Shares of Apple Inc. set a new closing high of US$502.60 on Monday after gaining $9.18 (+1.86 percent) on strong volume. That’s just shy of the intra-day record high of $503.83, which was set earlier in the day.

With 932.4 million shares outstanding, that means Apple inched closer to being the first company valued at half a trillion dollars since Microsoft hit a valuation of $600 billion in 1999. Apple’s market cap is currently $468.6 billion. Exxon Mobil, the world’s second most valuable company, ended the day at $84.42, a gain of $0.62 (+0.74%), giving the now distant #2 a market cap of $404.6 billion.

AAPL has been on a tear in 2012, rising some 24 percent from the $405 per share closing mark it set on the last day of 2011. For those keeping score at home, a 24 percent rise in just over six weeks qualifies as a rousing success that would be the envy of any CEO.

The company’s blowout December quarter prompted the run up—rumors of record iPhone sales began circulating in the final days of December, and Apple reported a stunning $46 billion revenue and earnings of more than $13 billion. Record sales of 37 million iPhones, 15.4 million iPads, and 5.2 million Macs all contributed to the results.

AAPL Chart for Last Six Months, Including Key Events for Apple

As Wall Street digested the news, shares in AAPL began a swift climb towards $500, which some considered a resistance point. Monday’s session should disabuse any Doubting Thomases of that idea. Most analysts The Mac Observer follows currently have price targets in the $550-$640 range.

In more recent weeks, fresh rumors of an impending iPad refresh and a major shift in MacBook Pro form factors might be garnering Apple some positive momentum with investors. There’s also been speculation about and rumors that Apple will engage in some kind of dividend in 2012, be it a one-time dividend payout or an ongoing quarterly dividend.

*In the interest of full disclosure, the author holds a tiny, almost insignificant share in AAPL stock that was not an influence in the creation of this article.