By Erik Ryan 

Stars over Sisters 3/08/2022


Last updated 3/8/2022 at Noon

Two galaxies that have recently merged lie in the constellation of Cancer, 253 million light-years from earth.phot courtesy NASA/ESA Hubble space telescope

This month’s featured constellation is Cancer the Crab. Being the dimmest member of the zodiac, it is not the easiest asterism to make out. (The zodiac is a strip of sky where the sun, moon, and all the planets of our solar system are always found.) Cancer is bordered by Gemini to the west and Leo to the east, and lies just above the head of Hydra, the Water Serpent. It’s positioned about 65 degrees in altitude from the southern horizon around 9 p.m. during March. Observers wishing to spot the celestial crustacean should pick a clear, moonless night away from interfering lights.

At magnitude 3.5, the Crab’s brightest star is Beta Cancri, also known as Altarf (Arabic for “end” or “edge”). It is an aging star that has expanded to around 50 times the sun’s diameter and shines with 660 times its luminosity. Altarf is about 290 light-years from the earth.

Only slightly dimmer is Delta Cancri, or Asellus Australis, which means “southern donkey.” But there’s another alias that makes this star particularly noteworthy: It holds a record for the longest name. “Arkushanangarushashutu” is derived from ancient Babylonian language that translates to “the southeast star in the Crab.”

For a medium-sized constellation, Cancer contains its fair share of deep sky objects (DSO), two of which hold Messier designations. The best known of these is M44, a nearby open star cluster. This object is also known as Praesepe, and the Beehive Cluster. Only the Pleiades Cluster (M45) in Taurus and the Andromeda Galaxy are brighter than M44 in Messier’s catalog. The Beehive lies only 577 light-years away.

Another interesting DSO is NGC 2623, an oddly shaped galaxy that displays tidal tails of interstellar gas containing bright star clusters. Astronomers believe two spiral galaxies have recently merged and that their cores have unified into one active galactic nucleus. It is located about 253 million light-years from the earth.

Cancer is known in Greek mythology as the giant crab Hera (wife of Zeus) sent to defeat Hercules in his quest to complete the Twelve Labors as penance for killing his family. Jealous of his successes, Hera also created the deadly beast Hydra to further thwart Hercules’ efforts. However, with the help of his nephew, Hercules was able to vanquish both foes. As a reward for their role in the battle, Hera placed both Hydra and Cancer into the sky as neighboring constellations.

The earth will arrive at the Vernal Equinox (one of the two points in space where the celestial equator and ecliptic intersect) on Sunday March 20 at 8:33 a.m. PDT. This event will signal the passing of winter and usher in the beginning of spring in the Northern Hemisphere.

This month’s planetary action will play out in the predawn sky. Venus, Mars, and Saturn should be easy to spot. Earlier in March, Mercury was there too, but it will become lost in the glare of the sun as the month progresses. In the early morning of March 28, Venus, Mars, Saturn, and a 26-day-old moon will gather to put on a superb display. Uranus is the only evening planet this month. Both Jupiter and Neptune are too close to the sun to be seen.

When the Pacific time zone is used to determine the lunar phases, there are two new moons this month. The first occurred on March 2 at 9:38 a.m., the next will arrive on March 31 at 11:27 p.m. The Full Crow Moon shows up on March 18.

The dark-sky preservation tip for March is to make sure your outdoor lights are properly shielded in such a way that light is directed downward. Use lamps that emit no more light than necessary, and at a warm-colored temperature of less than 3,000 Kelvin. Maintaining dark skies provides us an opportunity to more clearly understand our place in the universe, and at the same time appreciate its magnificent beauty.


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