Here is the first ever image processed from the James Webb space telescope’s primary mirror. It shows copies of a distant star HD 84406, individually imaged through Webb’s 18 honey-comb like mirror segments.
This is part of the primary mirror alignment phase. A bit like the process backyard observers go through when we collimate our telescopes.
Over the next several weeks these individual points will converge to form a single image of the star, completing the alignment process and ensuring all components of the 6.5 meter primary mirror are working as one.
You can see the gold plated hexagonal components of the primary mirror in this second picture, which is a selfie the telescope took of its main mirror from outer space.
The astrophysical community awaits Webb’s first active mission pictures which I understand will be images of three of the largest low-albedo asteroids, as well as Jupiter’s red spot and Neptune’s southern polar vortex.
Jupiter was recently hit by a giant space rock and astronomer @jose.luis_pereira (Instagram) was lucky enough to capture the impact in this incredible footage.
Encounters like this always remind me of our relative fragility on planet Earth. Although Jupiter’s gravity protects us from more frequent large impacts, there’s an inevitability when it comes to future encounters with big space rocks. You need only glance up at the Moon for clear evidence of this destructive heritage.
The statistics of space rock encounters are both reassuring (in terms of long timescales) but also gravely concerning (in terms of raw destructive power).
On average, every few hundred years, the Earth is hit by an object some 30-60 meters in diameter. Such an impact generates enough energy to devastate an entire city if the final shockwave is concentrated in the right position and direction. The 2013 Chelyabinsk and 1908 Tunguska events are recent example of such encounters.
Then every 10,000 years we’re hit by a 200-500 meter wide object, large enough to trigger short term but significant climate changes, potentially lowering global temperatures and disrupting crop growth and finely balanced ecological systems.
Then every million years a 2-4 kilometer wide impact can occur, releasing energy equivalent to the explosive output of every nuclear weapon on the planet!
Finally on a hundred million year timescale Earth can be visited by something like the Chicxulub event that wiped out the dinosaurs, an object some 10-20 kilometres across. That’s enough destructive power to wipe out vast swathes of life across the entire planet.
As a species we’re only a few million years old and our recorded history takes us back a paltry 10,000 years. It makes you wonder therefore, what unrecorded and long forgotten destructive encounters our distant ancestors experienced and survived? Or is our species yet to be challenged by any of the bigger impacts mentioned above?
Jupiter and Saturn can be seen setting low in the SW during early evenings and you might have noticed they’ve been steadily appearing closer together in the sky. This will continue in the weeks ahead, culminating in a great conjunction in the run up to Christmas.
On December 21st, at their closest, they’ll be just 0.1 degrees apart. That’s only 1/5 of a full moon diameter! With the gas giants appearing this close together you’ll be able to view them under high magnification in the same field of view with your telescope.
Have you ever seen the planet Mercury with your own eyes? It’s notoriously difficult to catch being situated so close to the Sun and often hard to pinpoint. You’ll only ever see it as a tiny disc in binoculars, very close to sunrise or sunset.
Over the next couple of days, centred on the Dec 21st solstice, there’s a unique opportunity to see Mercury as it forms a conjunction with bright Jupiter low in the south east in morning skies.
You’ll need a good unobstructed horizon to the SE to catch it. Use Venus as a guide to first find Jupiter, then look through your binoculars and you should see Mercury sitting above.
The window is pretty narrow, from around 7.30pm to 8.30pm. The longer you wait the higher Mercury will rise but the brighter the sky, as the Sun rises.
A line of the Moon, Jupiter and the bright star Spica can be seen tonight in the S/SW as the Sun sets (try after 11.30pm or later if it’s still too light). Spica is the brightest star in the constellation Virgo and was the star that helped unearth the 26,000 year cycle known as the Precession of the Equinoxes.
As the story goes a temple in Thebes built around 3000 BC was originally aligned with Spica but the Heliacal sighting was found to have significantly drifted off target some 3200 years later. This fact was taken up by the Greek astronomer, mathematician and geographer Hipparchus who used this and other data to approximate the precessional cycle time of the heavens (as he saw it) to be over 30,000 years. An over estimate but a respectable first guess.
Of course we now know the real reason for this apparent cyclic drift of the constellations over long time scales – 25,772 years to be accurate. A wobble in the earth’s local axis of rotation (see animation below) caused by the gravitational influence of the Moon and Sun on Earth’s equatorial bulge.
There are a couple of interesting side effects of this dynamic. Firstly our pole star slowly changes over thousands of years. In ancient Egyptian times (3000 BC) the northern pole star was Thuban in the Constellation Draco, and in around 12000 years time the pole star will have moved close to brilliant Vega.
The other effect is that the dates of the original Zodiacal star signs are now completely out of sync with the position of the Sun. A child born today (June 24th) is still designated as a ‘Cancer’ (because the Sun is supposed to be in the constellation Cancer right now). But the Sun isn’t in Cancer – it’s actually in Taurus.