Night Skies: July - when the Earth is furthest from the Sun

THIS is the month when the Earth is furthest from the Sun. Mars will be at its closest to us. The Summer Triangle is now overhead and there is an eclipse of the Moon.

Mars will be at its closest since 2003 which was the year when the Earth and Mars were the closest they had been in 60,000 years. This month it will be slightly further away at 35.7 million miles. Mars will appear as a bright red spot in the south and will be difficult to miss, being so bright in the sky that it will even outshine Jupiter. It is not difficult to see why people living thousands of years ago named it the God of War.

Astronomers using telescopes always wait for these close encounters so they can try to look at the surface of Mars in more detail. The big problem they face is that as Mars gets closer to the Sun the heat causes massive dust storms on the red planet, making large parts of the planet invisible. This is exactly the case at the moment as NASA's Opportunity rover is in the middle of one of these vast storms. There is a lot of concern among the scientists that the storm will blow dust onto the solar panels which could cause the batteries on Opportunity to go flat and end the mission. This is a possibility, but remember that when Opportunity landed in January 2004 it was scheduled to have a 90 day mission time, and 14 years on it is still going.

Following on from June's long days, the nights in July are slowly becoming darker, although that will not really be noticeable until the end of the month. The Summer Triangle stars of Vega, Deneb and Altair are now at their best.

If you look directly overhead the bright star you see is Vega, in the constellation of Lyra the Lyre, which is a small but distinctive constellation. Look to the left of Vega and you will see the star Epsilon Lyrae which is the famous double star. Normal sighted people on a clear night should be able to see that the star is made up of two stars side by side. In a telescope each of the components is itself a double star so we could refer to it as a 'double double' or quadruple star.

The rest of Lyra is made up of a quadrilateral of stars with Beta, at the bottom right of the quadrilateral, being a variable star that was discovered to vary by the deaf astronomer John Goodricke in York in 1784.

Deneb is the brightest star in Cygnus the Swan, sometimes referred to as the Northern Cross. The stars are spread out over a much larger area and are fainter than in Lyra but once you have located Cygnus it will be easily recognised in the future. It lies in the milky way so there are many stars to see in this part of the sky and through binoculars you can see countless more stars. At the end of the cross shape is the star Beta Cygni or Albireo. When viewed through binoculars or a small telescope it appears as one of the most glorious looking double stars, made up of a blue star and a yellow star.

The third member of the summer triangle is the most southerly; Altair, in the constellation of Aquila the Eagle. The constellation does give the slight appearance of an eagle in the sky. It has, like Vega, a connection with York, because the star Eta is variable and was discovered by Edward Pigott who worked in York with John Goodricke.

Both Beta Lyrae and Eta Aquilae were discovered on September 12th 1784, a night I often refer to as a 'night to remember' as far as astronomy is concerned. In fact Goodricke and Pigott contributed so much to variable star astronmy in the brief time they worked together from 1781 until 1786 that I refer to them as 'the fathers of variable star astronomy'.

The Summer Triangle shows us that appearances can be deceptive. When we look at the three stars that form the triangle, Vega appears much the brightest, Altair and Deneb appearing significantly fainter, but when we consider how far away they are a different picture appears. Altair is a mere 17 light years away, Vega a slightly more distant 25 light years, but Deneb, which appears the faintest, is 2,500 light years away. This means that if they were all placed the same distance from the Earth, Deneb would massively outshine the other two stars.

Another bright star that can be seen in the summer months, this time very low down in the south, is Antares in the constellation of Scorpius the Scorpion, sometimes known as 'the rival of Mars' because of its colour. Unfortunately, because Antares is so low in the sky when seen from from Britain, it never rises high in the sky. To see it at its best you would need to be in the Mediterranean area. It is a red super giant and in fact so big that the orbits of the four planets closest to the Sun; Mercury, Venus, Earth and Mars, would comfortably fit inside Antares.

At the moment due to its closeness to us Mars appears much the brighter than its 'rival' Antares in the southern sky. Apart from Antares, the rest of the southern sky is made up of large faint groups of stars.

With regards to the more familiar groups of stars in the sky, the Plough is still high in the north west, which means that the 'W' of Cassiopeia has now become a little higher in the north east.

The planets in July

I have already indicated that Mars will become very noticeable in the south eastern sky from about 11pm onwards. In the south west the bright white spot you will see in the sky is Jupiter, the largest planet in the solar system. Jupiter has been visible in the night sky for most of the year but is now beginning to appear slightly lower in the sky in the south west. Jupiter will still be visible all through July but will become much lower in the sky, especially as we approach the end of the summer months. Located midway between Jupiter and Mars is the famous ringed planet Saturn which appears as a dirty yellow bright 'star' low in the sky.

Just as the Sun sets, look low to the west and you will see the brightest planet in the night sky:Venus, or 'the evening star' as it is sometimes called. The other naked eye planet, Mercury, is very close to the horizon this month so you would be unlikely to see it.

Meteor Showers

The only meteor shower this month is the Delta Aquarids, these meteors or shooting stars as some people call them are the remains of comet Macholz. The shower's maximum will be on the night of July 30 when normally around 15 meteors per hour can be seen, but this year, with the maximum being close to the full moon, the sky will be bright making it more difficult to see these meteors.

Phases of the Moon for July

Last Quarter 6; New Moon 13; First Quarter 19; Full Moon 27.

There will be an eclipse of the Moon on the evening of the 27th . An eclipse of the Moon occurs when the Moon passes into the shadow of the Earth. The Moon has no light of its own, but we see it because it reflects sunlight that hits it. We could say that moonlight is simply reflected sunlight. When the Moon passes into the shadow the direct sunlight is cut off, but light still reaches the Moon by passing through the atmosphere of the Earth and being bent, or 'refracted', onto the surface of the Moon. The Earth's atmosphere will block off the blue light so most of the light that reaches the Moon will be red, hence the Moon will become a coppery red colour, or as some people call it a 'blood moon'.

The eclipse will begin when the Moon is still below the horizon as seen from Britain. When the Moon rises in the south east sky at 8.47pm it will already be in eclipse and will appear reddish and quite dark because it is so low in the sky. The eclipse will end at 10.13 pm when the Moon will be still be low in the sky.

The full moon in July is known as the Thunder Moon as this is the month of the year when we are most likely to get thunder storms.

On July 6, the Earth will be at Aphelion, or furthest point from the Sun on its annual path, when it will be 95 million miles from the Sun. We are at Perihelion, or closest point to the Sun, in January when the Earth is around 91 million miles away. It is the tilt of the Earth that determines which season we are in, rather than our distance from the Sun. In July the northern hemisphere is tilted towards the Sun hence we have summer, while in January the northern hemisphere is tilted away and we experience winter.

The Earby Astronomical Society will be taking its summer break from meetings now which means that the next meeting will be on Friday September 29 at All Saints’ Church, Earby, from 7.30pm-9pm pm. The speaker will be Martin Lunn MBE FRAS, Earby Astronomical Society, and the title of the talk will be ‘The Autumn Sky’. Everyone is welcome.