The appearance of ISON near Mars is not simply a line-of-sight coincidence — the two bodies actually reside near each other in space. They make their closest approach October 1, when the comet whizzes 6.7 million miles (10.8 million kilometers) from the planet.
Keep a watch on the morning sky during October’s first two weeks, and you can’t help but notice that Mars and its cometary companion are approaching a conspicuous star. This is magnitude 1.4 Regulus, Leo’s brightest sun and a near match to Mars in terms of brightness. The star’s subtle bluish hue, however, contrasts nicely with the ruddy planet.
The seemingly lockstep motions of Mars and ISON carry them to within a stone’s throw of Regulus on October 15. The three objects form a spectacular straight line that morning, with Mars 1° north of Regulus and ISON 1° north of the planet. The trio rises shortly before 3 a.m. local daylight time and climbs one-third of the way to the zenith by the time morning twilight starts around 5:30 a.m. ISON picks up speed later in the month and will leave the star and planet behind as it moves closer to the Sun during the next several weeks.
Follow Comet ISON’s travels at www.Astronomy.com/ISON
, and pick up the October issue of Astronomy
and the special issue The Great Comet of 2013
for even more coverage of ISON’s voyage to the inner solar system.