# MTH 448/563 Data-Oriented Computing

Fall 2018

Day 16, Thursday, Oct 18

# A little more SQL

UPDATE mytable SET foo = NULL WHERE foo = "NA";

HAVING vs WHERE

# Sloan Digital Sky Survey

## Astronomical coordinate system

My own observations of Halley's comet using binoculars

Quiz: In which year did I make those observations?

### Right ascension and declination

equatorial coordinate system

ra = right ascension, a sky coordinate comparable to geographic longitude (traditionally measured in hours, minutes, seconds, where 24h = 360 degrees)

dec = declination, a sky coordinate comparable to geographic latitude

steradian measure of solid angle (and square degrees)

### Exercise: your patch of sky

Stake out a small patch of sky for yourself: choose an (ra,dec)-rectangle, somewhere in the DR14 footprint, that subtends the same solid angle as the moon does hear on Earth. (What is the solid angle of a small (ra,dec)-rectangle?) Best if you avoid including any bright foreground star.

Your answer will be in the format: a < ra < b, c < dec < d. You could look at a sky map like this one to get your bearings.

An example of big data accessed with SQL queries ...

## Sloan Digital Sky Survey (SDSS)

Exercise: Please enter the coordinates of your own patch of sky (all in degrees) on this spreadsheet (change the Z to an A).

SDSS Data Release 14 (2014)

http://skyserver.sdss.org/dr14/en/tools/started/startedhome.aspx

## Querying the SDSS

SQL Search Tutorial

Sloan Digital Sky Survey, SkyServer DR14: SQL Search

### Brightest objects

Exercise: Get the coordinates and some properties of the brightest objects in your own patch of sky from SDSS PhotoPrimary table.

The Schema Browser is useful.

Measures of brightness: Apparent magnitudes is the negative logarithm of the brightness as seen from here: larger number therfore means dimmer. Magnitude 9.5 is about as faint as you can see with binoculars. Measures of flux and magnitude in SDSS: explanation here. Here is a chart of the filters used by SDSS.

Can you make a plot of your brightest objects?

### Galaxy count

Exercise: Guess how many galaxies the SDSS found in your own patch of sky, and enter it in the spreadsheet. Then find out the actual number and enter that.

# Algorithms for recognition

Examples:

• identity of speaker or singer in an audio clip
• words spoken in an audio clip
• identity of a person in a security video
• bots from people on Twitter
• species of a tree from a photo of a leaf
• handwritten numeral in a photo
• galaxies vs stars in a telescope image
• good versus bad move in a chess game
• earthquake imminent from seismic/other measurements

Group exercise: identify the stars in a photo with no metadata.

Preparatory activity: Here is a photo of Halley's comet taken on March 8. Figure out the correspondences between objects in the photo and objects in the star chart. Then, using the photo and the chart, determine the location in celestial coordinates (Epoch 1950.0) of (the nucleus of) Halley's comet on March 8. Give the ra and dec.

Main question: Assuming you have a list of all the bright stars in the sky with their coordinates, how would you identify the stars in any photo of a portion of the sky, given no info except the photo itself?