Earth approaching closest pass to sun

Meteor shower coming

When I tell people Earth will be at its closest approach to the sun (perihelion) for the year on Jan. 2, 2021, they have a hard time understanding why the weather isn't warmer.

One would logically assume that being approximately 10 million kilometres closer to the sun, we would experience warmer weather. And if the Earth's northern hemisphere was tilted towards the sun at this time of the year, we would, indeed.

However, as the Earth travels along its orbital path around the sun each year, it wobbles slightly, its poles transcribing circles much like a child's spinning top, tilting about 21 degrees from perpendicular (relative to its orbital plane around the sun). First, Earth tilts towards the sun, then away from it, at different times of the year. This is what gives us our summer season and winter season respectively.

Only at the two equinoxes (vernal and autumnal) are the Earth's two poles aligned at 90 degrees relative to Earth's orbital plane to the sun.

Earth's annual orbit around the sun is not circular, but is, instead, elliptical in shape, with the sun just slightly closer to one end of Earth's oval-shaped orbital path than the other.

On Jan. 2, Earth is on the end of the oval shape closest to the sun, and, thus, at its closest point to the sun. Because the northern hemisphere is tilted away at this point, it receives less direct sunlight; what it does receive is spread out at a lower angle over that portion of the hemisphere facing the sun, resulting in less warmth and the onset of colder weather.

The southern hemisphere, because it's pointed towards the sun at this time of the year and approximately 10 million km closer, receives a greater amount of direct sunlight, and enjoys hot summer weather.

Take heart, though: from Dec. 21 (the winter solstice), the days are slowly getting longer, and, as the Earth continues its journey around the sun, are working their way towards the summer solstice in June.

METEOR SHOWER COMING

Early January brings the new year's first meteor shower as the Quadrantids peak overnight on Jan. 2-3.

The radiant (the meteor shower's apparent point of origin in the night sky) lies between the constellations of Draco — the Dragon and Bootes - the Herdsman.

This meteor shower (first observed in 1825) is named after a now-defunct constellation called Quadrans Muralis after an angle measuring device used by the ancient Egyptians and Greeks. This was removed from the official

list of constellations in 1922 by the International Astronomical Union, but because the shower had already been named, the label Quadrantid was retained.

The Quadrantids are debris from the asteroid 2003 EH1, discovered on March 6, 2003, and subsequently found to be the parent source of the Quadrantid meteors. Unlike many meteor showers whose peak may last a couple of nights, the Quadrantids last only about six hours.

Begin to look for the Quadrantids once the radiant has cleared to the north-northeast horizon just before midnight, with the best viewing likely during the pre-dawn period. Unfortunately, the waning, gibbous moon will be up all night and will wash out the fainter meteors.

The Quadrantids hit the

Earth's upper atmosphere at about 150,000 kms/hr, so you can expect to see some bright fireballs, despite the moonlight, especially away from city lights.

THIS WEEK'S SKY

Mercury is still too close to the sun to be seen.

Venus (magnitude -3.94) remains just visible in the eastern, pre-dawn sky, rising around 6:20 a.m., reaching nine degrees above the southeast horizon before fading from view by about 7:35 a.m.

Mars (magnitude -0.32) is visible shortly after 5 p.m., 44 degrees above the southeast horizon, reaching an altitude of 54 degrees above the southern horizon by about 7:15 p.m., and remaining visible until about 1:10 a.m. when it drops below nine degrees above the western horizon.

Jupiter and Saturn have now drifted far apart from one another in the western, post-sunset sky. Jupiter (magnitude -1.96) is visible about 12 degrees above the southwest horizon shortly before 5 p.m., setting by about 6:30 p.m. Saturn is now too close to the Sun to be seen.

The last full moon of the year occurs on Dec. 30, 2020. It is often referred to as the cold moon, the reasons for which are, no doubt, selfevident.

Until next week, clear skies, and may 2021 be a prosperous and healthy year for you all.

EVENTS

Dec. 30: Full (cold) moon Jan. 2: Earth at perihelion (closest approach to the sun) Quadrantid meteor shower peak (after midnight)

On Jan. 2, Earth will be at its closest to the sun, known as the perihelion.