The planets
Our celestial neighbourhood in April
Mars
Best time to see: 1 April, from
75 minutes before sunrise
Altitude: 5˚ (low)
Location: Capricornus
Direction: Southeast
Features: Phase, dark markings, polar caps and weather
Recommended equipment: 75mm or larger
Mars remains low as seen from the UK, currently visible above the southeast horizon in the early dawn twilight. On 1 April Mars lies a fraction under a degree southsoutheast of Saturn. From the UK when due southeast, Saturn appears directly above Mars. With Mars at mag. +0.8 and Saturn at mag. +0.9 the 1st presents a good opportunity to compare the appearance of both objects in terms of colour. Saturn’s offwhite colour should contrast well against orange-hued Mars. The only issue here will be the rapidly brightening background sky, which will make their colours that bit harder to see. Jupiter is also nearby, located 6.3˚ west of Saturn. Together, all three should be a stunning sight in the morning sky.
On 1 April a telescopic view of Mars will show it to be 6 arcseconds across and presenting an 88%-lit phase. By the end of the month this will have changed slightly with the planet’s apparent diameter slightly larger at 7 arcseconds and a marginally reduced phase of 86%. At the end of the month, Mars will appear brighter at mag. +0.4. On 16 April, mag +0.6 Mars will appear 2.8˚ north of a 37%-lit waning crescent Moon.
Mars is no slouch, and can appear to move rapidly against the background stars. Throughout April it heads east, almost managing to completely cross the west-east length of Capricornus. This eastward motion isn’t particularly favourable in terms of positioning the planet for observation. It’s rapid motion east keeps it embedded in the dawn twilight, the bright sky engulfing it as it attempts to gain any serious altitude. Things will improve over coming months but for the time being, Mars remains a tricky planet to observe through a telescope.
Mercury
Mercury’s poor morning appearance in March continues through April. The planet will be poorly placed in the morning sky and is unlikely to be seen.
Venus
Best time to see: 3 April, from 30 minutes after sunset
Altitude: 35˚
Location: Taurus
Direction: West
Venus is a spectacular sight in the west after sunset. Shining at mag. –4.3, it will be approaching the Pleiades open cluster on 1 April, separated from the cluster stars by less than 2˚.
There’s plenty of time to enjoy this view too, Venus remaining above the horizon for nearly five hours after sunset on 1 April, three hours in true darkness.
The planet-cluster separation is less than 1˚ on 2 April, with
Venus appearing to pass in front of the cluster stars on the evening of the 3rd. As the planet and cluster will be visible against a dark background, it will open up opportunities for imaging. On 4 April, Venus will appear 0.4˚ to the east of the star Atlas, the easternmost of the main Pleiades stars. However, the positioning will be perfect. The Pleiades looks like a box with a handle and the placement of Venus on the evening of 4 April serves to extend that handle.
Through a scope, things are changing rapidly too. On 1 April, Venus presents a 25 arcsecond disc, 46%-illuminated. By the month’s end the Venusian disc appears 38 arcseconds across and shows a 25% phase.
The planet’s monthly visit from the Moon occurs on 26 April when a 12%-lit waxing crescent Moon sits 6.5˚ south of Venus. As April’s end approaches don’t become complacent with Venus’s appearance in the evening twilight sky. Having been a dominant fixture for several months, it’s now moving along the part of its orbit closest to Earth. Its favourable position in the sky and dominant appearance will change. Venus will set four hours after the Sun at the end of April, one hour less than it did at the month’s start.
Jupiter
Best time to see: 30 April, 90 minutes before sunrise
Altitude: 10˚
Location: Sagittarius
Direction: Southeast
A low morning planet that currently appears close to Saturn. A 47%-lit waning crescent Moon is nearby on 15 April, forming an isosceles triangle with Jupiter and Saturn. Jupiter shines at mag. –2.2 by the end of the month, which makes it the second brightest planet in the sky after Venus. As an aside, Jupiter appears 45 arcminutes from Pluto on the morning of 4 April.
Saturn
Best time to see: 30 April, 90 minutes before sunrise
Altitude: 9˚
Location: Capricornus
Direction: Southeast Saturn is in Capricornus and visible in the morning sky near to Jupiter. A 47%-lit waning crescent Moon sits nearby on the morning of 15 April. Saturn currently shines at mag. +0.9.
Neptune
A morning planet, Neptune is not well placed for observing.
NOT VISIBLE THIS MONTH:
Uranus
Uranus is in conjunction with the Sun on 26 April and not visible this month.