and push some material back into Europa's interior for
recycling. "There has been no
solid evidence for compression folds or material cycling on any other icy
satellite, though many show extensional features," Pappalardo says.
"This finding potentially has applications for other icy moons as well."
A team led by astronomers at
Columbia University have found the youngest pulsar yet, a hot, spinning,
highly-magnetized infant no larger than Manhattan, born in a massive star
explosion about 700 years ago. The pulsar possesses unusual properties that may
force scientists to reconsider how pulsars are created and evolve. Other known pulsars, in comparison, are
thousands to millions of years old. This pulsar, in the supernova remnant Kes
75, is about 300 years younger than the second-youngest pulsar, the Crab, which
scientists have long considered to be the archetypal young pulsar. Yet,
compared to the Crab, the Kes 75 pulsar spins ten times more slowly; it is
slowing down at a rate ten times faster; and it has a magnetic field that is
ten times greater -- all unexpected findings that may cause scientists to
rethink the birth properties and evolution of pulsars.
"People have been
searching for this pulsar for years," said Dr. Eric Gotthelf,
Associate Research Scientist at Columbia's Astrophysics Laboratory and lead
author of a paper submitted to The Astrophysical Letters. "We have seen
bright radio waves in the core of Kes 75, telltale evidence for a pulsar. The
problem was that we were expecting to find a rapidly spinning 'Crab-like'
pulsar. What we found is quite different from our expectations." Dr. Gotthelf located the pulsar, 60,000
light years from Earth on the far side of the Milky Way, with NASA's Rossi
X-ray Timing Explorer, a powerful observatory that has been finding pulsars,
neutron stars and black holes for the past four years. His colleagues are Dr.
Gautam Vasisht, Michael Boylan-Kolchin, and Dr. Kenichi Torii.
A pulsar is a type of neutron
star, the core remains of a giant star that was once at least ten times more
massive than the sun. Such a star, upon depleting all of its nuclear fuel,
explodes, ejecting most of its outer shell and leaving only a core, which
collapses upon itself to form a hot ember about 10 miles in diameter. The
ejected material forms a beautiful supernova remnant of colorful gas, visible
for several millennia in visible light and at X-ray and radio wavelengths.
Pulsars have strong magnetic
fields that channel electrons along the magnetic field lines away from the
pulsar's polar regions. These electrons, accelerated to nearly the speed of
light, radiate at the poles, particularly as radio waves, X rays and
gamma-rays. Astronomers see pulsars "pulse" on and off as the beams
of radiation from the rotating pulsar sweep across the Earth, like a beam from
a lighthouse. Locating the pulsar associated with a given supernova remnant is
not so straightforward. When the star explodes, the shock might kick the
resulting pulsar away from the site of the explosion. Other times, the pulsar's
beams of light might not sweep past the direction of the Earth, so it is never
seen. Or, as is suspected in recent 1987a supernova, the stellar core might
collapse into a black hole. "This
pulsar is located right in the center of the supernova shell," said
Gotthelf. "We only see this for a few other pulsars. So, the Kes 75
pulsar provides rather strong observational evidence that the neutron star is
born in the stellar explosion that gives rise to the supernova remnant shell."
Dr. Gotthelf found the newly
born pulsar, now named PSR J1846-0258, through a deep observation with the
Rossi Explorer of the area around Kes 75 lasting nearly three hours. He
narrowed his search to a central region within the Kes 75 supernova remnant
using archived X-ray data from another satellite, the Japan-US Advanced
Satellite for Cosmology and Astrophysics.
X-ray data reveals that the Kes 75 pulsar spins upon its axis once every
0.3 second, which is slow for young pulsars albeit fast compared to older ones.
The pulsar's age is 700 years, consistent with the age of the supernova remnant
that houses it. The Kes 75 pulsar is
also at least 10 times more magnetic than ordinary pulsars and about 10 times
weaker than magnetars, a mysterious, newly identified class of highly
magnetized objects. The Kes 75 pulsar may therefore be a missing link between
these classes of objects. The pulsar's magnetic field is 100 trillion times
that of the Earth's and would distort compass readings a half million miles
away. Such a strong magnetic force is actually rapidly slowing down the spin of
the pulsar.
Younger, highly magnetized,
rapidly spinning pulsars provide astronomers with a wealth of information about
this strange class of objects, first discovered only 33 years ago. Young
pulsars are prone to starquakes, which changes the spin rate and reveals clues
to their internal structure. Monitoring their change in spin rate allows
astronomers to measure the rotational energy loss and compare it to the
observed radiation. This provides a powerful probe of this central engine
powering bright radio cores of supernova remnants.
Dr Philip Diamond of the
Jodrell Bank Observatory and Dr Athol Kemball of the National Radio Astronomy
Observatory (NRAO) in Socorro, New Mexico have for the first time made a
time-lapse 'movie' of gas being ejected from the surface of a star. Their
images are the most detailed ever obtained of activity close to any star other
than the Sun.
The star they studied, called
TX Cam, is in the constellation Camelopardalis and lies almost 1000 light years
from Earth. Its brightness changes regularly over a period of 80 weeks. It is
an example of what is known as a 'Mira' variable, named after the famous
variable star Mira which exhibits very regular changes in brightness on a
time-scale of about a year.
As the Sun approaches the end
of its life in a few billion years it will become a much more violent object
than it is now. It will begin to grow quite rapidly until it swells to fill the
inner part of our Solar System, swallowing the Earth and the other inner
planets. Jupiter and the more distant planets may survive, but they will be
subject to a considerable bombardment as the outer layers of the Sun are
expelled when it begins to pulsate with a period of about a year. Eventually,
much of the Sun's mass will have been thrown back into the depths of
interstellar space, from whence it first came, and the Sun will shrink to a
shadow of its former glory becoming what astronomers call a white dwarf.
This scenario is in the far
distant future for our own star, however it is a reality now for the many
thousands of Mira variable stars throughout the Milky Way. Studies of the
regions close to these stars show them to be losing their outer layers at a considerable
rate, they can shed an Earth mass of material every year. Astronomers can study
this mass-loss process in a variety of ways and can deduce much about the
mechanism by which the stars expel this material and the nature of the star in
its crotchety old age.
Radio astronomers in
particular can use a technique known as Very Long Baseline Interferometry
(VLBI) to study this process in incredible detail. Diamond and Kemball used the
National Science Foundation's VLBA to make their time-lapse movie of the gas
being ejected from the surface of the star. They can do this because there are
radio beacons sitting in the gas. These beacons, called masers (the radio
equivalent of lasers) show up as bright spots in the radio images. The masers
arise from one of the gases in the outflow, Silicon Monoxide (SiO), which emits
in a narrow frequency band close to 43 GHz.
The images, made with the VLBA at 43 GHz are 500 times more detailed
than is possible with the Hubble Space Telescope. The movie can be found on the
internet at http://www.jb.man.ac.uk/~pdiamond/txcam44.gif It shows the complex gas motions that arise
close to the star. "They show immensely complex motions which cannot be
explained by current theory" Diamond said.
The movie covers a period of
88 weeks, with observations being made every 2 weeks. "The structures
that we observe in the outflow suggest that we might be seeing the effects of
shock waves passing through the gas," Kemball said. "However,
it is difficult to explain why most of the gas is moving away from the star
whilst, at the same time, some is falling towards it." Diamond and Kemball have continued to
observe TX Cam with the VLBA. They have data covering another 80 weeks. They
hope that, when this is incorporated into their movie, they will be able to
understand the nature of this dying star and so cast some light on what awaits
our own Sun in its dotage.
Triggered by phone calls from
amateur astronomers about a flaring white dwarf star, scientists quickly
repositioned two NASA satellites to observe the event from start to finish in
unprecedented detail. Full analysis of the observations made of this event in
October 1996 have recently been completed. They combined the 'backyard' optical
data obtained by amateurs with extreme ultraviolet and X-ray data from orbiting
satellites to reveal the nature of the flow of gas from a small red star onto
its shrunken, dying companion.
The results were announced by
Dr Janet Mattei, director of the American Association of Variable Star
Observers (AAVSO), with co-authors Dr Christopher W. Mauche who led
observations with the Extreme Ultraviolet Explorer (EUVE) and Dr Peter J.
Wheatley who led the observations made with the Rossi X-ray Timing Explorer
(RXTE).
"For years, amateur
astronomers have tipped off professionals to bursting star systems and other
cosmic events" said Mattei. "This time we nipped the action in
the bud and notified scientists working on two different satellites. The result
was an in-depth, multi-wavelength observation of an entire event, not just the
start or a tail end."
The outburst took place in SS
Cygni, a close binary star system in the constellation Cygnus (the Swan). SS
Cygni contains a red dwarf star and white dwarf. A red dwarf is a star a little
cooler than the Sun. The white dwarf was once as large as the Sun but
subsequently ran out of nuclear fuel, blew its outer shell into space and
collapsed to form a white-hot ember. The dense white dwarf, with its strong
gravitational attraction, pulls a stream of gas from its companion star. This
transferred gas collects in a disk, called an accretion disk, around the white
dwarf star. The dramatic brightening
that occurs is the result of an instability in the disk, which forces the disk
material to rain down onto the surface of the white dwarf. This causes a
titanic release of energy equivalent to billions of atomic bombs exploding
every second. Such stellar explosions, which often occur without warning and
rarely last more than one or two weeks, serve as flood-lights that brighten a
dim star system for scientists to study.
The SS Cygni outburst was discovered in its very earliest stages by observers
in Kansas and California and confirmed by a Hawaiian observer, all amateur
astronomers and members of the AAVSO. They called Mattei and she called Mauche
and Wheatley, who respectively arranged for the EUVE and RXTE to turn to the
event. This was within 12 hours of the initial optical observation, still
before the outburst was producing the high-energy radiation that the EUVE and
RXTE observe.
The optical, EUVE and RXTE
observations show that a white dwarf outburst starts with the radiation of visible
light, which comes from the outer part of the accretion disk. The radiation
changes its character about a day later, and X-rays are observed. Extreme
ultraviolet radiation is detected when the gas flow reaches the white dwarf.
The dramatic switch at the beginning of the outburst from X-ray to extreme
ultraviolet emission is the result of a drop in the temperature of the boundary
layer between the accretion disk and the white dwarf from one hundred million
degrees to a hundred thousand degrees Kelvin (Celsius). The increased density
around the boundary allows the region to cool.
"This transition has never been observed before, and was only
detected due to the superb response by the staff of the EUVE and RXTE to the
observations by the amateur astronomers" says Mattei. "A
similar transition occurs in other accreting systems like SS Cygni and to
observe it one needs fast response and multi-satellites, observing at different
wavebands. “
In gratitude for the
successful SS Cygni observations and to give new opportunities to amateur
astronomers, the EUVE director granted the AAVSO nearly three days' worth of
observation time on EUVE for an object of their choice. The AAVSO was founded in 1911 at Harvard
College Observatory to coordinate variable star observations made largely by
amateur astronomers and became an independent non-profit organization in 1954.
Today, AAVSO has members in over 40 countries and maintains the world's largest
computer-readable variable star data archive with nearly 10 million observations,
growing by almost half a million yearly. For more information, refer to the
AAVSO web site http://www.aavso.org
Like children blowing bubbles on the front porch steps, the
merging Antennae Galaxies in constellation Corvus are producing massive bubbles
of expanding X-ray-emitting gas at such astonishing rates that they are bumping
into each other, forming "superbubbles" -- and surprising astronomers
with their sheer numbers and X-ray luminosity.
Drs. Giuseppina Fabbiano, Andreas Zezas and Stephen Murray used NASA's
Chandra X-ray Observatory to capture in unprecedented detail this phenomenon
that is anything but child's play. In a talk presented at the General Assembly
of the International Astronomical Union, Fabbiano said that the observations
provide a nearby example of the what it was like fifteen billion years ago when
our universe was young and galaxies were just forming.
"Galaxies were much
closer together then," explained Fabbiano. "Collisions like
the ones that produced the Antennae were much more common, and played a major
role in shaping the galaxies we see around us today." The Antennae Galaxies, about 60 million
light-years from earth (in the constellation Corvus), are two colliding and
visually stunning galaxies named NGC 4038 and NGC 4039. They acquired their
nickname from the wispy, antennae-like streams of gas caused by their merging,
seen by early optical telescopes.
Many astronomers believe our
own Milky Way galaxy is the product of a merger. While galaxies may collide,
the stars contained within usually do not, because stars comprise only a small
fraction of the space within a galaxy. However, during a hundred-million-year
collision, one galaxy can pull the other apart gravitationally. Shock wave
compression of massive clouds of gas and dust can lead to the rapid birth of
millions of stars. The explosion of
these stars a few million years later creates thousands of supernova remnantsbubbles
of multimillion degree Celsius gas enriched with oxygen, iron and other heavy
elements. These expanding bubbles, collide and coalesce to form superbubbles
that are five thousand light years in diameter.
Earlier data from the Rosat
X-ray observatory showed extended patches of X-ray light in the Antennae, but
according to Fabbiano, "We didn't know for sure that the superbubbles
existed." Now scientists know that in addition to the superbubbles,
the Antennae contain dozens of bright point-like sources -- neutron stars and
black holes -- left behind by the flurry of supernova activity. The X-rays from
these sources are generated by gas that is heated to tens of millions of
degrees Celsius as it streams from nearby companion stars onto neutron stars or
into black holes. The ability to
observe the neutron star/black hole sources and the superbubbles in the
Antennae will enhance astronomers' understanding of the evolution of galaxies
over the eons through the interplay of galaxy collisions, star formation, gravity
and supernovae. "What we are
witnessing with Chandra is galaxy ecology in action," said Andreas
Zezas, "Over tens of millions of years, the superbubbles gradually
enrich the galaxy's supply of oxygen and other elements, and may provide the
energy needed to trigger the collapse of more clouds to form more stars and
more supernovae in a continuing cycle of star birth, death and renewal."
The next step will be to pin
down the temperature and energy content more exactly, and to determine how much
iron and other heavy elements are in the bubbles, and do some statistics based
on the number of bubbles to refine the "galactic ecology."
Mankind will lose its view of
the stars altogether -- unless we learn very soon to shine our light onto the
ground, where we need, instead of into the night sky. Astronomers at the
International Astronomical Union (IAU) General Assembly have sounded a wake-up
call for everyone on the planet.
In 1999, the IAU held a
Symposium on 'Preserving the Astronomical Sky', which was organized jointly
with the Committee on Space Research (COSPAR) and the United Nations Office of
Outer Space Affairs in parallel with the UN conference UNISPACE III in Vienna.
The ongoing urgency for action was reinforced this week.
'Light pollution' affects
everyone, not just professional observatories. An average person in the
countryside away from city lights can see several thousand stars in the sky.
Bit by bit, Europe is losing this view of the heavens as we add more and lamps,
and waste energy by sending the light uselessly into the sky. Thousands of
millions of pounds worth of energy are tossed upwards into the European sky
each year -- instead of down onto the ground which we want to illuminate.
Dr Malcolm Smith, Director of
the Cerro Tololo Interamerican Observatory in Chile, issued this challenge.
"Look around your city or town. See how many street lamps allow plenty
of light to shine upwards. Count how many stars you can see. If you are old
enough to remember how the sky looked 30 years ago, could you see the Milky Way
then? Can you now?" "Bit by
bit, without realizing, we are all losing a direct connection with the universe"
commented Dr Smith. "Not only that, light pollution is one of the most
rapidly increasing alterations to the natural environment created by humans.
Reported adverse effects of this fog of artificial light involve plants and
animals as well as humankind. Human culture, from philosophy to religion, from
art to literature and science, has always developed in relationship with the
night sky and the universe beyond. Are we going to deprive future generations
unnecessarily?"
Astronomer Pierantonio
Cinzano from Padua, Italy and his colleagues have been using measurements from
satellites looking down at the Earth and measure the light shining upwards from
the world's towns and cities. Some of his maps showing the serious extent of
light pollution can be found on his home page, at http://debora.pd.astro.it/cinzano/defaulten.html Large areas in and near cities are already
very seriously affected. Good lighting design can save a third or more of the
cost of public lighting. Better lighting means less energy is needed and
pollution from unnecessary power stations can be reduced. Preserving dark, starlit skies - There are still pristine, remote, dark-sky
sites where astronomers construct huge telescopes to reach out to the edges of
the universe. The most famous of these special sites are in Hawaii, Chile and
the Canary Islands. Even in these places, city lights can be seen. A great
effort is being made to protect these sites and to avoid the situation that has
already affected most of Europe by obtaining legislation to control the wastage
of light from cities and towns near these special regions. Dr Smith spoke about
the success in a town in Chile near the Cerro Tololo Observatory which is
saving 40% of its former annual electricity bill, uses its starlit sky to
attract amazed tourists from urban areas in Europe and the USA, and uses its
Municipal Observatory to educate local school children in the need to preserve
this natural treasure of mankind.
Also at the meeting, radio
astronomers discussed issues relating to the interference they encounter when
using large radio telescopes. Mobile telephones, television, satellites and
airport radars are all essential to modern life but they create a noisy radio
environment that makes it very difficult to make sensitive astronomical
measurements of quasars, pulsars, black holes and the cosmic microwave
background. As an example, the tiny amount of energy transmitted by a mobile
phone could easily be picked up by the giant 250-foot radio dish at Jodrell
Bank -- even if the phone were on Mars!
Radio astronomers are working with the regulatory authorities to reserve
slices of the radio spectrum for receiving natural signals from the universe
amid the cacophony of modern life. They are also seeking to establish 'international
radio quiet zones', preserves with special regulations rather like national
parks. Such a zone might well be the site of a huge square-kilometer array of
radio telescopes now being proposed by the world's radio astronomers.
Information and education on
light pollution - Much of the energy wasted as light pollution is produced
because people do not think about where the light goes when installing outside
fixtures. To help explain more clearly the issues involved, the International
Dark-Sky Association (IDA) has set up an education working group. For more
information, see http://www.darksky.org, or our own Dark Skies Northwest http://www.scn.org/darksky/.
To subscribe to the Dark Skies NW E-Mail List about local light
pollution issues: To
subscribe to dsnw,
mail a
message to majordomo@scn.org with no
subject and the message body containing: subscribe dsnw
Astronomers have found a star
that will produce one of the biggest explosions in our universe. The star,
known as KPD1930+2752, will explode within the next 200 million years. It is
the first star of its kind to be found and may hold the clues to where the
stuff that makes up our bodies comes from and perhaps to the future of the
Universe itself. KPD1930+2752 is
actually two stars, one hot bright star and a faint, dense star known as a
white dwarf. The hot star whirls around the white dwarf, just like the Earth
revolves around the Sun, but traveling at over one million kilometers per hour,
it takes only 137 minutes to complete one trip around its companion. But KPD1930+2752 is doomed. Energy is being
sucked away by 'gravitational waves' -- a type of energy predicted by
Einstein's Theory of General Relativity -- so the stars will collide within the
next 200 million years. What makes KPD1930+2752 special is that the star will
then be too massive and dense to survive. The star will be ripped apart in a
vast thermonuclear explosion bright enough to be seen from the other side of
the Universe.
These explosions, known as
Type Ia Supernovae, hurl their metallic debris into space, particularly iron,
nickel and cobalt. Almost all the iron on the Earth comes from Type Ia
Supernovae which exploded billions of years ago, including the iron in our
blood. Type Ia Supernovae seen in
nearby galaxies all reach the same brightness when they explode, so astronomers
can look for Type Ia Supernovae in very distant galaxies and use them to
measure the distance -- the fainter the supernova looks, the further away the
galaxy is. By using this method, astronomers have found that the Universe is
not only expanding, but that the expansion appears to be speeding up and will
prevent the Universe collapsing in a 'Big Crunch'. But this method only works if Type Ia Supernovae in distant
galaxies are the same as the ones nearby. Astronomers have worried about this
problem for several years because they have not been sure what causes Type Ia
Supernovae.
Now that KPD1930+2752 has
been found it can be studied in detail so that astronomers can work out how
Type Ia Supernovae in distant galaxies might behave and so, perhaps, determine
the fate of the Universe itself. The key observations of KPD1930+2752 were
obtained in April using the Isaac Newton Telescope on the island of La Palma.
The Royal Observatory
Greenwich has published a leaflet 'What is a supernova?' which is available
from its web site www.rog.nmm.ac.uk/leaflets/supernovae/supernovae.html
There are many supernova related sites on the internet, such as
http://rsd-www.nrl.navy.mil/7212/montes/sne.html
KPD1930+2752 will be very
distant from the Earth when it explodes so it poses no threat to us. KPD1930+2752 is a subdwarf B star. It is
about one fifth the size of the Sun and is about half as massive. Unlike normal
stars, which are composed almost entirely of hydrogen, KPD1930+2752 is made of
helium. It is not entirely clear how stars like KPD1930+2752 are made, but
recent work suggests they are the remains of stars like the Sun which lose half
their mass just before they complete the end of the red giant phase of their
evolution. Only some small fraction of stars evolve this way and this is
thought to be related to the fact that most subdwarf B stars are binary stars.
We observed KPD1930+2752 as
part of a program to study subdwarf B stars to understand how they are formed.
We measured the Doppler shift of the star over the course of one orbit. The
Doppler shifts shows that the star is orbiting an unseen companion every 137
minutes at a speed of 350km/s. We used Kepler's laws to show that the unseen
companion has almost the same mass as the Sun, but it is much smaller and
fainter. The unseen companion star could be a neutron star or black hole, but
is much more likely to be a white dwarf star. Many subdwarf B stars have been
found with white dwarf companions.
When binary stars have
orbital periods as short as two hours, they produce 'gravitational waves' which
drain energy from the orbit, so the stars gradually spiral in towards each
other. This effect was predicted by Einstein's theory of General Relativity and
was first seen directly by Hulse and Taylor in the pulsar PSR 1913+16 and
earned them the Nobel prize.
KPD1930+2752 will merge within 200 million years. The white dwarf will
then gain extra mass from the subdwarf B star and will exceed a critical mass,
called the Chandresekhar limit. This is thought to lead to a Type Ia supernova
explosion.
There has been some debate
among astronomers over the cause of Type Ia supernova explosions. Most agree
that they are caused by the explosion of a white dwarf star which gains too
much mass but what is not clear is how it gains this mass. There are many white
dwarfs which are known to be gaining mass from a normal star, but these are
made of hydrogen which causes a series of small explosions before the
Chandresekhar limit is reached. This is what causes a nova explosion. To make a
supernova, the white dwarf has to be supplied with helium, which explodes less
easily but releases much more energy. KPD1930+2752 is the first star found
where helium will be dumped onto a white dwarf star which will then exceed the
Chandresekhar limit.
July 31 -- Astronomers around
the world continue to monitor the unexpected disintegration of comet C/1999 S4
(LINEAR). Intense solar heating apparently triggered a massive disruption of
the comet's fragile icy core when it passed close to the Sun last week. It was
still bright enough to see through small telescopes so even amateur astronomers
could watch the comet as it dissolves. If you do plan to look, don't wait.
Experts think that comet LINEAR might disappear completely in a few days.
The break up of a bright
comet is unusual but not unprecedented. For example, comet Shoemaker-Levy 9
(SL-9) broke up before it struck Jupiter in 1994. SL-9 was discovered after it
fragmented, so there is no record of what happened as it came to pieces. With
comet LINEAR, astronomers have a ringside seat for the entire show. "We have observed a few comets in
the process of breaking up -- comet West in 1976, comet Ikeya-Seki in 1965 and
others -- but never with so much detail as we're seeing in comet LINEAR,"
says Mark Kidger, an astronomer at the Instituto de Astrofisica de Canarias.
Comet LINEAR's demise seems to be a bit unusual. "Cometary splittings
rarely ever lead to the rapid disappearance of a comet like this - in fact, I
don't know of another case".
Kidger was the first to notice comet LINEAR disintegrating as he
monitored a cloud of gas (called the "coma") surrounding the comet's
core using the 1-meter Jacobus Kapteyn Telescope. Comet LINEAR, which has been
falling toward the Sun since it was discovered in September 1999, made its
closest approach to our star (perihelion) on July 26, 2000. Perihelion is a
critical time for any comet. It's when solar heating of the icy core is most
intense and when the comet swings around for its long return trip to the outer
solar system.
"At perihelion there
are very rapid aspect changes as regions of the nucleus previously in shadow
are suddenly subjected to intense heating," continued Kidger. "This
causes strong thermal stresses" that may have been a primary cause of
LINEAR's breakup. Nightly observations
made since July 23 in different broadband filters with the Kapteyn Telescope,
show what appears to be the complete disruption of the nucleus of comet LINEAR. Dr. Kidger reports: "The central
condensation was highly condensed and showed the typical 'teardrop' form in the
evening of July 23rd and July 24th, although its brightness decreased by a
factor of about 3 between the two nights. In the evening of July 25th something
very odd was happening to the comet: the central condensation was seen to be
strongly elongated, with a very flat brightness distribution. The
condensation's brightness faded further and its length increased on the
following nights.” Something was
already amiss the day before Comet LINEAR reached perihelion at a distance of
114 million km (0.74 AU) from the Sun.
"The very first images on July 25th were enough to show me that
something odd was going on," recounts Kidger. "The comet's
inner coma was no longer teardrop-shaped (the solar wind flowing around the comet's
head causes this shape). It had a shape like a short, fat cigar. My first
thought was 'Shoemaker-Levy.' It looked just like those first images of
Comet Shoemaker-Levy 9 after it was discovered." Kidger's images on subsequent nights confirmed that something
dramatic was happening and he announced his findings in an International
Astronomical Union (IAU) Circular (IAUC #7467) on July 27, 2000. “On July 27
there was no evidence of any local brightness peaks that would indicate the
presence of sub-nuclei." In
other words, it does not appear to have broken into individual fragments in the
way that Comet Shoemaker-Levy 9 did in 1993. Instead, it has completely blown
apart. The expansion velocity of the condensation is about 40 m/s, indicating
that it is solid particles and not gas. The gas tail, which virtually
disappeared between July 23rd and 24th, has reformed as an extension of the
major axis of the central condensation.
As news of the breakup spread, astronomers around the world trained
their telescopes on the comet. In another IAU Circular (IAUC # 7468) published
July 28th, three teams of observers reported that they too saw evidence of a
major event in the comet's nucleus.
Unlike comet Shoemaker-Levy
9, which broke into many well-defined bright fragments, comet LINEAR seems to
be dissolving into an amorphous haze of gas and dust. "There is some similarity of appearance to the two comets,"
says Brian Marsden of Harvard's Minor Planet Center. "An observation by
Ian Griffin in New Zealand on July 29th shows the nucleus of C/1999 S4 (LINEAR)
extended into a long, bright string. However, it does not seem to show discrete
nuclei in that string, as D/1993 F2 (SL-9) did." The differences between comets SL-9 and
LINEAR result from their different sizes and distances from the Sun. Comet Shoemaker-Levy 9 was larger than
comet LINEAR, and it broke apart as the result of tidal stresses it experienced
when it passed less than 100 thousand kilometers from Jupiter (within 1.4
Jupiter radii from the planet's center). SL-9 was far from the Sun (812 million
km) when it fragmented and solar heating was not the primary cause of the break
up. In fact, SL-9 wasn't even orbiting the Sun. The comet had been captured by
the gravitational pull of Jupiter and was orbiting the giant planet
instead. Comet LINEAR is a much smaller
object that has been losing mass rapidly during its approach to the Sun. The
Hubble Space Telescope recorded a house-sized fragment blowing away from the core
on July 5th and powerful jets of gas vaporized by solar radiation have been
pushing the comet to and fro. Solar heating is a more important factor in its
breakup than gravitational effects. [more information]
"The small size of
comet LINEAR and its exposure to solar radiation is causing a more complete and
rapid dissolution than we saw in Shoemaker-Levy 9," continued Marsden.
"The initial break-up of SL-9 was surely caused by tidal forces from
Jupiter. If they had not later collided with Jupiter, several of those
fragments would presumably still exist. C/1999 S4 (LINEAR), on the other hand,
will probably have completely dispersed in a week or so." Comet LINEAR may still be bright enough for
amateur astronomers to view in small telescopes, but it's fading fast. On July
27th, binocular observers in South America and Europe estimated the comet's
visual magnitude to be +6.6. That's almost bright enough to see with the
unaided eye from dark-sky observing sites. Two days later, an experienced
amateur in the Canary Islands reported a visual magnitude of +8.3, a factor of
6 decline in brightness. "The
surface brightness of the innermost coma is fading fast," says Kidger.
"This should translate to a somewhat slower fade of the outer coma
[that binocular and small telescope observers see] as the gas and dust in it
disperses and is not replenished. Typically a comet may take several weeks for
the coma to expand and fade down to the brightness of the sky background."
Many well-known annual meteor
showers, including the Perseids, Leonids and Geminids, are caused by dusty
debris from comets burning up in the atmosphere of Earth. Such displays are
harmless and beautiful. Unfortunately for meteor lovers, the orbit of comet
LINEAR comes no closer to our planet than 28 million kilometers (0.18 AU).
There will be no "Linearid" meteor shower. When comet LINEAR finally
disappears from view in a few days or weeks, this memorable visitor from beyond
the orbit of Neptune will be gone forever.
Comet LINEAR is a by-product
of the automated LINEAR minor-planet survey. Discovered nearly as far out as
Jupiter last September, this comet passed 114 million kilometers from the Sun
on July 26 and only 56 million kilometers from Earth on July 22. Comet LINEAR
is a "new" comet which means that it is making its very first passage
through the inner solar system. The surfaces of new comets are believed to be
covered almost completely by a very thin, fragile layer of highly volatile ices
such as carbon dioxide intermixed with dust.
When discovered, Comet LINEAR was immediately regarded as a candidate
likely to reach naked eye visibility based on its relative brightness and large
heliocentric distance. New comets though, are notoriously difficult to predict
as far as their light curve behavior is concerned, particularly many months in advance. The Kapteyn Telescope will continue to
observe its disintegration, hopefully giving new insights into the nature of
comet nuclei and their structure.
FROM THE EDITOR'S TERMINAL
The Stargazer is your newsletter
and therefore it should be a cooperative project. Ads, announcements, suggestions, and literary works should be
received by the editor before the 1st of the month of publication, for example,
material for May's newsletter should be received May 1st. If you wish to contribute an article or suggestions
to The
Stargazer please contact Mark Folkerts by telephone (425) 486-9733 or
by mail (18925 - 67th Ave SE, Snohomish, WA 98296), or co-editor
Bill O’Neil, at (425) 337-6873.
