Hun Kal (crater)

{{short description|Crater on Mercury}}

{{Infobox feature on celestial object

| name = Hun Kal

| image = Hun Kal crater on Mercury cropped.png

| caption = Hun Kal is indicated by the arrow.

| location = Kuiper quadrangle, Mercury

| type = Impact crater

| coordinates = {{coord|0.46|S|20.01|W|globe:mercury_type:landmark|display=inline,title}}

| diameter = {{cvt|1.13|km}}

| eponym = '20' in the Mayan language

}}

Hun Kal is a small (about 1.5 km in diameter) crater on Mercury that serves as the reference point for the planet's system of longitude. The longitude of Hun Kal's center is defined as being 20° W, thus establishing the planet's prime meridian.{{cite web|url=https://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html|access-date=22 October 2009|title=USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE)|archive-url=https://web.archive.org/web/20111024101856/http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html|archive-date=24 October 2011|url-status=dead}} The name "Hun Kal" means '20' in the language of the Maya.{{gpn|62753|Hun Kal}}

Hun Kal was chosen as a reference point since the actual prime meridian was in shadow when Mariner 10 photographed the region, hiding any features near 0° longitude from view.

The prime meridian of Mercury is thermocentric, it runs through the point on the equator where the planet is hottest (due to the planet's rotation and orbit, the sun briefly retrogrades at noon at this point during perihelion, giving it more sun).Davies, M. E., "Surface Coordinates and Cartography of Mercury," Journal of Geophysical Research, Vol. 80, No. 17, June 10, 1975.{{cite journal |last1=Archinal |first1=Brent A. |display-authors=4 |last2=A'Hearn |first2=Michael F. |last3=Bowell |first3=Edward L. |last4=Conrad |first4=Albert R. |last5=Consolmagno |first5=Guy J. |last6=Courtin |first6=Régis |last7=Fukushima |first7=Toshio |last8=Hestroffer |first8=Daniel |last9=Hilton |first9=James L. |last10=Krasinsky |first10=George A. |last11=Neumann |first11=Gregory A. |last12=Oberst |first12=Jürgen |last13=Seidelmann |first13=P. Kenneth |last14=Stooke |first14=Philip J. |last15=Tholen |first15=David J. |last16=Thomas |first16=Peter C. |last17=Williams |first17=Iwan P. |title=Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009 |journal=Celestial Mechanics and Dynamical Astronomy |volume=109 |issue=2 |date=2010 |pages=101–135 |issn=0923-2958 |doi=10.1007/s10569-010-9320-4 |bibcode=2011CeMDA.109..101A|s2cid=189842666 }}{{cite web |url=https://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |access-date=October 22, 2009 |title=USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE) |archive-url=https://web.archive.org/web/20111024101856/http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |archive-date=October 24, 2011 |url-status=dead}}

The large crater in which Hun Kal lies is not named. To the northwest is Al-Jāhiz crater, and to the west is Lu Hsun crater.

Image:Hun Kal crater on Mercury.jpg|This Mariner 10 image shows the surrounding context of Hun Kal, which is almost invisibly tiny near the center.

File:Hun Kal crater EN1007130467M.jpg|MESSENGER NAC image with Hun Kal at center

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