CAPTURE

Morning conjunctions

A month of planetary encounters offers opportunities to test out the full capabilities of your astro imaging skills

There are a number of interesting morning meetings of planets in April, ending with a spectacular conjunction of Venus and Jupiter. Both planets will be bright, but their altitudes and positions are not ideal at this time of year due to the shallow angle of the morning ecliptic with the eastern horizon. As such, you’ll need good photographic skills (including adaptability, the most important skill of all) to capture this and the other conjunctions that can be seen throughout the month.

On 3 April, a 6%-illuminated waxing crescent Moon sits close to Uranus, which is always close to the naked-eye threshold from a dark-sky location. On the evening of 3 April, Uranus will appear 1.1° from the Moon’s centre. The difference in brightness between the two will make this conjunction hard to capture well: if you set an exposure for the Moon’s crescent then Uranus won’t show, and if you set an exposure for Uranus you will overexpose the Moon.

A tricky meeting between Saturn and Mars occurs on the morning of 5 April, with both planets rising just 80 minutes before the Sun. They will appear separated by 19 arcminutes and be of almost the same brightness. You’ll need to be lucky with the weather and figure out how best to catch them in the brightening twilight of dawn.

The morning planet line-up becomes impressive towards the end of April; recording the waning crescent Moon’s journey as it visits each planet will be a good test of skills. But its low altitude means it will remain challenging to catch. The same low altitude and brightening sky will cause problems for the Venus –Jupiter conjunction at the end of April into May.

Dramatic as this event is, how can you make a photograph of these worlds look like anything other than a pair of dots in the sky? Fortunately, the geometry of this alignment will help. If you have a wide-field setup, the pair’s low altitude will allow you to incorporate some horizon in the shot. Plus, the proximity of Venus to Jupiter on 1 May means it should be possible to capture both planets as discs through a telescope. Venus will be showing a 68%-illuminated disc with an apparent diameter of 17 arcseconds on this date; Jupiter’s disc will be 35 arcseconds and accompanied by the Galilean moons.

Brightening dawn skies present unique issues for astrophotographers, because you need to adapt to conditions on almost a minute-by-minute basis. The low altitude will mean you need to consider foreground objects carefully too, in case a conjunction moves behind a tree. Adding interest to a shot is a vital skill and this month’s conjunctions will test you to the limit. For each one, think about the characteristics of the subjects and how you’ll bring them to the fore.

Equipment: a DSLR or equivalent camera with a telephoto lens; an equatorial tracking mount

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Step by step

STEP 1

With so many conjunctions this month, it’ll pay to plan ahead. This table shows the approximate minimum span (in degrees) needed to cover the conjunctions and the recommended focal length for the lens or telescope. Aim to include the objects with some space around them to create a relaxed, uncramped shot.

STEP 2

Consider the nature of each conjunction and plan to bring out the best of it. The Uranus and Moon conjunction on 3 April has a large exposure differential; if you expose so that the Moon’s crescent burns out, it will reveal the Moon’s earthshine portion and Uranus at the same time –a great shot if you can pull it off.

STEP 3

Before the conjunction of Mars and Saturn on 5 April, plan how you can best bring out the colours of the two planets. Allowing them to trail through the frame is one way, as well as deliberately defocusing slightly. The defocused discs will avoid the usually over-exposed core at low magnification.

STEP 4

The Venus-Jupiter conjunction at the end of April is a chance to capture both planets through a telescope. The closest approach occurs on 1 May when both planets will appear separated by 22.4 arcminutes. A telescope/camera combo that can capture the Moon’s disc will also be able to capture Venus and Jupiter.

STEP 5

Add interest by trying to capture and combine the closing, closest and separating phases of a conjunction. By using the same setup with an unchanged orientation, take images and load them into layer-based photo-editing software. Align a planet between layers and set the blend mode of the higher levels to lighten.

STEP 6

Although it’s interesting to focus on single pairs, there’s also an impressive morning line-up of four bright planets. On 25 April, the line spans 33° and includes the Moon too. A 30mm lens for APS-C cameras (48mm lens for full frame) will catch them all in one shot. Your biggest battle will be the bright dawn twilight.

Send your images to: gallery@skyatnightmagazine.com

ALL PICTURES: PETE LAWRENCE