Delta Cancrids Shower Night Sky From Dec. 14 to Feb. 14

Summary: The Delta Cancrids shower the night sky from mid-December to mid-February and peak in mid-January during the main shower.

The Delta Cancrids appear to radiate from the constellation of Cancer the Crab ~ Cancer, as viewed with unaided eyes, with added connecting lines: Till Credner, CC BY SA 3.0, via Wikimedia Commons

As a minor meteor shower, the Delta Cancrids appear Dec. 14, shoot the main shower from Jan. 1 to Jan. 24, peak around Jan. 15 to 17, and finish Feb. 14.

The peak for 2016 occurs between Sunday evening, Jan. 17, and pre-dawn Monday, Jan. 18. The shower contends with the Moon’s first quarter phase. With visibility at 57 percent, the first quarter moon may block viewing of the meteor shower’s shooting stars. Viewing improves after the Moon’s setting around midnight.

The Delta Cancrids’ minor show barely ups its low hourly rate, known in astronomy as Zenithal Hourly Rate (ZHR), for its peak in mid-January. Normal rates that flag at less than one meteor per hour increase to three or four per hour during the Delta Cancrids’ peak. According to the International Meteor Organization, Delta Cancrid meteors enter Earth’s atmosphere at speeds of 28 kilometers per second (over 62,634 miles per hour). Their speed approximates the Earth’s orbital speed of about 30 kilometers per second (67,000 miles per hour).

The constellation of Cancer the Crab serves as apparent, though not actual, host for the Delta Cancrids. The meteor shower’s name reflects the Crab constellation as the radiant, or apparent point of origin, for Delta Cancrid shooting stars. The name also recognizes orange giant star Delta Cancri (δ Cnc, δ Cancri) as the specific radiant in the constellation’s center. Traditionally known in Latin as Asellus Australis (“southern donkey colt”), Delta Cancri is Cancer’s central star. Delta Cancri marks the southern flank of Praesepe, an open, or galactic, star cluster also known as the Beehive Cluster.

Cancer’s prime visibility in the Northern Hemisphere, from late autumn to spring, offers a convenient context for the Delta Cancrid meteor showers. Cancer rises above the eastern horizon in the early evening as the Sun sets, shines overhead after midnight and sets in the west as the Sun rises in the eastern skies.

Meteor shower activity, however, is not confined to the sector of the sky in which namesake constellations are located. The shower only appears to originate in the namesake constellation from the perspective of Earthlings. The misperception is helpful for identifying different meteor showers that overlap. Tracing shooting stars back to their apparent constellationary radiant solves the mystery of which known meteor shower is which.

Meteor showers flare as Earth’s orbit passes through streams of debris released from a parent comet. The source of the Delta Cancrids is presently unknown.

The takeaway for the Delta Cancrids is that classification as a minor meteor shower should not discourage viewers. Minor meteor showers may lack the busyness of the major showers but they still entertain.

The clarity of winter’s skies frame Delta Cancrids’ shooting stars. With their appearance over two Northern Hemisphere winter months, the Delta Cancrids ring out the old year, ring in the new year and take leave on Valentine’s Day.

Delta Cancri (δ Cancri), known traditionally as Asellus Australis ("southern donkey colt"), lies at the center of Cancer the Crab constellation and hosts the Northern Hemisphere's Delta Cancrids as the meteor shower's radiant; red dashed line = ecliptic; yellow dashed line = constellation boundaries; blue smudges = Milky Way areas of different brightness; Cancer the Crab constellation created by PP3 celestial map generation program: Torsten Bronger, CC BY SA 3.0, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Cancer the Crab constellation: Till Credner, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:CancerCC_cropped.jpg

Delta Cancri (δ Cancri) at center of Cancer the Crab constellation: Torsten Bronger, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Cancer_constellation_map.png

For further information:

“Cancer Constellation.” SolarSystemQuick > Constellations.
Available @ http://www.solarsystemquick.com/universe/cancer-constellation.htm

“January 2016 Sky Events Calendar.” Arkansas Sky Observatory >ASO Sky Events Calendars. Dec. 30, 2015.
Available @ http://www.arksky.org/smf/index.php?topic=2660.0;prev_next=next

“January to March.” International Meteor Organization > Meteor Science > Meteor Shower Calendar > IMO Meteor Shower Calendar 2004.”
Available @ http://www.imo.net/calendar/2004/winter?PHPSESSID=1fb18a1401ae2541b2a2c.

Kronk, Gary W. Meteor Showers: An Annotated Catalogue. The Patrick Moore Practical Astronomy Series. 2nd ed. New York: Springer Science + Business Media, 2014.

Lunsford, Robert. “Meteor Activity Outlook for January 16-22, 2016.” American Meteor Society > Meteor Showers. Jan. 15, 2016.
Available @ http://www.amsmeteors.org/2016/01/meteor-activity-outlook-for-january-16-22-2016/

McClure, Bruce. “Cancer? Here’s your constellation.” EarthSky > Tonight > Constellations. March 7, 2014.
Available @ http://earthsky.org/constellations/cancer-heres-your-constellation