Of all the cosmic events that can be seen with the naked eye from Earth, few can parallel the beauty of lunar and solar eclipses. Once believed to be bad omens and harbingers of impending disasters, eclipses are today understood in their entirety and valued for the windows of possible scientific study they provide.
While both lunar and solar eclipses occur when the Earth and the moon are aligned with the sun, the positions of our planet and its natural satellite are reversed for the two eclipse types. A solar eclipse occurs when the moon passes directly between the Earth and the sun, and thus can only happen on a new moon. Conversely, the Earth has to pass directly between the sun and the moon for a lunar eclipse, ergo making it only possible on a full moon. Depending on how exact the alignment is, an eclipse can be partial or total.
A further type of solar eclipse may occur. Due to the moon having an elliptical orbit around the Earth, it changes its distance slightly during its orbit around our planet. This means that even though the moon might pass directly between Earth and the sun, the moon’s disc might in some instances appear just a little too small to cover the sun’s entire disc, leading to an annular solar eclipse.
One might consider eclipses to be rather normal, albeit occasional, events. On average, there is some form of a lunar or solar eclipse every year, even though many of these are unfortunately only visible from the middle of oceans. However, total solar eclipses in particular are a slowly expiring phenomenon.
The moon is gradually moving farther away from Earth, at an admittedly slow rate of about four centimetres per year. This means that, in a few hundred million years, the size of the moon as it appears from Earth will not remain large enough to ever cover the sun’s disc completely. At that point, only partial and annular solar eclipses will be visible from Earth. Total lunar eclipses will last for a longer time, as the Earth will continue completely covering the sun, from the moon’s perspective.
Eventually, the moon will be too far away to form any kind of eclipse whatsoever.
The next eclipse event visible from Malta will be tomorrow evening.
A partial lunar eclipse will be visible at moonrise, peaking at around 8.20pm. Due to it occurring at moonrise, viewing the partial eclipse from an east-facing location would be ideal.
Unfortunately, the total solar eclipse occurring on August 21 will not be visible from the Maltese islands, with the path of totality traversing the entire US instead.
Josef Borg is a PhD student at the Institute of Space Sciences and Astronomy of the University of Malta and vice-president of the Astronomical Society of Malta.
Sound bites
• New clue to solving the mystery of the sun’s hot atmosphere. A team of scientists analysed observations from the Solar Dynamics Observatory at a time of low activity (solar minimum) starting in 2010 and through till 2014 when huge magnetic active regions crossing the solar disk were common. An unknown mechanism preferentially transports certain elements, such as iron, into the corona instead of others, giving the corona its own distinctive elemental signature. The team think that the mechanism that separates the elements and supplies material to the corona may also be closely related to the transport of energy, and that understanding it may provide clues to explain the whole coronal heating process.
Source: https://phys.org/news/2017-08-clue-mystery-sun-hot-atmosphere.html
• Partial lunar eclipse observation event to be held tomorrow. The Institute of Space Sciences and Astronomy, in collaboration with the Astronomical Society of Malta, is organising an observation event at L-Aħrax tal-Mellieħa, close to the Immaculate Conception chapel, starting at 7.30pm.
While the partial eclipse itself will be visible with the naked eye, telescopes will be set up for all those attending to see the planets Jupiter and Saturn, as well as to observe the moon itself.
To find out some more interesting science news listen in on Radio Mocha on every Monday and Friday at 13:00 on Radju Malta 2.
Did you know?
• The longest a total solar eclipse can potentially last is around 7.5 minutes. Most total solar eclipses last for a much shorter period of time, some of them even less than a minute. However, a total solar eclipse occurring in the year 2186 will actually last for just over seven minutes from northern Guyana, which will be the longest solar eclipse between 4,000BC and AD 8,000.
• Eclipses can only happen in ‘eclipse season’. The moon’s orbit can vary by a few degrees above and below the ecliptic plane, which is the plane along which it would be exactly aligned with the Earth and sun. This alignment is called a syzygy, and occurs only within a period of approximately 34 days, referred to as the eclipse season. If this inclination in the moon’s orbit did not exist, and had the moon always been perfectly aligned with the Earth and sun, we would have a solar eclipse and a lunar eclipse every new moon and full moon respectively.
• It is possible to follow the path of a total solar eclipse, extending the view time possible. The 7.5-minute cap on total solar eclipse duration only applies for a fixed point on the Earth’s surface. If one were to be on an airplane flying through the path of totality at the path’s speed (approximately twice the speed of sound), an extended viewing of the eclipse could be carried out. This was, in fact, done by four teams of scientists in 1973, who chased the path of total solar eclipse over Africa for 74 minutes on board a Concorde.
For more trivia see: www.um.edu.mt/think.