The Night Sky This Month: March 2021

Hydrocarbon-filled lakes on Titan
Image Credit: JPL-Caltech/NASA/ASI/USGS

The vernal equinox occurs on March 20th, on which date spring arrives in the Northern Hemisphere, and summer ends in the Southern Hemisphere.

In the meantime, the excitement around the successful deployment of the Perseverance rover on Mars, it is sometimes easy to forget that the data from similar exploration efforts on Saturn’s moon Titan is currently yielding huge amounts of information.

For instance, the image above shows the range and extent of only a few of the estimated 650 hydrocarbon-filled lakes on Titan, some of which can more properly be described as “seas” whose dimensions are comparable to the Mediterranean Sea on Earth. Analysis of data received from the Cassini craft has also revealed that some lakes appear to have formed when frozen methane on Titan exploded when temperatures on Titan rose sharply.

This view is supported by the differences between types of lakes: some seemed to have formed when “cocktails” of acidic hydrocarbons dissolved patches of the moon’s icy surface, while others have sharply defined vertical walls and raised rims, which suggests that some lakes were excavated when underground reservoirs of methane exploded. Investigations are continuing.

The Moon phases In March 2021

Last Quarter New Moon First Quarter Full Moon
March 5th March 13th March 21st March 28th

The Planets in March 2021

Planetary viewing will be particularly poor during March, as several planets are now very near points of conjunction with the Sun, or have recently moved in behind the Sun. Nonetheless, and purely as a matter of interest, here is what we can expect in terms of viewing the planets during March-

Mercury is now approaching its point of greatest western elongation from the Sun when it will be about 27 degrees west of our star. However, the little planet will not be observable from latitudes south of London, as it will be only about 1 degree above the horizon at dawn as March begins, and about 3 degrees below the horizon during the daylight hours by the end of the month.

Venus will spend much of March either behind the Sun or within about 6 degrees of it. Therefore, the planet will not be visible for most northern hemisphere observers during the month.

Mars is the only planet that is readily visible during this month. Seen from London and its surrounds, the Red Planet becomes visible as an early evening object, rising to about 47 degrees above the southwestern horizon. Note though that Mars will set at about 01:50 (GMT) for most of the month.

Jupiter recently moved in behind the Sun, and will therefore be above the horizon during the daylight hours. However, as the month begins, the king of the planets will be about 2 degrees above the horizon at dawn, increasing to about 6 degrees above the horizon by month’s end.

Saturn is still very close to its point of conjunction with the Sun and is therefore above the horizon during the daylight hours. Nonetheless, Saturn will be about 2 degrees above the horizon at dawn as the month begins and about 7 degrees above the horizon at dawn by the end of March.

Uranus is now approaching a point of conjunction with the Sun, but it will nevertheless become visible to observers based at mid-northern latitudes at about 07:00 (GMT) at an elevation of about 35 degrees above the south-western horizon.

Meteor Showers in March 2021

No significant meteor activity is expected to occur during the month.

Deep Sky Objects to Look For In March 2021

Two constellations, Cancer and Monoceros, both of which contain a large number of star clusters, are particularly well placed in the northern sky at this time of the year. Moreover, most of the clusters in these constellations are easy targets for large binoculars and small telescopes, so see if you can spot the three open star clusters we have listed here-

M44 (Beehive Cluster, Praesepe, NGC 2632, Cr 189)

Beehive Cluster
Image credit: Second Digitized Sky Survey (DSS2)

With an estimated distance of between 510 and 620 light-years from Earth in the constellation Cancer, M44 is one of the closest star clusters to Earth, as well as one of the most densely populated to our planet. This image shows the inner core of the cluster, which spans across some 23 light-years.

The Beehive Cluster is of some scientific interest, since its age and proper motion both suggest a common origin with the Hyades cluster in Taurus, although this has not yet been demonstrated conclusively. Nonetheless, the cluster is visible as a faint patch of light with the naked eye, but since its apparent diameter is only about 1.5 degrees, it fits in a single field of view of most binoculars and small telescopes at low magnifications.

Look for the cluster at an elevation of about 40 degrees above the eastern horizon from about 19:00 (GMT). Note, however, that M44 will rise to about 56 degrees or so before sinking to below 16 degrees above the western horizon at around 04:00 (GMT).

NGC 2232

NGC 2232
Image credit: Second Digitized Sky Survey (DSS2)

Located about 1000 light-years away in the constellation Monoceros, the cluster is centred on the star 10 Monocerotis. The cluster is also one of the closest star clusters to the Sun, it being located in the Gould Belt, near the Orion Nebula Cluster. In the image above, the stars showing diffraction spikes are overdeveloped foreground stars and are not related to the cluster.

The cluster is notable for the fact that some of its member stars have higher iron abundances than the Sun, with an average metallicity value of 0.22±0.09, or 0.32±0.08 depending on which source is consulted. Moreover, at least four members of the cluster display excess infrared radiation at a wavelength of 8μm, which suggests that these stars may be surrounded by warm, if not hot, dusty discs or clouds. This is a further indication that these stars may still be partially shrouded in their birth cocoons.

Look for this cluster at an elevation of about 29 degrees above the south-western horizon from about 20:44 (GMT). The cluster will subsequently set just after midnight (GMT).

M50 (NGC 2323, NGC 2244, Cr 99, Mel 47)

Image credit: Second Digitized Sky Survey (DSS2)

Located about 2, 900 light-years away, also in the constellation Monoceros, this small, compact open cluster may or may not be gravitationally bound to the Canis Major OB1 association. The cluster is relatively young, with an age of only about 140 million years, which explains the fact that its 508 confirmed member stars, and around 100 suspected member stars fit into an area of only 17.8 light-years. However, despite its relative youth, the cluster contains at least two high-mass white dwarfs, indicating that there might be something to the theory that the cluster could be related to an association of massive, hot stars. The cluster also contains two chemically peculiar stars.

Look for the cluster at an elevation of about 40 degrees above the southern horizon from about 18:54 (GMT). The cluster will then set just after midnight (GMT).

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