The top sights to observe or image this month

DON’T MISS: Mercury and Regulus – a daytime target

BEST TIME TO SEE: 3 and 4 August around 14:30 BST (13:30 UT)

Although nights are slowly getting longer, there’s an awful lot of day to contend with too. An interesting opportunity occurs at the start of August, when Mercury appears close to the brightest star in Leo the Lion, Regulus.

This will be nigh on impossible to see after sunset due to low altitude, so other arrangements need to be made.

Mercury will shine at mag. –0.4 on 3 August and –0.3 on 4 August, bright enough for the planet to be seen in daylight, as long as you know where to look. Regulus shines at mag. +1.3 but, being a point source of light, can also be seen during the day. Consequently, if your telescope is pointing at the right place in the sky, you should be able to see both Mercury and Regulus together in broad daylight.

At 14:30 BST (13:30 UT) on 3 August, Mercury is due south at an altitude of 50º from the centre of the UK. At this time, the planet is located 1.6º from Regulus. At the same time on 4 August, the pair are in a similar sky position, separated by 44 arcminutes.

Closest separation occurs earlier that morning at 10:00 BST (09:00 UT), when planet and star are just 40 arcminutes apart. There are various ways to locate Mercury during the day. If you have a Go-To telescope set up the night before, it should locate Mercury easily. If this isn’t an option, and if your Go-To allows you to sync on the Sun, it can be used as a jumpingoff point – as long as you remember to filter the telescope and cap any finders.

If your mount has setting circles, an appropriately filtered view of the Sun can be used to locate Mercury manually. Here, with the solar filter fitted, centre on the Sun accurately, focusing on its disc. Look up the Sun’s RA and dec., adjusting the setting circles to match. Look up the coordinates for Regulus and slew the telescope to that position. Check the Sun is out of the field of view (it should be 18º to the west), remove the filter and look for the planet.

As ever with daylight observing, please take great care not to allow the Sun anywhere near your telescope’s field of view when you are looking through the eyepiece. If you do navigate to the target using the Sun as a jumping-off point, make sure you have all optics protected with the appropriate filters or safety caps.

Mars, Uranus and the Pleiades

BEST TIME TO SEE: Mornings of 2 and 19–23 August

Mars has a couple of interesting encounters this month, passing close to Uranus and the Pleiades. On 2 August, mag. +0.2 Mars sits just 1.3º south of mag. +5.8 Uranus. Both planets rise around 00:00 BST (23:00 UT) and reach an altitude of 25º above the eastern horizon as the darkest part of the night comes to an end at around 03:00 BST (02:00 UT).

Mars slowly drifts east from Uranus over the following mornings, but remains fairly close to the dimmer planet for several days. On 5 August, for example, Mars and Uranus are 2.3º apart.

After this planetary encounter, Mars continues tracking east, appearing to pass 5.7º south of the Pleiades open cluster on the morning of 22 August. Before this, on 19 August, both planet and cluster are joined by the last-quarter Moon, located 5º west of Mars on this date. The Moon will pass 2º north of Mars at 13:00 BST

(12:00 UT) on 19 August under daylight conditions, while 16º above the western horizon. On the morning of 20 August, the now 41%-lit waning crescent Moon sits 7.7º east of Mars.

Mars has now reached its opposition constellation of Taurus and will remain within this constellation’s boundaries for the remainder of 2022 and into 2023. As it does this, it’ll also be performing a retrograde loop, reversing direction to head west before repeating the action to resume its eastern track.

If you’re interested in long-term astrophotography of the position and brightness of Mars against the backdrop of Taurus, the coming weeks will allow you to record and present the retrograde loop against the stars of the Bull. It will also offer an opportunity to compare the colour of Mars with the orange-tinted Aldebaran (mag. +0.8 Alpha (α) Tauri).

Lunar X and V

BEST TIME TO SEE: Evening of 4 August just before sunset

Another opportunity to see the popular lunar X and V clair-obscur effects occurs late in the afternoon on 4 August. The effects take place when the Sun is up, adding an extra element of difficulty in seeing them. The X and V appear in their letter forms near to the lunar terminator for a short period of just a few hours. On 4 August, they will appear optimally around 20:00 BST (19:00 UT) when the Moon is 20º above the south-southwest horizon.

Sunset will be approaching.

The V forms when the lunar dawn’s early light illuminates elevated features near to the 23km crater Ukert, which appears just above the central point of the Moon’s disc on 4 August. Similarly, the lunar X is formed when rim sections of three craters 58km Blanchinus, 68km La Caille and 118km Purbach catch the lunar dawn.

Contrast will be reduced for both effects because of the daylight conditions, but using a small telescope, it should still be possible to see them. If you’re into imaging, consider using an infrared sensitive mono high-frame-rate camera combined with an infrared pass filter.