The September 2015 Night Sky

It’s September and the schools are back in session. The summer holidays have come to an unfortunate end and now we all have to get back to our daily routines. July and August have been great months for stargazing, but with the coming of September comes longer nights, which is optimal for stargazing. So let’s kick off the start of term with a bang and look for some amazing objects in the sky.

Image of Neptune as taken by the Voyager probe. (Image credit: NASA)

Image of Neptune as taken by the Voyager probe. (Image credit: NASA)

 

To start off the month we have our best view of Neptune, the furthest planet away from us in our solar system. On 1st September Neptune will be at opposition to the Sun, so its face will be illuminated by our local star, and will be visible in the night sky. To the naked eye it will not even be visible in the sky as it is so far away from the Earth. If you have a powerful telescope however, you will be able to see it in a bit more detail but still just as looking like a faint blue dot and not in its impressive glory. Neptune is the eighth planet in our solar system and its existence was discovered by Urbain Le Verrier , a brilliant (but allegedly rather “difficult”) French mathematician who specialised in celestial mechanics, in 1846. He was able to predict the existence of the planet Neptune using only mathematics (and similarly but less impressively the imaginary planet Vulcan too). Neptune is roughly 30 Astronomical Units (au) from the Sun and takes 165 years to complete an orbit. In 2011 Neptune completed its first full orbit since its discovery in 1846. The planet will not complete its next full orbit until the year 2176. The planet is primarily made up of the gases hydrogen (H), helium (He) and methane. Methane absorbs red light, which makes Neptune appear to be blue.

Looking South you can see Neptune with the naked eye, but using a pair of binoculars or a telescope would make for a much better viewing. (image credit Heather Taylor, Stellarium)

Looking SE about midnight in the middle of September you cannot see Neptune with the naked eye, but using  a telescope will make viewing possible. Capricornus the Seagoat seems to form an arrow pointing to the outer planet. (image credit Heather Taylor, Stellarium)

 

Another planet will make its grand appearance in the night sky is Mercury. On 4 September it will be at its greatest eastern elongation, which means it will have reached an elongation of 27 degrees from the Sun. A planet’s elongation is the angle between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given planet arises when this inner planet’s location, in its orbital path to the Sun, is at tangent to the observer on Earth. If the planet is visible just after sunset, this means that it is at its greatest eastern elongation, and if the planet is visible just before sunrise then it is at its greatest western elongation. Mercury will be at its highest point above the horizon so your best chance to see it will be just after sunset, looking low into the western sky.

Looking West just after sunset you will be able to glimpse Mercury, however it will be difficult to see with the light still shining from the sun. Credit Heather Taylor, Stellarium

Looking west just after sunset in early September you will be able to glimpse Mercury, however it will be difficult to see with the light still shining from the Sun. Credit Heather Taylor, Stellarium

 

On 13 September there will be a New Moon, so this is the time to look out for some celestial objects without being hindered by the light of the moon. A partial solar eclipse will also happen on this day, unfortunately for us though it will only be visible in Southern Africa, the Indian Ocean and Antarctica. So what can we see on 13 September? Here is what we recommend for you:

 

A DSLR camera and tripod (with optional star tracker) as you would need to image the Milky Way (Image credit: Colin Johnston/Armagh Planetarium)

A DSLR camera and tripod (with optional star tracker) as you would need to image the Milky Way (Image credit: Colin Johnston/Armagh Planetarium)

 

The Milky Way will still be running over our heads at this time of year, so why not try and locate it. How do you try and find such an object though? Well, first you have to find the constellation of Sagittarius, which is lying on the southern horizon. Sagittarius is a centaur, a half man, half horse creature. More often than not, Sagittarius is often identified as the centaur in Greek mythology called Chiron, who is actually represented by the constellation of Centaurus (located in the southern hemisphere). When searching for the Milky Way, do not try and find the mythical creature of Sagittarius, instead look for the “teapot” asterism. Once you have found the teapot, you should be able to spot something that looks like celestial steam coming from the spout. This is the Milky Way. In Northern Ireland and throughout the Northern Hemisphere it is becoming increasingly popular to try and photograph the night sky, with the Milky Way taking centre stage in many budding photographers images. As well as looking at the Milky Way with the naked eye, or through binoculars or a telescope, why not get out your camera and try and take a snap of our home galaxy.

 

Looking South and trying to find the teapot shape, you will be able to find Sagittarius and then see the Milky Way running above it. (Image credit Heather Taylor, Stellarium)

Looking South and trying to find the teapot shape, you will be able to find Sagittarius and then see the Milky Way running above it. (Image credit Heather Taylor, Stellarium)

 

On 23 September we have the September Equinox. This is the day when summer officially ends, and we see the start of autumn. In the Southern Hemisphere this equinox sees the start of their spring. The September equinox transpires the instant the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from north to south. This happens either on September 22nd, 23rd, or 24th every year.

September 28th will see a Full Moon in the sky. The night sky will be flooded with moonlight, so some of the more distant objects in the sky will be harder to find. This particular full moon is known as the Full Corn Moon. This name was first given by the early Native Americans because this is the time of year that the corn was ready to be harvested. In other cultures this full moon is also known as the Harvest Moon, and the Harvest Moon is the full moon that always occurs closest to the September equinox.

Image of a total lunar eclipse. You can see the brilliant coppery-red colour the Moon has during the eclipse. (Image Credit: Brian Day/NASA Lunar Science Institute)

Image of a total lunar eclipse. You can see the brilliant coppery-red colour the Moon has during the eclipse. (Image Credit: Brian Day/NASA Lunar Science Institute)

 

Finally at the end of the month we have a total lunar eclipse. A lunar eclipse occurs when the Moon passes directly behind the Earth into its shadow, known as its umbra. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely, with the Earth in the middle. A lunar eclipse can only occur on the night of a full moon. The type and length of an eclipse depend upon the Moon’s location relative to its orbital nodes. This Moon will be coppery-red in colour, and will be the last in the so-called “blood moon tetrad”. For more information on this eclipse and the superstitions that have created around it see The Truth About the Blood Moon Tetrad.

(Article by Heather Taylor, Education Support Officer)