STARGAZING: Summer solstice 2016

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton.

Universal Time on June 20, which translates to 18:34 EDT and 15:34 PDT, the Sun reaches the northernmost point in its yearly travels — the summer solstice.

On this day we have the most hours of daylight and the sunrise and sunset points on the horizon are at their furthest north. On any day the Sun is highest in the sky at local (standard time) noon, but at noon on the summer solstice the Sun is the highest it gets. Actually this applies only in the Northern Hemisphere. South of the equator it is the Winter Solstice, with its lowest noontime Sun and minimum hours of daylight.

What we are seeing here is the process that gives us the seasons. The cause is the inclination of the Earthís axis.

Imagine an orange with a knitting needle stuck through its centre and out the other side. The orange represents the Earth and the needle its axis of rotation. In a tidy picture of the Solar System, one might expect all the planets to have their axes of rotation nicely perpendicular to the plane in which they orbit the Sun. However, when we look at ours and the other planets, we don’t see this.

The only planet that is rotating perpendicular to the orbital plane is Mercury; all the others are leaning, some at absurd angles. The values for the inclination in degrees of the planets of the Solar System are given here in brackets are Mercury (0), Venus (3), Earth (23), Mars (25), Jupiter (3), Saturn (27), Uranus (82), Neptune (28), and Pluto (60). Since these axes of rotation vary only very slowly, over tens of thousands of years, when the Earth or other planet is on one side of the Sun, its northern hemisphere is leaning toward the Sun and the southern hemisphere away, making it summer in the north and winter in the south. Then when its orbit has carried it to the other side of the Sun, the northern hemisphere is leaning away and the southern hemisphere is leaning toward the Sun, and it is now winter in the northern hemisphere and summer in the south. Uranusí axis is leaning over almost at a right angle. That planet is more or less rolling around the Sun.

How could this situation arise? The answers are buried in the early history of the Solar System.

Several billion years ago, a cloud of cosmic gas and dust started to collapse. This could have been triggered by the explosion of a nearby giant star. If we take any cloud of interstellar material and take the average of how every atom and grain in the cloud is moving, we wind up with two motions: movement in a particular direction and a rotation. So as a cloud collapses it will gradually turn into a rotating disc which is moving through space at the average velocity of the cloud.

In the disc the grains of dust start to collide and stick together. As they get larger they become bigger targets, and get hit more often. Then eventually they develop a strong enough pull of gravity to pull in other chunks of material. Initially their spins will be the same as the disc, but after a few oblique impacts by other large chunks of material the embryo planets got their spins scrambled.  It would be really interesting to know what sorts of collisions shifted Uranus’ axis of rotation by almost a right angle.

Even after the planets had grown to almost their current sizes, there were still occasional collisions. There is evidence that something big hit the Earth, blasting debris off into space, and that this debris eventually formed the Moon. It is intriguing to consider the series of cosmic accidents that gave us the seasons we have today. If the Earth’s axis had a smaller inclination we would have milder summers and winters, a larger inclination would give us hotter summers and colder winters. Imagine the seasons on Uranus!

Jupiter is descending in the west, and Mars and Saturn lie in the southern sky. Mars is the bright one; Saturn is fainter and to Mars’ left. The Moon will reach Last Quarter on the 27.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton.


Just Posted

New trial date set in Penticton for Thomas Kruger-Allen’s triple assault charges

May trial was delayed after Crown witnesses failed to show up

A for sale sign is shown in by new homes in Beckwith, Ont., just outside Ottawa, on Wednesday, Jan. 11, 2018. THE CANADIAN PRESS/Sean Kilpatrick
Thompson-Okanagan population grew despite COVID-19: report

The Chartered Professional Accountants of BC said there are 8,462 new residents in the region

Scales of Justice
Acquittal in Okanagan crash that killed vacationing dentist

Daerio Romeo, 29, was charged with dangerous driving causing death and bodily harm

Renderings of what the skating rink could look like beside City Hall between Martin and Main in downtown Penticton. (Activate Penticton image)
Penticton to get outdoor ice rink this winter

It’s hoped the rink will be ready to host 2022 BCHL’s 60th year celebration

The fate of Skaha Marina and its operations will be decided Saturday, June 19 on general election day. (File photo)
Penticton city hosted last forum before voters decide on fate of Skaha Marina

Residents share concerns about length of operations agreement, parking and control of park

People watch a car burn during a riot following game 7 of the NHL Stanley Cup final in downtown Vancouver, B.C., in this June 15, 2011 photo. THE CANADIAN PRESS/Geoff Howe
10 years ago: Where were you during the 2011 Vancouver Stanley Cup Riots?

Smashed-in storefronts, looting, garbage can fires and overturned cars some of the damage remembered today

Vernon-Monashee NDP MLA Harwinder Sandhu supported a motion in the B.C. legislature for Canada to create a national Indigenous History month Monday, June 13, 2021. (Contributed)
Canada needs a national Indigenous History Month, Vernon MLA agrees

Harwinder Sandhu supports motion to recognize June as month to advance reconciliation efforts with First Nations

Orange ribbons are tied to the fence outside Vernon’s Gateway Homeless Shelter on 33rd Street. (Jennifer Smith - Morning Star)
POLL: Low-key Canada Day in the works for Vernon

Councillor calling for Indigenous recognition for 2022

A conceptual design of Vernon’s new Active Living Centre, which will go to referendum Oct. 15, 2022. (Rendering)
Active living centre 2022 referendum planned in Vernon

City hoping to get Coldstream and Areas B and C back on board

Closure of the 2900 block of 30th Avenue will allow restaurants and other businesses to extend their patios onto the street. (Jennifer Smith - Morning Star)
Green light given to downtown Vernon road closure

Single block of 30th Avenue to close over summer months to boost business

Graduating Grade 12 student Savannah Lamb has been awarded an approximate $40,000 scholarship from the Beedie Luminaries foundation. (Contributed)
Dedicated Salmon Arm student earns scholarship to pursue post-secondary education

Savannah Lamb is graduating from Salmon Arm Secondary with a $40,000 scholarship

A provided photo of the suspect. (Kelowna RCMP/Contributed)
Kelowna RCMP investigating after business robbed

An undisclosed amount of money and merchandise were taken from the business

(Black Press Media file)
Dirty money: Canadian currency the most germ-filled in the world, survey suggests

Canadian plastic currency was found to contain 209 bacterial cultures

Most Read