Busy weekend in the sky

Saturn should be visible tonight.

Not only is it the General Election on the ground on Saturday, but there are a few things happening in the sky as well.

September 23 is the date of the spring equinox, when days and nights have the same length. 

It is also at 2am on Sunday when clocks are set forward an hour and Daylight Savings time begins.

The equinox this year happens at 8am on Saturday morning. That is when the sun crosses the celestial equator and moves from the northern to the southern hemisphere. The celestial equator is an imaginary line in the sky above Earth's Equator – which is also an imaginary line.

The sun is not actually crossing anything; it is the part of the cycle when the earth's rotational tilt is neutral, not toward or away from the sun.

The September equinox marks one of the four major turning points or corners of the seasonal cycle. Seasons occur on Earth because the planet's axis is tilted with respect to its orbit around the sun. During an equinox, the tilt effectively vanishes, and both hemispheres experience equal amounts of sunshine. Day and night are also about the same in length—the word ‘equinox' derives from the Latin for ‘equal night'.

In the night sky Jupiter is heading for conjunction and will be behind the sun from an earth dweller's viewpoint. One of the last chances to see it is on Friday night, along with Saturn.

On the Saturday morning of polling day early risers with a clear sky may be able to see Venus, Mars and Mercury. They are all very close in the morning sky before sunrise, but the sight will be lost in a dawn.

Mars and Mercury would be very hard to see because they are dim, and the sun's light would quickly block them out, says Josh Kirkley at the Auckland Stardome Observatory.

From an astronomer's point of view it doesn't really make the cut as a planetary alignment.

“Most planetary alignments are when the five naked-eye visible planets; Mercury, Venus, Mars, Jupiter and Saturn form an arc across the sky on our solar plane, either after sunset or before sunrise,” says Josh.

“There doesn't appear to be a planetary alignment by most descriptions. Jupiter and Saturn are both visible after sunset on the 23rd, but they are too far apart to be considered in an alignment.”



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Supermoon from Dive Cresent, 8pm last Sunday evening. Photo: Sally Garner.

Send us your photos from around the Bay of Plenty. kendra@thesun.co.nz