The Double Comet Show of 2004
By Greg Bryant, John E. Bortle, and Alan M. MacRobert

Comet LINEAR, C/2002 T7, was already 7th magnitude and showing a wispy double tail on January 24, 2004, when Michael Jäger and Gerald Rhemann took this picture. They used a 180-millimeter lens at f/3.3 on a Starlight Xpress SXV-H9 CCD camera for 5-minute exposures through red, green, and blue filters.  Courtesy Michael Jäger and Gerald Rhemann.
Comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) were discovered in August 2001 and October 2002, respectively, by the automated sky-survey programs for which they’re named: Near-Earth Asteroid Tracking (NEAT) and Lincoln Laboratory Near Earth Asteroid Research (LINEAR). Amateurs have been tracking the comets for more than a year as they’ve been approaching the inner solar system and gradually brightening.

How bright will they get? With a little luck, one or both could become distinctly visible to the naked eye. Or they could remain targets only for binocular users who know just where to look. Predicting the brightness of “new” comets — those freshly arrived from the outermost reaches of the solar system, like these — is fraught with risk. Some such comets in recent years have broken up and dissipated completely as they neared the Sun, the most recent being C/2002 O7 (LINEAR). Others suddenly ebbed in their brightening after a promising start; famous cases are comets Kohoutek in 1973-74 and Austin in 1990, both of which were supposed to become bright to the naked eye but ended up only 3rd or 4th magnitude when easily visible, much to the world’s disappointment.

View from the Northern Hemisphere

Path of Comet NEAT
In early May, Comet NEAT climbs higher every day above the southwestern sunset horizon. The comet could be visible to the naked eye, but binoculars provide a much better chance of seeing it. By mid-May, NEAT will be well up in the west even after twilight gives way to darkness — though the comet will be fading daily. The dates plotted are civil dates for North America. The horizon is drawn for early May; later in the month the horizon will be higher at dusk with respect to the stars. S&T illustration.
The two comets will put on rather different performances.

For skywatchers living at north temperate latitudes, Comet NEAT promises the easiest show to watch. In early May, just when NEAT is brightest, it will rapidly climb out of the Sun’s glare into good view above the southwest horizon after sunset. By the middle of May it will be high in the dark sky of late evening even as it begins to fade. It will remain ideally placed for viewing high in the northwest after dark through June and July as it dwindles away into the distance, eventually becoming visible only in telescopes.

Comet LINEAR may get a little brighter, but it will act more coy. In April and the first days of May it just peeks over the eastern dawn horizon, appearing quite low in the brightening dawn; bring your binoculars. When LINEAR is at its brightest in mid-May, it will be hidden in the Sun’s glare (well to the Sun’s south). Then in late May and June it will show itself a little higher above the west-southwest horizon at dusk, fading all the while.

View from the Southern Hemisphere

Paths of Comets NEAT and LINEAR
Observers in the world’s midsouthern latitudes — Australia and New Zealand, southern Africa, and southern South America — get a grand view. Comet NEAT stays very high in the evening sky throughout its brightest times, while Comet LINEAR shows itself well during both its morning and evening displays. Click on the image to see the complete chart. S&T illustration.
Southern Hemisphere observers have a much better vantage point for both of these comets. Seen from south temperate latitudes, NEAT will remain beautifully placed high in the evening sky after dark throughout April and May, including its early-May period of peak brightness. At the same time LINEAR will be much less shy about showing itself before dawn, from mid-April to mid-May, and then after dusk from mid-May on.

Comet Highlights

Here is a timetable of noteworthy events during the long comet show. Tables listing each comet's position and its predicted magnitude, based on projections by John Bortle, can be found on the next page.

In the first week of April, NEAT is passing 7° north of the Small Magellanic Cloud, creating an inviting target for far-southern astrophotographers. Around April 22nd NEAT will pass a little less than 10° from the Large Magellanic Cloud.

Meanwhile, on April 23rd Comet LINEAR passes through perihelion, its closest approach to the Sun. At 0.615 astronomical unit (91.9 million kilometers), LINEAR’s perihelion is substantially closer to the Sun than NEAT’s three weeks later.

Comets LINEAR and NEAT at dawn in Southern Hemisphere
 Sky & Telescope illustration.
For the midlatitudes of the Southern Hemisphere, mid- and late April offer the first of two observing windows when both comets can be seen at the same time. As LINEAR rises out of the glimmer of dawn low in the east-northeast, dimmer NEAT will be descending day by day low in the south-southeast. During this time both comets should still be brightening. By late April LINEAR and NEAT could both be as bright as 3rd magnitude.

Comet LINEAR at dawn
For skywatchers at the latitudes of the US and Europe, Comet LINEAR peeks above the eastern dawn horizon in late April and early May. Sky & Telescope illustration.
On the night of May 4–5, a total eclipse of the Moon occurs for eastern South America and Europe in the evening; the Middle East, Africa, and central and south Asia late at night; and Southeast Asia and Australia before sunrise. Fortuitously placed viewers will be able to catch one or the other comet at the same time as a totally eclipsed Moon! In particular, observers in eastern South America can witness NEAT during the eclipse when it is among the three bright stars forming the hindquarters of Canis Major.

On May 5th Comet NEAT passes 9° from Sirius, the sky’s brightest star. On the 6th NEAT is closest to Earth (0.321 a.u.) and should be about at its peak brightness, perhaps magnitude 2.5. On May 7th NEAT passes just 1° northwest of the 5th-magnitude open cluster M47 in Puppis.

Comet NEAT reaches perihelion on May 15th, 0.962 a.u. from the Sun, barely closer to the Sun than Earth is. At this time the comet will be just a couple of degrees away from M44, the Beehive Cluster.

May 19th brings Comet LINEAR’s closest approach to Earth (only 0.266 a.u.) and its time of greatest brightness: perhaps magnitude 2. By this time Southern Hemisphere viewers will be seeing both comets in the evening sky at once (see the lower chart on the previous page). On the 22nd (local date for North America), only about 3° will separate LINEAR’s head and Sirius.

Comet LINEAR at dusk for Northern Hemisphere observers
After it ducks back around the Sun, Comet LINEAR will be visible to observers in the US and Europe in the west during evening twilight. Sky & Telescope illustration.
Late in May midnorthern observers get their turn to see both comets at once — NEAT high in the western evening sky at about 4th magnitude, LINEAR emerging low in the west-southwest a little past its prime.

During June both comets should fade to below naked-eye visibility. NEAT will become lost to Southern Hemisphere observers in June; conversely, it will turn circumpolar for those in north temperate latitudes. As LINEAR fades, by contrast, it will move back into the glare of the Sun for northerners, but from the Southern Hemisphere it should remain a telescopic sight through July and August, glowing dimly at perhaps 11th magnitude by the end of that period.

The May issue of Sky & Telescope contains a large chart that shows the comets’ paths (and tail direction) among the constellations. The comets’ positions are marked for 0:00 Universal Time on the indicated dates, for worldwide use. The same issue also includes tables indicating each comet’s altitude above the western horizon in very late dusk, and/or the eastern horizon in very early dawn (when the Sun is 15° below the horizon), for skywatchers at midnorthern and midsouthern latitudes. The May S&T will be available on newsstands March 30th.

Positions for NEAT and LINEAR

Use our interactive sky chart to follow Comet NEAT as it moves through the skies of the Southern and Northern Hemisphere during April and May 2004. The southern chart shows the sky for 8:00 p.m. on April 20th at 35° south latitude; the northern chart is set to 10:00 p.m. on May 7th at 40° north. To adjust the date and time, highlight the month, day, hour, or minute and click the "+" or "-" button. To alter your viewing location, press the "Change" button on the location bar.

Comet C/2001 Q4 (NEAT)
R.A. (2000)
h   m
°   '
Mar. 22   0 22 -65 30 6.8 Tuc
Apr.   1   0 57 -65 48 6.1 Tuc
Apr. 11   1 57 -66 00 5.2 Hyi
Apr. 21   3 44 -63 18 4.1 Ret
May   1   6 14 -44 30 2.9 Pup
May   4   6 54 -32 00 2.7 Cma
May   7   7 28 -16 48 2.5 Pup
May 10   7:56 -  1 30 2.5 Mon
May 13   8 19 +11 24 2.9 Cnc
May 16   8 38 +21 18 3.2 Cnc
May 19   8 54 +28 49 3.5 Cnc
May 22   9 07 +34 06 3.8 Lyn
May 27   9 24 +40 24 4.3 Lyn
June   1   9 38 +44 36 4.7 UMa
June   6   9 49 +47 36 5.1 UMa
June 11   9 59 +49 54 5.5 UMa
June 21 10 15 +53 00 6.2 UMa
July   1 10 30 +55 06 6.8 UMa

The double comet apparition should provide us with many treasured memories. If you don't normally use binoculars much on the sky, now's certainly the time to get them out. The chance to follow the progress of comets LINEAR and NEAT every clear night will make this a fascinating time to be an amateur astronomer.

Comet C/2002 T7 (LINEAR)
R.A. (2000)
h   m
°   '
Mar. 21   0 01 +10 06 6.0 Psc
Apr.  1 23 56 +  8 42 5.6 Psc
Apr. 11 23 53 +  6 54 5.0 Psc
Apr. 21 23 53 +  4 24 4.3 Psc
May   1   0 06 +  0 36 3.6 Psc
May   6   0 26 -  2 12 3.3 Psc
May 11   1 07 -  6 48 2.8 Cet
May 16   2 43 -14 30 2.4 Cet
May 19   4 24 -19 12 2.3 Eri
May 22   6 14 -20 00 2.7 CMa
May 25   7 34 -17 42 3.3 Pup
May 28   8 22 -15 12 4.1 Pup
May 31   8 53 -13 12 4.7 Hya
Jun.   5   9 23 -11 00 5.6 Hya
Jun. 10   9 42   -9 36 6.4 Sex
Jun. 20 10 03   -8 06 7.7 Sex
Jun. 30 10 17   -7 24 8.7 Sex

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Greg Bryant is one of Sky & Telescope's southern-sky columnists. John Bortle has been reporting comet news for S&T since 1969. Alan MacRobert is an S&T senior editor.

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