Once, while camping in the Quetico in Canada, a mouse crawled under my jeans and up my leg. My brother and I were relaxing around the fire at the time. I instantly stood up and shook and slapped my legs, forcing the mouse to make a hasty exit. This week, Mars takes me back to that moment as it slowly crawls up Castor's left leg under his toga. Castor is one of the Gemini twins. He and his brother Pollux embrace in the western sky at the end of evening twilight.

As the Red Planet surreptitiously pads its way up Gemini it passes very close to M35, one of the finest star clusters in the sky. On Monday, April 26, and Tuesday, April 27, the planet and cluster will be in conjunction and separated by just a half-degree or one full-moon-diameter.

Our area of interest lies within the circle at Castor's feet. The best time to see the Mars-M35 conjunction is at the end of evening twilight (around 9:30 p.m. - 10 p.m.) when they're highest in the western sky and the moon is low in the east. (Stellarium)
Our area of interest lies within the circle at Castor's feet. The best time to see the Mars-M35 conjunction is at the end of evening twilight (around 9:30 p.m. - 10 p.m.) when they're highest in the western sky and the moon is low in the east. (Stellarium)

The cluster glows at 5th magnitude and is faintly visible without optical aid from moonless, rural skies. A pair of 7x35 or larger binoculars will show it as a small, misty patch punctuated by faint stars. Its twinkly, granulated texture makes a nice contrast with the fiery pinhead of Mars. A small telescope at low magnification offers the best view, with dozens of stars arranged in arcs and whorls.

This is an enlarged view of the circle in the first map and represents the field of view of a typical pair of binoculars. Mars is shown in relation to M35 as it moves to the east from April 26-30. (Stellarium with additions by the author)
This is an enlarged view of the circle in the first map and represents the field of view of a typical pair of binoculars. Mars is shown in relation to M35 as it moves to the east from April 26-30. (Stellarium with additions by the author)

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I saw the duo in my 8x40s on April 24 despite a very bright moon. Under Monday night's full moon, the cluster will be diminished but still visible with concentration. From Tuesday onward, the moon begins to exit the evening sky, and M35 will come into its own. To find it, point your binoculars at Mars, focus sharply, and then use the map to see where the cluster is in relation to the planet.

M35 stays put, but Mars moves a little more than a moon-diameter up and to the left each night as it travels along its orbit. On April 26-27, it lies about 0.5 degrees north of the star cluster, and 2 degrees northeast by the 30th.

M35, discovered in 1745 by a Swiss astronomer, received its humdrum name when the 18th century French comet observer Charles Messier included it as the 35th entry in his list of clusters, galaxies and nebulae called the Messier Catalog. It's located 3,870 light-years away and has around 400 members bound together in a compact swarm by their mutual gravities.

M35 is one of the brightest and richest open clusters and looks awesome in a telescope. The smaller, fainter star cluster, NGC 2158, appears to the southwest of M35. Visible in a telescope, it's more than five times as distant and unrelated. (Hunter Wilson)
M35 is one of the brightest and richest open clusters and looks awesome in a telescope. The smaller, fainter star cluster, NGC 2158, appears to the southwest of M35. Visible in a telescope, it's more than five times as distant and unrelated. (Hunter Wilson)

Born about 175 million years ago from a massive cloud of gas and dust, M35 is one of about 1,100 open clusters known in the Milky Way Galaxy. Many more likely await discovery. Other similar clusters include the Pleiades (Seven Sisters), the Hyades and the Beehive.

They're called open clusters because they're relatively young, loosely-bound groups of stars. Most hang out in the galaxy's spiral arms. As they orbit the galactic center, gravity exerted by dense clouds of dust as well as other star clusters gradually strip away their members until the cluster merges with the background stars.

The average life of an open cluster is only several hundred million years. I know that sounds like a long time, but it's peanuts compared to the richer, denser globular clusters, which have been around for more than 10 billion years.

No matter. You've got plenty of time to get a gander at M35 the next clear night. Let Mars take you there. Just make sure no mice run up your pants while your head is in the stars.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.