ANOTHER month down the track means the Earth has progressed a further 30 degrees along its orbit around the Sun.
This is the result of our orbital speed at just under 30 kilometres a second, 107.280kmh, or 2.574 million km every 24 hours. This is the reason we see the changing constellations in space as we look out from the night side of our tiny planet.
The plane of the Milky Way is revealing itself more fully now, as over to the northwest our summer favourite, the Orion constellation with stars Rigel on the left and Betelgeuse on the right is setting. This is followed by Sirius, in Canis Major and fainter, Procyon in Canis Minor with Castor and Pollux, the Twins of Gemini in turn.
Just past due north is the bright star Regulus in Leo the lion. Regulus is a very oddball star in that it rotates at a very high velocity, 1.1 million kmh at its equator, compared with the Sun’s 7202 kmh. Large telescopes have also discovered it has two small companions, an orange and a red star at about 4200 astronomical units (Earth-to-Sun distance), and they take about 130,000 years to complete one orbit of Regulus. The other prominent star to the northeast at present is Arcturus, in Bootes.
Around to the southeast and it’s “Wow” time now with much more of our galaxy in view.
The easily identified Scorpio has now cleared the south-east horizon, with the three stars of its head and claws then diagonally down to the right, the red giant Antares in its body.
Look for the string of similar white stars that rise up, then continue on and around and back under, until you come to its sting, the two stars very close together. Like Orion, this is a very large constellation, and very easy to find.
The centre of our galaxy, below Scorpio’s sting in Sagittarius, will come into view not long afterwards. Much higher up, just south of the ecliptic, is star Spica, in Virgo. Then scanning up along the plane of the Milky Way, there are a host of very interesting objects to view in a telescope.
There are the pointers with our next nearest star, Alpha A and B Centaurus, then out from them to the east, the glorious cluster, Omega Centauri, a very tight ball of stars, about 170 light years in diameter and 170,000 light years distant, containing an estimated 7 to 10 million stars.
The Southern Cross is now perpendicular in the evenings, while below it and skimming the horizon to the east you may be able to see Achernar as they rotate on opposite sides of the South Celestial Pole. This goes for all the other stars and objects that are greater than minus 60 degrees south.
Continuing along the vastness of the plane of our galaxy and the host of lesser constellations, we come to the vast Carina Nebula, the gaseous nursery where a great number of new stars are forming, and also where the massive and unstable, Eta Carinae, likely a triple system or more, is to be found. This one is regularly monitored with the large telescopes, due to the fact the activity there is obscured by a very dense cloud of gas equal to the size of our solar system.
This was the result of a massive explosion that occurred in1837 when it flared so bright, it was visible in the daytime. The current consensus is that one of its companion stars collided with it to cause this conflagration.
Continuing on toward the northwest, we pass Canopus, lower down and just off the plane, then we arrive back over to Sirius. So right now is the prime time to get out and take in the major extent of our galaxy
Meanwhile, regarding the planets. There has been a dramatic change over the past month. Both Mercury and Venus might still be seen in the morning sky and are both very close. Mercury, in the constellation of Aries, rising at 6.07am and 1.282au distant.
Venus is rising at 4.57am and 1.501au in Pisces. Mars is in Gemini, setting at 7.18pm and is 2.312au, nearly as far as it can be right now. Jupiter is in Ophiuchus and is 4.423au, and closing as Earth catches up to it once again. Jupiter is rising at 7.05pm this weekend and you can see it near Scorpio. It has edged closer to Saturn this time around.
Saturn is still in Sagittarius, rising not long after at 9:08pm and at 9.499au. Saturn doesn’t appear to move very far across the stellar background each year because it takes 29.4 years for Saturn to orbit the Sun one time, or 10,755.7 Earth days. Jupiter is much closer than Saturn, taking 11.86 years to orbit the Sun or 4.331 Earth days.
The spacecraft Juno has been orbiting Jupiter since July 5, 2016 in a very elliptical polar orbit initially. But the plans to control it to a tighter orbit were abandoned due to the discovery of faulty helium valves on the guidance system. So the controllers had to settle for the original 33 days to make each orbit of Jupiter. It is virtually halfway at its amended target date of July 2021 right now and the longer orbit means far fewer images of the planet and its moons will be gathered.
By Norman Izett