The two brightest nighttime stars available in the Minnesota and Wisconsin sky are Sirius and Arcturus. April is the only month of the year we can enjoy both of them at the same time in the early evening: Sirius in the low southwest sky and Arcturus in the low eastern heavens.
Sirius is the king of stellar brightness and is often referred to as the star of winter, although it’s visible every evening from late December into early May. As most stars do in our celestial dome, it migrates from east to west from night to night as Earth orbits the sun. This is Sirius’ swan song as it shines away in the southwest evening sky. By mid-May, it’ll already be below the horizon as twilight ends, as it begins its summer vacation. Incidentally, when you’re looking for Sirius in the southwest this week, don’t mistake Jupiter for Sirius. Without a doubt, Jupiter is brighter than Sirius, but of course, Jupiter isn’t a star. It just happens to be in that part of the heavens this spring.
(Mike Lynch)
Sirius is so bright because it’s one of the closest stars to the Earth, a little over eight and a half light-years away, with just one light-year, the distance light travels in a year, equaling nearly 6 trillion miles. That puts Sirius at nearly 50 trillion miles away. Astronomically, that is considered just down the street. Sirius’ brightness is also helped by its size, nearly 1.5 million miles in diameter. Our sun isn’t even a million miles across.
Meanwhile, Arcturus, the star of summer, is on the rise in the eastern sky. It’s by far the brightest evening star in the east this spring. You’ll notice that it has an orange glow to it. That’s because it’s considered a red giant star, a bloated star nearing the end of its life. It’s over 25 times the diameter of our sun. It’s also considered to be a nearby star at a little over 36 light-years away. Since a light-year is the distance light travels in a year, the light that we see from Arcturus tonight left that star just over 36 years ago when Madonna was in her prime. Eventually Arcturus will belch away most of its gas and will shrink down to a white dwarf star.
Arcturus is the brightest star in the constellation Bootes, which is supposed to outline a herdsman or plowman, but honestly, it much more resembles a sideways kite with Arcturus marking the tail. Just below Bootes is a very small constellation, Corona Borealis, the Northern Crown. It arguably resembles a crown or a tiara on its side. To me, I see it this time of year as a backward C.
T-Coronae Borealis (Mike Lynch)
Corona Borealis is the home of a potential “guest star.” At the lower left side of the backward C that makes up the northern crown is an extremely faint star, T-Coronae Borealis. It’s very close to the star Epsilon at the end of the C. There’s no way you can see that star with the naked eye. Even with a moderately large telescope, it’s extremely difficult to find. The big news about T- Coronae Borealis is that there’s a decent chance that it’ll suddenly dramatically brighten into a new naked star, at least temporarily. T-Coronae Borealis is also known as the “Blaze Star,” but it sure doesn’t blaze that often. In the last 150 years, it’s only blazed up for a few days back in 1866 and again in 1946, but many astronomers predict it could blaze again in the very near future.
So, what’s going on? T-Coronae Borealis, about 3,000 light-years away, is a double star system comprising a large red giant star and a dying white dwarf star. As the two orbit each other, the intense gravity of the white dwarf pulls gas off the red giant star. The details are complicated, but the white dwarf star can only acquire so much additional gas before it becomes extremely unstable and ignites in a brief flash of nuclear fusion on its surface, triggering what is known as a nova outburst. When this happens to T-Coronae Borealis, it could temporarily become as bright as Polaris, the North Star. But after about a week, T-Coronae Borealis will fade back to obscurity.
No one really knows for sure when T-Coronae Borealis will flare up but most astronomers think it’ll be soon. In fact, there were predictions that it would flare up last summer. I heard one wild prediction about a month ago that it would brighten up on March 27. Obviously, that didn’t pan out. I think someone was trying to create some overhyped headlines. My advice is to keep an eye on Corona Borealis. The Northern Crown might soon process another jewel very, very soon!
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