Stargazing • June 2020

by Roger Davies



W arm summer evenings bring the most comfortable nights — if the shortest — for stargazing.

The Sun reaches its most northerly point at the summer solstice which is around 9.00am on the 21st June, the real start of summer (don't believe the weather presenter when they tell us summer starts on 1st June!). From then, the Sun rises at a point on the horizon further and further south until 21st September when it moves into the southern hemisphere and our (northern) Autumn begins.


Noctilucent Clouds. Image source: here.

The night sky in June never gets completely dark. Astronomers mark the start of true darkness when the Sun is lower than 18° below the horizon. From the 23rd May to the 21st July there is no part of the night when that condition is satisfied, no time when it is truly dark. The sky is not black but a beautiful velvet deep blue, merging to turquoise on the northern horizon. These are good conditions to spot the rare Noctilucent Clouds [ref: image above]. The clouds are made of ice crystals very high in the atmosphere (65,000m = 200,000 feet) and they reflect the light of the Sun that is not far below the horizon.

The New Moon occurs in the early hours of June 21st. If you have friend or relative in SE Asia, northern India, Saudi Arabia and central Africa tell them they will be treated to an annular eclipse, where the Moon covers most of the Sun but a ring (an annulus) of the Sun remains visible throughout.

A map of the track of the eclipse can be found here.

There is not much planet spotting this month but don't forget to look out for Mercury in the last week of May and first week of June. On June 4th it will be at its greatest angular separation from the Sun (23.6°) and so you'll have your best chance to see it in the western sky just after sunset — it will be at its highest point above the horizon, 16°, in the evening sky at sunset. The trick to successfully spotting Mercury is to have a clear north western horizon. The best time is 10.15-10.30pm, that is early enough so that Mercury is not too low in the sky, and late enough that the sky has darkened. At that time it is just 10° above the horizon so a clear view to the north-west is essential. At the end of the month, as dawn breaks, Jupiter and Saturn (which is about ten times fainter) will be low in the southern sky between the constellations of Capricorn & Sagittarius. Jupiter will be more spectacular in July when it reaches opposition (opposite the Sun in the sky) on the 14th.

Help with locating these events can be found using the interactive sky map here.

Almost all professional telescopes on mountain tops around the world have ceased operation in response to the Covid-19 pandemic. Some of the world's best telescopes are in Chile which is now particularly hard hit. However telescopes in space continue to operate and I mentioned last month the 30th anniversary of the remarkable 2.5m diameter Hubble Space Telescope. It's successor, the 6.5m James Webb Space Telescope [ref: pictured below] has recently been fully assembled in California.

The primary mirror is made of 18 separate hexagonal mirrors and the whole telescope is folded up to fit into the fairing of the European Space Agency Ariane 5 rocket to be launched from northwest of Kourou in French Guiana sometime in 2021. You might like to watch the video of the first full deployment of the telescope here.

Think about unfolding this complex structure in space!

The telescope will be launched into an orbit that takes it beyond the Moon where it cannot be visited to be repaired if anything goes wrong. JWST is tasked with observing the first stars in the Universe and characterising the atmospheres of the many planets beyond our solar system we have now discovered.

Happy stargazing!


The James Webb Space Telescope.
It’s primary mirror, made of 18 gold coated hexagonal mirrors, is 6.5m across. The structure below it is a sophisticated sunshield to stop the telescope warming up.
Who was James Webb?
He was the NASA Administrator from 1961-68 during the Mercury, Gemini & finally the Apollo missions. While recognising the technical achievement and political importance of the manned space programme he maintained the vision of putting a large telescope in space.



SEE ALSO by Roger Davies:
Stargazing • September 2020
Comet Neowise • July 2020
Stargazing • July & August 2020
Stargazing • June 2020
Stargazing • May 2020
Stargazing • April 2020

Roger Davies is a resident of the village of Kidlington, Oxfordshire.

Roger is the Philip Wetton Professor of Astrophysics and Director of the Hintze Centre for Astrophysical Surveys at the Department of Physics, University of Oxford,

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