University Lowbrow Astronomers

Hale-Bopp Watch.

by Bernard Friberg and Kurt Hillig
Printed in Reflections:  February, 1997.

Hale-Bopp (also known as Periodic Comet 1995 O1) may well turn out to be the brightest comet of this century.  If not, it will certainly be one of the brightest, and those of us who saw Hyakutake will have had the rare privilege of seeing two once-in-a-lifetime comets only one year apart.

Hale-Bopp is easily located in the east-northeastern sky before dawn in February and early March; it’s already bright enough to be visible to the naked eye, though binoculars can help.  The Feb. 8 rise time of H-B (for southeast Michigan) is 4 am, local time, and it rises earlier each day - 3 am on Feb. 10, and 2 am on March 20 - making it an easily observed object in the early mornings.  A good rule of thumb is to wait an hour or two after the rise time before going out to look for it, to give it time to climb above the horizon; but don’t wait too long, as the eastern sky starts to brighten about 1.5 hours before sunrise.  5:30 to 6 am should be a good viewing window for the next week or two; then you’ll have to start getting up earlier (or staying up later, if you’re a night owl like me - KH).

The path of the comet through the morning skies in February is more or less parallel to the horizon as it heads north.  On Feb. 12 H-B enters the constellation Vulpecula, and on Feb. 24 it enters Cygnus.  The path continues into the constellation Andromeda, and H-B will be just above the Andromeda galaxy M31 - only 4 degrees away - on March 25.  This is two days past the full Moon, so the skies will be bright if you try to see this in the morning; but H-B will also be visible in the early evening, and you might see a real treat at the end of twilight.

The plane of Hale-Bopp’s orbit is nearly perpendicular to the ecliptic plane.  On Feb. 10, H-B is 1.8 AU away from the Earth and 1.25 AU from the Sun.  H-B is at its closest distance to the Earth - 1.3 AU (about 200 million km) - on March 22, when it lies almost directly above the Sun’s north pole; and it makes its closest approach to the Sun (perihelion - 0.91 AU, about 85 million miles, 140 million km) on April 1.  So it should be at its brightest from mid-March through mid-April.

As Hale-Bopp moves to the north in February and March, it will become visible in the evening sky as well as in the morning.  On Feb. 24, H-B will be 9° above the horizon at sunset (6:20 pm), so it will set before twilight ends.  By March 15, H-B will be 34° above the horizon at sunset - 10° up at the end of twilight - making it an evening object as well as a morning object for the next month.  There’s a partial lunar eclipse on March 23, which could make for a nice night of “double-dipping” if the clouds cooperate.

At the beginning of April, Hale-Bopp will be 20° above the northwest horizon at the end of twilight (about 8:30 pm on April 1) and stays about the same for a few weeks while it moves back to the south.  Meanwhile, the early birds will see H-B disappear into the morning twilight in mid-April.  April 12 is Astronomy Day, and a good time to share H-B with a friend - although with a six day old moon only 30 degrees away, you might want to think about celebrating this one a few days early.

Hale-Bopp crossed the ecliptic plane heading north over a year ago, near Jupiter; but after perihelion, it swings back south in a hurry, crossing the ecliptic again in mid-May.  In early May, it will be getting low in the west at sunset, and by the end of the month it will be too far south to be seen from Michigan - unless you’re willing to wait 2380 years until its next visit!


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