There will be a few fleeting conjunctions of planets and moons in July, but with the Sun just past its northernmost point in the sky, all of the planets will be south of it and low on the horizon.
On July 11, just after sunset around 10:00 p.m., look low in the WNW about 5 degrees above the horizon to see a very thin crescent of New Moon and about six lunar diameters to its left a very bright Venus . With binoculars and firm hands, you will also see a faint Mars about a lunar diameter to the left of Venus. Over the next two days, Venus will pass above Mars upward and eastward (left). Three clear nights in a row and you will understand why the Greeks called them “planets” or “wanderers”. Later in the month, July 23-25, you can watch the Full Moon just passed from west to east under Saturn, then Jupiter after 11:00 p.m. lowest in the southeast.
Jupiter’s four big moons show up a bit this month. You can see them all three times on one side of the planet: east of Jupiter before midnight on July 9, after 1:30 a.m. on July 19 west of Jupiter, and left to right in order of distance, Io, Europe, Ganymede and Callisto! Four days later, you can see them after 10:30 p.m. on July 23 in reverse order on the east side of Jupiter.
The rest of this month’s article features the constellation Scorpio. It’s one of the few constellations that actually resemble their namesake, along with Orion, Cygnus, and Leo (sort of). Scorpio is located 30 degrees south of the celestial equator and just west of the center of our Milky Way galaxy in Sagittarius and is visible just after sunset in the SSW.
The brightest star in Scorpio is Antares, nicknamed by the ancient Greeks Ἀντάρης, or “rival of Mars”, perhaps because its color and luminosity are very similar and it is only 4 degrees apart. south of the ecliptic where we see the planets. It is in fact a binary star; the main one is the variable red giant star we see which has burned off much of its hydrogen nucleus and is now fusing helium into heavier elements. When this additional cycle of fusion started, the star enlarged and left the main cycle types to become a red supergiant. It appears to have formed about 12 million years ago with an initial mass of about 17 solar masses; contrasts this with our Sun with a solar mass and an age of 4500 million years. Antares now appears to be reduced to around 12 solar masses, which may sound odd, but when these stars light up during the helium fusion, the extra energy entering the stellar plasma increases the temperature and everything expands. In the case of Antares, it is estimated that its radius would lie somewhere between the orbits of Mars and Jupiter. At this distance, the gravitational hold on its outer atmosphere is quite tenuous and the upper layers begin to be washed away into space. Antares A is actually very similar in size, mass, star type, and ultimate fate to Betelgeuse in the upper left corner of Orion. Its unfortunate companion, Antares B, is a blue-white, B-type main sequence star of about seven solar masses that probably formed around the same time as Antares A but burned off its fuel. more slowly and haven’t done so yet. blown in a giant phase. Both suffer the same fate as supernovae, but Antares B is in an exciting time when Antares A explodes. Let’s all be happy to be 500 light years away.
One source I’ve read indicates that many Scorpio and Centaur stars are at similar distances, suggesting a common origin from a single source of gas dust. The three stars to the right of Antares (like scorpion claws, of sorts) are all about 400-600 light years apart and are all blue-white stars of the B-type main sequence. down, they are called Acrab, Dschubba and Fang. Seriously. Apparently, this is part of a Chinese asterism made up of the other two plus a few. It is also a triple star with two very close B-type stars in orbit every 1.57 days with a third much further away. At the bottom left of Antares is Paikauhale, to the right Al Niyat and the shining star in the tail of the scorpion is Shaula; the first name is Hawaiian and the last two are Arabic. All of them are the same type B stars at a distance of 400 to 600 light years.
There will be no Sunshine Coast Astronomy Club Online Zoom Meeting in July, but we do hope to have an attempted meeting at Davis Bay Seawall on the evening of Friday, August 13, near Perseid Peak. meteor shower. Details will be posted on the club’s website at: sunshinecoastastronomy.wordpress.com.