Moonstruck: Big treats in the skies

What’s in store for stargazers in 2021? Science reporter Jamie Morton gets a preview fromstardome astronomer Dr Grant Christie

Eclipses and supermoons

If it’s big, bright and white — it might just be a “supermoon”.

And this year brings three of these lunar shows — over three consecutive months.

The phenomenon occurs when a full moon coincides with its closest approach to Earth.

As its orbit around Earth is an ellipse, not a circle, the moon’s distance from Earth can vary from a distant apogee of 406,000km to a closer perigee of 357,000km, although these ranges can also vary because the orbit of the moon is affected by the sun’s gravity.

The moon passes through apogee and perigee each lunar cycle, and the phases of the moon and the orbit aren’t directly linked, so a full moon can coincide with perigee, creating a supermoon.

Stardome astronomer Dr Grant Christie said April 27 will present a supermoon — and if it’s cloudy, the following night should offer a viewjust as good.

“The day before and the day after can still be pretty good — but photographers like to capture it on the right night, so there’s no shadow . . . it appears as a perfectly illuminated disc,” he said.

“But you’d have to have a pretty damn good camera to see that little extra bit of shadow.”

Two further supermoons are due onmay 27 and June 25.

Christie said supermoons were best enjoyed while they were rising. “When it gets higher in the sky, you have no reference size, even though it looks a little brighter. It’s not really until it’s rising above trees, or past buildings, that it really does look strikingly different.”

The May supermoon is a night after a total eclipse. “However, the total eclipse phase will be very brief as the moon only just grazes the dark inner shadow of the Earth, called the umbra,” he said.

“Mid- totality occurs at 20 minutes after midnight. To top it off, the moon will also be near its highest in our sky.”

Another eclipse is on November 19. “While this is a partial eclipse, it is almost total. The moon only just fails to fully enter the darkest part of the moon’s shadow. It will look very much like the one on May 26 — except that it won’t be a supermoon.”

This “mid- eclipse” is due at midnight.

Giants in the sky

On early evenings in early to mid spring, people will have a good chance to view the two largest planets in our solar system.

Saturn and Jupiter have excited much interest from astronomers over past weeks, with the planets coming their closest to the Earth since 1623.

On December 21, Jupiter moved some 763 million kmfrom Earth — with Saturn sitting 856 million km behind it — and the two appeared as one object.

In September and October this year Jupiterwill be as close as 680 million km, and Saturn 800 million km beyond Jupiter.

“Likeearth, Jupiter and Saturn are orbiting the sun, and the Earth is looking back out through space in the same ecliptic plane,” Christie said. “All of these planets’ orbits are slightly tilted — particularly Saturn’s and Jupiter’s.

“Most of the time, when Jupiter happens to pass in line of sight to Saturn, it passes fairly well above or belowit,” he said.

“But occasionally, when the Earth just happens to be in the right spot in its orbit, the three end up in a line — and that’s the rare part about it.”

To look, he said, “the best thing todowouldbetoget upona high spot with a pair of binoculars, let the sun get down a little bit below the horizon, and wait until it gets slightly darker.

“Even with binoculars, you’ll see the moons of Jupiter, and the brighter moons of Saturn.”

Saturn is the most distant planet that can be seen with the naked eye, and orbits the sun once every 29.4 Earth years.

Jupiter, the largest planet, has amass about one-thousandth that of the sun — but 2½ times that of all the other planets in the solar system combined. It orbits the sun once every 12 years.

Meteor showers

Any meteor shower is a sight to behold — and the Leonid happens to be ourmost active.

It’s named after the constellation of Leo, because it’s where the meteors seem to appear from.

These “shooting stars” appear each year around mid-november — peaking about the 17th — but an early wake is needed to see them.

They’re seen around 3am until just before dawn, low in the northeast below the bright star Regulus. We see meteor showers because Earth is moving through the orbital path of a comet, in this case, Comet Tempel-tuttle.

Themeteorswe see are debris, broken off fromthe comet.

When the comet moves closer to the sun than the orbit of Mars, it’s heated by the sun’s radiation and the ice melts, releasing dust, rocks and gas.

While they look impressive, each meteor is only about the size of a pea or a grain of sand.

They appear to emanate from the same point in the sky called the “radiant”.

This is an illusion of perspective, similar to rain in car headlights at night seeming to come towards us from a point in the distance as the carmoves forward.

Thesemeteors can flash across the sky in only a few seconds — so you’ll only spot them if you’re looking in the exact right direction at the exact right time.

Christie said the more faint meteors may be harder to make out this year because the peak activity is predicted to be close to the full moon.

“However, during the lunar eclipse in November the full moon will be much fainter than normal so expect to see more meteors,” he said.

“So of all the Leonid showers, it’s probably the best one to get out and look at.”