I often get emails asking, "If you think a stock is so cheap, then why don't you own it?" But price alone does not qualify a company as investment-worthy; timing is also an important aspect. And in the case of Sirius XM Radio Inc (NASDAQ: SIRI ), which has soared close to 40% over the past several months, many investors feel they've missed the boat. One of the major catalysts for Sirius' recent movement has been Liberty Media Corp (NASDAQ: LMCAD ). The company has been buying shares of Sirius on the open market, and on Jan. 17 Liberty officially became majority owner of Sirius. According to an SEC filing, to seal the deal, Liberty acquired an additional 50 million shares of Sirius at an average price of $3.15. Contrary to recent opinion, this was not a ceiling. However, although the stock has fluctuated — reaching a high of $3.25 on Feb. 1 — shares have essentially traded flat since Liberty took over.