Astronomer Biography: Jacobus Kapteyn

Jacobus Cornelius Kapteyn was a Dutch astronomer, best known for his extensive studies of the Milky Way and as the first discoverer of evidence for galactic rotation. Kapteyn was born in Barneveld, and went to the University of Utrecht to study mathematics and physics in 1868. In 1875, after having finished his thesis, he worked for three years at the Leiden Observatory, before becoming the first Professor of Astronomy and Theoretical Mechanics at the University of Groningen, where he remained until his retirement in 1921.
Between 1896 and 1900, lacking an observatory, he volunteered to measure photographic plates taken by David Gill, who was conducting a photographic survey of southern hemisphere stars at the Cape Town Observatory. The results of this collaboration were the publication of Cape Photographic Durchmusterung, a catalog listing positions and magnitudes for 454,875 stars in the Southern Hemisphere. In 1897, as part of the above work, he discovered Kapteyn's Star. It had the highest proper motion of any star known until the discovery of Barnard's Star in 1916. In 1904, studying the proper motions of stars, Kapteyn reported that these were not random, as it was believed in that time; stars could be divided into two streams, moving in nearly opposite directions. It was later realized that Kapteyn's data had been the first evidence of the rotation of our Galaxy, which ultimately led to the finding of galactic rotation by Bertil Lindblad and Jan Oort. In 1906, Kapteyn launched a plan for a major study of the distribution of stars in the Galaxy, using counts of stars in different directions. The plan involved measuring the apparent magnitude, spectral type, radial velocity, and proper motion of stars in 206 zones. This enormous project was the first coordinated statistical analysis in astronomy and involved the cooperation of over forty different observatories. His life’s work, First attempt at a theory of the arrangement and motion of the sidereal system was published in 1922, and described a lens-shaped island universe of which the density decreased away from the center, now known as the Kapteyn's Universe model. In his model the Galaxy was thought to be 40,000 light years in size, the sun being relatively close (2,000 light years) to its center. It was only after Kapteyn's death, in Amsterdam, that Robert Trumpler determined that the amount of interstellar reddening was actually much greater than had been assumed. This discovery increased the estimate of the galaxy's size to 100,000 light years, with the sun replaced to a distance of 30,000 light years from the galactic center.

APOD 3.5

This picture, "WISE Infrared Andromeda" caught my eye immediately for several reasons. The picture is very vibrant and has a multitude of colors and depths that can be seen when viewed closely. Not only this, but the content of the picture interested me as well. The picture deals with the Andromeda Galaxy, in the Andromeda constellation, which we have studied and thus is very relevant to my interests. It is very cool to see detailed and scientific pictures about material that we have studied in this class. Furthermore we have recently been learning about infrared light, the way it looks in pictures when observed, and how it emphasizes certain aspects of astronomical objects when observed. The article itself was very educational, and I learned two things which were very interesting to me. The first was that the Andromeda Galaxy is the largest one in its region, and thus it is very important. And the second thing that I learned is that the particular infrared detector used to take this picture, is so powerful that it needs to be cooled by frozen hydrogen.

APOD 3.4

This picture "Star Cluster M34" caught my eye as I was browsing through the APOD articles for several reasons. The picture itself is very interesting, with its depiction of a very dark night sky, encrusted with diamond-like stars and so incredibly radiant and bright, that I very much wish I could go to some place with almost no light pollution to see the sky in its clear and unadulterated form. The picture also depicts an aspect of a constellation that we as a class have studied, and I have witnessed up in the sky. This is the constellation Perseus, or more specifically, the picture depicts the M object that is found in the constellation, M34. While reading through the article and relevant links, I learned a few things about this object in the sky. Firstly, that the stars found in M34 are rather young astronomically speaking, being only 200 million years old. I also learned that most open star clusters share one very similar trait at least, which is the fact that over time, the stars found within the cluster will drift apart due to gravitational tides and interactions with the Milky Way's interstellar dust and other stars.

Nightly Observations: 3.1

So far this quarter my observations have been slightly sporadic. Nonetheless though, I have been able to do a pretty consistent observation of the Southern sky near my Osprey home. Usually when I do my observations, and over the past few weeks, I can at least identify distinctly where the constellation Orion is, thanks to its signature 'Belt' (it is usually found rather high in the Southeastern sky). Also obviously I have been able to find the Moon (hoorah!) which last night and the night before in particular, was a very bright and sharp crescent. Two very new things happened to me this quarter though, that I feel the need to share. One of them actually happened over Winter Break once already, so I was not as surprised when I saw it. This was the appearance of an phosphorescent 'halo' around the Moon on one clear Friday night, which is caused by the Moon's light interacting with ice crystals in the atmosphere. Also this quarter I finally made good use of the Evening Sky Maps which we have been given each month. With this paper, I was very astonished to realize, that I could actually identify almost every constellation of stars what was visible in the sky that particular night. Specifically these astronomical objects included, Auriga and Capella, Gemini and the Twins, Perseus, Taurus and the Pleiades, Betelgeuse and Rigel, Mars, and Sirius. This was a most incredible experience for me, as I got to see first hand just how predictable and cool these constellations are when you can find them and point them out. I was also very surprised to notice, that constellations are BIG (I had vaguely known this before, but never truly realized it) just identifying these 4 or so constellations, took up the entire night sky of stars above my head. Truly using this Sky Map is very helpful, and I will be sure to bring it outside with me in future observation sessions.

APOD 3.3

This picture, "Mars and a Colorful Lunar Fog Bow", is one that is surely a memorable picture in the history of my Astronomy blogging. The picture is very stunning, with its display of a smooth and flowing fog cover, with a large rainbow in the foreground and a dazzling night sky in the background. Especially noticeable in the night sky is Mars, which sparkles brighter than any other object in the sky. The most unique aspect of this picture, is actually the rainbow, or rather 'fog bow' as it is actually. While perusing the relevant links to this article, I learned that fog bows are created by light being reflected off thick fog cover (as one might expect). This particular one however, was created by MOONLIGHT being reflected off the fog, which is incredibly rare. Further making this picture a rarity, is the fact that most fog bows appear to be all white with no color. This one however was inexplicably vibrant with color.