July 2024

Noctilucent Clouds

Credit: Royal Museums Greenwich

Noctilucent Clouds

Many of us in the Northern Hemisphere can look out for noctilucent clouds during their peak season in June and July.

Noctilucent clouds are clouds which appear to glow silver or blue during the late evening or early morning hours. This happens when the Sun is below the horizon but still illuminates the nighttime clouds from below.

These clouds are formed in the mesosphere when ice crystals form on suspended dust particles. Although their occurrence is quite unpredictable, there are ways you can give yourself the best chance of seeing them.

Look up an hour or two after sunset or before sunrise from somewhere with a flat horizon and a clear view of a wide patch of sky. In the evening, look west around 40 minutes after the Sun has set. In the early morning, look towards the northeast where the Sun will soon be rising.

Summer Triangle

The Summer Triangle — Vega, Deneb and Altair — light up the eastern part of the evening sky and their blazing radiance is visible to the unaided eye even for observers from the most light-polluted areas. The Summer Triangle isn’t a constellation but an asterism, which is a noticeable group of stars, and consists of 3 stars in 3 constellations.

Mars - Jupiter

July mornings Looking East - Mars and Jupiter

Mars and Jupiter will be visible in early July near the ecliptic.

n the early morning twilight on June 4, 2024, Mercury will pair with up Jupiter. The largest and smallest planets of our solar system will be 0.1 degrees apart. Look for them very low above the horizon. Binoculars may help spot them about 30 minutes before sunrise.

Orion

The constellation Orion

Orion, perhaps the most beautiful of constellations, will be seen in the south at around 11 - 12 pm during January. Orion is the hunter holding up a club and shield against the charge of Taurus, the Bull up and to his right. Alpha Orionis, or Betelgeuse, is a read supergiant star varying in size between three and four hundred times that of our Sun. The result is that its brightness varies somewhat. Beta Orionis, or Rigel, is a blue supergiant which, at around 1000 light years distance is about twice as far away as Betelgeuse. It has a 7th magnitude companion. The three stars of Orion's belt lie at a distance of around 1500 light years. Just below the lower left hand star lies a strip of nebulosity against which can be seen a pillar of dust in the shape of the chess-board knight. It is thus called the Horsehead Nebula. It shows up very well photographically but is exceedingly difficult to see visually - even with relativly large telescope.

Ursa Major

The constellation of Ursa Major

The stars of the Plough, shown linked by the thicker lines in the chart, form one of the most recognised star patterns in the sky. Also called the Big Dipper, after the soup ladles used by farmer's wives in America to serve soup to the farm workers at lunchtime, it forms part of the Great Bear constellation - not quite so easy to make out! The stars Merak and Dubhe form the pointers which will lead you to the Pole Star, and hence find North. The stars Alcor and Mizar form a naked eye double which repays observation in a small telescope as Mizar is then shown to be an easily resolved double star. A fainter reddish star forms a triangle with Alcor and Mizar.

Ursa Major contains many interesting "deep sky" objects. The brightest, listed in Messier's Catalogue, are shown on the chart, but there are many fainter galaxies in the region too. In the upper right of the constellation are a pair of interacting galaxies M81 and M82 shown in the image below. M82 is undergoing a major burst of star formation and hence called a "starburst galaxy". They can be seen together using a low power eyepiece on a small telescope.

Lyra & Cygnus

The constellations Lyra and Cygnus

This month the constellations Lyra and Cygnus are seen almost overhead as darkness falls with their bright stars Vega, in Lyra, and Deneb, in Cygnus, making up the "summer triangle" of bright stars with Altair in the constellation Aquila below. (see sky chart above)

Lyra
Lyra is dominated by its brightest star Vega, the fifth brightest star in the sky. It is a blue-white star having a magnitude of 0.03, and lies 26 light years away. It weighs three times more than the Sun and is about 50 times brighter. It is thus burning up its nuclear fuel at a greater rate than the Sun and so will shine for a correspondingly shorter time. Vega is much younger than the Sun, perhaps only a few hundred million years old, and is surrounded by a cold,dark disc of dust in which an embryonic solar system is being formed!
There is a lovely double star called Epsilon Lyrae up and to the left of Vega. A pair of binoculars will show them up easily - you might even see them both with your unaided eye. In fact a telescope, provided the atmosphere is calm, shows that each of the two stars that you can see is a double star as well so it is called the double double!

Cygnus
Cygnus, the Swan, is sometimes called the "Northern Cross" as it has a distinctive cross shape, but we normally think of it as a flying Swan. Deneb,the arabic word for "tail", is a 1.3 magnitude star which marks the tail of the swan. It is nearly 2000 light years away and appears so bright only because it gives out around 80,000 times as much light as our Sun. In fact if Deneb where as close as the brightest star in the northern sky, Sirius, it would appear as brilliant as the half moon and the sky would never be really dark when it was above the horizon!
The star, Albireo, which marks the head of the Swan is much fainter, but a beautiful sight in a small telescope. This shows that Albireo is made of two stars, amber and blue-green, which provide a wonderful colour contrast. With magnitudes 3.1 and 5.1 they are regarded as the most beautiful double star that can be seen in the sky.

Planets

Mercury
Mercury

As an evening star, Mercury appears in the western sky and sets about an hour after the sun does. As a morning star, it appears in the eastern sky, rising about an hour before the sun. There must be a clear, unobstructed horizon on these occasions.

Mars
Mars

This will be another "off" year for Mars, as for much of 2024 it will appear relatively dim while dawdling in the morning sky. Mars will actually be invisible for the first 10 days of the new year, too deeply immersed in the bright dawn twilight to be seen.

Venus
Venus

Always brilliant, and shining with a steady, silvery light, you can catch Venus during mornings in the eastern sky at dawn from Jan. 1 to April 8; evenings in the western sky at dusk from July 30 to Dec. 31

Jupiter
Jupiter

Jupiter will be quite brilliant with a silver-white luster in 2024. It starts the year in the constellation Aries the Ram, then crosses over into Taurus the Bull on April 28 where it will remain for the balance of the year.
During evenings from Jan. 1 to April 26, it'll shine brightly, as well as during mornings from June 8 to Dec. 6. Evening viewing will be optimal again from Dec. 7 to December 31.

Saturn
Saturn

Saturn shines like a yellowish-white "star" of moderate brightness. The famous rings, however, are only visible in a telescope.
The rings were at their maximum tilt toward Earth in Oct. 2017, but are now rapidly closing to our line of sight. They will turn edge-on to the Earth during the spring of 2025. The process will begin in 2024 within the boundaries of the constellation Aquarius, the Water Carrier, and the planet will remain there for the rest of the year.
You can catch Saturn during evenings from Jan. 1 to Feb. 11, mornings from March 17 to Sept. 7, then evenings again from Sept. 8 to Dec. 31. Saturn's brightest in 2024 will fall between Aug. 25 to Oct. 1. Saturn will be in opposition to the sun on Sept. 8. Saturn and Venus will appear dramatically close to each other (with Saturn just 0.2-degree S) on the morning of March 21 and will be 0.4-degree S of Mars on April 10.

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