This was me on the road and heading into the western Highlands last Saturday for my final stargazing gig of the season with the Woodland Trust.
Skies this far north will shortly be too bright to stargaze with only Astronomical Twilight levels of darkness left near midnight and no official ‘night’ again until mid to late August. So do get out while you still can. Of course the further south you are the less impacted you will be by this ‘near’ midnight Sun.
I had an eventful stargazing session with the Woodland Trust who were based at the Torridon for several nights. We first headed outside at about 10.30pm to view the crescent Moon with binoculars during early twilight skies – still too bright to see many stars apart from brilliant Arcturus.
The spring star Arcturus ‘Bear Watcher’ was bright enough to see in early twilight during our Moon gazing session.
After heading back inside for more projector based astronomy we ventured outside once more after 11pm and were fortunate to see a decent collection of bright stars and constellations despite some hazy cloud overhead.
Vega, Capella, Arcturus and Spica were all visible, in addition to the main stars in the Plough. I’d like to thank the Woodland Trust for inviting me and wish them well in their rewilding endeavours across the Highlands.
The star Earendel is located at the point of the arrow in the image above, surrounded by the light from diffuse and distant galaxies.
The NASA Hubble space telescope has imaged the most distant star ever detected at a staggering 12.9 billion light years away. The light captured from Earendel (dubbed the ‘Morning Star’) is a snapshot from an epoch when the universe was only 1 billion years old, making it significantly older than the previous furthest star detected by Hubble in 2018. (That star was dated to 4 billion year after the big bang).
Normally stars at such immense distances would be undetectable, but its discovery was aided by the gravitational distortion from distant galaxy clusters, magnifying the star and its host galaxy in a phenomena called ‘gravitational lensing.
An example of a distant galaxy, revealed by the distortion of space (and therefore light) near a closer area of high mass, in the form of a galaxy cluster.
Gravitational lensing is analogous to the refraction of light from a glass lens, magnifying and revealing objects that would normally be occulted by closer structures by the bending of space near areas of high mass – like galaxy clusters. Sometimes duplicate images of the same object can be seen, creating copies of the object along symmetrical arcs. The image below illustrates this effect on a star cluster which appears either side of Earendel.
A closer image of Earendel with a mirrored image of a nearby star cluster created by gravitational lensing
You might wonder how immense distances like this can be calculated given the complexity and uncertainty in pin pointing the distance to relatively close stars, let alone objects billions of light years away?
The principle tool used to measure these vast distances is an object’s spectral redshift – a measure of how much its light rays have been stretched (made longer) due to the fabric of space itself being stretched the further away we observe. Larger redshifts indicate objects that are further away – a relationship first accurately established by Edwin Hubble when cataloging the spectra from many distant galaxies.
A measured spectra shifted towards the red end of the spectra, signalling longer wavelengths and higher recessional speeds.
Given the redshift of an object we can calculate its recessional speed (related to the global expansion of the universe) and from this its distance can be determined using the Hubble’s constant Ho. These calculations can be set out very simply:
V (recessional speed) = Red-shift x Speed of Light
In the case of Earendel the detected redshift from its spectra was 6.2. Therefore:
V (Earendel) = 6.2 x 300 million m/s = 1860 million m/s.
It’s important to note that this speed is faster than the speed of light! How can this be? Well this is actually a measure of the speed that space itself is expanding. Light cannot travel faster than 300 million m/s – our cosmological speed limit – but there is no limit on the rate at which the fabric of space can expand. In fact for general relativity to work space must be permitted to expand at potentially unlimited rates.
From the recessional speed we then use Hubble’s law to find the distance to the star:
D (distance) = V (recessional velocity) / H0 (Hubble’s constant)
This gives our published distance to Earendel of 12.9 billion light years! A staggering distance taking us back to the earliest period of star formation when the abundance of atomic elements in the universe was very different to today.
We believe the very first population of stars emerged around 100 to 250 million years after the big bang, so Earendel formed only a few hundred million yeas after this. The new James Webb telescope will likely continue to study Earendel in the infrared, at longer wavelengths, potentially revealing the star’s temperature and luminosity and therefore its stellar classification.
Globular cluster NGC 6717. The colour of light from the stars is a general indicator of surface temperature.
The colour of a star tells us how hot it burns. From the dull red of Arcturus to the brilliant blue of Rigel, you can actually see these subtle colour differences with your own eyes when looking up at the night sky.
Just like an iron cast into the blacksmith’s forge, which slowly changes from red to white hot, stars emit light at different frequencies depending on their overall luminosity and energy output.
The same relationship between colour and temperature is noted when metal objects are heated.
The Planck-Einstein equation E = hf is a basic way of understanding this. E is energy, f is frequency and h is the famous Planck’s constant. Higher frequency light (blue) is more energetic than lower frequency light (red) and therefore hotter and more luminous stars tend to appear more blue. Meanwhile cooler stars whose external atmospheric envelopes has expanded (red giants like Betelgeuse) appear redder.
A simple way to highlight the colour of star light is to take your smartphone camera or DSLR and manually defocus it on a target star. This will emphasise the colour and you can even produce beautiful star trails like the one below by taking a movie or long exposure star trail.
Fine phasing of James Webb’s honeycomb mirror segments is now complete, revealing this first fully aligned image of star 2MASS J17554042+6551277 via the telescope’s NIRCam sensor.
This test image has exceeded NASAs expectations in terms of resolving power and clarity. You can even see well defined distant spiral galaxies in the background.
Unlike the Hubble space telescope the wavelengths of light gathered here is around 2 microns, within the infrared band of the electromagnetic spectrum (the region Webb has been designed to observe). These are wavelengths longer than the human eye can detect but ideal for revealing the evolutionary structure and morphology of stars and distant galaxies.
The Webb team will now continue with calibration of the on-board spectrographs, completing the full scientific instrument setup.
This process is expected to take several more months, but so far so good.
Stargazing and Moon Observing with Scotland’s Astronomer Royal Catherine Heymans.
Join me up at Abriachan Forest (a Dark Sky Discovery site) for an evening of stargazing, Moon observing and astronomy with our special guest Scotland’s astronomer royal Catherine Heymans.
If skies are clear Catherine and local astronomer Stephen Mackintosh will host an outdoor Moon observing session with binoculars and telescope. Following this Catherine will present her indoor guest talk titled “Do Look up! Space Rocks and Killer Asteroids”
Refreshments provided plus binoculars for stargazing. Under 16s with accompanying adults go free.
Catherine Heymans is the Astronomer Royal for Scotland and Professor of Astrophysics at the University of Edinburgh. She’s also director of the German Centre for Cosmological Lensing at the Ruhr-University Bochum. She is an experienced science communicator, visiting schools across Scotland, in addition to art, music, comedy, philosophy and science festivals.
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.
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