The recurrent nova T Pyxidis, which had its last outburst in December 1966 and has been very overdue for its next, finally began a new flareup on April 14th. By the next day it had brightened to about magnitude 8.4. In 1966–67 it reached 6.5 within about a month, and now it has done so again.
Here's a blink animation showing before and after, courtesy Ernesto Guido and Giovanni Sostero in Italy. South is up.
The star is in the dim constellation Pyxis east of Puppis and Canis Major, sinling out of sight for northern observers in May. (Here are finder and comparison-star charts from Sky & Telescope. For larger-scale comparison-star charts, you can use the chart-making site of the American Association of Variable Star Observers).
As a white dwarf accreting mass from a binary partner, T Pyx is a prime candidate to explode completely as a Type Ia supernova within the next 10 million years. Last year, careless reporting led to a flurry of media buzz that if it blows up soon it could endanger Earth. Not so. At its distance of about 3,000 light-years, T Pyx would shine as brightly as magnitude –9 if it went Type Ia (as bright as a thick crescent Moon), but its radiation wouldn't harm us. The current Wikipedia article on T Pyx explains this story well.
In its past known outbursts (1890, 1902, 1920, 1944, and 1966), T Pyx took about 20 days to reach 7th magnitude or so and remained 8th mag or brighter for about two months.
Elaborating on this, Bradley Schaefer writes: "Judging from the 1967 eruption light curve, the current eruption light curve will... slowly rise to a peak near V=6.4 around 20 May, slowly fade to V=10 by middle August, then have a sudden drop by two magnitudes over the next 20 days (with drop being invisible due to the Sun). The 1967 eruption did show fast intra-night variations, but the old data does not have the time resolution to tell what is going on."
UPDATE May 13: As T Pyx disappears to the twilight horizon for Northern Hemisphere observers, it has brightened to magnitude 6.5 as of last night according to various observers reporting to the AAVSO. Here are recent observations and a light curve for the most recent 50 days.