June Sky Notes
The Summer Solstice
The summer solstice in the northern hemisphere falls on 21 June, when the Sun reaches its greatest altitude in the sky on the ecliptic (the path it takes across the sky during a year).
It is surprising how many people wrongly assume that Earth is closer to the Sun at this time of year; in fact the opposite is true. Earth is actually furthest from the Sun on 4 July at almost 95 million miles, nearly 3 million miles more than when it’s at its closest approach in early January. It is the inclination of the northern hemisphere towards the sun which causes days to ‘grow longer’ and feel warmer due to the higher concentration of sunlight per unit area. Think of this as similar to directing a spotlight on to the palm of your hand, your palm feels hotter under direct radiation, whereas when the light is tilted, the angle reduces the heat intensity. The actual intensity of solar radiation in June is equivalent to approximately 1.2KW of heat for each square metre, although sometimes it feels as if someone’s forgotten to feed the meter!
Often called the longest day, earliest sunrise and latest sunset times do not occur on the summer solstice date. Earliest sunrise falls around 16 June (from Whitby, 4.25 am) whilst latest sunset occurs on 25 June (Whitby, 21.42 pm). It is the duration of useable daylight which reaches a maximum on the 21st, at just over 17 hours, with a meagre four hours of semi-darkness. Not much good for observing the starry sky. However, there is one object you may like to take a peek at . . .
Our Neighbour in Space – The Moon
Next month sees the 50th anniversary of the first Moon landing, which I shall be covering in greater detail in July’s notes, but for this month I thought perhaps to take a look at the moon from an observing standpoint, especially as June ‘nights’ are so short.
Situated around 240,000 miles away, our near neighbour is often overlooked by observers, especially when near full: a pity as it is a wonderful object to explore as it waxes and wanes, even observable well before the sunset. At some 2,160 miles in diameter, roughly a quarter the size of Earth, the fifth largest satellite in the solar system is best appreciated when viewed through a telescope, even a very modest one. Many features, such as the dark ‘lunar seas’, or Maria, can be distinguished easily through binoculars; even with the naked eye you can follow the appearance of these regions as the moon changes phase. These less ‘ancient’ areas of the Moon formed when lava flooded lower lying regions of the lunar surface 3–3.8 billion years ago. The heavily cratered highland areas are the most ancient: up to 4.4 billion years old.
We can begin our lunar watch from near the start of June, following the terminator: the border between day and night, marching across the lunar surface, transforming its appearance with almost magical spectacle as it does so. The moon is new on the 3rd so start observing on the 6th or 7th, by which time the isolated dark circular patch of Mare Crisium, the ‘Sea of Crises’, as well as Mare Fecunditatis, ‘Sea of Fertility’, are already visible. Prominent craters visible include Cleomedes, Langrenus and Petarvius, all of which are around 100 miles in diameter, whilst further north on the lunar surface, look for the striking crater pair of Atlas and Hercules close to the terminator.
By 9 June the observer’s eye is drawn towards Mare Nectaris, ‘Sea of Nectar’, and the splendid crater trio of Theophilus, Cyrillus and Catharina. Theophilus is the best defined of the three and overlaps Cyrillus and therefore must be the youngest. The following evening the moon reaches First Quarter, when it appears half phase. To the naked eye the most striking aspect are the four interconnected seas that resemble a ‘claw’ formation. The actual ‘pincers’ of the claw comprise two seas: Mare Foecunditatis, ‘Sea of Fertility, and Mare Nectaris, ‘Sea of Nectar’. Adjoining both is Mare Tranquillitatis, ‘Sea of Tranquility’, the location where ‘just one small step’ focused the world’s attention on the ‘giant leap’ mankind was making back in July 1969. The large circular sea of Mare Serenitatis, ‘Sea of Serenity’, butts up to Tranquility.
Around the 8th day after new moon, the advancing sun’s rays uncover some of the moons most spectacular features. Note the large dark mass of Mare Imbrium, ‘Sea of Showers’, bounded to the north and east by the vast mountain chains of the lunar Alps and Apennines. Look in particular for the dark floored ringed plains of Plato and Archimedes as well as the Alpine valley, an 80-mile long gash that cuts through the lunar Alps. The following evening one of the moon’s largest and most majestic formations, the 140-mile diameter walled plain Clavius (the only crater directly visible to the naked eye), emerges to prominence. Across its floor an arc of ‘smaller’ craters sweep, initially resembling inky wells until sunlight penetrates their shadowy depths. By 13 June the spectacular crater Copernicus takes centre stage, some 54 miles in diameter and almost four miles deep with a fine central peak. My personal favourite crater, Eratosthenes, lies close by at the terminus of the rugged Apennine Mountain range. Yet another stunning vista awaits 24 hours later, when the first gleams of sunlight catch the pinnacles of the Jura Mountains forming the northern perimeter of the dark floored Sinus Iridum, ‘Bay of Rainbows’.
The moon is now gibbous with the great dark expanse of Oceanus Procellarum slowly becoming uncovered, along with the smaller seas of Mare Nubium, ‘Sea of Clouds’, and Mare Humorum, ‘Sea of Humours’. When the Moon reaches full (17 June) it lies opposite the Sun in the sky and when viewed its surface features appear washed out, indeed formations that looked so spectacular earlier in the lunar cycle are now rendered almost invisible by sunlight. Only around full moon do the lunar rays, the bright ejecta streaks emanating from more recently formed impact craters such as Kepler, Copernicus and most conspicuous of all, Tycho, become prominent to the eye. The brightest of all lunar features, the crater Aristachus, is visible on Oceanus Procellarum and can even be glimpsed when the moon is in earthshine. The darkest lunar feature, the flooded plain Grimaldi lies further south near the lunar limb. As the moon wanes, you can then watch the whole magical process in reverse, and marvel how it all looks so different.
So, find a pair of binoculars, or better still a small scope, and take a good look at our travelling companion in space – a whole world just waiting to be explored!
Mark Dawson,
Whitby & District Astronomical Society
For more information about Whitby & District Astronomical Society see: www.whitby-astronomers.com
The summer solstice in the northern hemisphere falls on 21 June, when the Sun reaches its greatest altitude in the sky on the ecliptic (the path it takes across the sky during a year).
It is surprising how many people wrongly assume that Earth is closer to the Sun at this time of year; in fact the opposite is true. Earth is actually furthest from the Sun on 4 July at almost 95 million miles, nearly 3 million miles more than when it’s at its closest approach in early January. It is the inclination of the northern hemisphere towards the sun which causes days to ‘grow longer’ and feel warmer due to the higher concentration of sunlight per unit area. Think of this as similar to directing a spotlight on to the palm of your hand, your palm feels hotter under direct radiation, whereas when the light is tilted, the angle reduces the heat intensity. The actual intensity of solar radiation in June is equivalent to approximately 1.2KW of heat for each square metre, although sometimes it feels as if someone’s forgotten to feed the meter!
Often called the longest day, earliest sunrise and latest sunset times do not occur on the summer solstice date. Earliest sunrise falls around 16 June (from Whitby, 4.25 am) whilst latest sunset occurs on 25 June (Whitby, 21.42 pm). It is the duration of useable daylight which reaches a maximum on the 21st, at just over 17 hours, with a meagre four hours of semi-darkness. Not much good for observing the starry sky. However, there is one object you may like to take a peek at . . .
Our Neighbour in Space – The Moon
Next month sees the 50th anniversary of the first Moon landing, which I shall be covering in greater detail in July’s notes, but for this month I thought perhaps to take a look at the moon from an observing standpoint, especially as June ‘nights’ are so short.
Situated around 240,000 miles away, our near neighbour is often overlooked by observers, especially when near full: a pity as it is a wonderful object to explore as it waxes and wanes, even observable well before the sunset. At some 2,160 miles in diameter, roughly a quarter the size of Earth, the fifth largest satellite in the solar system is best appreciated when viewed through a telescope, even a very modest one. Many features, such as the dark ‘lunar seas’, or Maria, can be distinguished easily through binoculars; even with the naked eye you can follow the appearance of these regions as the moon changes phase. These less ‘ancient’ areas of the Moon formed when lava flooded lower lying regions of the lunar surface 3–3.8 billion years ago. The heavily cratered highland areas are the most ancient: up to 4.4 billion years old.
We can begin our lunar watch from near the start of June, following the terminator: the border between day and night, marching across the lunar surface, transforming its appearance with almost magical spectacle as it does so. The moon is new on the 3rd so start observing on the 6th or 7th, by which time the isolated dark circular patch of Mare Crisium, the ‘Sea of Crises’, as well as Mare Fecunditatis, ‘Sea of Fertility’, are already visible. Prominent craters visible include Cleomedes, Langrenus and Petarvius, all of which are around 100 miles in diameter, whilst further north on the lunar surface, look for the striking crater pair of Atlas and Hercules close to the terminator.
By 9 June the observer’s eye is drawn towards Mare Nectaris, ‘Sea of Nectar’, and the splendid crater trio of Theophilus, Cyrillus and Catharina. Theophilus is the best defined of the three and overlaps Cyrillus and therefore must be the youngest. The following evening the moon reaches First Quarter, when it appears half phase. To the naked eye the most striking aspect are the four interconnected seas that resemble a ‘claw’ formation. The actual ‘pincers’ of the claw comprise two seas: Mare Foecunditatis, ‘Sea of Fertility, and Mare Nectaris, ‘Sea of Nectar’. Adjoining both is Mare Tranquillitatis, ‘Sea of Tranquility’, the location where ‘just one small step’ focused the world’s attention on the ‘giant leap’ mankind was making back in July 1969. The large circular sea of Mare Serenitatis, ‘Sea of Serenity’, butts up to Tranquility.
Around the 8th day after new moon, the advancing sun’s rays uncover some of the moons most spectacular features. Note the large dark mass of Mare Imbrium, ‘Sea of Showers’, bounded to the north and east by the vast mountain chains of the lunar Alps and Apennines. Look in particular for the dark floored ringed plains of Plato and Archimedes as well as the Alpine valley, an 80-mile long gash that cuts through the lunar Alps. The following evening one of the moon’s largest and most majestic formations, the 140-mile diameter walled plain Clavius (the only crater directly visible to the naked eye), emerges to prominence. Across its floor an arc of ‘smaller’ craters sweep, initially resembling inky wells until sunlight penetrates their shadowy depths. By 13 June the spectacular crater Copernicus takes centre stage, some 54 miles in diameter and almost four miles deep with a fine central peak. My personal favourite crater, Eratosthenes, lies close by at the terminus of the rugged Apennine Mountain range. Yet another stunning vista awaits 24 hours later, when the first gleams of sunlight catch the pinnacles of the Jura Mountains forming the northern perimeter of the dark floored Sinus Iridum, ‘Bay of Rainbows’.
The moon is now gibbous with the great dark expanse of Oceanus Procellarum slowly becoming uncovered, along with the smaller seas of Mare Nubium, ‘Sea of Clouds’, and Mare Humorum, ‘Sea of Humours’. When the Moon reaches full (17 June) it lies opposite the Sun in the sky and when viewed its surface features appear washed out, indeed formations that looked so spectacular earlier in the lunar cycle are now rendered almost invisible by sunlight. Only around full moon do the lunar rays, the bright ejecta streaks emanating from more recently formed impact craters such as Kepler, Copernicus and most conspicuous of all, Tycho, become prominent to the eye. The brightest of all lunar features, the crater Aristachus, is visible on Oceanus Procellarum and can even be glimpsed when the moon is in earthshine. The darkest lunar feature, the flooded plain Grimaldi lies further south near the lunar limb. As the moon wanes, you can then watch the whole magical process in reverse, and marvel how it all looks so different.
So, find a pair of binoculars, or better still a small scope, and take a good look at our travelling companion in space – a whole world just waiting to be explored!
Mark Dawson,
Whitby & District Astronomical Society
For more information about Whitby & District Astronomical Society see: www.whitby-astronomers.com
