Astrophilia

Galaxies are mainly of three types - Spiral, Elliptical and Irregular. They are subdivided into classes and designated a specific type. Spiral Galaxies :  They have three main features namely a bulge , a halo and a disc . The bulge is the central portion of the spiral which is significantly brighter than the rest of the galaxy. The bulge of most galaxies is known to contain a super massive black hole (SMBH) in it. The disc consists of the spiral arms around the bulge. The halo is a faint enclosure around the galaxy. The halo mainly contains globular clusters which contain old stars. Spiral galaxies are categorised into two varieties. The spiral galaxies, whose arms extend right from the bulge are termed as ordinary spiral galaxies and designated as SA. On the other hand, some spiral galaxies have spiral arms which don't extend from the bulge, but extend from an elongation of the bulge. Theses galaxies are known as Barred Spiral Galaxies and are designated as SB.  T...

Longitudes of the Earth are great spheres passing through the North Pole and the South Pole of the Earth.In the figure shown all the blue lines going from the top to the bottom are longitudes. Longitude is measured as the angular distance east or west between the great circle (or meridian) of the point and the Greenwich Meridian.  It can be measured in degrees as well as hours. It is more convenient to calculate longitude in hours because the time difference between two points on the Earth can be measured easily. Since the Earth takes 24 h to spin around itself once and also that a sphere has to rotate 360° to return to its original configuration, 24 h is equivalent to 360°. So 1 h is equivalent to 15° of the globe.

The latitudes of the Earth are small circles except the Equator. We consider the Earth to be a perfect sphere for simplicity. We define the latitude  (Φ)   of a point as the angle which between the point, the centre of the sphere, and the corresponding point in the great circle directly below it. In the diagram shown, the latitude of a point B is the angle BOD. Latitude is measured in degrees, arc minutes and arc seconds north or south from the Equator. It is obvious that the latitude of the Equator is 0° and that of the North/South pole is 90° N/S.  Another useful term related to latitude is the colatitude. The colatitude is angle from the pole to the centre to the point. In other words, colatitude is the complementary angle of the latitude. In the diagram the colatitude of B is the angle POB. So POB = 90° - DOB.  Hope that was useful...

So what's a spherical triangle ? We know that a normal triangle lies on a plane. Spherical triangles, on the other hand, lie on a sphere. The sides of a spherical triangle lie on great circles. The triangle ABC in the figure shown is a spherical triangle. Spherical angles:  The angles of the spherical triangle, ie, spherical angles are defined as follows.  Consider two sides of the triangle. Draw tangents at the meeting point of the two sides in the plane of the two sides. The angle between the tangents is called the angle between the two sides. Properties of a spherical triangle : 1. Unlike a normal triangle, the angles of a spherical triangle don't add up to 180°. In fact the sum of the angles of a triangle always adds up to more than 180° but is always less than 540° . 2. So each angle of a spherical triangle is always less than 180°. 3. Sum of any two sides of the triangle is always greater than the third side. More posts coming soon....

In this series of posts I will be explaining the various terminology and methods involved in Spherical Geometry and Trigonometry and how it is used in Astronomy. So let's begin... Consider a sphere as shown A great circle is defined as the intersection of the sphere with a plane which contains the sphere's centre. Another way to think about this is that a great circle  divides the sphere into two symmetric hemispheres. The radius of a great circle is same as that of the sphere itself. For example, the equator of the Earth and all the longitudes could be great circles of the Earth. A small circle, on the other hand, is simply an intersection of any other plane with the sphere. In other words, circles on the sphere which aren't great circles are said to be small circles . It is obvious that small circles have smaller radii than  the great circles, hence the name. For example, the latitudes of Earth other than the equator are small circles. When the a line is draw...

The James Webb Space Telescope is to be launched in 2019. It is considered to be a successor of Hubble. NASA has this awesome 3 D model of it where you can zoom into its components and view detailed information about its components and instruments. Check it out here https://jwst.nasa.gov/Webb3d/

Wolfram Alpha has this cool widget that takes in a value of wavelength in nanometres and shows what color it corresponds to. Check this out at  http://www.wolframalpha.com/widgets/gallery/view.jsp?id=23c041a005eec913db5a74171ea72e63  . It also displays properties of the color like frequency, temperature and energy associated with it. A screen shot of the widget is shown here.