Here Comes Comet Linear
Comet Linear is expected to become a faint naked-eye
object similar in appearance to the Andromeda Nebula as it glides
by the Big Dipper this month.
July 5, 2000 -- Later this
month a fuzzy blob will glide across the sky near the Big Dipper.
Called "C/1999 LINEAR S4", or LINEAR-S4 for short,
it's the brightest comet to come along in more than 3 years.
Comet LINEAR-S4 was discovered on September 27, 1999, by the Lincoln Near-Earth Asteroid Research program in New Mexico. It appears to be a first-time visitor to the inner solar system traveling in an orbit that will return it beyond distant Pluto after it passes 114 million km from the Sun on July 26, 2000.
Right: This time-lapse sequence of Comet LINEAR-S4 was taken on July 2, 2000, from Arizona and shows the comet's movement over only 19 minutes. Credit & Copyright: Wil Milan
"Estimating how bright this comet will become is tricky," says an astronomer at the NASA Marshall Space Flight Center. "Comet LINEAR hasn't been here before so we can't use past experience as a guide."
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Nevertheless, comet LINEAR-S4 could be a beautiful sight as it moves through the relatively star-poor area around the Big Dipper in late July. In fact, if the comet reaches 4th magnitude it will probably resemble another popular fuzzy blob, our nearest neighboring galaxy, the Andromeda Nebula. Experts stress that predicting what LINEAR-S4 will do is more of an art than hard science. The comet might fail to develop or it could be far more striking than expected.
Above: Comet LINEAR-S4 is expected to reach peak brightness
around July 23, 2000. Skywatchers in the northern hemisphere
should look for the comet near the Big Dipper around 9 p.m. local
time approximately 30 degrees above the northern horizon. Although
the comet will appear to be stationary when viewed for a short
time, it is actually moving 8 degrees per day with respect to
background stars. (The bowl of the Big Dipper is 10 degrees across.)
The comet will move past the Big Dipper in just a few days. To
view finder charts for other dates, visit Sky
& Telescope and CometLinear.com.
Note for Southern Hemisphere observers: when comet LINEAR
is brightest on July 23 it will be impossible to view from most
southern latitudes as it rises just a few degrees above the horizon
during the day. In August the fading comet will be a good target
for southern telescopes for a few hours after sunset.
LINEAR-S4 is expected to become a naked-eye object around July 17, 2000, when it brightens to 6th magnitude. Even if the comet eventually reaches 4th magnitude, it will be invisible in light polluted urban areas. Dark skies are essential. For comet watchers, this is a good time for a vacation in the country!
The comet will fade after its closest approach to our planet
on July 23rd and by the end of July, LINEAR-S4 it will be too
dim for naked-eye observations. It will remain a good target
for binoculars and small telescopes well into September. On August
20th, telescopic observers in the southern hemisphere will be
treated to a rare sight when the 7th magnitude comet passes almost
directly in front of the Sombrero galaxy M104. [See Sky
& Telescope for more information.]
By the end of 2000, LINEAR-S4 is expected to be a faint 13th magnitude object, fading as it races back to the outer solar system. Comets like LINEAR-S4 may originate in the Oort Cloud, a giant reservoir of comets 50,000 AU from the Sun. (One AU is an Astronomical Unit, 149.6 million km, equal to the average distance between the Earth and Sun.) Although the Oort Cloud is speculative, many astronomers believe that it exists and is populated with icy relics from the formation of the solar system more than 4 billion years ago. Occasionally a galactic gravitational perturbation tweaks the orbits of the Oort comets and sends some of them plunging toward the Sun. Comet LINEAR-S4, with its highly elliptical long-period orbit, is probably one of these. After it passes by the Sun later this month it may not return for millions of years, if ever.
Right: This 10-minute exposure of comet LINEAR S4 was captured in Austria on June 28, 2000. Copyright © 2000 by Michael Jäger and Gerald Rhemann.
Although we probably won't see comet LINEAR-S4 again after this summer, it's almost certainly not the last "Comet LINEAR." The LINEAR project has discovered more than 40 new comets since 1998 and shows no signs of slowing.
Will this Comet LINEAR be worth watching? Only time will tell. The best way to find out is to go outside and look!
Science@NASA readers are invited to send their descriptions and photos of Comet LINEAR to the editor for possible inclusion in future articles about this comet.
The nucleus of a comet is an irregular
ball of ice and dust typically 1 to 10 km in diameter. When the
nucleus approaches the Sun, sunlight warms the surface and the
solid ice sublimes (turns to vapor). The resulting cloud of water
vapor and carbon dioxide surrounding the nucleus is called the
coma. Most comets come from the most distant reaches of
the solar system, far beyond the orbit of Pluto. By the time
they are as close to the Sun as the Earth, the coma can be larger
than Jupiter. Together the coma and the nucleus form the head
of the comet.
Elements of C/1999 LINEAR S4
- from the Harvard Center for Astrophysics
Daily Ephemeris for C/1999 LINEAR S4 - from the Harvard Center for Astrophysics
CometLinear.com -pictures, updates, and a discussion board for observers of comet Linear.
Comet LINEAR's Summer Show - from Sky & Telescope,
includes detailed finder charts and ephemerides.
C/1999 S4 (LINEAR) -- images and historical highlights from Gary Kronk's popular Comets & Meteors web site.
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|For lesson plans and educational activities related to breaking science news, please visit Thursday's Classroom||Author: Dr. Tony Phillips
Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Media Relations: Steve Roy
Responsible NASA official: Ron Koczor