This Week in Billboard Chart History: In 2009, Lady Gaga Led the Hot 100 With Her First No. 1, 'Just Dance'

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Lady Gaga performs on the Other Stage at the Glastonbury Festival on June 26, 2009 in Glastonbury, England. 

The song became her first of three No. 1s. Plus, remembering feats by George Harrison, Michael Jackson & a then-days-old Blue Ivy Carter.

Your weekly recap celebrating significant milestones from more than seven decades of Billboard chart history.

Jan. 15, 2000
The first song to ascend to No. 1 on the Billboard Hot 100 in the 2000s? Christina Aguilera earned the honor with "What a Girl Wants."

Jan. 16, 1988
The last No. 1 to date by a member of The Beatles topped the Billboard Hot 100, as George Harrison's "Got My Mind Set on You" (featuring Ringo Starr on drums) reached No. 1. Co-produced by ELO's Jeff Lynne, the song sparked the supergroup Traveling Wilburys – Harrison, Lynne, Bob Dylan, Roy Orbison and Tom Petty – which released two hit albums, in 1988 and 1990. (Another Beatles anniversary just ahead …)

Jan. 17, 2009
Birth of a Monster: Lady Gaga crowned the Billboard Hot 100 for the first time, as her debut entry, "Just Dance," featuring Colby O'Donis, spent its first of three weeks at No. 1. She's since led with follow-up "Poker Face" and 2011's "Born This Way."

Jan. 18, 1964
When Beatlemania began: The Beatles made their first appearance on a Billboard chart, as "I Want to Hold Your Hand" entered the Billboard Hot 100 at No. 45. The iconic song would go on to become the first of the Fab Four's record 20 Hot 100 No. 1s.

Jan. 19, 1980
Michael Jackson ruled the Billboard Hot 100 with "Rock With You." The song marked his first of nine No. 1s in the '80s, the most of any artist in the decade. (He totaled 13 career No. 1s as a soloist.)

Jan. 20, 1990
Michael Bolton banked the first new Billboard Hot 100 No. 1 of the '90s, as "How Am I Supposed to Live Without You" jumped 4-1. Laura Branigan had first taken the ballad to No. 12 in 1983.

Jan. 21, 2012
Days-old Blue Ivy Carter made Billboard chart history, receiving featured credit on dad Jay Z's "Glory." As the track, featuring her cooing, debuted on Hot R&B/Hip-Hop Songs at No. 74, she became the youngest person ever to appear on a Billboard chart.