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Orion constellation
Source: Wikipedia

Betelgeuse is a red giant star in the Orion constellation. Since October it has dimmed considerably.

Red giant stars are those which are nearing the end of their lives. The image left shows the Orion constellation with the distinctly red-coloured Betelgeuse in the upper right (click on image for larger).

Betelgeuse has a mass that is 12 times greater than our Sun. It is estimated that is has a diameter of 1.2 billion kilometers. It is about 642 light-years from Earth.

Due to its high mass Betelgeuse has a very short life. It is believed to be about 10 million years old compared to the 4.5 billion years of the Sun. This is because large stars burn their fuel much more quickly.

Being a variable star variation in the brightness of Betelgeuse is not unusual. It undergoes variations on a number of different cycles. There is the main 5.9 year cycle with several smaller ones. The image below shows the brightness difference between 2016 and December last year.

Betelgeuse Dimming
Betelgeuse during 2016 on the left and on the 31st of December 2019 (note the other stars in both images are identical). Credit: Brian Ottum via EarthSky.

You may have read reports that the star is about to go supernova (AKA ‘blowing up’ in layperson speak). Despite the fact that the star will do this in the very near future on a Universe time-scale (in the next 100,000 years) it is unlikely that the current dimming is an indication that it will occur soon on a human time-scale. The current dimming is likely to be the result of the coincidental alignment of the minimum points on two or more of the cycles discussed earlier.

In any event, the star is of no danger to the Earth of life on the planet.

Globular clusters are aggregations of stars in a spherical shape. They are bound by their mutual gravity and have high star density towards their centers. These ancient star clusters orbit the center of galaxies.

Globular clusters are considered to be old because they mostly contain low mass stars. It is important to understand that large stars have much shorter lives than low mass stars do. Smaller stars burn their fuel more slowly than larger stars. Also, large mass stars emit more blue light than do smaller stars resulting in them appearing blue.

Blue stragglers are young large mass stars in globular clusters. Their much younger age is incompatible with the age of the host globular cluster.

Astronomers believe that blue stragglers are the result of the merger of smaller stars in the cores of globular clusters. The relatively high concentration of stars in the cores of globular clusters facilitates these mergers.

The globar cluster NGC 6752 is located approximately 13,000 light-years away in the direction of the constellation Pavo. The cluster is over 10 billion years old and is a companion of our Milky Way. It contains more than one hundred thousand stars in a sphere 100 light-years across.

NGC6752 and its blue straggles
NGC6752 and its blue straggles. Note the star in the top left of the cluster is located between Earth and the cluster (click photo for larger image).

Image source: Globular Star Cluster NGC 6752

This is a lovely time-lapse of the Earth from the ISS. In this video 15 seconds of real-time is compressed into 15 seconds.

Due to the altitude of ISS (about 400km) it is not possible to see an entire hemisphere. From the station the distance from one point on the horizon to one 180 degrees around from it is about 4300km.

We only see one side of the moon due to the tidal locking of the Moon to Earth. However, we get to see a little more than half the moon. Due to lunar libration we see about 59% of the Moons surface. This libration is due to the dynamics between the Earth and Moon.

The video shows a simulation of one phase cycle of the Moon.

Lunar libration video

In actual terms the Earth has a diameter of 12 742km and is 40 075km around the equator. That may sound large but in the scheme of the solar system it is it not that big. In the terms of the universe it is totally insignificant. This video compares the size of the objects in our solar system and to other stars.

Ever wanted to take your own photos of the night sky but never knew how. This video gives a very brief explaination of what is involved to get started in this exciting hobby. Just be aware that there is a huge difference in skill level from where he starts (ie a camera on a tripod) to where he finishes. It is very easy to use a camera on a tripod. It takes a lot more determination and money to take good photos like the ones towards the end of this video.

Using the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) scientists have found a galaxy that is 13.1 billion light years away. To date this is the most distant galaxy found. Since the light has taken 13.1 biliion years to reach us we are seeing how the galaxy was when the Universe was only 600 million years old. Not only is that impressive but it tells us the galaxies had formed by that time placing restrains models for the formation of the Universe.

The image below shows the location of the galaxy on the Ultra-Deep Field image taken by the HST in 2009. I posted the full version of this image on the 4th of October. The post is called Hubble Ultra Deep Field.

While this is a very deep image deeper images should be generated from the soon to be launched James Webb Space Telescope. It is hoped that this telescope will find the very first formed galaxies in the universe

This video is a short documentary on the Collisional Ejection Theory for the creating on the Earth’s moon. It features Bill Hartmann and Robin Canup who were important figures in the development of this theory.

Ever felt insignificant? If you have an understanding of what is presented in this image you should. Nearly every object in this image is a galaxy containing millions and in most cases billions of stars. The image is called the Hubble Ultra Deep Field and was taken in 1995 and 1998.

The objects in this image are extremely dim and not detectable by ground-based telescopes. Even the Hubble Space Telescope cameras had to collect light over 278 hours to produce this image. There are 10,000 galaxies in the image. Using this image it has been estimated that there are 130 billion galaxies in the Universe at least as bright as the dimmest galaxy in the image.

For a larger version click the image. For a very large version (60MB) see the Hubble Ultra Deep Field image.

Today every point on Earth has a day and night of very nearly 12 hours for each. This is called an equinox and since this one occurs in September every year it is called the September Equinox. It is also called the Autumnal Equinox in the northern hemisphere as it marks the onset of Autumn.

Only one other equinox occurs every year and it occurs in March. Obviously this is called the March equinox. It is also referred to as the Vernal Equinox and in the northern hemisphere marks the start of spring.

Equinoxes occur when the tilt of the Earth’s of rotation is at a right angle to the line connection the Earth and Sun. This can only occur twice in a single orbit of the Earth around the Sun (ie one year). At the time of each equinox the Sun lies at the intersection of the plane containing the Earth and Sun and the plane defining the Earth’s Equator.

In the figure on the right the blue plane is defined by the Earth’s equator. The yellow plane is the plane containing the earth and Sun (the line the Sun appears to follow is called the ecliptic). The position of the Sun at an equinox is marked as Autumnal and Vernal Equinoxes on the figure. Today the Sun is at the pointed marked as Autumnal Equinox.

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