July's night sky with Martin Lunn, of Earby Astronomical Society

July marks the second half of the noctilucent season.

We can see the two giants of the solar system Jupiter and Saturn in the sky before midnight and the first of the major summer meteor showers can be seen this month.

On July 4 the Earth is at aphelion, or furthest point from the Sun, on its yearly orbit.

At aphelion Earth will be 95 million miles (152 million km) from the Sun.

In the northern hemisphere we are now experiencing summer.

In January however, the Earth was at Perihelion, or closest to the Sun, being only 91 million miles (147 million km) away.

The seasons are caused not by how close the Earth is to the Sun, but by which hemisphere is tilted towards it.

In July the northern hemisphere is tilted towards the Sun, while in January when the Earth is closest to the Sun the northern hemisphere is tilted away from the Sun.

There have been some sightings of the noctilucent clouds in June and with the upper part of the atmosphere, the mesosphere, being incredibly cold (very like last year when we had spectacular noctilucent clouds).

There is a very good chance that these magical night shining clouds will be seen again this month.

Following June’s long days, the nights in July are slowly becoming darker, although that won’t 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 component stars 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 quadritalteral, 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, which is sometimes referred to as the Northern Cross.

The stars are spread out over a much larger area and are fainter than those 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 called 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, which was a night to remember as far as astronomy is concerned.

In fact Goodricke and Pigott contributed so much to variable star astronomy 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 decpetive.

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 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 supergiant 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.

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.

Last month the two giants, Jupiter and Saturn, were attracting attention in the morning sky.

This month they can be seen low down in the south east before midnight. Jupiter, the largest of the planets in the solar system, and Saturn the famous ringed planet, can be seen low in the sky in the south east at about 11pm.

Jupiter will appear as a bright white dot in the sky. Close by and to the left of Jupiter will be Saturn, a slightly less bright looking star which appears as a dirty yellow looking dot.

Mars rises much later in the morning sky while Mercury and Venus are still very close to the Sun in the sky, making them difficult to see.

The first of the summer meteor showers is the Delta Aquarids which can be seen on the night of the 30th.

These meteors or shooting stars as some people call them are the remains of comet Macholz. Around 15 meteors per hour can be seen.

Phases of the Moon for July are: full moon 5th last quarter 12th new moon 20th first quarter 27th

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.

Due to the current coronavirus situation there will be no meetings for members of the Earby Astronomical Society until further notice.