Venus and the waxing crescent Moon will put on a stunning show this month. Credit: Pete Lawrence
Venus currently dominates the evening twilight. It reaches greatest eastern elongation on 24 March 2020, separated from the Sun by 46˚. Telescopically, the planet presents an 18 arcsecond disc, 62%-illuminated on 1 March.
At the start of the month it sets 4 hours and 20 minutes after the Sun. On 9 March, mag. –4.1 Venus appears 2.5˚ north of mag. +5.9 Uranus.
By the end of March, Venus remains above the horizon after sunset for nearly five hours, appearing against a truly dark sky for nearly three hours.
As the end of the month approaches, Venus appears to track ever closer toward the Pleiades open cluster, a prelude to a spectacular passage across the cluster early in April.
Venus reaches dichotomy in March, the term used to describe when it appears with a 50% phase seen through the eyepiece.
Although expected on 27 March, during evening apparitions the 50% phase typically occurs a few days earlier than predicted by geometry.
This is known as the Schröter effect and is an anomaly believed to occur because of the way Venus’s thick atmosphere scatters light.
Phase estimates are easy to do. Simply estimate how far the terminator stretches across the planet as a percentage of its diameter.
A Moon-Venus conjunction occurs on 28 March, when a 16%-lit waxing lunar crescent appears 7.2˚south of the planet.
This occurs when both the Moon and Venus are relatively close to the Pleiades, a situation which enhances the photographic attraction of the scene.
By 31 March, Venus appears through the eyepiece with an angular size of 25 arcseconds and a phase of 47%.
The planet’s magnitude increases to –4.3 by the end of March.
Catch a Venus-Uranus conjunction
Look through 7×50 binoculars on 8 March at 20:00 UT for a conjunction of the bright and dim planets, Venus and Uranus. Credit: Pete Lawrence
On the evening of 27 January 2020, Venus had a conjunction with Neptune. On that occasion, as both objects approached setting, they appeared around 4 arcminutes apart.
Since then Venus has moved east against the background stars and this month it’s the turn of Uranus to get a visit.
The separation and brightness levels of both planets makes this an ideal target for binoculars.
This meeting won’t be as close, with Venus passing Uranus by 2.2˚ on the evening of 8 March.
The meeting between Venus and Neptune at the end of January saw a situation where both the brightest and dimmest planets seen from Earth were in conjunction.
This month’s meeting between Venus and Uranus represents a conjunction between the brightest and dimmest planets which can be seen from Earth using the naked eye.
However, as Uranus is on the threshold of naked-eye visibility, this definition might be stretching it a bit.
This particular meeting is quite favourable, with both objects being around 20˚ altitude up as true darkness falls.
Venus is of course much brighter than Uranus, the magnitudes being –4.2 and +5.9 respectively. In terms of brightness difference, Venus is 11,000 times brighter than Uranus.
Don’t forget Mars, Jupiter and Saturn
Catch Jupiter and Mars after 04:00 UT low above the southeast horizon on 20 March (inverted telescope view with south up). Credit: Pete Lawrence
While Venus steals the show by quite some margin in this month’s evening sky, there’s plenty happening in the pre-dawn morning twilight too: the three planets Mars, Jupiter and Saturn all appear together low in the southeast.
As dawn is breaking at the start of March, all three appear in a line, visible low in the southeast.
Mag. +1.1 Mars appears more first, followed by mag. –1.8 Jupiter and mag. +1.0 Saturn.
An interesting exercise is to compare the colours of Mars and Saturn, which are a similar brightness. Mars has a definite orange hue, while Saturn is more off-white.
As March progresses, so the mornings start to get lighter and this doesn’t help the situation.
However, with slight timing adjustments, it will still be possible to see the trio right up to the end of the month as long as you have a flat southeast horizon.
At the start of March, from the centre of the UK, all three planets will be above the horizon in brightening skies around 06:00 UT.
At the month’s end you’ll need to set the alarm earlier, with all three visible above the southeast horizon around 04:30 UT.
Remember the clocks go forward on 29 March, which will mean you get an extra hour lie-in right at the end of the month.
Mars slowly draws closer to Jupiter throughout much of the month, lying just 43 arcminutes from the gas giant on the morning of 20 March. Just before this, don’t miss the monthly Moon pass which begins on 17 March with a 41%-lit waning crescent Moon lying 15.4˚ west of Jupiter.
On 18 March, the now 31%-lit waning crescent Moon nestles in close to Mars and Jupiter. Mars will have brightened slightly on this date to mag. +0.9.
Then on 19 March, the now 22%-lit waning crescent Moon will sit 4˚ southeast of Saturn, rising as the sky starts to get quite bright.
On the morning of 31 March, it’s Saturn and Mars which appear as a close pair.
Not to be outshone by beautiful Saturn, Mars will have brightened to mag. +0.8 with Saturn sticking at +0.9. Both planets appear separated by a fraction under a degree on this date.
The appearance of the ‘line’ on 1 March changes noticeably during the month.
On 31 March all three planets form a pointed isosceles triangle with Jupiter at the tip, and Mars and Saturn forming the base.
The phase and relative sizes of the planets this month. Each planet is shown with south at the top, to show its orientation through a telescope. Credit: Pete Lawrence
This month’s planets at a glance
Best time to see 31 March, shortly after sunset
Features Phase, subtle markings
Recommended equipment 75mm or larger
Best time to see 15 March, 30 minutes before sunrise
Altitude 2˚ (very low)
Mercury is a morning object low in the east-southeast mid-month. A balancing act then takes place: as the planet becomes brighter it drops south beneath the ecliptic and loses altitude. It reaches greatest western elongation on 24 March (27.8˚) but will only be visible for a short time before the sunrise.
Best time to see 19 March, around 05:00 UT
Altitude 6˚ (low)
Slowly improving in apparent size and brightness, morning planet Mars remains low from the UK. It appears to jostle for position with Jupiter and Saturn over the month, a close 43 arcminute conjunction with Jupiter occurring on 20 March and a 1˚ separation from Saturn on the 31st. Mars remains tiny through the eyepiece, with a disc just 5 arcseconds across. At this size only large-scale markings can be seen on the planet’s surface. The planet’s brightness increases from mag. +1.1 on 1 March to mag. +0.9 on 31st.
Best time to see 31 March, 04:40 UT
Altitude 8˚ (low)
Jupiter is visible low in the southeast morning sky in brightening dawn twilight. It sits close to Mars and Saturn, having a close conjunction with Mars on 20 March. It shines at mag. –1.8 at the month’s start, brightening to mag. –2.0 by the month’s end. All three planets are close to the most southerly position they can attain in the sky and this means that any telescopic view of them is likely to be compromised due to poor atmospheric stability, which occurs at low altitude. This may limit high magnification views from the UK, but the naked-eye show is still remarkable to witness.
Best time to see 31 March
Altitude 6˚ (low)
Saturn is close to Mars and Jupiter this month, all three planets lying within Sagittarius. It’s similar in brightness to Mars, at mag. +0.9 and lies close to the Red Planet on 31 March, appearing 1˚ to its north. This is a good opportunity to compare the colours of both planets. Mars appears to have an orange hue, while Saturn is off-white.
Best time to see 8 March, 20:00 UT
Uranus is now a compromised planet, appearing to the west of south with diminishing altitude as the sky gets dark. It still has a decent altitude against dark skies at the start of March, but this degrades. On 8 March this distant ice giant appears just 2.2˚ from mag. –4.2 Venus.
Neptune is in conjunction with the Sun on 8 March and is not currently visible.
Pete Lawrence is an experienced astronomer and a co-host of The Sky at Night. This guide originally appeared in the March 2020 issue of BBC Sky at Night Magazine.