November 5, 2023
Sunday, November 5, 2023
Did you remember to set your clocks back an hour? Our digital devices take care of it automatically but there are probably still the microwave and stove clocks to take care of. The moon was at third (or last) quarter last night, so this week will see it shrink in size as it gets closer to the sun on our sky. Tomorrow early morning, the waning crescent moon will be near the star Regulus at the end of the Sickle part of Leo (at the bottom of the question mark that represents the lion’s head and chest).
Regulus is a B-type “main sequence” normal star that is blue-white hot, over twice as hot as the sun. It radiates about 360 times the energy of the sun and is nearing the end of the normal adult stage of its life. Regulus spins extremely fast with a rotation period of just 16 hours (compared to the over 25 days for the sun). That rapid spin distorts Regulus’ shape into an oblate spheroid that is 32% larger at the equator than the polar diameter.
Regulus is actually part of a quadruple system. The system consists of two binaries that orbit each other. One of the binaries is made of a cool, orange K-type star and a cooler, red M-type star that orbit each other at a distance of 97 astronomical units (1 AU = the Earth-to-sun distance) with a period of 880 years. Orbit times can be found from orbit circumference / speed found from doppler shift. M-type stars make up about 75% of the stars in the universe and K-type stars make up about 12% of the stars. The sun is a member of the hotter, yellow G-type stars making up about 8% of the stars out there. Most of the bright stars we see from the city are the extraordinary, rare type ones that are much hotter and more luminous than the sun. Just one-tenth of a percent of the stars are B-type stars like Regulus.
The second binary is a small dead star called a white dwarf that orbits Regulus at just 0.35 AU distance every 40 days. The progenitor star of the white dwarf was even more massive and hotter than Regulus. During its dying red giant stage, it would have transferred its outer gas layers to Regulus, spinning up Regulus as it did so. The white dwarf is just the cooling core remnant of the star.
The two binaries orbit each other at a distance of 4200 AU or about 100 times Pluto’s distance from the sun with an orbital period of at least 125,000 years. Quite the complicated system!
On the morning of November 9 (Thursday), early risers will be treated to a thin waning crescent moon right next to the brilliant “morning star” Venus low in the eastern sky with just a pinky width at arm’s length separating the two. The pair will rise at about 2:45 a.m., so they’ll be about a third of the way up in the eastern sky by 5:30 a.m.
On the pre-dawn morning of November 11, a very thin waning crescent moon will be next to Spica, the brightest star of Virgo. Spica is actually a close binary system made of two B-type “main sequence” normal stars (like Regulus) that orbit each other at just 0.12 AU apart (about one-third the distance between Mercury and the sun) in just 4 days. The larger one of the two radiates about 12,100 times the energy of the sun. It has a mass that is 10.5 times the sun, so when it dies, it may go supernova. The smaller one radiates about 1500 times the energy of the sun and has a mass about six times the sun, so it won’t have the explosive death of its companion.
The moon will be at new moon phase on November 13, so by November 18, the moon will be a fat waxing crescent. The night of November 18/19 is the peak of the Leonid meteor shower. The moon will set in the early part of the evening, so it won’t wash out the meteors as the numbers pick up later in the night. The Leonids form from Earth passing through the dust trail left behind by Comet 55P/Tempel-Tuttle.
In the evening sky, you’ll see brilliant Jupiter rising in the east at about 5:15 p.m. with the stars of Pisces and Aries. Saturn will already be up in the southeast by then at the right (west) edge of Aquarius. Saturn reaches the meridian due south a little after 7 p.m. and Jupiter will reach the meridian by about 11:30 p.m.
On Thursday, November 16, the William M Thomas Planetarium will present “Dynamic Earth” about Earth’s climate system. The fall season of shows will end with the double showing of the traditional holiday show, “Season of Light” on November 30 and December 7. Visit the Planetarium’s new website for more information about the shows and purchasing tickets.
Wishing you dark skies!
—
Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
