| 21. | He studied comets, and discovered the periodic comet 4P / Faye on 22 November 1843.
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| 22. | She co-discovered the periodic comet 61P / Shajn Schaldach.
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| 23. | In 1933, he discovered the periodic comet 36P / Whipple and the asteroid 1252 Celestia.
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| 24. | He also discovered two periodic comets : 171P / Spahr and P / 1998 U4.
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| 25. | Ikeya discovered the periodic comet 153P / Ikeya-Zhang on February 1, 2002 in Mori, HokkaidM.
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| 26. | He observed the bright comet of the 1860 and two years later discovered a periodic comet.
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| 27. | He discovered the periodic comet 37P / Forbes.
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| 28. | Periodic comet 153P / Ikeya-Zhang is discovered by his self-made telescope on Feb . 1st 2002.
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| 29. | A number of periodic comets discovered in earlier decades or previous centuries are now lost comets.
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| 30. | Abell also co-discovered periodic comet 52P / Harrington-Abell.
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