{{Short description|Main-belt asteroid}} {{Use dmy dates|date=October 2019}} {{Infobox planet | minorplanet = yes | name = 1720 Niels | background = #D6D6D6 | image = | image_size = | caption = | discovery_ref = <ref name="jpldata" /> | discovered = 7 February 1935 | discoverer = K. Reinmuth | discovery_site = Heidelberg Obs. | mpc_name = (1720) Niels | alt_names = 1935 CQ{{·}}1940 WH<br />1951 AL{{·}}{{mp|1953 VO|1}}<br />1959 RA{{·}}1963 WE | named_after = {{nowrap|Niels {{small|(discoverer's grandson)}}<ref name="springer" />}} | mp_category = main-belt{{·}}{{small|(inner)}}<ref name="lcdb" /> | orbit_ref = <ref name="jpldata" /> | epoch = 4 September 2017 (JD 2458000.5) | uncertainty = 0 | observation_arc = 89.52 yr (32,697 days) | aphelion = 2.4170 AU | perihelion = 1.9593 AU | semimajor = 2.1881 AU | eccentricity = 0.1046 | period = 3.24 yr (1,182 days) | mean_anomaly = 240.21° | inclination = 0.7301° | asc_node = 127.86° | arg_peri = 308.86° | dimensions = {{val|6.394|0.091}}<ref name="Masiero-2014" /><br />{{val|6.566|0.063}} km<ref name="WISE" /><br />8.18 km {{small|(calculated)}}<ref name="lcdb" /> | rotation = {{val|9.976}} h<ref name="Clark-2007" /><br />{{val|19.2}} h<ref name="geneva-obs" /> | albedo = 0.20 {{small|(assumed)}}<ref name="lcdb" /><br />{{val|0.2154|0.0284}}<ref name="WISE" /><br />{{val|0.227|0.017}}<ref name="Masiero-2014" /> | spectral_type = LS<ref name="Veres-2015" />{{·}}S<ref name="lcdb" /> | abs_magnitude = {{val|12.22|0.25}}<ref name="Veres-2015" />{{·}}12.8<ref name="jpldata" /><ref name="lcdb" />{{·}}13.2<ref name="WISE" /> }}
'''1720 Niels''', provisional designation {{mp|1935 CQ}}, is a stony asteroid from the inner regions of the asteroid belt, approximately 6.4 kilometers in diameter. It was discovered on 7 February 1935, by German astronomer Karl Reinmuth at Heidelberg Observatory in southern Germany, and named after a grandson of the discoverer.<ref name="springer" /><ref name="MPC-Niels" />
== Orbit and classification ==
''Niels'' orbits the Sun in the inner main-belt at a distance of 2.0–2.4 AU once every 3 years and 3 months (1,182 days). Its orbit has an eccentricity of 0.10 and an inclination of 1° with respect to the ecliptic.<ref name="jpldata" /> First observed at Heidelberg in 1927, ''Niels''{{'}} observation arc begins with its official discovery observation in 1935.<ref name="MPC-Niels" />
== Physical characteristics ==
Pan-STARRS classifies this stony asteroid as a LS-type, an intermediate to the rare L-type asteroids.<ref name="Veres-2015" />
=== Rotation period ===
A rotational lightcurve of ''Niels'' was obtained by astronomer Maurice Clark in December 2005. It gave it a rotation period of 9.976 hours with a brightness variation of 0.15 magnitude ({{small|U=1}}). In November 2008, photometric observations by amateur astronomer Pierre Antonini gave another period of 19.2 hours with an amplitude of 0.01 ({{small|U=1-}}). As of 2017, a secure period for ''Niels'' has not yet been obtained.
=== Diameter and albedo ===
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, ''Niels'' measures 6.394 kilometers in diameter, and its surface has an albedo of 0.227,<ref name="Masiero-2014" /> superseding a preliminary result that gave a slightly larger diameter and lower albedo.<ref name="WISE" /> The ''Collaborative Asteroid Lightcurve Link'' assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 8.18 kilometers based on an absolute magnitude of 12.8.<ref name="lcdb" />
== Naming ==
The minor planet was named by the discoverer after his grandson, Niels. Reinmuth also named 1719 Jens after one of his grandsons.<ref name="springer" /> The official {{MoMP|1720|naming citation}} was published by the Minor Planet Center on 20 February 1976 ({{small|M.P.C. 3933}}).<ref name="DoMP-Circular-dates" />
== References == {{reflist|30em|refs=
<ref name="jpldata">{{cite web |type = 2017-05-05 last obs. |title = JPL Small-Body Database Browser: 1720 Niels (1935 CQ) |url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2001720 |publisher = Jet Propulsion Laboratory |accessdate = 7 June 2017}}</ref>
<ref name="springer">{{cite book |title = Dictionary of Minor Planet Names – (1720) Niels |last = Schmadel | first = Lutz D. |publisher = Springer Berlin Heidelberg |pages = 136–137 |date = 2007 |isbn = 978-3-540-00238-3 |doi = 10.1007/978-3-540-29925-7_1721 |chapter = (1720) Niels }}</ref>
<ref name="MPC-Niels">{{cite web |title = 1720 Niels (1935 CQ) |work = Minor Planet Center |url = https://www.minorplanetcenter.net/db_search/show_object?object_id=1720 |accessdate = 22 December 2016}}</ref>
<ref name="DoMP-Circular-dates">{{cite book |title = Dictionary of Minor Planet Names – Addendum to Fifth Edition (2006–2008) |chapter = Appendix – Publication Dates of the MPCs |last = Schmadel |first=Lutz D. |publisher = Springer Berlin Heidelberg |page = 221 |isbn = 978-3-642-01964-7 |doi = 10.1007/978-3-642-01965-4}}</ref>
<ref name="geneva-obs">{{cite web |title = Asteroids and comets rotation curves – (1720) Niels |last = Behrend |first = Raoul |publisher = Geneva Observatory |url = http://obswww.unige.ch/~behrend/page4cou.html#001720 |accessdate = 22 December 2016}}</ref>
<ref name="lcdb">{{cite LCDB|number = 1720 |accessdate = 22 December 2016}}</ref>
<ref name="WISE">{{cite journal |display-authors = 6 |first1 = A. |last1 = Mainzer |first2 = T. |last2 = Grav |first3 = J. |last3 = Masiero |first4 = E. |last4 = Hand |first5 = J. |last5 = Bauer |first6 = D. |last6 = Tholen |first7 = R. S. |last7 = McMillan |first8 = T. |last8 = Spahr |first9 = R. M. |last9 = Cutri |first10 = E. |last10 = Wright |first11 = J. |last11 = Watkins |first12 = W. |last12 = Mo |first13 = C. |last13 = Maleszewski |date = November 2011 |title = NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results |journal = The Astrophysical Journal |volume = 741 |issue = 2 |page = 25 |bibcode = 2011ApJ...741...90M |doi = 10.1088/0004-637X/741/2/90 |arxiv = 1109.6407}}</ref>
<ref name="Clark-2007">{{Cite journal |author = Clark, Maurice |date = March 2007 |title = Lightcurve Results for 1318 Nerina, 222 Lermontov 3015 Candy, 3089 Oujianquan, 3155 Lee, 6410 Fujiwara, 6500 Kodaira, (8290) 1992 NP, 9566 Rykhlova, (42923) 1999 SR18, and 2001 FY |url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2007MPBu...34...19C |journal = The Minor Planet Bulletin |volume = 34 |issue = 1 |pages = 19–22 |issn = 1052-8091 |bibcode = 2007MPBu...34...19C |access-date= 22 December 2016}}</ref>
<ref name="Veres-2015">{{cite journal |display-authors = 6 |first1 = Peter |last1 = Veres |first2 = Robert |last2 = Jedicke |first3 = Alan |last3 = Fitzsimmons |first4 = Larry |last4 = Denneau |first5 = Mikael |last5 = Granvik |first6 = Bryce |last6 = Bolin |first7 = Serge |last7 = Chastel |first8 = Richard J. |last8 = Wainscoat |first9 = William S. |last9 = Burgett |first10 = Kenneth C. |last10 = Chambers |first11 = Heather |last11 = Flewelling |first12 = Nick |last12 = Kaiser |first13 = Eugen A. |last13 = Magnier |first14 = Jeff S. |last14 = Morgan |first15 = Paul A. |last15 = Price |first16 = John L. |last16 = Tonry |first17 = Christopher |last17 = Waters |date = November 2015 |title = Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results |url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2015Icar..261...34V |journal = Icarus |volume = 261 |pages = 34–47 |bibcode = 2015Icar..261...34V |doi = 10.1016/j.icarus.2015.08.007 |arxiv = 1506.00762 |access-date= 22 December 2016}}</ref>
<ref name="Masiero-2014">{{cite journal |display-authors = 6 |first1 = Joseph R. |last1 = Masiero |first2 = T. |last2 = Grav |first3 = A. K. |last3 = Mainzer |first4 = C. R. |last4 = Nugent |first5 = J. M. |last5 = Bauer |first6 = R. |last6 = Stevenson |first7 = S. |last7 = Sonnett |date = August 2014 |title = Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos |url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2014ApJ...791..121M |journal = The Astrophysical Journal |volume = 791 |issue = 2 |page = 11 |bibcode = 2014ApJ...791..121M |doi = 10.1088/0004-637X/791/2/121 |arxiv = 1406.6645 |access-date= 22 December 2016}}</ref>
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== External links == * [http://www.minorplanet.info/PHP/lcdbsummaryquery.php Asteroid Lightcurve Database (LCDB)], query form ([http://www.minorplanet.info/lightcurvedatabase.html info] {{Webarchive|url=https://web.archive.org/web/20171216050541/http://www.minorplanet.info/lightcurvedatabase.html |date=16 December 2017 }}) * [https://books.google.com/books?id=aeAg1X7afOoC&pg Dictionary of Minor Planet Names], Google books * [http://obswww.unige.ch/~behrend/page_cou.html Asteroids and comets rotation curves, CdR] – Observatoire de Genève, Raoul Behrend * [https://www.minorplanetcenter.net/iau/lists/NumberedMPs000001.html Discovery Circumstances: Numbered Minor Planets (1)-(5000)] – Minor Planet Center * {{AstDys|1720}} * {{JPL small body}}
{{Minor planets navigator |1719 Jens |number=1720 |1721 Wells}} {{Small Solar System bodies}} {{Authority control}}
{{DEFAULTSORT:Niels}} 001720 Category:Discoveries by Karl Wilhelm Reinmuth Category:Named minor planets 19350207