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Observing the planets

venus and the moon
It’s quite easy to see some of the other planets in our Solar system from your garden, balcony or on an evening walk. In fact, you might have already seen them without realising it, explains Dr David Brown from Warwick’s astrophysics team.

Have you ever seen a particularly bright point of light in the sky and wondered what it is? Chances are that you’re looking at a planet, not a star.

The easiest way to tell them apart is that stars seem to twinkle, but planets don’t.

Another way to tell them apart is that they change position in the night sky. Because the planets orbit the Sun they appear in different constellations throughout the year. In fact the word planet comes from the Greek word for “wanderer”, which seems appropriate. The planets’ wanderings mean that they sometimes appear close to each other and/or the Moon, making interesting groupings that are called “conjunctions”. These are some of the best times to observe the planets.

Five of the planets are visible with just your eyes, and they can be some of the brightest objects in the sky. But their brightness changes throughout the year (this is more obvious for Mars than it is for Jupiter), so they are not always as easy to see as when they are at their best.

Mercury

Because Mercury is the planet nearest the Sun, it can only be seen just before sunrise or just after sunset. In both cases it will be low down, near the horizon in the east in the morning, or in the west in the evening. That makes it difficult to spot in towns because of buildings can block your view of the horizon.

Mercury usually appears yellowish or pale orange in colour. Your best chance to see it this year will be in the morning sky in November.

Venus

Venus is a lot easier to observe than Mercury, appearing much higher in the sky and shining with a steady, silvery light. It’s the brightest star-like object in the night sky, and at its brightest can even be seen during the day. In fact Venus is so bright that it’s sometimes reported as a UFO!

Venus can be seen at most times of the year, but it will be brightest in July and furthest from the Sun in August. So the best time to observe it is over the summer holidays, in the mornings. In mid-June there will also be a nice conjunction of Venus and the crescent Moon which will be worth looking out for.

Mars

Mars earns its nickname of “the Red Planet”, appearing as a mix of yellow-orange-red to the eye. It can change considerably in brightness, and this year will be brightest in the first half of October this year. At that point it will be the third brightest object in the night sky (after the Moon and Venus) and visible throughout the night. You may already be able to spot it as it’s starting to become noticeable already as it shines low in the southeast morning sky. Keep an eye out for it gradually brightening and appearing higher in the sky as the year goes on.

Jupiter

Jupiter is usually third in brightness only to the Moon and Venus, appearing pale yellow or white. It’s much more consistent in brightness than the inner planets, and like Venus is usually fairly easy to spot. The best time to observe Jupiter this year is in July, but towards the end of 2020 there will be a spectacular conjunction of Jupiter and Saturn that will be well worth a look.

The two largest planets of the Solar system only appear close together every couple of decades, and when they do are usually still separated by a distance two or three times the size of the full Moon. But this year, on 21 December, Jupiter and Saturn will be visible together in the sky separated by a distance of only around 20% the diameter of the full moon. That’s incredibly close together for these planets; the last time they appeared so close together was in 1623, so this is an opportunity not to be missed. Sadly though it might be difficult to see this rare event, as the planets will be low down in the evening sky to the southwest.

Saturn

Apart from the conjunction with Jupiter on the 21 December, the best time to observe Saturn this year is throughout July when it’s at its brightest. Saturn is a similar pale yellow colour to Jupiter, but unfortunately the famous rings are only visible through a telescope. But if you have access to one then have a closer look because it is a spectacular image.

Using binoculars or a telescope

Those are the planets that you can see without using any special equipment. If you have a pair of binoculars then both Uranus and Neptune are also visible, and you’ll be able to start picking out some interesting features like the phases of Venus or the Galilean moons of Jupiter. If you have access to a small telescope then even more detail becomes visible, like the rings of Saturn, the polar caps of Mars, and the stripes of Jupiter.

If you want more information about which planets you’ll be able to see each night, as well as other interesting things to look out for, try https://www.timeanddate.com/astronomy/night/ or https://earthsky.org/tonight.

Published:

5 June 2020

About:

The Astronomy and Astrophysics group at Warwick is interested in a huge range of scales across the Universe: planetary systems, how they form, live and die; stars, stellar binaries and and the exotic physical processes that they allow us to explore; as well as the transient events which mark the end of stellar lifetimes and the galaxies stars inhabit across the Universe. The group started in September 2003 and is both an observational and theoretical group. The group makes use of a wide range of ground-based telescopes, such as ESO's Very Large Telescope (VLT) in Chile and the Isaac Newton Group of telescopes (ING) in the Canary Islands, or the Atacama Large Millimetre Array (ALMA), as well as space telescopes such as NASA's Chandra and ESA's XMM-Newton X-ray observatories and the Hubble Space Telescope. The Warwick astro group partners in the four large spectroscopic surveys (DESI, SDSS-V, WEAVE, and 4MOST) that will start operations throughout 2020-2021.

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