Archnemesis of the Avengers / MON 4-8-24 / Tube that uses gravity to transfer liquids / Dip with avocado, casually / Radioactive element discovered by the Curies / 1997 U2 hit that would be apt to play during a 46-Across / 2007 Santana hit that would be apt to play during a 46-Across

Constructor: Peter Gordon

Relative difficulty: Easy (solved Downs-only)

THEME: TOTAL ECLIPSE (46A) — three songs that would be "apt" to play during a TOTAL ECLIPSE:

Theme answers:

• "MOONSHADOW" (17A: 1971 Cat Stevens hit that would be apt to play during a 46-Across)
• "INTO THE NIGHT" (23A: 2007 Santana hit that would be apt to play during a 46-Across)
• "STARING AT THE SUN" (36A: 1997 U2 hit that would be apt to play during a 46-Across)
• "TOTAL ECLIPSE / OF THE HEART" (46A: Event across the U.S. on 4/8/24 ... and, with 57-Across, 1983 Bonnie Tyler hit that would be apt to play during a 46-Across)

Word of the Day: POLONIUM (40A: Radioactive element discovered by the Curies) —

Polonium is a chemical element; it has symbol Po and atomic number 84. A rare and highly radioactivemetal (although sometimes classified as a metalloid) with no stable isotopes, polonium is a chalcogen and chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238. Though longer-lived isotopes exist, such as the 124 years half-life of polonium-209, they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.

Polonium was discovered on July 18, 1898 by Marie Skłodowska-Curie and Pierre Curie, when it was extracted from the uranium ore pitchblende and identified solely by its strong radioactivity: it was the first element to be so discovered. Polonium was named after Marie Curie's homeland of Poland. Polonium has few applications, and those are related to its radioactivity: heaters in space probes, antistatic devices, sources of neutrons and alpha particles, and poison e.g. poisoning of Alexander Litvinenko. It is extremely dangerous to humans. (wikipedia)

Greetings from just south of the Path of Totality. There's a campus-wide viewing party from noon to 3pm, and even though I don't teach today, I might go check it out. Free anti-blindness glasses and everything! I thought this puzzle was ingenious, primarily in the way that it handled the revealer. I can't remember ever seeing an answer that was a revealer in its first part, but then ... went on to be a completely distinct theme answer in its ... totality! "OF THE HEART" is totally eclipsed in the revealer, but then comes out at 57-Across. It's such a weird little flourish. I love it. My only problem with the puzzle is that I think it's using the term "hit" very loosely. Well, not with the Cat Stevens and Bonnie Tyler—those are both classics. But "INTO THE NIGHT," what? "STARING AT THE SUN," what? I know the former only as a very creepy 1980 Benny Mardones song (a real, two-time (!?!) Top 20 hit!), and the latter ... the latter, I don't know at all. In a bizarre coincidence, both the Santana and the U2 "hits" peaked at 26 on the US charts. And "MOONSHADOW" only hit No. 30?! But ... but ... "MOONSHADOW" I know like the back of my hand, why? Maybe because it's been on every Cat Stevens compilation album for half a century. That song is more  my generation than the other two, I guess (even though I was a baby when it came out (US 1971)). I can sing you the entirety of "MOONSHADOW" but don't even know the tune for "INTO THE NIGHT" or "STARING AT THE SUN." This makes the climactic Bonnie Tyler song the only *genuine* hit of the bunch—No. 1 for four weeks in 1983, and now an all time epic-pop classic. So the hits aren't all that hitty today, but at least the puzzle closed big, which is what you gotta do with a themed puzzle! A big finish goes a long way toward making up for any small blemishes or infelicities.