This image, assembled from 24 exposures taken from the Hubble Space Telescope in October 1999, January 2000, and December 2000, shows the Crab Nebula, or Messier 1, in the constellation of Taurus.
It is the result of a star that blew apart in a massive explosion in 1054. It became a very bright light that could be viewed from Earth even during the day, and second only in brightness to the Moon. It faded out of sight after two years.
ANOTHER month has passed, and the changes are obvious. Over to the west, in our long summer twilight, the main part of the Milky Way has now set, with the Great Square of Pegasus following behind.
Low in the north-east quarter comes M33 and Andromeda, followed by Triangulum and Aries higher up. Next and now well positioned is the Pleiades-Matariki cluster, followed by Taurus the bull with the giant red star Aldebaran as one of the bull’s eyes.
Then comes the unmistakable Orion with the very bright star, Rigel, above, and the red supergiant Betelgeuse below. The three stars that represent Orion’s belt and often called, The Pot are in the middle. These and most other constellations appear the wrong way up to us here in the southern hemisphere.
Also in this part of the sky, while the major part of our galaxy rotates out of sight below our southern horizon, appears the part of the Milky Way where our sun is and the part that has been circling below our southern horizon over the winter.
Rigel, or Beta Orionis, is a class B supergiant, some 800-light-years distant with a surface temperature of 21,632 degrees, much hotter than the 9941 degrees of our Sun. It radiates this energy in ultra violet light mainly, hence its blue-white appearance, shining at 17,000 times brighter than our sun. It also has two small companion stars orbiting it at a great distance.
Following Orion comes Sirius in Canis Major, the brightest star we can see and sometimes known as the eye of the hunter’s dog. It is more than twice the size of our sun and 25 times more luminous. Continuing around high in the southeast, you can’t miss another supergiant, Canopus, also appearing in the darker background, just off the mainstream of the Milky Way stars.
Canopus is the second brightest star in the sky, circling much closer to the south celestial pole and just dipping briefly below the southern horizon because of its -53.4 degrees south latitude.
Gamma Crucis, the top star of the Southern Cross, is just over -57 degrees south, or seven moons side by side nearer the pole. All the other main stars of the Cross, as well as the Pointers, are always visible in our southern skies as a result. Achernar, the ninth brightest star, is now crossing at its highest and is part of the constellation Eridanus, the river, that starts way back at Rigil in Orion, meandering all over the sky and ending at Achernar.
Achernar, at 139 light years away and seven times larger and 1350 times brighter than our Sun, is quite an enigmatic character to observe due to its extremely high rotation of 250 kilometres a second at its equator. This enormous spin has resulted in it becoming rather squashed causing its diameter to be 57 percent larger around the equator than over its poles.
Below and closer to the South Celestial Pole are the large and small Magellanic Clouds and at present, 47 Tucanae, the lovely globular cluster that contains at least 10,000 stars, is just starting to curve down in the southwest.
Now back to the west and the bright lights we enjoyed over the winter have largely gone from the evening skies. Only Mars remains, now out to 1.121 astronomical units – slightly more than the distance to the sun – and rising at 12.39pm.
Mars is the focus of much attention right now with the successful landing of the recent InSite probe, which is hard at work already, sending information daily back to NASA. The rest of the visible planets that were lined up across the evening sky are now in the morning sky. This is because our closer orbit means we have left them behind due to our shorter rotation, with the exception of Venus, which sped by us on the inside, and rising at 3.28am at 0.508 AU. It is getting brighter in the morning skies as it clears the sun on its way to the furthest point of its orbit.
Jupiter, presently in Ophiuchus and now out to 6.3 AU, rises at 4.52am and is not readily observable for now. Saturn has also just moved from the evening sky and is much further away now, out to 11.001AU, still in Sagittarius and rising at 7am so is also right in the glare of the sun.
We are in for a treat on December 21, 2020 however, when both Jupiter and Saturn pass one another, a rare conjunction, appearing 0.06 of a degree together. But the anticipated spectacle will only be visible about 15 degrees above the west at around 9.15pm, setting at 10.50pm. A mid-winter conjunction would have given us all a great view of this, but this is the way the cookie crumbles so to speak.
Summer Solstice occurs on December 22 giving us our longest day.
By Norman Izzet