Sky Notes For November& December 2024
Brought to you by Dr. Roy Gretton, Journal Editor of The Nottingham Astronomical Society.
Contact details are on the Nottingham Astronomy website: hps://nonghamastro.org.uk/
Please note, the NAS new permanent venue for our main meetings on the first Thursday in the month.
Nottingham Emmanuel School Gresham Park Road,
West Bridgford, Nottingham, NG2 7YF
Tilting Toward the Planets
As you probably know, we experience summer and winter because the Earth’s axis is tilted by about 23.5degrees relative to the plane of its orbit.
This year the Northern Hemisphere will be tilted furthest away from the Sun on December 21st whereas our tilt toward the Sun was at its maximum back on June 20th, and will again be at it greatest next June. It so happens that this winter the two nearest of the outer planets, Mars and Jupiter, are on roughly the opposite side of the sky to the Sun, so our axis is tilted toward them. This means that both planets are high in our sky this winter, and therefore deserve at least a glance or, if you are a keen sky watcher, a closer look through a telescope.
Looking south at midnight on Christmas Day Mars in Cancer, Jupiter in Taurus
Interestingly, Mars’ axial tilt, at 25 degrees, is very similar to that of the Earth, so Mars goes through a similar cycle of seasons to ours, but over a longer period of time because the planet takes 687 days to travel around the Sun. For Mars’ northern hemisphere, midwinter last occurred on 7th June 2024, and the next midsummer will be on 29th May 2025, so the north of Mars is currently passing through its springtime. Like Earth, Mars has polar ice caps, in Mars’ case made of a mixture of solid carbon dioxide (‘dry ice’) and ordinary water ice, and these grow and shrink according to the seasons. As we observe Mars this winter, the northern ice cap will be shrinking and the southern cap growing.
Jupiter, by contrast, has a very small axial tilt of only 3degrees, so it has negligible seasons. But by far the oddest tilt of any planet is that of Venus, quoted as 177degrees. You might wonder how a planet’s tilt can possibly be more than 90 degrees. Wouldn’t 177degrees effectively be the same as 3 degrees? The reason for this apparent paradox is that Venus rotates the “wrong” way round. While most planets, when viewed from above the north pole, rotate anticlockwise(and they all travel around the Sun anticlockwise),Venus rotates in a clockwise fashion – as if she is upside down! So a tilt of 177 degrees makes scientific sense.
The Planets
On a clear evening, Jupiter is unmissable as it climbs above the eastern horizon, a bright golden white “star” with no twinkle. It will be rising at 5:30 pm in mid November, at 3:30 pm in mid December, and before 3pm as the New Year begins.
Jupiter is at opposition to the Sun, and therefore due south at midnight, on December 7th. A small telescope or binoculars will show the four brightest moons, Io, Europa, Ganymede and Callisto buzzing around the planet from night tonight. Mars, dimmer than Jupiter and distinctly orange, follows the gas giant, rising at 9 pm in mid November, 7pm in mid December, and it will be at opposition on January 16th.
Saturn, lower in the sky than the two previous planets, will be an evening object, due south at 7:30 pm in mid November and at 5:30 pm in mid December. Throughout the autumn and winter Venus will be lurking in the evening sky after sunset, brighter and whiter than any of the other planets, and in mid January it will pass close by Saturn. In the second half of December early risers may catch a glimpse of Mercury low in the southeast an hour or so before sunrise.
Phases of the Moon
November December
New Moon 1st 1st
First Quarter 9th 8th
Full Moon 15th 15th
Last Quarter 23rd 22nd
