:61P/Shajn–Schaldach

{{Short description|Periodic comet with 7 year orbit}}

{{Infobox comet

| name=61P/Shajn-Schaldach

| image= 61P 2022-10-19 image ZTF-sso-449-zr-fov-7.0arcmin.png

| discoverer=Pelageja F. Shajn at the Simeiz Observatory, Crimea and
Robert D. Schaldach at the Lowell Observatory, Arizona, US

| discovery_date=18 September 1949 and 20 September 1949

| designations=

| epoch= 2014-Dec-9

| semimajor= 3.5769 AU

| perihelion= 2.1080 AU

| aphelion= 5.2458 AU

| eccentricity= 0.4267

| period=7.49 yr

| inclination= 6.0097°

| last_p= 2022-10-23{{cite web

|title=61P/Shajn-Schaldach Orbit

|url=http://www.minorplanetcenter.net/db_search/show_object?object_id=61P

|publisher=Minor Planet Center

|access-date=2017-04-07}}
2015-10-02
2008-09-06

| next_p= 2029-Nov-25{{cite web

|title=Horizons Batch for 61P/Shajn–Schaldach (90000662) on 2029-Nov-25

|publisher=JPL Horizons

|type=Perihelion occurs when rdot flips from negative to positive

|url=https://ssd.jpl.nasa.gov/api/horizons.api?format=text&COMMAND=%27DES%3D61P%3BCAP%27&START_TIME=%272029-Nov-24%27&STOP_TIME=%272029-Nov-26%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27

|accessdate=2023-07-06}} (Soln.date: 2023-May-04)

}}

61P/Shajn–Schaldach is a periodic comet in the Solar System with a current orbital period of 7.49 years.{{cite web|url = http://cometography.com/pcomets/061p.html| title= 61P/Shajn-Schaldach|access-date = 21 February 2015}}{{cite web|url = http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=c&o=0061P|title = Elements and Ephemeris for 61P/Shajn-Schaldach|publisher = International Astronomical Union|access-date = 21 February 2015|archive-url = https://web.archive.org/web/20130828231022/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=c&o=0061P|archive-date = 28 August 2013|url-status = dead|df = dmy-all}}

It was discovered on 18 September 1949 on a photographic plate by Pelageja F. Shajn at the Simeiz Observatory, Crimea, part of the Crimean Astrophysical Observatory. It was also discovered independently two days later by Robert D. Schaldach at the Lowell Observatory in Arizona, US, also on a photographic plate. Shajn then found evidence of the comet on earlier photographs taken on August 28 and September 4.

The first computations of the comet's orbit gave a perihelion date of between December 1949 and October 1950 with a periodicity of 7.76 years. After taking into account perturbations due a close approach to Jupiter the next perihelion was calculated to be on 15 March 1957 but in that year it was never found. It was also not discovered on its next predicted appearance in 1964. The most likely explanation for the two failures was the comet's faintness.

It was, however, re-located on 29 September 1971 by Charles T. Kowal of the Department of Astrophysics, California Institute of Technology, US, using the 122 cm Palomar Schmidt telescope, who estimated its brightness at a faint magnitude of 16. Other astronomers confirmed the sighting.

The comet was successfully observed on its subsequent returns in 1979, 1986, 1993, 2001 and 2008.

Based on observations by the Hubble Space Telescope the nucleus of the comet has an effective radius of 0.61 ± 0.03 km.{{cite journal |last1=Lamy |first1=P. L. |last2=Toth |first2=I. |last3=Weaver |first3=H. A. |last4=A'Hearn |first4=M. F. |last5=Jorda |first5=L. |title=Properties of the nuclei and comae of 10 ecliptic comets from Hubble Space Telescope multi-orbit observations★: HST observations of 10 ecliptic comets |journal=Monthly Notices of the Royal Astronomical Society |date=11 April 2011 |volume=412 |issue=3 |pages=1573–1590 |doi=10.1111/j.1365-2966.2010.17934.x|doi-access=free }}