The planets
Our celestial neighbourhood in March
Venus
Best time to see: 31 March, shortly after sunset
Altitude: 35˚
Location: Taurus
Direction: West
Features: Phase, subtle markings
Recommended equipment: 75mm or larger
Venus currently dominates the evening twilight. It reaches greatest eastern elongation on 24 March, 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 the month, 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.
This month’s 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.
Mercury
Best time to see: 15 March, 30 minutes before sunrise
Altitude: 2˚ (very low)
Location: Aquarius
Direction: East-southeast 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.
Mars
Best time to see: 19 March, around 05:00 UT
Altitude: 6˚ (low)
Location: Sagittarius
Direction: Southeast 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 the 31st.
Jupiter
Best time to see:
31 March, 04:40 UT
Altitude: 8˚ (low)
Location: Sagittarius
Direction: Southeast 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. See page 46.
Saturn
Best time to see: 31 March
Altitude: 6˚ (low)
Location: Sagittarius
Direction: Southeast 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.
Uranus
Best time to see: 8 March, 20:00 UT
Altitude: 22˚
Location: Aries
Direction: West
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. See page 46.
NOT VISIBLE THIS MONTH: Neptune
Neptune is in conjunction with the Sun on 8 March and is not currently visible.